1 00:00:00,000 --> 00:00:01,968 [SQUEAKING] 2 00:00:01,968 --> 00:00:04,428 [RUSTLING] 3 00:00:04,428 --> 00:00:05,412 [CLICKING] 4 00:00:15,267 --> 00:00:16,059 JOHN DOLHUN: Hello. 5 00:00:16,059 --> 00:00:18,280 Good afternoon, everyone. 6 00:00:18,280 --> 00:00:24,040 And welcome to the second to the last lecture. 7 00:00:24,040 --> 00:00:26,920 Next week, the X-ray diffraction, Peter Mueller 8 00:00:26,920 --> 00:00:30,190 will deliver that, I believe, on Tuesday. 9 00:00:30,190 --> 00:00:32,439 And this is the mass spec lecture, 10 00:00:32,439 --> 00:00:37,690 and then we'll keep you posted as what happens in between. 11 00:00:37,690 --> 00:00:41,170 There are a couple of workshops for the oral reports, 12 00:00:41,170 --> 00:00:44,830 and we'll also have a couple of town hall meetings, one of them 13 00:00:44,830 --> 00:00:52,660 being, I believe, next week, next Thursday, which 14 00:00:52,660 --> 00:00:55,570 will cover all three of the labs that you're working on. 15 00:00:55,570 --> 00:00:58,330 You can come here with your questions and computers 16 00:00:58,330 --> 00:01:03,280 and calculations, and all the TAs and both instructors 17 00:01:03,280 --> 00:01:07,450 will be here to help you navigate through the third lab. 18 00:01:07,450 --> 00:01:11,410 So today, I'm going to talk about mass spectrometry. 19 00:01:11,410 --> 00:01:20,080 And J.J. Thompson, discoverer of the electron, 20 00:01:20,080 --> 00:01:24,010 won the Nobel Prize in 1906 in physics, but not 21 00:01:24,010 --> 00:01:26,410 for the discovery of the electron, 22 00:01:26,410 --> 00:01:29,350 for the conduction of electricity 23 00:01:29,350 --> 00:01:33,370 through various gases and discharge tubes. 24 00:01:33,370 --> 00:01:35,500 And then, after he won that Nobel Prize, 25 00:01:35,500 --> 00:01:40,630 seven members of his research group won Nobel Prizes. 26 00:01:40,630 --> 00:01:44,890 And then, in 1937, his son won a Nobel Prize 27 00:01:44,890 --> 00:01:48,580 for figuring out the wavelike properties of the electron 28 00:01:48,580 --> 00:01:50,950 that his father discovered. 29 00:01:50,950 --> 00:01:53,890 Nine Nobel prizes in one research group. 30 00:01:53,890 --> 00:01:56,290 It's just amazing. 31 00:01:56,290 --> 00:01:59,770 So J.J. went on to build the first mass 32 00:01:59,770 --> 00:02:02,530 spectrometer in 1912. 33 00:02:02,530 --> 00:02:08,169 And in honor of him, we're going to do a little electrical demo, 34 00:02:08,169 --> 00:02:12,370 just to start off with you today. 35 00:02:12,370 --> 00:02:14,500 So what we're going to be doing is 36 00:02:14,500 --> 00:02:19,750 I'm going to be showing you an incandescent light bulb. 37 00:02:19,750 --> 00:02:21,610 And you all know them. 38 00:02:21,610 --> 00:02:22,780 This is a big version. 39 00:02:22,780 --> 00:02:24,610 This is the small version. 40 00:02:24,610 --> 00:02:30,160 Inside of the incandescent light bulb, there's the filament. 41 00:02:30,160 --> 00:02:33,520 And they've used tungsten since the turn 42 00:02:33,520 --> 00:02:37,780 of the century, the turn of the last century, 1906, 43 00:02:37,780 --> 00:02:40,270 because tungsten has the highest melting 44 00:02:40,270 --> 00:02:42,190 point of all the metals. 45 00:02:42,190 --> 00:02:46,520 Melts at around 3,400 degrees Celsius. 46 00:02:46,520 --> 00:02:49,690 So inside of there, you can see it in this bulb, 47 00:02:49,690 --> 00:02:55,100 but I'm just going to turn this on, just for a moment. 48 00:02:55,100 --> 00:02:57,820 So you all know the incandescent bulbs. 49 00:02:57,820 --> 00:02:59,350 They get so hot. 50 00:02:59,350 --> 00:03:02,590 When the electrons flow, they flow through the circuit, 51 00:03:02,590 --> 00:03:07,120 and then the tungsten atoms start to vibrate inside 52 00:03:07,120 --> 00:03:11,590 and it heats up to about 2,200 degrees. 53 00:03:11,590 --> 00:03:14,560 Have any of you ever touched one of these? 54 00:03:14,560 --> 00:03:18,040 You do it only one time because they are so hot, 55 00:03:18,040 --> 00:03:20,590 and that's why they're so wasteful of electricity. 56 00:03:20,590 --> 00:03:23,350 That's why we're going to the LED lights today. 57 00:03:23,350 --> 00:03:27,130 But what I've done here is inside 58 00:03:27,130 --> 00:03:30,370 of that light bulb and this bulb, 59 00:03:30,370 --> 00:03:33,070 there is an inert atmosphere. 60 00:03:33,070 --> 00:03:37,600 There's argon and nitrogen gases to protect that filament. 61 00:03:37,600 --> 00:03:40,750 If they weren't in there, I scratch my head 62 00:03:40,750 --> 00:03:43,040 and I'd wonder what would happen to that filament. 63 00:03:43,040 --> 00:03:46,240 So what I did is I took a bulb here 64 00:03:46,240 --> 00:03:48,010 and I'm going to break one. 65 00:03:48,010 --> 00:03:48,850 Hold your ears. 66 00:03:51,940 --> 00:03:54,820 And out-- oh, beautiful. 67 00:03:54,820 --> 00:03:57,010 The filament's completely intact. 68 00:03:57,010 --> 00:03:59,320 See, I didn't break it. 69 00:03:59,320 --> 00:04:03,170 But I've already got one here to show you this demo with. 70 00:04:03,170 --> 00:04:06,550 So what we're going to do is I am 71 00:04:06,550 --> 00:04:13,760 going to take one of these filaments outside 72 00:04:13,760 --> 00:04:16,700 of the light bulb and I'm going to turn on the electricity 73 00:04:16,700 --> 00:04:19,529 and see what happens. 74 00:04:19,529 --> 00:04:20,839 Let's turn the lights down now. 75 00:04:20,839 --> 00:04:22,510 Yeah. 76 00:04:22,510 --> 00:04:26,980 And he just shut this light off here. 77 00:04:30,010 --> 00:04:30,510 You ready? 78 00:04:35,370 --> 00:04:36,350 AUDIENCE: Whoa. 79 00:04:36,350 --> 00:04:38,780 JOHN DOLHUN: Wow, didn't take long, right? 80 00:04:38,780 --> 00:04:42,470 In the oxygen atmosphere, the electrons 81 00:04:42,470 --> 00:04:44,720 are flowing through there and the tungsten atoms 82 00:04:44,720 --> 00:04:46,880 are boiling off with the electrons 83 00:04:46,880 --> 00:04:50,880 and the thing just disintegrates pretty instantly. 84 00:04:50,880 --> 00:04:54,900 So I said to myself, I want to do one more experiment. 85 00:04:54,900 --> 00:04:57,480 And Amanda's going to assist me with this. 86 00:04:57,480 --> 00:05:01,590 We're going to fill this beaker with liquid nitrogen 87 00:05:01,590 --> 00:05:05,340 and we're going to take one of these filaments 88 00:05:05,340 --> 00:05:08,640 and we're going to stick it down into the liquid nitrogen 89 00:05:08,640 --> 00:05:11,200 and then we're going to turn it on. 90 00:05:11,200 --> 00:05:12,820 So think about that for a minute. 91 00:05:12,820 --> 00:05:14,362 What do you think is going to happen? 92 00:05:17,888 --> 00:05:19,872 AUDIENCE: [INAUDIBLE] 93 00:05:20,980 --> 00:05:22,230 JOHN DOLHUN: Go ahead, Amanda. 94 00:05:25,890 --> 00:05:27,030 I just blew one. 95 00:05:27,030 --> 00:05:29,380 OK. 96 00:05:29,380 --> 00:05:31,920 OK. 97 00:05:31,920 --> 00:05:32,820 All right. 98 00:05:32,820 --> 00:05:34,500 I ruined one, sorry. 99 00:05:34,500 --> 00:05:36,060 I forgot this was on. 100 00:05:36,060 --> 00:05:37,480 OK. 101 00:05:37,480 --> 00:05:39,580 All right, let me turn this off for a minute. 