Document M40XabvGmqk01K8qjJB9vMjok

6y Ernest J. Sono/li .1 t.M> 1 . j .y^f7. I *.* Computer-controlled GC/MS for the analysis of polychlorinated biphenyls ill: w;iMc products of a tech scene more recently are poly Tnological society inevitably find their wav into the en chlorinated biphenyls (PCB's). These industrial compounds have vironment. Many of thesebeen widely employed as plasti to this problem is to allow a computer to handle the data and to control the GC/MS system. Figure 2 is a simplified block dia products have the capacity to cizers. as sealers in waterproofing gram of such a system, basically permanently change the ecology compounds and putty, in printing a Finnigan GC/MS and System/ of liv ing beings. One of the most inks, in waxes, in synthetic ad- 150. System/150 comprises a noteworthy of these products, hcrivc*. in cutting oils, as dielec dichloro diphcnxl trichloro ethane trics, as hydraulic fluids, as Digital Equipment Corporation PDP-8/L computer, a System (DDT), was discovered in 1939 high-pressure lubricants, and as a Industries interface #1152, two by a Swiss organic chemist, Paul heat-transfer medium. DECtape transports TU55, an H. Muller. Since that time the PCB's, as shown in (Figure 1), ASR 33 teletypewriter set, and a production of DDT and related arc structurally similar to the chlorinated hydrocarbon pesti chlorinated hydrocarbon pesti Houston Instrument DP-1 digital plotter. cides has increased until today cides nnd, thus, arc toxic. The the annual production of DDT presence of PCB's in samples alone exceeds 100 million lb. along with commonly occurring Mass spectrometer An incident in 1962 that had pesticides seriously complicates The mass spectrometer can be an explosive effect on the general a routine gas chromatographic either the Finnigan Model 1015 ptihlic was the publication of analysis to a degree that necessi or 3000, coupled with any Rachel Carson's book Silent tates the use of a gns chromato variety of gas chromatograph. Spruit,'1 which revealed the haz graph/mass spectrometer (GC/ These mass spectrometers arc of ards of pesticides. This book MS). This article describes a the qundrupolc type. Charged precipitated a report2 by Presi computer-controlled GC/MS sys dent John F. Kennedy's Science tem ns well as applications in particles arc separated according to their mass-to-chnrgc ratio by Advisory Committee that brought water pollution. into focus the great merits of While use of the GC/MS has sweeping an rf and dc voltage across the qundrupolc mass filter pesticides hut suggested that risks contributed much to the under assembly (Figure 3). Ions that arc involved in their use. The standing of organic compounds, have passed through the quadru- panel concluded that ultimately rearrangement products, and pole mass filter impinge upon the society must decide whether or identity of unknown samples, first dynodc of the electron multi not to use pesticides. there is still a considerable plier. This causes a current flow; Products that appeared on the amount of work involved in the analog signal is sent to the assigning mass numbers to MS interface where it is digitized spectra obtained, measuring rela nnd then into the computer. Each tive abundance and ion intensity voltage sweep sends a complete Mr. Ihmctli it Manager of Techni cal Mark ciitic, Finnigan Corporation. The author gratefully acknowledges the temples provider! by the U.S, Geological Survey, Menlo Fork, Calif. (Oottnhl Goeriitz and Leroy Law); the federal Water Quality Adminis tration Laboratory, Alameda. Calif. of each of the spectral lines ob served, etc. The obvious solution mass spectrum to the computer. All of the data ere stored on Figure 1 Polychlorinated biphenyls. * 10 xs4 m/e =290 (Jerald Math and Margaret Chn); and the Department of Fish and Game, Sacramento. Calif. (William Cattle and Leon Woods). ** 5 xs6 m/e = 324 m/e a 358 AMERICAN LABORATORY : 27 HONS 0 8 2 8 0 1 GC/MS continued sample times of 1 to 4096 msec. Also, it is capable of automati cally adjusting the integration time as a function of signal strength. This signal optimization mode provides a nearly constant signal-lo-noisc ratio over the en- tire spectrum. The interface also consists of logic and registers necessary to interface the mass spectrometer with the computer. System/150 A small-scale, general-purpose computer with a 12-bit word length and 4096 words of core storage is used. The Digital Equipment Corporation's ma chine is widely used for scientific applications. The chemist communicates Figaro 2 Computer-controlled get chrometogreph/mass spectrometer. with the system in a conversa