Mass spectrometry in environmental organic analysis

Anaiyhca Chtmlca Acta, 263 (1992) 1-19

Elsewer Science Pubhshers B V , Amsterdam

Review

Mass spectrometry in environmental organic analysis D Barceld Envwonmental ChemutsrryDepartment, CID-CSIC,

c /Jordr Gwona 18, 08034 Barcelona (Spam)

(Received 27th September 1991)

Abstract

An ovemew of the use of mass spectrometty III environmental orgamc analysis IS presented It Includes conventlonal gas chromatography-mass spectrometry wth electron unpact and posltlve and negative chenucal lomzatlon and modem mass spectrometnc methods such as fast atom bombardment, tandem mass spectrometxy and hqmd chromatography-mass spectrometry Apphcatlons to the determmatlon of envlronmentally relevant compounds such as polychlormated brphenyls, polycychc aromatlc hydrocarbons, surfactants and pestlcldes are outhned The advantages and hmltatlons of the different mass spectrometnc techmques for these four groups of pollutants are dIscussed Keywords Gas chromatography, Llqmd chromatography, Mass spectrometry, Environmental samples, Pestlades, Review

Mass spectrometry (MS) IS a highly sensltlve and specrflc techmque smtable for use m envlronmental organic analysis The combmatlon of chromatography and MS combines the high dlscrmunatmg power of one mstrument with the high separating power of the other so complementarlty of the quahtatlve and quantltatwe performance of the mdlvldual techniques can be achieved For example, gas chromatography (GC) 1s an excellent quantltatwe but a poor quahtatlve techmque, but 1s very well matched with MS, whrch offers good quahtatlve and poor quantltatlve properties The most common coupled methods used m environmental orgamc analysis melude chromatographlc techniques [GC, hqmd chromatography (LC) or supercrltlcal fluid chromatography (SFCll and MS In GC-MS the selectlvrty 1simproved, compared with MS alone, by the physlcal separation of the components of a mixture by chromatography prior to mass analySE The selectlvlty can be enhanced by either the 0003-2670/92/$05

use of different reagent gases m the posltlve and/or negative chemical lomzatlon (PC1 and NCI, respectively) modes or by the use of two or more techmques m tandem, such as GC-MS-MS Numerous pubbcatlons covering the whole field of envlronmental orgamc analysis, either using conventlonal and/or mpdem MS techmques, have been published Two different aspects can be dlstmgmshed Instrumental developments and fundamental aspects of modem MS techniques such as fast atom bombardment (FAB), contmuous-flow FAB, LC-MS and SFCMS, which have been dlscussed m several papers [l-6] and m books [7,8], and apphcatlons m envlronmental orgamc analyss, which have been compiled m two books [9,10] and several general reviews 111-141 Specific applications employmg either NC1 as a very selectwe techmque for the detection of electrophlbc compounds, e g , polychlormated blphenyls (PCBs) m complex matrices [15,16] or LC-MS for thermally labile and/or

00 0 1992 - Elsevler Science Pubhshers B V All rights reserved

2

D Ban&

polar compounds of environmental interest, have been described [17,18] and a book on MS-MS apphcatlons has appeared [ 191 This review will illustrate some of the ways in which MS can be applied for the charactenzation of four groups of environmentally nnportant compounds PCBs, polycychc aromatic hydrocarbons (PAHs), surfactants and polar pesticides It is beyond the scope of this review to cover the great many studies whrch have used different MS techniques for the ldentlflcatlon and determination of environmental organic compounds In this regard, the review is not intended to be complete and only highlights of conventional and modem MS techniques applied m this field will be presented

GAS CHROMATOGRAPHY-MASS (GC-MS)