102 00:05:47,988 --> 00:05:53,520 And I think I can put in the one that I took out here 103 00:05:53,520 --> 00:05:55,030 on the desk. 104 00:05:55,030 --> 00:05:58,930 I'm going to put that one in because the filament is intact. 105 00:05:58,930 --> 00:05:59,820 OK, Amanda. 106 00:06:04,640 --> 00:06:06,170 Just tighten it a bit. 107 00:06:06,170 --> 00:06:06,670 Go ahead. 108 00:06:09,580 --> 00:06:10,825 You OK? 109 00:06:10,825 --> 00:06:11,450 AUDIENCE: Yeah. 110 00:06:15,780 --> 00:06:19,125 JOHN DOLHUN: Liquid nitrogen, minus 196 degrees Celsius. 111 00:06:22,770 --> 00:06:25,580 Beautiful stuff. 112 00:06:25,580 --> 00:06:28,190 Put your finger in there and you know what's going to happen. 113 00:06:32,970 --> 00:06:35,140 It's the skin effect. 114 00:06:35,140 --> 00:06:37,880 Won't get you for the first few seconds. 115 00:06:37,880 --> 00:06:40,180 OK, good. 116 00:06:40,180 --> 00:06:42,070 So here we go with our experiment. 117 00:06:42,070 --> 00:06:44,210 That's good, Amanda. 118 00:06:44,210 --> 00:06:46,740 So we're going to lower this down in. 119 00:06:46,740 --> 00:06:48,964 Amanda, do you want to hold this? 120 00:06:48,964 --> 00:06:49,845 AUDIENCE: Sure. 121 00:06:49,845 --> 00:06:51,720 JOHN DOLHUN: Just try to get it in the center 122 00:06:51,720 --> 00:06:53,463 and just lower it all the way down in. 123 00:06:53,463 --> 00:06:54,380 AUDIENCE: All the way? 124 00:06:54,380 --> 00:06:55,020 JOHN DOLHUN: All the way. 125 00:06:55,020 --> 00:06:55,850 Just go ahead. 126 00:06:55,850 --> 00:06:57,530 Take it down. 127 00:06:57,530 --> 00:06:59,180 Leave more slack. 128 00:06:59,180 --> 00:06:59,930 Yeah. 129 00:06:59,930 --> 00:07:01,130 Let it go down in. 130 00:07:01,130 --> 00:07:03,240 OK, good. 131 00:07:03,240 --> 00:07:03,740 Ready? 132 00:07:06,560 --> 00:07:09,693 There it is in the liquid nitrogen. Is it burning out? 133 00:07:09,693 --> 00:07:10,235 AUDIENCE: No. 134 00:07:10,235 --> 00:07:10,777 AUDIENCE: No. 135 00:07:10,777 --> 00:07:12,710 JOHN DOLHUN: No. 136 00:07:12,710 --> 00:07:13,740 Take it out, Amanda. 137 00:07:17,690 --> 00:07:20,180 Doesn't take long in the air, does it? 138 00:07:20,180 --> 00:07:23,690 So even the liquid nitrogen is surrounding that filament 139 00:07:23,690 --> 00:07:24,810 and protecting it. 140 00:07:24,810 --> 00:07:31,070 And you've got the situation where you don't have 141 00:07:31,070 --> 00:07:33,586 the oxidation that's going on. 142 00:07:33,586 --> 00:07:35,330 OK, so we take the lights back up. 143 00:07:38,280 --> 00:07:42,590 So in case you're interested, tungsten it had-- 144 00:07:42,590 --> 00:07:45,530 anyone read Oliver Sacks book, Uncle Tungsten? 145 00:07:45,530 --> 00:07:47,090 It's a great book. 146 00:07:47,090 --> 00:07:48,710 You've got to get that. 147 00:07:48,710 --> 00:07:52,685 Tungsten plus oxygen goes to tungsten oxide. 148 00:07:58,250 --> 00:08:00,320 And you can actually-- if you take 149 00:08:00,320 --> 00:08:03,590 one of these filaments that burned out, 150 00:08:03,590 --> 00:08:08,000 you can actually see the yellow-white powder 151 00:08:08,000 --> 00:08:13,590 that from the tungsten oxide that was left over. 152 00:08:13,590 --> 00:08:20,660 So J.J. Thompson, because of his discovery of the electron, 153 00:08:20,660 --> 00:08:23,480 I wanted to show you this electrical demo. 154 00:08:23,480 --> 00:08:31,903 And now, we're going to get into the mass spec, which 155 00:08:31,903 --> 00:08:33,320 is pretty important because you're 156 00:08:33,320 --> 00:08:38,450 going to be using the mass spec to characterize your ester 157 00:08:38,450 --> 00:08:40,590 products in this lab. 158 00:08:40,590 --> 00:08:46,970 So the inside of the mass spec has several basic components. 159 00:08:46,970 --> 00:08:49,700 You've got an area outside here that 160 00:08:49,700 --> 00:08:54,170 is at atmospheric pressure, and the area inside that 161 00:08:54,170 --> 00:08:56,660 is under a high vacuum. 162 00:08:56,660 --> 00:09:00,030 Anyone have an idea why that area is under a high vacuum 163 00:09:00,030 --> 00:09:00,530 inside? 164 00:09:10,010 --> 00:09:12,630 No? 165 00:09:12,630 --> 00:09:15,000 So you're generating ions. 166 00:09:15,000 --> 00:09:18,660 The ion are going to get generated in this source. 167 00:09:18,660 --> 00:09:22,530 The filament is going to shoot electrons onto your molecule 168 00:09:22,530 --> 00:09:24,840 and it's going to ionize your molecule, 169 00:09:24,840 --> 00:09:27,600 and then the molecule's going to break apart. 170 00:09:27,600 --> 00:09:31,270 And positive ions are very short-lived species, 171 00:09:31,270 --> 00:09:33,930 so we manipulate them under vacuum. 172 00:09:33,930 --> 00:09:38,460 And the vacuum-- the vacuum actually 173 00:09:38,460 --> 00:09:42,525 is great because it allows us to let the ion 174 00:09:42,525 --> 00:09:46,260 have a mean-free pathway from the ion source 175 00:09:46,260 --> 00:09:50,830 to the detector without any biomolecular collisions. 176 00:09:50,830 --> 00:09:52,830 So the ions are generated here and then 177 00:09:52,830 --> 00:09:54,690 they go into the mass analyzer and they're 178 00:09:54,690 --> 00:09:58,260 sorted by their mass to charge ratios, 179 00:09:58,260 --> 00:10:01,330 and then they're counted at the detector, 180 00:10:01,330 --> 00:10:05,320 and out comes a spectrum. 181 00:10:05,320 --> 00:10:14,590 You kind of get something like this with abundance here 182 00:10:14,590 --> 00:10:17,630 and the mass to charge ratio. 183 00:10:17,630 --> 00:10:20,920 And depending on the iron, so you might-- 184 00:10:20,920 --> 00:10:28,510 the detector may see a lot of this, less of that 185 00:10:28,510 --> 00:10:29,570 and less of that. 186 00:10:29,570 --> 00:10:32,650 So you're going to get vertical lines representing 187 00:10:32,650 --> 00:10:36,700 the abundance of the ions that were detected in that spectrum. 188 00:10:36,700 --> 00:10:40,030 Each vertical line represents an ion. 189 00:10:40,030 --> 00:10:43,810 And we're talking about mass to charge ratios, 190 00:10:43,810 --> 00:10:46,240 the charges are usually plus 1. 191 00:10:46,240 --> 00:10:48,490 So what we're looking at in a mass spectrum 192 00:10:48,490 --> 00:10:53,920 are the masses of the individual ions. 193 00:10:53,920 --> 00:10:58,540 Mass spec is-- the basic principle of mass spec 194 00:10:58,540 --> 00:11:03,310 is you have to have an ion that enters the magnetic field 195 00:11:03,310 --> 00:11:05,570 and it gets deflected. 196 00:11:05,570 --> 00:11:10,700 It gets deflected dependent on the actual mass to charge 197 00:11:10,700 --> 00:11:14,300 ratio, how big that system is. 198 00:11:14,300 --> 00:11:17,990 Bigger, heavier atoms are going to be deflected 199 00:11:17,990 --> 00:11:20,600 less than small, lighter atoms. 200 00:11:20,600 --> 00:11:24,890 But that's the whole underlying principle of mass spectrometry. 201 00:11:24,890 --> 00:11:26,780 And now, I'm going to talk about a couple 202 00:11:26,780 --> 00:11:31,550 of the types of ionization. 