tional dialogue through the tele type. This requires simple "yes," magnetic tape and can later be retrieved. and convert it to an analog rod voltage. By typing in the first and "no,'' or numeric responses to prompting originated by a com . Because the scanning voltage Is varied in a linear manner and the last mass the user sets the mass range that the mass spec puter program. No special training or knowledge of com because of the mass-separating trometer will scan. puters is required. qualities of hyperbolic electric helds created within the quadru ple rod assembly, the final mass presentation is inherently linear. The spacing between mass 17 The output analog signal from the mass spectrometer is fed to an integrator that integrates this ion current over a length of time initially specified by the chemist. A full software package is provided with the machine; in addition, compilers arc available for those who wish to develop their own programs to expand and 18 is, for example, identical The output of (he integrator is the system. For example, one to thut between mass 500 and 50!. This mukes computerization converted to digital form by a may wish to develop a program 12-bit onalog-to-digital conver that will compute all possible easy. The sweep time of the quudrupolc mass spectrometer ter and is then transmitted to the combinations of C, II. and O computer, which normalizes the whose molecular weights add up cun be as fast as 0.01 see, making data and transfers them onto to various masses observed on a it ideal for scanning extremely magnetic tape. The timing gen spectrum. fast eluting peaks, such as those erator is capable of generating Die Mode) A SR 33 Teletype found in gas chromatography with capillary columns, Figure 3 Quadrupote mast fitter assembly. MS/computer interface ITte interface between the computer and the mass spectrom eter has several components. The function of the 15-bit digitnl-toanalog converter is to take a number typed in by the chemist Ctocirefl fettm Jl Lot 1 I rT<5i / mm mr 28 FEBRUARY 1971 MGNS 082802 i F A GqglupgogQ FDE) cs AtfG:2c:!buQ Po-@ra ^J-fw^A<3 (TTY) has a keyboard, a paperlapc reader, a paper punch, and a lO'Cliaractcr, see printer. The keyboard and papcr-lapc reader serve as input devices, enabling the chemist to control the GC/ MS system. The paper-tape punch and the Teletype printer serve as output devices for the system. The Honston-lnstrumcnts Model DP*1 incremental plotter is another output device. It is used for plotting bar charts of spectra or of the total ion current. A magnetic tape unit buffers and controls the information transfer between the two TU55 tape trans ports and the computer. Software The executive program interprets the chemist's inputs from the TTY, loads the required pro grams from the magnetic tape into <hc computer memory, and transfers control to the particular program. Certain utility and maintenance functions are pro vided. These arc LIST, COPY, SAVE. DELETE, DUPLICATE, and TEST. LIST allows the user to list on the Teletype the contents of the tape and the number of blocks contained in the fdc. COPY allows the user to copy a file from* one tape to another. SAVE al lows the user to copy a portion of a file (c.g., a spectrum) from one tape to another. The DE LETE mode can delete a named file from the tape and close up the tape to take maximum ad vantage of the space available. DUPLICATE is used to dupli cate tapes. TEST is a diagnostic routine that is capable of check ing the performance of the inter face independent of the mass spectrometer and indicating any malfunctions that may occur. Two other extremely important modes of operation, OUTPUT and CONTROL, will be dis cussed in detail. In response to demand. Called the 69-700, it has many desirable fea tures. For example, operation in excess of 300 "C. Three-step input attenuator. Ten step, binary output attenuator. Sensitivity of 1 x 1011 g/sec hydrocarbon. Pyrometer readout, coarse and fine suppression con trols and many other features which will provide rugged, continuous performance. The 69-700, Standard FID is a companion to GOW-MAC's compact thermal conductivity instru ments. These units are all tough, inexpensive, reli able and deliberately simple in design. They don't replace research gas chromatographs but they can perform equally with them in routine analysis. This makes the research units avail- . | |i able for the more sophisticated ^ \ work for which they were de signed. It is not economical to do routine analysis on a re search instrument. Send for our literature. The technical facts ara worth having. fGOW 'i MAC) GOW MAC