SPECTROMETRY

Electron impact (EI) wnuatton

GC-MS with EI lomzatlon is the most widely used MS technique by laboratories involved m environmental organic analysis The most cornmon practice 1s to identify the compounds of interest by a library search and/or with a second inJection wth co-elutlon using authentic standards The use of available libraries with more than 120000 spectra for ldentlficatlon of the dlfferent environmental compounds 1sof great mterest [12,13] A book wrth EI spectra of envlronmental pnonty pollutants has been pubhshed [201 Cahbratlon of the instruments 1scarried out by automatic programs such as the AUTOTUNE program and usmg perfluorotnbutylamme GC-MS with EI usually gives good sensltlvlty and reproduclblhty of the spectral data and can reveal structural information A disadvantage of EI IS that it does not always provide molecular weight mformatlon, as the molecular ion species, [Ml+, of many compounds 1s too labile to be observed m the mass spectrum The reproduclblhty of EI data on a given mass spectrometer, and between different mass spectrometers using smular condotlons, 1s generally good, so that rapid tdentlflcatlon of spectra by comparison with mass spectral databases IS possible Thrs technique 1s usually performed usmg three different types of mstru-

/Anal

Chm Acta 263 (1992) l-19

ments quadrupole analysers, ion traps and magnetic sector instruments Dependrng on the mstrument used, differences m relative abundances of the EI spectrum for a given compound have been observed Thus, for organophosphorus pesticides, it has been found that the use of a quadrupole analyser may result m a weaker abundance of the ions at high mass as compared with a magnetic sector with differences varymg from 3% to 100% [211 Smularly, when using an ion trap, which has a completely different design to a quadrupole analyser and 1s clalmed to have equal or better sensltlvlty [ 11, considerable differences m the EI mass spectra of chlorotrlazmes were noticed, e g , cyanazme showed a base peak at m/z 68 using an ion trap whereas with a quadrupole analyser the base peak corresponded to m/z 225, with dtierences m the relative abundances m the two instruments of more than 50% [22,231 The technique 1s adequate for environmental organic analysis as the limits of detection CLOD) are usually m the low pg 1-l or kg kg-’ level for the deterrnmatlon of organic pollutants m water and sod samples, with absolute injected amounts lower than 1 ng, when working under full-scan conditions with a scan range from m/z 30-50 up to 600 u This scan range 1s common m most of the quadrupole and ion trap mstruments, also called bench-top mstruments When higher m/z values are needed, the use of quadrupoles up to m/z 2000-4000 or magnetic sectors is required The sensltlvlty of GC-MS (and also of the other chromatography-MS combmatlons) can be increased by one to two orders of magnitude by usmg only a few selected ions by the technique of selected ion momtormg (SIM) Quantification m GC-MS 1s usually achieved by using SIM or labelled compounds A limitation of GC-MS is that the compound must be sufflclently volatile to be amenable to GC, so for polar compounds derlvatlzatlon 1s ofteh needed There are a large number of apphcatlons of GC-MS with EI in the determmatlon of organic pollutants As already mentioned, applications will be restricted to a few envnonmentally lmportant compounds One of these groups 1s surfactants, which consist of four types anlomc, having

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Chm Acta 263 (1992) 1-19

3

a negattve charge on the surface active moiety, e g , sulphonates, catlomc, with a posmve charge, e g , quatemary ammonium salts, non-lomcs, which are solublhzed by chams of ethylene omde groups, e g , ethers made by ethoxylatmg lmear alcohols and alkylated phenols, and amphotenc, e g , unldazolmlum denvatlves The use of GC-MS m this particular field has permitted the characterlzatlon m river water samples of various non-lomc surfactants such as polyethoxylates having a low degree of polyethoxylatlon (n = O-7), and of hnear alkylbenzenes, identified m urban waste waters and sednnents, which are the raw matenal for alkylbenzenesulphonates (LAS) [24-271 (see Table 1) The ldentlficatlon of chlormated and brommated denvatlves of nonylphenol and octylphenol polyethoxylate surfactants obtamed after wastewater dlsmfectlon was also feasible, with the [M - 71]+ ion as base peak, corresponding to a benzyhc cleavage [25] Other non-lomc surfac-

tants from alcohols of natural sources were ldentiled that exhibIted a fragmentation at the ether bond and enabling a structure to be assigned uneqmvocally to the hydrocarbon cham of an unknown ethoxylate alcohol It was shown that hydrogen transposltlon takes place, which mcreases with mcreasmg number of oxygen atoms, thus makmg rt possible to dlstmgmsh between mono- and polyethoxylate denvatrves [27] For the charactenzatlon of amomc detergents, e g , linear alkylbenzenesulphonates, the trdluoroethyl or methyl ester denvatlves are usually needed prior to the GC-MS determmatlon 1281 The last group of surfactants usually determmed by GC-MS with EI 1s the catlomc-type alkylmtnles and tnalkylammes and related compounds, such as octadecylmtrlle and methyldmctadecylamme, which were determmed m urban coastal environments 1291 The characterlzatlon of dtierent photoproducts of envnonmental mterest such as fatty acids, aldehydes, alkenes, alkanes and