203 00:11:31,550 --> 00:11:36,360 Electron impact is the basic form. 204 00:11:36,360 --> 00:11:40,130 So what we have is we've got our molecule 205 00:11:40,130 --> 00:11:44,060 and we send it into the ion source. 206 00:11:44,060 --> 00:11:53,360 It gets bombarded by electrons, and you 207 00:11:53,360 --> 00:12:00,050 create an ionized molecule, an M plus dot. 208 00:12:00,050 --> 00:12:02,855 And this ionized molecule can do one of two things. 209 00:12:09,050 --> 00:12:11,300 This could break apart. 210 00:12:11,300 --> 00:12:15,540 So the positive charge could be retained on one part of it. 211 00:12:15,540 --> 00:12:17,700 The radical would be retained on the other. 212 00:12:17,700 --> 00:12:20,360 So you could get something like A plus 213 00:12:20,360 --> 00:12:24,560 plus some radical given off. 214 00:12:24,560 --> 00:12:27,230 Or it could break apart. 215 00:12:27,230 --> 00:12:31,940 So one part retains both the plus and radical. 216 00:12:31,940 --> 00:12:36,101 So you could get this type of ion 217 00:12:36,101 --> 00:12:39,990 and a neutral molecule given off. 218 00:12:39,990 --> 00:12:43,020 What we detect with mass spectrometry 219 00:12:43,020 --> 00:12:48,000 is we're detecting these daughter ions here. 220 00:12:48,000 --> 00:12:49,920 These are the peaks we see. 221 00:12:49,920 --> 00:12:53,280 We don't see the radicals or the neutron molecules, 222 00:12:53,280 --> 00:12:57,450 but we could figure them out by subtracting the fragments 223 00:12:57,450 --> 00:12:59,670 from the molecular weight. 224 00:12:59,670 --> 00:13:03,580 And then we can-- we'll know what's been lobbed off. 225 00:13:03,580 --> 00:13:10,530 So if you have a molecule like this, 226 00:13:10,530 --> 00:13:14,550 it could ionize anywhere in this chain. 227 00:13:14,550 --> 00:13:18,540 And if it ionizes, say, here, and then you 228 00:13:18,540 --> 00:13:22,740 have a homolytic cleavage of the bond, 229 00:13:22,740 --> 00:13:28,650 you're going to get an R prime CH 2 plus fragment, 230 00:13:28,650 --> 00:13:35,130 and you'll get an R2 CH2 radical. 231 00:13:35,130 --> 00:13:36,290 So that's the idea. 232 00:13:38,990 --> 00:13:41,810 Now, sometimes, some of these bigger molecules, 233 00:13:41,810 --> 00:13:47,540 these proteins and peptides, you don't see molecular ion peaks 234 00:13:47,540 --> 00:13:49,440 in the mass spectrum. 235 00:13:49,440 --> 00:13:52,460 Even for some small molecules you may not see them. 236 00:13:52,460 --> 00:13:56,060 So we have another technique, a softer ionization technique 237 00:13:56,060 --> 00:13:59,240 called chemical ionization that we can use. 238 00:14:02,570 --> 00:14:07,450 So in chemical lionization, what we do is we take a guess 239 00:14:07,450 --> 00:14:11,590 and we flood the ion source with a gas. 240 00:14:11,590 --> 00:14:14,740 I'm going to choose methane for this. 241 00:14:14,740 --> 00:14:17,560 Methane is often use. 242 00:14:17,560 --> 00:14:19,195 And we ionize that methane. 243 00:14:24,610 --> 00:14:37,300 And then the ionized methane reacts with more methane 244 00:14:37,300 --> 00:14:45,880 to produce a super acid, CH5 plus, and a methyl radical. 245 00:14:45,880 --> 00:14:53,517 Now, your molecule goes in and it encounters the CH5 plus. 246 00:14:53,517 --> 00:14:54,850 What do you think happens to it? 247 00:14:58,105 --> 00:14:59,402 AUDIENCE: It's acidified? 248 00:14:59,402 --> 00:15:01,360 JOHN DOLHUN: Yeah, it's going to get acidified. 249 00:15:01,360 --> 00:15:03,160 It's going to get protonated. 250 00:15:03,160 --> 00:15:08,350 So this CH5 plus protonates your molecule, 251 00:15:08,350 --> 00:15:11,250 and you get this huge M plus 1 peak. 252 00:15:15,500 --> 00:15:16,540 So this is great. 253 00:15:16,540 --> 00:15:19,780 If we have these big proteins and peptides 254 00:15:19,780 --> 00:15:22,630 and we want to know what the molecular weight is, 255 00:15:22,630 --> 00:15:26,680 we can use chemical lionization, put them in there, 256 00:15:26,680 --> 00:15:28,540 and we'll see the big M plus 1. 257 00:15:28,540 --> 00:15:31,030 We won't see a lot of fragmentation, 258 00:15:31,030 --> 00:15:34,620 but at least we can get some molecular weight information 259 00:15:34,620 --> 00:15:36,810 out of the system. 260 00:15:36,810 --> 00:15:42,100 CH5 plus is an interesting molecule. 261 00:15:42,100 --> 00:15:44,770 You all know from your chemical principles 262 00:15:44,770 --> 00:15:50,200 that CH4 is SP3 hybridized. 263 00:15:50,200 --> 00:15:55,060 So when those two methane molecules collide 264 00:15:55,060 --> 00:15:59,410 and it throws the hydrogen in, that hydrogen 265 00:15:59,410 --> 00:16:02,270 pushes another hydrogen out of the way 266 00:16:02,270 --> 00:16:05,395 and it forms a three-centered, two-electron bond. 267 00:16:09,830 --> 00:16:14,630 This is a pentavalent carbon atom with a positive charge. 268 00:16:14,630 --> 00:16:16,220 That's a carbocation. 269 00:16:16,220 --> 00:16:20,570 That's the definition of a carbocation in chemistry. 270 00:16:20,570 --> 00:16:22,940 This is also called the methanium ion. 271 00:16:26,830 --> 00:16:31,570 And this is one of the last unsolved problems in physics, 272 00:16:31,570 --> 00:16:34,630 because no one can isolate this stuff. 273 00:16:34,630 --> 00:16:36,790 It's very difficult to isolate. 274 00:16:36,790 --> 00:16:40,270 And about three years ago, at the University of Cologne, 275 00:16:40,270 --> 00:16:44,620 they actually trap some of this stuff in an ion chamber 276 00:16:44,620 --> 00:16:47,830 at very low temperatures, near absolute zero, 277 00:16:47,830 --> 00:16:50,530 and they studied the vibrational spectra. 278 00:16:50,530 --> 00:16:53,080 What they saw was all these hydrogens 279 00:16:53,080 --> 00:16:56,410 are coming off, moving around the carbon atom. 280 00:16:56,410 --> 00:16:58,730 They're breaking off and moving around. 281 00:16:58,730 --> 00:17:02,320 So now, scientists are wondering whether this thing actually 282 00:17:02,320 --> 00:17:06,170 has any structure at all. 283 00:17:06,170 --> 00:17:08,839 So that's chemical ionization. 284 00:17:08,839 --> 00:17:13,130 Sometimes, electron impact and chemical lionization, 285 00:17:13,130 --> 00:17:15,589 both of them won't work for us. 286 00:17:15,589 --> 00:17:18,530 We may have a molecule that's too big 287 00:17:18,530 --> 00:17:20,510 or that's too nonvolatile. 288 00:17:20,510 --> 00:17:24,349 So we go to fast atom bombardment, electrospray, 289 00:17:24,349 --> 00:17:28,160 or matrix-assisted laser desorption spectroscopy. 290 00:17:32,870 --> 00:17:36,150 Fast atom bombardment is pretty simple. 291 00:17:36,150 --> 00:17:40,400 You take your sample, mix it with a little bit of glycerol, 292 00:17:40,400 --> 00:17:43,820 put it on a metal target, and then we 293 00:17:43,820 --> 00:17:46,940 shoot xenon and argon atoms at it, 294 00:17:46,940 --> 00:17:49,340 very high speed, high energy. 295 00:17:49,340 --> 00:17:53,300 And the glycerol in your sample absorbs the shock 296 00:17:53,300 --> 00:17:56,450 of the impact with those atoms. 297 00:17:56,450 --> 00:18:00,440 And we have some trifluoroacetic acid in there, 298 00:18:00,440 --> 00:18:06,830 TFA, so that we can produce these M plus 1 peaks. 