INSTRUMENT CO. 100 Kings Road Madison, N.J. 07940 U S A. a Telephone 201 /377 3450 Ckcl* Raadar Sarvtc* Card No. 34 AMERICAN LABORATORY : 29 E 0 8 7 8 0 SNOW GC/MS contlnusd Calibration The control mode is used for calibration, mass spectrometer control, data acquisition, and signal optimization. After the MS zero is adjusted, the system is calibrated. Norma! calibration requires approximately 40 see. The software of the calibration procedure is set up to look at the spectrum of a reference com pound, perfluorotributy! amine. The major ion fragments, m/e 69, 100, 131, 219, 414, 502, 614, etc., arc located and arc stored, along with the appropri ate rod voltage, on magnetic tape. This calibration fife is used to assign mass numbers to spectra obtained in future an alyses, whether gas chromato graphic, batch inlet, or solid probe. The conversotionnl dialogue is shown below. The chemist's answers to the computer's queries are shown to the right of the colon. name for PCB's). A 10-/*g (10-5 g) sample was injected onto the 6-ft x V*-in. (2 mm id) glass column, packed with 3% OV-1 on 100/120 Gas Chrom Q. The column temperature was pro grammed from I75-23QC at 4 per minute. The cheroisicomputcr dialogue for mass spectrometer control and data acquisition is shown below: SYSTEM/150 IS ON SELECT MODE: CONTROL CALIBRATE?: NO TITLE: AROCl.OR 1254 CALIBRATION FILE NAME: CA1H6 FILE NAME: USGS MASS RANGE: 50-150:151 260:261-410 INTEGRATION TIME: 4;R;16 SAMPLES AMU: l;l;l THRESHOLD: 1 1015 RANGE SETTING: HIGH MAX RUN TIME: 60 DATA combtoM a llnaar aborb*r>c# rang* up to 3,0 O.D. wKh vary low noiao and drift-- Ion than .0004 0.0. Moaauramonta can bo modi on any of ton aboorbanco rangoo (from .01 O.D. full ocalo to S.12 O.D. full scale) or on a single 0 to 100% transmit' tones tealo. Racordtr outputs of 1 mv and 10 mv aro supplemented by a 0 to t ma output, which will drive low*cost gaivanometrlo recorders. Two interchange* obis pfugdn flow coils aro available; an 9-*J ceil for micro-column analyses and a 32-*d coll lor monitoring preparative separations, density-gradient centrifuga tion and electrophoresis. Free new technical bulletin. A technical bulletin describing the use of ultrasensi tive UV dotoclors In liquid chromatogra phy la yours for the asking. Please ad dress us at 2743 Ninth Street, Berkeley. California 94710. Phone (415) 641-7221. SYSTEM/150 IS ON SELECT MODE: CONTROL CALIBRATE?: YES CALIBRATION FILE NAME: CA1H6 MASS RANGE: 20-620 1015 RANGESETTING: HIGH This calibration procedure is unique in that the calibration compound need be used only once or twice a day. One docs not continuously have to "bleed in" the reference compound as the GC peak is eluting. This elim inates overlapping and possible ' reaction of MS peaks of the standard and unknown. | Setting up 1 for a typical analysis [] CHROMATRONIX Cm.In II. !>.i.v<ki ...... No litt Upon successful calibration wc were ready for a GC/MS run. The compound wc chose to an alyze is Aroclor 1254 (trade 30 FEBnUAHY 19/1 When the computer comes on the air with the statement SYS TEM 150 IS ON SELECT MODE, the chemist's response is CONTROL. He answers NO to (he query (o calibrate since this was done previously. The title the chemist tvped, ARO CLOR ) 254, nil) be shown on all the output reports. The calibration file name, CAIH6, defines the magnetic tape file that contains the cur rent calibration data. With the input, USGS, the operator iden tifies the acquisition run. I'SGS becomes the means by which the data file on tape is idcntilicd The computer assigns mass num bers to tbe specira in lhe data file (USGS) by compaiison to the calibration tile. A unique advantage of scan ning an electrostatic held is lliat one can intermpt llic 'can and HUNS 082804 mm* iki time average to enhance the signal-to-noisc ratio. In the above example the chemist sets up the analysis to scan from m c 50 to 410 in three ranees. The com mm* Figaro 4 Reconstructed get chromotogrom of 10p.g of Aroclor 1754. puter will integrate for 4 msec at each amu in the range 50 150, 8 msec from 151-200 armi, and 16 msec front 261-410 amu. If desired, (he computer can be asked to take up to 10 samples amu. This assists in the location of mass defects and accurately determines isotopic ratios. In the above example, the input for each of the three mass ranges will provide sampling at integer mass units only. The threshold inquiry repre sents a filler or noise threshold of the system. The input, I, refers to the least significant bit of the analog-to-digital converter. mm* iki t I Maximum run time specifies, in minutes, the duration of data acquisition. The computer