TABLE 1 Recommended mass spectrometrlc techmques for the determmatlon of different types of selected pollutants Group

Compound

EI Pestwdes

Qrganophosphorus

FAB MS

GC-MS

LC-MS

CI

X X X

Chlorotnazmes

X X X

Carbamate Urea Phenoxy acid Pyrethrold

X X

X X

Glyphosate Quats Includmg chlormated compounds toxaphene, chlordane, brommated, etc

X X

X

PAHS

Non-lomc, n < 7 Non-lomc, n > 7 Cationic, amomc, amphoterlc

X

Neutral NO,-PAHs OH-NO*-SOS-PAHs

X

109 100 101,118 32-41 72-80

X X

Skactants

21,23,42,43 23,61,62 106-108 22,23 23,85 103,112,113 102-105 108,111,112 113,140,142 44

X

PCBs

Selected references

X

X

X

X

24-27 24,121-123,139 98,99,26

X

SO-56,141 56,82 82 124

X

4

2-methyl ketones by oadatlon of the carbon m p to the nitrogen, obtamed after UV n-radiation of long-cham alkylammes, was also feasible [30,31] Another important group of contaminants 1s the PCBs, which have a total of 209 congeners contammg from 1 to 10 chlorines As a general feature, PCBs exhlblt with EI relatively high abundances of [Ml+ and [M - 70]+ and fragmentation usually occurs wth subsequent losses of Cl atoms The loss of the Cl ([M - 35]+ ) ion 1s favoured m the case of o-Cl-PCBs, m which three of the four ortho posltlons are chlormated [32] Such an orth effect 1s also unportant when two of the ortho posltlons are chlorinated, such as the 2,2’-positions, and so this effect was used for the dlfferentlatlon of chlormated blphenyls (CBS) No 163 and 138, which co-eluted under the usual GC conditions [33] However, CB No 138 has two Cl atoms m the 2- and 2’-poslt1ons, so the orrho effect was observed and the [M - Cl]’ ion was formed with a relative abundance of 2%, whereas for CB 163 it was not GC-MS with EI was usually employed for the charactematlon of PCBs in groups of isomers from technical Aroclor and Clophen mixtures 134-371 Determination of contaminated sedlments at levels varying from 0 2 to 50 mg kg-’ was feasible after using several sample preparation techniques mvolvmg a Florlsd column or gel permeation chromatography (GPC) 138,391 FInally, for this group of compounds, the highly toxic coplanar CBS Nos 77, 81, 105, 126 and 169 have gamed importance 111the last few years owing to then sumlar toxlclty to dloxms and have been determined m various envu-onmental samples [40,411 The presence of organophosphorus pesticides [21,23,42,43],tnazmes [22,23], pyrethrolds [44] and paraquat and dlquat after dehydrogenatlon [45] and urea herbicides after denvatlzafion with heptafluorobutyrlc anhydride [46] was confirmed by GC-MS with EI A multi-residue method for rapid screenmg of a variety of 50 polar pesticides m water matrices after solid-phase extraction was recently developed and sub-pg 1-l LODS were achieved [47] Depending on the pestlclde type, different dlagnostic ions are monitored Chlorotrlazmes are