299 00:18:06,830 --> 00:18:09,290 The advantages of fast atom bombardment 300 00:18:09,290 --> 00:18:14,060 are for high molecular weight samples, nonvolatile compounds, 301 00:18:14,060 --> 00:18:16,730 EICI don't work. 302 00:18:16,730 --> 00:18:21,530 Molecular weights here, I've seen 20,000 or so. 303 00:18:21,530 --> 00:18:26,060 So you can go out-- 304 00:18:26,060 --> 00:18:30,770 they're constantly making innovations with these. 305 00:18:30,770 --> 00:18:34,160 The next technique, electrospray ionization, 306 00:18:34,160 --> 00:18:36,090 is quite interesting. 307 00:18:36,090 --> 00:18:40,820 The ions are produced, the molecule is ionized, 308 00:18:40,820 --> 00:18:43,820 and it's done at a very low pH. 309 00:18:43,820 --> 00:18:48,260 And there's a nebulizer that actually shoots out 310 00:18:48,260 --> 00:18:51,440 like an aerosol through a high voltage 311 00:18:51,440 --> 00:18:54,590 and you get these charged droplets coming out, 312 00:18:54,590 --> 00:18:59,570 very large droplets with a lot of positive charges on them. 313 00:18:59,570 --> 00:19:06,020 And then we can take a stream of warm nitrogen gas 314 00:19:06,020 --> 00:19:12,500 and evaporate those down and you get a smaller droplet and then 315 00:19:12,500 --> 00:19:14,570 that disintegrates. 316 00:19:14,570 --> 00:19:19,570 And what you end up with are these multi-protonated 317 00:19:19,570 --> 00:19:21,460 molecular ion peaks. 318 00:19:21,460 --> 00:19:24,190 You could have an M plus 20. 319 00:19:24,190 --> 00:19:27,280 You could have 20 hydrogens on there, or 10 hydrogens, 320 00:19:27,280 --> 00:19:31,970 or you get a variety of numbers. 321 00:19:31,970 --> 00:19:36,140 And what that does is it expands the mass range. 322 00:19:36,140 --> 00:19:42,680 Let's say, for example, you have a molecule that maybe weighs 323 00:19:42,680 --> 00:19:48,710 70,000, and you produce a-- 324 00:19:48,710 --> 00:19:51,920 you produce an M plus 20. 325 00:19:51,920 --> 00:19:54,590 So what you have to do is-- 326 00:19:54,590 --> 00:19:58,730 you're going to have a molecule like that. 327 00:19:58,730 --> 00:20:00,230 You're going to have to divide, now, 328 00:20:00,230 --> 00:20:04,700 by the charge to get where this molecule is going to show up. 329 00:20:04,700 --> 00:20:07,110 Because it's mass to charge ratio, 330 00:20:07,110 --> 00:20:11,640 and if the charge is 20, if you divide this out, 331 00:20:11,640 --> 00:20:16,940 you're going to get something around 3,501. 332 00:20:16,940 --> 00:20:20,540 That's where the peak is going to show up in your spectrum. 333 00:20:20,540 --> 00:20:22,370 So the advantage of this technique 334 00:20:22,370 --> 00:20:26,000 is you can take molecules that are 70,000, 80,000, 335 00:20:26,000 --> 00:20:31,400 and your peaks could come out at 3,500 or much less. 336 00:20:31,400 --> 00:20:33,650 So it expands the whole mass range 337 00:20:33,650 --> 00:20:37,460 of using a mass spectrometer. 338 00:20:37,460 --> 00:20:41,810 The last technique is MALDI, Matrix-Assisted Laser 339 00:20:41,810 --> 00:20:45,950 Desorption Ionization, and we would use that principally 340 00:20:45,950 --> 00:20:47,510 for solids. 341 00:20:47,510 --> 00:20:51,800 And these would be like the big carbohydrates, the big peptides 342 00:20:51,800 --> 00:20:53,350 and proteins. 343 00:20:53,350 --> 00:20:57,410 And you take your crystal and you dissolve it 344 00:20:57,410 --> 00:21:02,570 in a matrix, a solvent, and you put a chromophore in 345 00:21:02,570 --> 00:21:07,580 to absorb the laser light, and then 346 00:21:07,580 --> 00:21:14,210 this sample begins to evaporate and you get beautiful crystals 347 00:21:14,210 --> 00:21:16,340 on this metal target. 348 00:21:16,340 --> 00:21:22,730 And then you shoot a nitrogen laser at it, 337 nanometers, 349 00:21:22,730 --> 00:21:29,180 and you end up getting M plus H speaks out. 350 00:21:29,180 --> 00:21:31,160 So you can take these large solids. 351 00:21:31,160 --> 00:21:36,450 And molecular weights here can go out quite a bit. 352 00:21:36,450 --> 00:21:38,660 So the advantages of all these techniques 353 00:21:38,660 --> 00:21:42,650 are they can help us with nonvolatile, high 354 00:21:42,650 --> 00:21:47,990 molecular weight samples and getting spectra. 355 00:21:47,990 --> 00:21:52,130 We've already talked about the inductively coupled plasma 356 00:21:52,130 --> 00:21:55,790 in one of the lectures, so I'm not going to talk about that. 357 00:21:55,790 --> 00:22:00,440 But I would like to cover a couple types of instruments 358 00:22:00,440 --> 00:22:03,630 that you will experience. 359 00:22:03,630 --> 00:22:06,860 The first is the magnetic sector. 360 00:22:06,860 --> 00:22:10,160 The last is the one we have in the undergraduate lab, 361 00:22:10,160 --> 00:22:15,430 the radio frequency quadrupole filter trap. 362 00:22:15,430 --> 00:22:17,890 So let's start with the magnetic sector. 363 00:22:17,890 --> 00:22:22,060 You'll see some similarities to these. 364 00:22:22,060 --> 00:22:23,830 So here is your ion source. 365 00:22:23,830 --> 00:22:26,170 You can see the filament here. 366 00:22:26,170 --> 00:22:28,870 And the filament is shooting out an electron beam 367 00:22:28,870 --> 00:22:30,630 at your sample. 368 00:22:30,630 --> 00:22:33,910 It's about 70 electron volts. 369 00:22:33,910 --> 00:22:38,710 That's like about 1,600 kcals of energy. 370 00:22:38,710 --> 00:22:42,160 And 100 kcals, you can break a bond. 371 00:22:42,160 --> 00:22:45,820 So with all that energy slamming into your molecule, 372 00:22:45,820 --> 00:22:48,940 it not only ionizers the molecule, 373 00:22:48,940 --> 00:22:52,120 it starts to break apart into fragments. 374 00:22:52,120 --> 00:22:55,510 And the fragments in this magnetic sector instrument 375 00:22:55,510 --> 00:22:59,050 get ushered through a pair of focal plates 376 00:22:59,050 --> 00:23:04,720 and then they get sent into the mass analyzer. 377 00:23:04,720 --> 00:23:06,820 There's an electric field perpendicular 378 00:23:06,820 --> 00:23:08,810 to a magnetic field. 379 00:23:08,810 --> 00:23:13,360 The electric field controls the velocity of the ions, 380 00:23:13,360 --> 00:23:17,200 and the magnetic field will cause the deflection 381 00:23:17,200 --> 00:23:23,230 with the heavier ions deflected less than the lighter ions. 382 00:23:23,230 --> 00:23:27,220 So you kind of get a spectrum here on the detecting screen 383 00:23:27,220 --> 00:23:30,715 based on how they're deflected by the magnet. 384 00:23:34,910 --> 00:23:40,160 Time of flight, this is actually one of my favorites. 385 00:23:40,160 --> 00:23:42,770 There are a couple advantages to this. 386 00:23:42,770 --> 00:23:48,020 One is it has almost an unlimited mass range. 387 00:23:48,020 --> 00:23:52,780 The second advantage is you can do very small amounts of sample 388 00:23:52,780 --> 00:23:54,650 with this. 389 00:23:54,650 --> 00:23:56,740 So what happens in time of flight 390 00:23:56,740 --> 00:24:10,520 is your samples get ionized in the ion source here. 391 00:24:10,520 --> 00:24:14,840 They get ionized similar to all the other mass spectrometers. 