loads the program for the analysis and then types DATA when ready. After introducing the sample the chemist may leave the system unattended for the entire run. During the run the computer keeps the chemist informed by plotting a chromatogram. At the end of the run the computer will reduce the data. Output mode As the name implies, this mode is used to output informa tion stored on the magnetic tape At the end of an analysis the computer can be employed to plot a reconstructed gas chro matogram. The actual computer plot is shown in l-'i^ttre J alone with the chemist-computer dia logue required to obtain the trace. Note that 250 complete mass spectra were taken dnnin: the analysis. Now the task was to determine the identity of each of the peaks We fust determined which com pounds are Icirachloio biphenyl 32 : FEOHUAHV 1971 MOMS 0 8 2 8 0 5 MbMM MMOt % isomers. This was done by ask ing the computer to search through the 230 mass spectra and locate spectra that contain mass fragments between m/e 290-291. This is shown in Fig ure 5. Similarly, we can search for the pentnchloro biphenyl (m'e 324) and hcxachloro bi phenyl (m/e 358) isomers in Figures 6 and 7, respectively. Wc cun now overlay these lim ited mass plots on the recon structed gas chromatogram to identify each of the GC peaks. The GC peak (Figure 4) whose maximum occurs at spectrum '#162 appears to have 4. 5, and 6 chlorine biphenyl substituents. However, this can be due to a single compound, hcxachloro bi phenyl, which gives rise to 4 and 5 chlorine biphenyl ion fr;mments in cite ion source. Figures 8, 9, and 10 arc of spectrum #76 (tctrachloro biphenyl), 34 FEBRUARY 1971 spectrum 118 (pontacMoro biphenyl), and spectrum irlM (hcxachloro biphenyl), respec tively. Figure l! is a printout of a limited portion of spectrum i76. Tills is of considerable help in determining the elemental composition of an unkmmn. Environmental samples Figure 12 is a reconstructed chromatogram of a Los Anodes HONS 082806 m mo WfCi iTtll* Ik ON kiiUl hum i oule rrMmNfhtnl*I i Ukos kl1C1*U" I.UW.Iht MMItlbMO nilUMTTlV N*|fc .* I ?IO*M rimroK i*cui n ki.MI.4lt |.4tW>0UMtl NOkM^Wk ONI Mki n* 10144. ION IMlNkMI* It ANWLOk T.I4 AU IMI '<11 IT prvffi..li*t J4I..V18* rtvjr..nr 4v..r*t rva.fi II.4* Kl.l V.U fvt.ll 4. Iff rvt.r i.st r*v. lot r*thini or ioim. iwUNkiiT I .00 flgut$ 11 Printout ot portion of tpoetrum 76. u* wo cor WMMfiflnwi K. HONS 0 8 2 8 0 7 Flguro 14 PCB's in $war ontroet. AMERICAN LABORATORY 36 QC/MS continue n/ l Figure 18 PCS'* in sturgeon ovtry axtract. sewer extract. The fact that this chromatogram shows very little is a strong, selling point for a computer. A limited mass search (Figure 13) for tetrachloro bi phenyl showed five areas where ion fragments of m/e 290-300 exist. Fifsure /4 (spectrum #105) proves the existence of PCB's by the isotopic cluster at m/e 290 296. Another application is shown in Figure IS, which is a recon structed chromatogram of an extract of ovaries from sturgeon fish. A limited mass plot showed the existence of PCB's, and Figure 16 proves the existence of hexachloro biphenyl by the iso topic cluster at m/c 358-364. An aid in discovering the PCB's is the expand amplitude option where all the spectra below 3% are expanded by 10 times (note the labeling of the ordinate). It is interesting to note that this sample also contained DDE. a metabolite of DDT. This was confirmed by a limited mass plot and Figure 17, which shows a spectrum of DDE (m'c 316). This compared favoiably with 38 : FEBRUARY 1971 the structure obtained by Sphon and Damico.1 The background subtract op tion allows the chemist to avoid misinterpretation due to un wanted MS peaks from column bleed and oilier impurities, Fie* tire IS repeats Figure 17, but with the background subtracted Note the absence of peaks in the area bevond the isotopic cluster at m-'e 316-324. In this paper we have focused on a computer-controlled C1C ` MS system rather than the con ventional data logging devices, MQNS 082808 IIn' advantages of quadrupolc vs 2. Chrm. Eng. Nrw,i (May 27. 1963). magnetic mass spectrometers, 3. si'HON. j. a. ami damico, j. n., t and have shown but a few of the "The mn* spectra of some chlo rinated aromatic pcslicidal com munv exciting applications for pounds." Org. htnxx Spectrum. 3, GC 'MS. 51-62 (Jan. 1970). Rofronct 4. Gustafson, c. o., "PCB's--prev alent and persistant." Environ. I. cahsov, n.. Silent Spring (Hough* ion Mifflin Co.. Boston, 1962). Sci. Techno! 4, 814-819 (Oct. 1970). 082809 Figure 17 OOE in sturgeon ovary extract. Figure It DDE in sturgeon ovary estract (background subtract). AMERICAN LABORATORY : 37