D Bar& /Anal Chm. Acta 263 (1992) l-19

charactemed by a base peak that usually corresponds to [M - CH$ or [Ml+ with other dlagnostlc ions due to the losses of [C*H$IH]+ or [C3H,NH]+ 1231Typical characteristic Ions mdlcatmg the functional group structure of dtierent organophosphorus pestlcldes are assigned to [(CH,O),POl+, e g , femtrothlon, to [(CH,O),PSI+, e g , fenchlorphos, and to [(HO),PS]+, e g , parathion-ethyl, with other main ions corresponding to losses of OH, C,H,, ClC,H, and ClC,Hs and Cl depending on the compound The molecular weight fragment 1s also obtained for most of the organophosphorus pestrcldes with relative abundances of 25-100% [231 An extensive list of the mam ions obtamed under EI for substltued phenyl phosphorothloates has been published [21] A notable aspect of that paper IS the dlscusslon of the ortho effect which also takes place as reported for PCBs It 1s demonstrated that for these specific organophosphates havmg an o-Cl, Br, I, NO, and other substltuents, their [Ml+ molecular ion mtenstltes are neghglble m comparison with meta and paru substltuents Hence, for ortho substltuents, an attack of the P=S+ group at the ortho posltlon takes place, and as a consequence, a cychc [M - Xl’ ion, X being the ortho substltuent, 1s generated which 1s energetltally favourable [21] Since photolysls can be one of the mam nonbiotic degradation processes affecting transformation of pestlcldes m the aqua& environment, GC-MS wth EI has been employed for the characterization of the photolysls products of pestlcldes after lsolatlon of the different subproducts, e g , femtrothlon In this regard UV irradiation of femtrothlon produced different oxldatlon, lsomerlzatlon and solvolysls products, of which femtrooxon, trnnethyl phosphate, carbomethoxyfemtrothion, 0,0,X-trimethyl phosphorothloate and the S-methyl isomer of femtrothlon were detected [48,49] A large number of papers have been published reporting the determmatlon of PAHs m differeAt environmental matrices by GC-MS with EI These compounds are of environmental interest owing to their proved toxlclty and carcmogematy, benzo[alpyrene, benzo[a,hlanthracene and mdeno[l,2,3_cdlpyrene are the most toxic of a total

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Chtm Acta 263 (1992) 1-19

of twelve PAHs listed by the US Envnonmental Protection Agency (EPA) PAHs have been Identified m vatlOus environmental matrices such as sediments [50,51], bivalves 152,531and air partlculate matter [54-561 In this regard, the US National Institute of Standards and Technology (NIST) has certlfled several reference matenals of urban ax particulate matter, such as SRM 1649 and 1650 In one of them over 80 polycychc aromatic compounds belongmg to many different classes (anbydndes, carboxyaldehydes, dlazaarenes, cychc lmldes, mtrohydroxy denvatlves, mtrolactones and qumones) have been ldentlfled [56] Ions monitored for the most common PAHs correspond to m/z values of 176 and 178 (phenanthrene, anthracene), 200 and 202 (fluoranthene, pyrene), 226 and 228 (chrysene, benzo[alanthracene), 250 and 252 (benzo[b and klfluoranthenes, benzo[a and elpyrenes, perylene) and 276 and 278 (mdeno[ 1,2,3_cdlpyrene, benzo[ ghr Iperylene) For the mtro denvatlves, such as mtroarenes, [M - NOJ+ or [M - I-INOJ+ have been usually obtamed as base peaks [54] Prior to the final GC-MS determmatlon of the vanous organic pollutants m environmental samples, extensive extraction and clean-up steps are needed For the lsolatlon and fractlonatlon of PAHs from environmental samples different methods have been used, such as hqmd-hqmd partltlonmg, nhca, alumma or Florlsd column chromatography, LC and GPC To illustrate an example of how unportant the fractlonatlon poor to GC-MS analysis IS, Fig 1 shows the total Ion current chromatogram of GPC fractions of a river sednnent extract The analytlcal protocol used conslsted of extractlon of PAHs assisted by somcatlon, fractlonatlon on a sihca-alumma column and lsolatlon of one of the fractions and a second fractlonatlon of the Isolated fraction on a GPC column contammg Blo-Beads SX-12, where several subfractions were obtamed and analysed by GC-MS The last two subfractlons are mdlcated m Fig 1 Compounds ldentlfied in the different fractions were polyestyrene trlmer Isomers and squalene (Fig lA), phenanthrene, C-l-substltuted dlbenzothophenes, phenanthrenes, fluoranthene, pyrene and chrysene (Fig 1B) PAHs were eluted entirely m this last fraction, exhlblt-

1 . . a0

“.