392 00:24:14,840 --> 00:24:23,690 But then they get shot out into a flight tube 393 00:24:23,690 --> 00:24:26,900 and they get shot out at the same kinetic energy, 394 00:24:26,900 --> 00:24:29,750 all the ions that are going in there. 395 00:24:29,750 --> 00:24:37,880 And kinetic energy is equal to 1/2MV squared, which is also 396 00:24:37,880 --> 00:24:41,570 proportional to the charge times the voltage 397 00:24:41,570 --> 00:24:44,010 when they're being shot out. 398 00:24:44,010 --> 00:24:46,490 So if you look at the kinetic energy, 399 00:24:46,490 --> 00:24:50,900 you can see that the velocity is square root of 2 400 00:24:50,900 --> 00:24:54,740 of the kinetic energy divided by the mass. 401 00:24:54,740 --> 00:25:01,880 So that means that the heavy ions are kind of lagging here. 402 00:25:07,160 --> 00:25:10,490 They're traveling slower because they're heavier. 403 00:25:10,490 --> 00:25:15,560 So when they're in this tube, they actually 404 00:25:15,560 --> 00:25:18,770 measure the time of flight through the tube. 405 00:25:18,770 --> 00:25:21,860 That's what this-- it's called time of flight, right? 406 00:25:21,860 --> 00:25:25,790 So the time of flight is the distance 407 00:25:25,790 --> 00:25:29,260 divided by the velocity. 408 00:25:29,260 --> 00:25:34,310 Now, if you put that back into this equation and you 409 00:25:34,310 --> 00:25:39,890 solve it out, you'll see that the mass to charge ratio 410 00:25:39,890 --> 00:25:46,160 is equal to the square of the time of flight 411 00:25:46,160 --> 00:25:49,210 divided by the distance. 412 00:25:49,210 --> 00:25:52,780 This is a great salute to the engineers. 413 00:25:52,780 --> 00:25:55,150 They designed this system. 414 00:25:55,150 --> 00:25:56,890 This machine is so simple. 415 00:25:56,890 --> 00:25:58,960 There's no electric field. 416 00:25:58,960 --> 00:26:01,240 There's no magnetic field. 417 00:26:01,240 --> 00:26:04,210 All there is is a tube. 418 00:26:04,210 --> 00:26:09,220 Doesn't this remind you of TLC with the spots? 419 00:26:09,220 --> 00:26:12,520 Except there's no mobile phase and no stationary phase here, 420 00:26:12,520 --> 00:26:13,600 right? 421 00:26:13,600 --> 00:26:15,910 So this is a great instrument. 422 00:26:15,910 --> 00:26:20,920 And that's how your mass spectrum is determined. 423 00:26:20,920 --> 00:26:26,000 Now, the next one, which is also kind 424 00:26:26,000 --> 00:26:30,140 of like the Cadillac of all mass spectrometers, 425 00:26:30,140 --> 00:26:35,066 is the Fourier-transform ion cyclotron resonance instrument. 426 00:26:39,084 --> 00:26:43,250 This instrument, ions are generated the same way 427 00:26:43,250 --> 00:26:46,010 as in the other mass spectrometers, 428 00:26:46,010 --> 00:26:47,690 but when they're generated, they start 429 00:26:47,690 --> 00:26:51,410 to get pumped to different pumping stations, 430 00:26:51,410 --> 00:26:57,210 and every pumping station has a higher and higher vacuum. 431 00:26:57,210 --> 00:26:59,880 So the pressures continue to drop 432 00:26:59,880 --> 00:27:07,050 until the ions reach this box, and then everything breaks 433 00:27:07,050 --> 00:27:07,680 loose here. 434 00:27:07,680 --> 00:27:10,740 Because in this box, you've got a temperature 435 00:27:10,740 --> 00:27:13,460 of about 2 Kelvin. 436 00:27:13,460 --> 00:27:18,590 You've got a magnetic field of about 21 tesla, 437 00:27:18,590 --> 00:27:21,090 and there's an electric field in there. 438 00:27:21,090 --> 00:27:28,810 And if you think about this, you have a charged particle 439 00:27:28,810 --> 00:27:32,920 traveling at a certain velocity and it enters-- 440 00:27:32,920 --> 00:27:36,010 it enters the magnetic field. 441 00:27:36,010 --> 00:27:37,320 What happens to it? 442 00:27:43,910 --> 00:27:47,180 What's going to happen to that charged particle when it 443 00:27:47,180 --> 00:27:48,790 gets into that magnetic field? 444 00:27:51,630 --> 00:27:52,387 Autumn? 445 00:27:52,387 --> 00:27:53,670 AUDIENCE: It'll go around. 446 00:27:53,670 --> 00:27:56,130 JOHN DOLHUN: It's going to start to spin, yeah, 447 00:27:56,130 --> 00:27:58,080 like a cyclotron. 448 00:27:58,080 --> 00:28:02,620 It's going to be-- it's going to be spinning like this. 449 00:28:02,620 --> 00:28:07,660 In fact, when the particle goes in there-- 450 00:28:07,660 --> 00:28:12,430 let me give you an example, like 100 molecular weight fragment, 451 00:28:12,430 --> 00:28:19,590 100 Dalton could travel 30 meters 452 00:28:19,590 --> 00:28:24,030 in about one second inside of that box just crazy. 453 00:28:26,910 --> 00:28:30,070 So it has a centripetal force on it. 454 00:28:30,070 --> 00:28:35,680 And force is mass times acceleration, right? 455 00:28:35,680 --> 00:28:40,450 So mass times acceleration. 456 00:28:40,450 --> 00:28:42,730 So this is our system. 457 00:28:42,730 --> 00:28:50,030 And the angular velocity of that particle 458 00:28:50,030 --> 00:28:53,000 is given by velocity over r. 459 00:28:53,000 --> 00:29:12,840 So if you plug that in here, the cyclotron frequency 460 00:29:12,840 --> 00:29:16,590 of that particle, that velocity is nothing 461 00:29:16,590 --> 00:29:18,570 to do with its velocity. 462 00:29:18,570 --> 00:29:22,010 It's only to do with mass and charge. 463 00:29:22,010 --> 00:29:23,420 That's the bottom line. 464 00:29:23,420 --> 00:29:25,720 That's incredible. 465 00:29:25,720 --> 00:29:30,220 And if we hold the magnetic field constant, 466 00:29:30,220 --> 00:29:32,900 then the cyclotron frequency is the mass 467 00:29:32,900 --> 00:29:37,060 to charge ratio of that particle. 468 00:29:37,060 --> 00:29:41,550 So what comes out of this is convoluted 469 00:29:41,550 --> 00:29:45,210 signals like this FID, these sine waves, 470 00:29:45,210 --> 00:29:49,920 and we do a Fourier-transform on that signal 471 00:29:49,920 --> 00:29:55,630 and pull out the mass spectrum that we want. 472 00:29:55,630 --> 00:30:00,270 So it's quite interesting. 473 00:30:00,270 --> 00:30:06,280 It's the most sensitive method of ion detection in the world. 474 00:30:06,280 --> 00:30:11,600 The resolution is greater than 10 to the 7 on this instrument. 475 00:30:11,600 --> 00:30:16,270 And if you think about it, that spinning particle, 476 00:30:16,270 --> 00:30:20,350 it's spinning so many times, the detector is on the outside 477 00:30:20,350 --> 00:30:22,210 here. 478 00:30:22,210 --> 00:30:25,330 The difference between this and all other forms of mass spec is 479 00:30:25,330 --> 00:30:29,380 the detector is on the outside, so it doesn't-- the ions never 480 00:30:29,380 --> 00:30:31,090 reach the detector. 481 00:30:31,090 --> 00:30:33,730 They only record the image current from the ions 482 00:30:33,730 --> 00:30:35,530 as they're going by. 483 00:30:35,530 --> 00:30:38,270 And it's recording it over and over and over again. 484 00:30:38,270 --> 00:30:42,550 That's why you've got such beautiful resolution here. 485 00:30:42,550 --> 00:30:45,790 And then you've got the system we're 486 00:30:45,790 --> 00:30:52,880 going to use, the quadrupole filter radio frequency system. 