.

, . ,

m

,*,

,

WC) tcnln)

Rg 1 Total 1011current chromatograms of the last two GPC fractions of a rwer sedtment Expermtental condltlons BtoBeads SX-12 column, elutlon volume, (A) 17 4-19 ml and (B) 19-275 ml, eluent, tetrahydrofuran at 05 ml mm-‘, GC capdlary column, CP-Sd 5 CB Mam compounds ldenttfied 1- polystyrene trlmer Isomers, 6 = phenanthrene, 7-10 = Cl- and C-2-substttuted dlbenzothtophenes and phenanthrenes, 11= fluroanthene, 13 = pyrene, 15 = chrysene [51]

mg a characterlstrc profile of fossll hydrocarbons with a predommance of alkylated over parent components [51] Recently the on-hne coupling of LC with GCMS has been apphed to the determmatlon of PAHs m 011 samples of different orlgm In this approach, the sample was dduted m n-pentane and introduced on to the LC column where a fraction was transferred to the LC-GC-MS system using a loop-type interface The advantages

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of this method are that not much sample mampulatlon 1s needed and an LOD at the low pg 1-l level IS obtamed [57] The use of GC-MS with EI is certainly the most widely employed technique m envlromnental orgamc analysis for confmnatlon and determlnation purposes Although it IS sunple, rehable and fast, emphasis should be placed on certam aspects the use of ion traps, quadrupoles or magnetic sectors m many mstances gives dlfferences m relative abundances of the compounds analyses and so dlfficultles may arise when comparmg spectra between instruments, compound should be sufflclently volatile or derlvatlzed prior to GC-MS mJectlon, which 1s a disadvantage for the more polar and mvolatlle environmental samples, and slgmflcant clean-up 1s required for dirty environmental samples prior to GC-MS mJectlon otherwlse column and source contammatlon will lead to problems m the analytical performance Chemical wnuatwn

GC-MS with either positive and/or negative chemical lomzatlon (PC1 and NCI, respectively) is often employed m environmental organic analysis Chemical lomzatlon 1s considered to be a soft lomzatlon technique that employs a CI reagent gas, generally methane, but also Isobutane and ammoma, at a source pressure varymg from 0 1 to 2 Torr The optmnnn reagent gas pressure used 1s strictly dependent on the reagent gas used [58,59] The source temperature 1s another nnportant parameter which has to be taken mto account because it affects fragmentation patterns and sensltlvlty An excellent book covering the fundamental aspects of chemical lomzatlon mass spectrometry has been published [60] and important research on the environmental orgamc analysis of prlonty pollutants, using NCI, has been reported by the groups of Dougherty [15,591 and Hates [16] Of the two modes of operation, PC1 has tradltlonally been employed for obtammg molecular weight mfonnatlon when conventlonal EI spectra do not provide It Combined EI-PC1 sources have been available for many years For many compounds, the sensltlvlty of PC1 1s slmllar to that of EI, e g , for the chlorotnazmes [23] The different ions obtamed m PC1