487 00:30:52,880 --> 00:30:55,930 So what we have for our mass analyzer 488 00:30:55,930 --> 00:31:02,080 is four rods in parallel, and the opposite rods 489 00:31:02,080 --> 00:31:04,210 are electrically connected. 490 00:31:04,210 --> 00:31:08,560 There's a DC voltage put on those rods. 491 00:31:08,560 --> 00:31:12,700 And then an RF voltage is superimposed on one pair 492 00:31:12,700 --> 00:31:15,320 of rods over the other. 493 00:31:15,320 --> 00:31:19,970 And it's the voltage of that pulsed radio frequency 494 00:31:19,970 --> 00:31:23,840 field and the frequency that determines which 495 00:31:23,840 --> 00:31:27,560 ions get through these rods. 496 00:31:27,560 --> 00:31:32,150 Only one ion can actually make it through the rods at a time, 497 00:31:32,150 --> 00:31:36,410 depending on the frequency of that radio frequency pulse 498 00:31:36,410 --> 00:31:39,740 and the ratio of voltages on those rods. 499 00:31:39,740 --> 00:31:43,580 And the other ions basically just crash into the sides here. 500 00:31:47,630 --> 00:31:52,120 So a couple of things, before you actually come in the lab 501 00:31:52,120 --> 00:31:54,460 and do the lab, we have to actually 502 00:31:54,460 --> 00:31:56,830 tune the mass spectrometer up. 503 00:31:56,830 --> 00:32:01,210 Because mass spectrometers have an internal mass scale. 504 00:32:01,210 --> 00:32:03,870 Can actually go off kilter. 505 00:32:03,870 --> 00:32:06,600 And so we've got to make sure that every mass is 506 00:32:06,600 --> 00:32:08,220 where it's supposed to be. 507 00:32:08,220 --> 00:32:11,340 The detector gain has to be cranked up so that we 508 00:32:11,340 --> 00:32:13,560 can see peaks far enough out. 509 00:32:16,230 --> 00:32:22,750 To do that, we use this compound, 510 00:32:22,750 --> 00:32:24,425 perfluorotributylamine. 511 00:32:27,300 --> 00:32:29,770 This is the stuff that we actually 512 00:32:29,770 --> 00:32:34,300 have in the mass spectrometer in a little vessel, 513 00:32:34,300 --> 00:32:37,390 and when we do the tune, the vessel opens up, 514 00:32:37,390 --> 00:32:40,010 and a whiff of this comes out. 515 00:32:40,010 --> 00:32:45,820 And the beauty of this is it can fragment down here. 516 00:32:45,820 --> 00:32:47,630 ScF3 can fall off. 517 00:32:47,630 --> 00:32:49,120 You get a 69 peak. 518 00:32:49,120 --> 00:32:51,340 Can do that from three directions. 519 00:32:51,340 --> 00:32:56,620 You can lose one of these polyfluorinated butyl groups 520 00:32:56,620 --> 00:33:00,550 from either of three directions and you get a 219 peak, 521 00:33:00,550 --> 00:33:05,050 or you can clip it right here and you get a 502 peak. 522 00:33:05,050 --> 00:33:07,240 And that's pretty much all you see. 523 00:33:07,240 --> 00:33:10,300 You see the 69, the 219, and the 502. 524 00:33:10,300 --> 00:33:12,280 The spectrum is very simple. 525 00:33:12,280 --> 00:33:14,990 And the molecular weight is 502. 526 00:33:14,990 --> 00:33:15,490 So 527 00:33:15,490 --> 00:33:18,670 We key in on these and adjust the internal mass 528 00:33:18,670 --> 00:33:20,650 scale of the instrument and make sure 529 00:33:20,650 --> 00:33:24,520 it can separate peaks 1 AMU apart. 530 00:33:24,520 --> 00:33:26,980 And for your samples, your samples 531 00:33:26,980 --> 00:33:29,930 will be under molecular weight of 200. 532 00:33:29,930 --> 00:33:32,890 So if we can go out to 500 and have it tuned up, 533 00:33:32,890 --> 00:33:33,700 we'll be fine. 534 00:33:36,920 --> 00:33:38,180 This is water. 535 00:33:38,180 --> 00:33:41,030 Very simple molecule. 536 00:33:41,030 --> 00:33:45,080 This is your chance to talk. 537 00:33:45,080 --> 00:33:47,090 I want you to-- 538 00:33:47,090 --> 00:33:49,255 we're going to actually look at this. 539 00:33:55,020 --> 00:33:59,190 What I'd like to do is I'd like to see 540 00:33:59,190 --> 00:34:06,030 what the mass spectrum of water looks like. 541 00:34:08,711 --> 00:34:10,211 So we're going to ionize some water. 542 00:34:17,270 --> 00:34:24,639 And we've got our abundance here and our mass-to-charge ratio. 543 00:34:24,639 --> 00:34:27,980 So what would you see in the mass spectrum of water? 544 00:34:27,980 --> 00:34:29,110 Which peaks would you see? 545 00:34:32,070 --> 00:34:32,570 Royce? 546 00:34:35,600 --> 00:34:37,080 Oh, you were scratching yourself. 547 00:34:37,080 --> 00:34:37,580 Yeah. 548 00:34:37,580 --> 00:34:42,889 [CHUCKLES] What would you see? 549 00:34:52,030 --> 00:34:54,040 Yes, Alec? 550 00:34:54,040 --> 00:34:55,780 AUDIENCE: M-to-C equals 18. 551 00:34:55,780 --> 00:34:56,880 JOHN DOLHUN: 18, yes. 552 00:34:56,880 --> 00:34:59,950 You'd definitely see an 18 peak. 553 00:34:59,950 --> 00:35:06,370 That's your ionized water molecule. 554 00:35:06,370 --> 00:35:08,630 What else? 555 00:35:08,630 --> 00:35:09,130 Alec? 556 00:35:13,090 --> 00:35:16,400 There's not much to fragment, is there? 557 00:35:16,400 --> 00:35:18,400 Well, what would you get if you tore this apart? 558 00:35:18,400 --> 00:35:21,700 AUDIENCE: You'd get a 1. 559 00:35:21,700 --> 00:35:24,970 JOHN DOLHUN: A 1, yes, you'd definitely see a 1 here. 560 00:35:24,970 --> 00:35:28,600 That's your hydrogen. What else? 561 00:35:28,600 --> 00:35:29,100 Yeah. 562 00:35:29,100 --> 00:35:30,350 AUDIENCE: You might see a 16. 563 00:35:30,350 --> 00:35:31,725 JOHN DOLHUN: Yep, you'd see a 16. 564 00:35:36,950 --> 00:35:37,520 What else? 565 00:35:41,630 --> 00:35:42,860 AUDIENCE: Will you see a 17? 566 00:35:42,860 --> 00:35:44,027 JOHN DOLHUN: Yes, you would. 567 00:35:44,027 --> 00:35:44,720 Very good. 568 00:35:48,090 --> 00:35:55,170 And that is-- that's the whole spectrum of water, four peaks. 569 00:35:55,170 --> 00:35:56,460 Yes, Autumn. 570 00:35:56,460 --> 00:36:00,380 AUDIENCE: Could you get 32 or 2 in the oxygen and hydrogen 571 00:36:00,380 --> 00:36:00,880 diagrams? 572 00:36:04,936 --> 00:36:06,510 JOHN DOLHUN: You could get-- 573 00:36:06,510 --> 00:36:14,240 if you're looking at air, air has diatomic gases in it. 574 00:36:14,240 --> 00:36:20,380 So if you put air in, you would see some of those peaks, yeah. 575 00:36:20,380 --> 00:36:24,250 Yeah, let's look at air, since you mentioned that. 576 00:36:28,110 --> 00:36:30,000 Let me just put this down here. 577 00:36:39,520 --> 00:36:41,930 I mean, air has diatomic gases. 578 00:36:41,930 --> 00:36:45,840 So what would you see in air? 579 00:36:45,840 --> 00:36:46,655 Yeah, Noah. 580 00:36:46,655 --> 00:36:47,280 AUDIENCE: A 28. 581 00:36:47,280 --> 00:36:49,690 JOHN DOLHUN: A 28, good. 582 00:36:49,690 --> 00:36:51,490 So you'd see a 28 here. 583 00:36:55,400 --> 00:36:56,590 Yep, what else? 584 00:37:00,730 --> 00:37:01,665 AUDIENCE: 32. 585 00:37:01,665 --> 00:37:03,040 JOHN DOLHUN: Yep, you'd see a 32. 586 00:37:11,270 --> 00:37:12,530 AUDIENCE: 44. 587 00:37:12,530 --> 00:37:13,880 JOHN DOLHUN: Very good. 588 00:37:13,880 --> 00:37:15,020 Good old carbon dioxide. 589 00:37:21,330 --> 00:37:22,800 Yep. 590 00:37:22,800 --> 00:37:23,360 What else? 591 00:37:26,671 --> 00:37:27,620 AUDIENCE: 18. 592 00:37:27,620 --> 00:37:29,440 JOHN DOLHUN: Yeah, you'd see water. 593 00:37:29,440 --> 00:37:31,540 We hate water, but it's in the air, right? 