Chm Acta 263 (1992) l-19

depend on the reagent gas and compound employed A typical spectrum usmg methane as reagent gas has as a base peak the [M + HI+ ion, together with other peaks correspondmg to [M + C,H,l+ and [M + C,H,l+ and some diagnostic ion of the molecule In the case of ammoma, the base peak can be either [M + HI+ or [M + NH,]+ depending on whether the proton affmlty of the compound 1s higher or lower, respectively, than that of ammonia Methane as reagent gas has been used for the determmatlon of a vanety of compounds such as chlorotrlazme herbicides [231, organophosphorus [23,61,62] and carbamate msectlcldes [631,surfactants [25,31], PCBs [64] and chlormated pesticides [65] Other reagent gases employed were ammoma [661for chlorotrlazmes and lsobutane for carbamate msectlcldes [631 Although m prmclple a group of compounds of the same type may give a better response under one mode of chemical ionlzatlon operation, It can happen that some partlcular compounds, with large structural differences, may give a better signal m another chemical lomzatlon mode This 1s the case with organophosphorus pesticides, which generally give a better signal with NC1 but m some cases, e g , wth crufomate, fenanuphos, fenthlon, metharmdophos, sulfotep and trlazophos, PC1 1s to be preferred [62] The increasing use of GC-MS with NC1 m envnonmental orgamc analysis 1s particularly due to the fact that most of the compounds of em+ ronmental interest have electron-withdrawing groups, e g , PCBs, NO,-PAHs and organophosphorus pesticides with NO,- or Cl-substrtuted aromatic moieties Hence stablhzatlon of the negative charge by electron capture 1s feasrble, thus leadmg to a better signal m the negative Ion mode Ion-formmg reactlons under NC1 are of different types such as resonance and dlssoclatlve resonance electron capture, ion-molecule reactlons, radical-molecule reactions, wall-neutral mteractlons and lomzatlon-neutrahzatlon-relomzatlon reactions [16] It IS clear that the formation of negative Ions under electron capture negative lomzatlon IS influenced by the presence of reagent gas lmpuntles, the charge density and composltlon of the plasma, long Ion source rest-

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Chm Acta 263 (1992) l-19

dence times and the elevated pressure The technique 1s very useful m environmental analysis as it provides the main features desired, namely selectw@ and sensltmty A disadvantage IS that no hbraries are avallable yet, although recently a compllatlon of NC1 spectra has appeared contammg mamly chlormated compounds of envlronmental interest [671 Two problems encountered with the use of NC1 m different instruments for obtammg potential spectral hbrarles have been reported recently, namely the NC1 mass spectra [68] and the determination of LODs [69] In this regard, It was found that under srmllar conditions of sample concentrations and ion source temperatures and pressures, the spectra showed good agreement m the molecular Ion mass range Differences were observed m the lower mass fragment ions formed by dlssoclatlve electron capture when a HewlettPackard instrument was compared wth a Fmmgan magnetic sector mstrument [68] The LODs for a series of compounds of environmental mterest were highly variable between the mstruments, and this was attributed to the “effectwe electron temperature”, caused by the different focussmg and extraction fields of the Instruments [69] Selected apphcatlons reported on the use of GC-MS with NCI, mamly with methane, include the characterlzatlon of a variety of organochlonnated aromatic compounds such as polycychc chlorinated msectlcldes [70,71], toxaphene [72,73], chlordane 1741, PCBs [71,75,76] methylthlo metabohtes of PCBs [771, dloxms [15,78,79] and brommated aromatlc compounds [791 Other reagent gases such as lsobutane [BO],methylene chloride [70], hydrogen and hehum [78] have been employed to enhance the selectlvlty and/or sensltlvlty m the NC1 MS of chlormated compounds The mcreased scnsltwlty wth the use of NC1 as compared with EI has been demonstrated [71] for a variety of chlormated PCBs Above SIXchlorme atoms, PCBs showed an increase m response versus El of 2-3 orders of magnitude, which makes the technique useful for momtormg such compounds m environmental matrices An illustrative example of the use of GC-MS with NC1 IS shown in Fig 2, where selected chlorobrphenyl congeners (CBS) were determined

i m/z=292

115

nvz.326 hH5C~s

I

TOTAL ION CURRENT

TIME (MINI Rg 2 Total Ion current (TIC) and selected Ion matograms (CC-NC1 MS) of a mussel extract The momtored correspond to p,p’-DDE (m/z 318) and the lsomenc groups C,,H,Cl, (m/z 2921, C,,H,Cl, (m/z and C,,H,Cl, (m/z 360) [75]

chroIons PCB 326)

m a mussel extract by GC-MS with NC1 The ions momtored at m/z 318 corresponded to pp’DDE, at m/z 292 to CB 52, at m/z 326 to CB 118 and at m/z 360 to CB 153 and 138 These three main Ions corresponded to the [Ml- ion of CBS contammg four, five and SK Cl atoms These are the mmnnum numbers of Cl atoms needed to observe good sensltlvlty m GC-MS with NC1 for such types of compounds These CBS are commonly observed m real samples and are of concern wlthm European Commumty leglslatlon [75] It should be noticed that, m general, for