594 00:37:31,540 --> 00:37:34,280 So you definitely, definitely would see an 18 peak. 595 00:37:40,780 --> 00:37:43,070 What else? 596 00:37:43,070 --> 00:37:46,050 How about some of the noble gases? 597 00:37:46,050 --> 00:37:46,860 They're in the air. 598 00:37:49,900 --> 00:37:50,400 Which one? 599 00:37:50,400 --> 00:37:51,270 AUDIENCE: Ne. 600 00:37:51,270 --> 00:37:52,500 JOHN DOLHUN: Neon, yeah. 601 00:37:52,500 --> 00:37:53,520 Neon is 20. 602 00:37:59,960 --> 00:38:01,100 Any others? 603 00:38:01,100 --> 00:38:02,350 AUDIENCE: Would you see argon? 604 00:38:02,350 --> 00:38:04,120 JOHN DOLHUN: Yes, argon. 605 00:38:04,120 --> 00:38:05,200 Argon is 40. 606 00:38:09,430 --> 00:38:11,470 What other gas? 607 00:38:11,470 --> 00:38:11,970 Yes. 608 00:38:11,970 --> 00:38:13,934 AUDIENCE: Would you see helium or not? 609 00:38:17,870 --> 00:38:19,070 JOHN DOLHUN: Very little. 610 00:38:19,070 --> 00:38:20,950 Very little. 611 00:38:20,950 --> 00:38:23,400 What else? 612 00:38:23,400 --> 00:38:27,120 What's a couple of the other big inert gases? 613 00:38:27,120 --> 00:38:28,500 AUDIENCE: Xenon? 614 00:38:28,500 --> 00:38:35,950 JOHN DOLHUN: Xenon, yes, 131. 615 00:38:35,950 --> 00:38:38,723 What about the Superman gas? 616 00:38:38,723 --> 00:38:39,640 AUDIENCE: Oh, krypton. 617 00:38:39,640 --> 00:38:42,370 JOHN DOLHUN: Krypton, yes. 618 00:38:42,370 --> 00:38:43,495 84, krypton. 619 00:38:47,120 --> 00:38:51,170 And you may see a 29 peak, because you might 620 00:38:51,170 --> 00:38:56,510 see nitrogen-15, nitrogen-14. 621 00:38:56,510 --> 00:39:00,650 Because the mass spec will detect isotopes. 622 00:39:00,650 --> 00:39:05,600 You also, for oxygen, you could see a 34 peak, 623 00:39:05,600 --> 00:39:13,340 because you've got-- you might have some oxygen-18, oxygen-16. 624 00:39:13,340 --> 00:39:15,740 But you've hit them. 625 00:39:15,740 --> 00:39:17,300 And these just came out-- 626 00:39:17,300 --> 00:39:22,652 this was I think in not Time magazine, but one of the-- 627 00:39:22,652 --> 00:39:25,550 one of the magazines came out with the periodic table. 628 00:39:25,550 --> 00:39:27,860 The whole issue was on the periodic table. 629 00:39:27,860 --> 00:39:33,690 And they listed all the gases that are in the air. 630 00:39:33,690 --> 00:39:36,410 So it's kind of neat. 631 00:39:36,410 --> 00:39:39,170 So let's move on here. 632 00:39:39,170 --> 00:39:43,580 I want to show you what a mass spectrum looks like. 633 00:39:43,580 --> 00:39:47,450 This is hexane, your good old friend, right? 634 00:39:47,450 --> 00:39:47,950 C6H14. 635 00:39:50,760 --> 00:39:54,050 So what you've got here is you've got your molecular ion 636 00:39:54,050 --> 00:39:57,230 peak at 86, right? 637 00:39:57,230 --> 00:40:02,800 And then everything to the left of that is fragments breaking-- 638 00:40:02,800 --> 00:40:05,560 the molecule breaking apart. 639 00:40:05,560 --> 00:40:08,890 And notice the intensity of the peaks. 640 00:40:08,890 --> 00:40:11,680 One of the peaks is a base peak. 641 00:40:11,680 --> 00:40:16,360 That means the detector counted that more than any other peak. 642 00:40:16,360 --> 00:40:18,640 So what the detector does is gives 643 00:40:18,640 --> 00:40:24,400 that 100 and all the other peaks are relative to that base peak. 644 00:40:24,400 --> 00:40:26,560 And when we give you your mass spectrum, 645 00:40:26,560 --> 00:40:31,090 we'll give you a sheet with the abundances on it. 646 00:40:31,090 --> 00:40:35,830 Notice, if you take this base peak, 57, 647 00:40:35,830 --> 00:40:43,480 and you subtract it from 86, that's a loss of 29, isn't it? 648 00:40:43,480 --> 00:40:49,360 So it's pretty much just an ethyl radical falling off, 649 00:40:49,360 --> 00:40:52,990 and you've got this butyl cation. 650 00:40:52,990 --> 00:40:54,940 The butyl group has the plus charge. 651 00:40:54,940 --> 00:40:57,310 That's your 57 peak. 652 00:40:57,310 --> 00:40:58,480 It's that simple. 653 00:40:58,480 --> 00:41:02,200 So you take your peak, subtract from the molecular ion, 654 00:41:02,200 --> 00:41:04,540 see what's been thrown off. 655 00:41:04,540 --> 00:41:08,530 What about the m plus 1 peak here? 656 00:41:08,530 --> 00:41:09,220 What is that? 657 00:41:17,760 --> 00:41:20,280 There's no chemical ionization going on here. 658 00:41:20,280 --> 00:41:27,900 [CHUCKLES] What's the m plus 1 peak? 659 00:41:27,900 --> 00:41:28,860 Yes, Deb. 660 00:41:28,860 --> 00:41:31,336 AUDIENCE: [INAUDIBLE] 661 00:41:32,740 --> 00:41:35,050 JOHN DOLHUN: Did you say something with carbon? 662 00:41:35,050 --> 00:41:36,040 AUDIENCE: Yeah, 13. 663 00:41:36,040 --> 00:41:38,500 JOHN DOLHUN: Carbon-13, very good. 664 00:41:38,500 --> 00:41:40,510 Yeah, carbon-13. 665 00:41:40,510 --> 00:41:47,890 So carbon-13 has an abundance of 1.1%. 666 00:41:47,890 --> 00:41:50,950 1.1% of all carbon is carbon-13. 667 00:41:50,950 --> 00:41:52,120 Look up here. 668 00:41:52,120 --> 00:41:54,640 You got six carbons, right? 669 00:41:54,640 --> 00:41:58,180 So 6 times that-- 670 00:41:58,180 --> 00:42:02,980 6.6% of the carbons are carbon-13. 671 00:42:02,980 --> 00:42:07,210 So if I take this molecular ion peak, which is-- 672 00:42:07,210 --> 00:42:13,870 my eye is saying it's about 15% abundance, 673 00:42:13,870 --> 00:42:22,960 if I multiply that by 0.066, I get 1%, that m plus 1 peak. 674 00:42:22,960 --> 00:42:26,350 That's approximately what we're talking about. 675 00:42:26,350 --> 00:42:29,500 What if we didn't know the number of carbons? 676 00:42:29,500 --> 00:42:31,690 We didn't know the structure? 677 00:42:31,690 --> 00:42:35,500 We could work backwards and figure it out 678 00:42:35,500 --> 00:42:40,000 from the molecular ion abundance and the m plus 1 abundance. 679 00:42:40,000 --> 00:42:47,840 The number of carbons would be equal to the abundance 680 00:42:47,840 --> 00:42:59,190 of the m plus 1 divided by the abundance of the m 681 00:42:59,190 --> 00:43:07,930 plus dot times 100 divided by 1.1. 682 00:43:07,930 --> 00:43:11,710 That would give you the number of carbons in your molecule. 683 00:43:11,710 --> 00:43:15,480 So mass spec can not only determine the molecular weight, 684 00:43:15,480 --> 00:43:20,680 you can determine the molecular formula of your system. 685 00:43:20,680 --> 00:43:25,140 You can also determine the number of isotopes and elements 686 00:43:25,140 --> 00:43:30,160 that are present in your system. 687 00:43:30,160 --> 00:43:32,880 So there are other isotopes. 688 00:43:32,880 --> 00:43:36,420 Look at chlorine-35 and chlorine-37 here. 689 00:43:39,210 --> 00:43:49,720 If you see this in the molecular ion region of your spectrum, 690 00:43:49,720 --> 00:43:55,140 and your molecular ion is separated by 2 mass units, 691 00:43:55,140 --> 00:43:56,490 it's a dead giveaway. 692 00:43:56,490 --> 00:43:58,200 That's chlorine's signature. 693 00:43:58,200 --> 00:44:00,900 That means you have a chlorine in your molecule. 694 00:44:00,900 --> 00:44:03,450 Bromine is even simpler. 695 00:44:03,450 --> 00:44:07,980 Bromine has two peaks, both equal abundance-- 696 00:44:07,980 --> 00:44:15,360 the 79 and the 81 separated by 2 mass units. 