8

organochlormated compounds the base peaks corresponded to [Ml- ions, such as for the PCBs m Fig 2, but a variety of other ions such as [M + Cl]- [701, [M + HI-, [2M + Cl]- [801, [M Cl]- [7], [M - Cl+H]- and [M - 2HCll- [74l, [M - lS]- [77] and [M - Br]- [79] have also been reported Although other compounds of environmental interest have been analysed by GC-MS with NCI, the applrcatlon of this technique to organochlonnated compounds 1s stdl the most often used Other compounds determined were anion detergents with prior derlvatlzatlon [281and the PAHs m fly ash, which usually gave [M - HI- as the base peak, and occasionally [Ml- Other peaks of mterest corresponded to [M + HI-, formed by either a fast radical reaction between H- and [Ml- or a hydnde transfer process of the Hamon to the netural PAH molecule [M + 141and [M + El- attributed to [M + 0 - 2Hl- and iIvi]+ 0 - HI-, respectively, were also formed The ldentlflcatlon of polar substituted NO,PAHs m diesel exhaust particulate usually gave [Ml- as base peaks, other peaks corresponded to [M - NO,]- and [M - NOI- [56,821 Mxtures of 20% 0,-N, and CO, as reagent gases were used for obtammg speafz mformatlon on PAHs substltuents, e g , the posmon of methyl substltuents m methyl-substituted PAHs These reactions are called wall-catalysed oxldatron reactions, because there 1s an addition of oxygen at elevated Ion source temperatures Ions formed were [M + 14]-, [M + 30]- and [M + 44]-, corresponding to [M+O-2H]-,[M+20-2H]-and[M+304H]-, respectively [83] Apphcatlons to pesticides included the characterlzatlon of organophosphorus [23,62,63,84] and chlorotrlazme types [23,85] In the case of organophosphorus pestlades, the formation of the [Ml- ion as base peak for the parathion group compounds is a consequence of the aromatic moiety structure of these organophosphorus pesticides, which 1s easily stabrhzed by the mtro group under negative ion condltlons Cl losses, e g , as CH,Cl and HCl, have been observed for chlorme-contammg organophosphorus pesticides The base peaks correspond either to the different functlonal group fragment or to

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/Anal

Chm Acta 263 (1992) l-19

the thlophenolate anions formed by transfer of the aromatic moiety from the oxygen to the sulphur atom, as was observed for phosphorothronate pestlcldes contammg an aromatlc moiety with electronegatwe groups [23] Further research has been carned out to mcrease selectlvlty by using other reagent gases Instead of methane In these cases the mass spectrum pattern undergoes important changes accompamed by an enhancement of selectxwty, thus provldmg a useful way for characterlzmg pollutants Methylene chloride at a pressure of 1 Torr was used as reagent gas to perform chlonde-attachment NC1 MS for a variety of organophosphorus pesticides, m a slmllar way to that reported prewously for organochlormated compounds In general, the functional group of the organophosphates was the base peak wth values of the [M + Cl]- attachment ion which varied, depending on the compound, from 1 to 100% This chloride attachment ion 1s very useful m pestlclde screenmg apphcatlons as it allows an unambiguous ldentlficatlon of the pesticide [84] Methane enhancement vvlth argon as reagent gas was used for the characterization of chlorotnazmes, giving [M + 14]- and [M + 28]- adducts corresponding to [M + CH,]and [M + C,H,l- , respectively [851 Interesting peaks were obtamed by methane-enhanced NC1 using oxygen for the characterlzatlon of a variety of organophosphorus pestlades, leading to ion-molecule reactlons such as the formation of [M - HCl + &I- [621 GC-MS with NC1 1s an appropriate technique for the confumatlon of a great variety of envlronmental pollutants with the mam advantage of selectivity, which can even be enhanced by using various reagent gas nuxtures The mcreasmg use of this techmque 1s supported by the fact that m the last few years many of the GC-MS manufacturers have included PC1 and NC1 as options m their bench-top instruments However, there are some drawbacks there 1s no posslblhty of mtercomparison of spectral data between laboratones, which necessitates laboratones bulldmg up their own hbrarles with the additional cost of obtammg standards, the Ion source IS much more easily fouled because of the use of a high-pressure gas