697 00:44:15,360 --> 00:44:18,000 Here's an example. 698 00:44:18,000 --> 00:44:20,180 So here's a mass spectrum. 699 00:44:20,180 --> 00:44:24,780 Look at our molecular ion region here, 700 00:44:24,780 --> 00:44:31,260 separated by 2 mass units, ratio of 3 to 1. 701 00:44:31,260 --> 00:44:32,328 What do we have? 702 00:44:32,328 --> 00:44:33,120 AUDIENCE: Chlorine. 703 00:44:33,120 --> 00:44:35,410 JOHN DOLHUN: A chlorine, yes. 704 00:44:35,410 --> 00:44:35,910 OK? 705 00:44:35,910 --> 00:44:37,530 So if you take this-- 706 00:44:37,530 --> 00:44:42,330 take this peak here, this is 77, subtract 112, 707 00:44:42,330 --> 00:44:45,180 you have a loss of 35. 708 00:44:45,180 --> 00:44:46,410 So if you take the-- 709 00:44:49,750 --> 00:44:54,490 if you simply take the two things and put them together, 710 00:44:54,490 --> 00:44:56,580 the 77 is the phenyl ion. 711 00:45:00,460 --> 00:45:03,040 So if you just stick a chlorine on there, 712 00:45:03,040 --> 00:45:05,042 you got chlorobenzene. 713 00:45:05,042 --> 00:45:05,875 That's the spectrum. 714 00:45:09,140 --> 00:45:10,820 Here's another spectrum. 715 00:45:10,820 --> 00:45:15,350 This is very interesting, because all these peaks 716 00:45:15,350 --> 00:45:21,200 are separated by methylene units, 14 mass units, CH2 717 00:45:21,200 --> 00:45:22,970 units, all through the whole spectrum. 718 00:45:22,970 --> 00:45:24,680 When you see that, you know you've 719 00:45:24,680 --> 00:45:29,220 got a long chain of carbon atoms as part of your spectrum. 720 00:45:29,220 --> 00:45:32,360 So this particular spectrum is decane. 721 00:45:32,360 --> 00:45:37,190 And it ionizes at all these different bonds, 722 00:45:37,190 --> 00:45:44,050 producing this spectrum with this logical lost ion series. 723 00:45:47,330 --> 00:45:49,770 There's another one, dodecanoic acid, 724 00:45:49,770 --> 00:45:52,490 which has all these methylene units, which 725 00:45:52,490 --> 00:45:55,430 is a dead giveaway for a long chain of carbons connected 726 00:45:55,430 --> 00:45:56,565 to something. 727 00:45:59,680 --> 00:46:02,500 Here is a simple spectrum. 728 00:46:02,500 --> 00:46:06,260 This is 2-propanol. 729 00:46:06,260 --> 00:46:10,250 Now, the molecular weight of this is 60. 730 00:46:10,250 --> 00:46:11,730 But look down here. 731 00:46:11,730 --> 00:46:12,800 Do you see 60? 732 00:46:16,300 --> 00:46:18,970 There's no molecular ion there. 733 00:46:18,970 --> 00:46:22,780 So this molecule is doing something 734 00:46:22,780 --> 00:46:27,010 that's energetically very favorable to itself 735 00:46:27,010 --> 00:46:28,652 to produce a 59 peak. 736 00:46:28,652 --> 00:46:29,860 What do you think it's doing? 737 00:46:37,590 --> 00:46:40,990 It's one less than the molecular ion, right? 738 00:46:40,990 --> 00:46:41,490 Yeah. 739 00:46:41,490 --> 00:46:43,380 AUDIENCE: It's losing the H on the OH. 740 00:46:43,380 --> 00:46:43,660 JOHN DOLHUN: Yes? 741 00:46:43,660 --> 00:46:44,780 AUDIENCE: It's losing the H on the OH. 742 00:46:44,780 --> 00:46:45,940 JOHN DOLHUN: Yes, Hannah. 743 00:46:45,940 --> 00:46:48,850 Loses the H, right. 744 00:46:48,850 --> 00:46:49,615 So if you take-- 745 00:46:53,950 --> 00:46:55,660 this guy ionizes here. 746 00:47:02,980 --> 00:47:06,250 And it has resonance, because you 747 00:47:06,250 --> 00:47:17,510 can throw that positive charge out onto the oxygen. 748 00:47:17,510 --> 00:47:20,530 So it's really, really a very stable system. 749 00:47:20,530 --> 00:47:22,840 It loves to do that. 750 00:47:22,840 --> 00:47:27,960 And look at the base peak in this spectrum, 45. 751 00:47:27,960 --> 00:47:32,190 You can lose a methyl group from either side here, 752 00:47:32,190 --> 00:47:33,630 and you've got a 45. 753 00:47:33,630 --> 00:47:35,250 It's left over. 754 00:47:35,250 --> 00:47:39,120 And it's resonance-stabilized, because the positive charge can 755 00:47:39,120 --> 00:47:43,260 resonate with this oxygen here. 756 00:47:43,260 --> 00:47:44,730 So that's the idea. 757 00:47:44,730 --> 00:47:46,480 When you see a base peak, you know 758 00:47:46,480 --> 00:47:49,230 the molecule is loving to do something 759 00:47:49,230 --> 00:47:50,490 that's very favorable. 760 00:47:50,490 --> 00:47:55,210 And in this case, it could cleave from two sides. 761 00:47:55,210 --> 00:47:57,150 So this is an ester. 762 00:47:57,150 --> 00:48:00,180 This is ethyl-isobutyrate. 763 00:48:00,180 --> 00:48:04,680 I don't know if this is one that's been given out. 764 00:48:04,680 --> 00:48:06,810 I'm not talking. 765 00:48:06,810 --> 00:48:09,150 But this is a simple spectrum. 766 00:48:09,150 --> 00:48:11,880 And the idea here is, what you do 767 00:48:11,880 --> 00:48:13,950 is you're going to take this, and you're 768 00:48:13,950 --> 00:48:16,590 going to break it apart to try to figure out where 769 00:48:16,590 --> 00:48:19,090 those peaks are coming from. 770 00:48:19,090 --> 00:48:24,430 So if you cleave the ester here, right, right by this carbonyl, 771 00:48:24,430 --> 00:48:25,840 you lose this-- 772 00:48:25,840 --> 00:48:30,790 do this alpha cleavage, you'll get this 71 fragment, 773 00:48:30,790 --> 00:48:34,930 which can then lose carbon monoxide to give you 774 00:48:34,930 --> 00:48:37,160 a 43 fragment. 775 00:48:37,160 --> 00:48:40,670 So if we actually go back here, there's our 71, 776 00:48:40,670 --> 00:48:43,070 and there's our 43. 777 00:48:43,070 --> 00:48:46,710 And then, look at this right here. 778 00:48:46,710 --> 00:48:51,470 You can actually lose a neutral molecule of ethylene. 779 00:48:51,470 --> 00:48:53,930 Transfer the hydrogen back to this point. 780 00:48:53,930 --> 00:48:57,310 And you're losing CH2-CH2. 781 00:48:57,310 --> 00:49:00,640 That's an example where one piece of the molecule 782 00:49:00,640 --> 00:49:04,910 retains both the plus charge and radical that I talked about. 783 00:49:04,910 --> 00:49:08,280 And here's your fragment, your 88. 784 00:49:08,280 --> 00:49:10,390 There it is there. 785 00:49:10,390 --> 00:49:15,930 So the idea is to go through here and try to take your ester 786 00:49:15,930 --> 00:49:18,450 and try to break it up and substantiate 787 00:49:18,450 --> 00:49:21,810 some of the fragments from-- 788 00:49:21,810 --> 00:49:26,670 in a table or something, to show that what you've got. 789 00:49:26,670 --> 00:49:32,610 And that way-- that way you'll convincingly convince someone 790 00:49:32,610 --> 00:49:36,350 that you-- indeed that is your product. 791 00:49:36,350 --> 00:49:38,690 Do you have some questions about this? 792 00:49:42,440 --> 00:49:48,140 So if you're on day four, you'll be doing the mass spectra 793 00:49:48,140 --> 00:49:49,430 today. 794 00:49:49,430 --> 00:49:52,880 And I guess you turn in your guesses for your unknowns 795 00:49:52,880 --> 00:49:54,800 today, right? 796 00:49:54,800 --> 00:49:57,510 Good. 797 00:49:57,510 --> 00:50:00,100 It was easy, right? 798 00:50:00,100 --> 00:50:00,610 Yes. 799 00:50:00,610 --> 00:50:02,896 It was too easy, wasn't it? 800 00:50:02,896 --> 00:50:03,630 AUDIENCE: Nah. 801 00:50:03,630 --> 00:50:06,680 [CHUCKLING]