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Chun Acta 263 (1992) I-19

operatmg in many mstances at low source temperatures such as 150°C and the analysis of envlronmental samples requires the use of extensive clean-up methods pnor to GC-MS Hrlth NC1 As mentioned, the Ion source IS more easdy fouled than m EI operation, so samples need to be injected as clean as possible

molecules (helium, argon or xenon) m the fragmentation regon to yield vartous daughter ions The four most common MS-MS operating modes are daughter scan, parent scan, neutral loss scan and multi-reaction momtormg (MRM) Up to SIX or more tandem MS options are possible, such as MS-MS-MS, but two arrangements are most commonly used “hybrid MS’, which consists of a double-focusmg mstrument Hrlthelectrostatic field (E&magnet (B) configuration, which 1s followed by a collision quadrupole and finally by a mass analyser quadrupole (= EBQQ) and the tnplestage quadrupole, which consists of two quadrupole filters and a colhslon chamber “Hybnd MS” can be used either as a h&-resolution MS or as an MS-MS system, whereas the triple--stage quadrupole can only be used as an MS-MS mstrument Although CAD MS-MS has rarely been applied m envrronmental analysis, the development of “hybrid MS” instruments permltted the accurate determmatlon of polychlormated dlbenzo-pdloxms and dlbenzofurans m environmental sam-

GC-TANDEM MS (GC-MS-MS)

The dtierent techniques and applications of MS-MS were reported m a book by Busch et al 1191 In general, an MS-MS Instrument consists of an ion source, two mass analysers separated by a fragmentation region and an ion detector Such an arrangement can be used to separate mdlvldual components m a murture or to obtam addltlonal structural information on a smgle component After mass selection of the character&c ion of the analyte by the first mass analyser, this parent ion undergoes colhslonally activated dlssoaatlon (CAD) through colhslons with neutral gas

a

I

!_I-.*.

2) I

iC3H7NHJ+

58

(0

a

91

215

IM- C3H61’ 173 IM- CH31’ IM- CqH91+ 200

60

48

El’

Ill

ll..lt

IZI

_.-.

III

158

.I. I61

. .

II

! _.. . .

al

m

HI

m/x

Fig 3 Atrame daughter eon spectra obtamed m GC-MS-MS usmg CAD of [M - CH,l+ and [Ml+ Ions

10

ples at the ng 1-l level by using the MRM mode of specific daughter ions or by usmg high resolution By monitoring the transitions corresponding of [Ml’ to [M - COCl]+ ions it 1s possible to ehmmate interferences from PCBs and other mterfermg compounds m the environmental matrix with higher selectlvlty than high-resolution MS at resolving powers of 10000 and 18000 [86-891 However, It was stated that GC-high-resolution MS surpasses GC-MS-MS m LOD, lmeanty and reproduclblhty [89] Recently, the use of a hybrid MS instrument with various MS techmques such as CAD mass-analysed ion kmetlc energy MS (MIKE MS-MS) permitted the analysis of compounds related to polychlormated dlbenzo-p-d+ oxms and dibenzofurans such as polychlorodibenzothlophenes, the sulphur analogues of polychlorodlbenzofurans and their occurrence m envlronmental samples 1901 Most work reported using GC-MS-MS mvolves the use of tnple quadrupole MS This IS due to the relatively low price compared with a hybnd instrument and also to much easier operation The use of the daughter scan mode 1spartlcularly useful for environmental organic analysis because m this mode of operation a parent ion characterlstlc of the analyte IS selected m the first mass analyser, fragmenting it by CAD m the fragmentation region and scanning the second mass analyser to obtain a daughter mass spectrum Analogous to a normal mass spectrum, the daughter mass spectrum can be used for ldentlflcation of an analyte by standard mass spectral interpretation or by matching the spectrum with an authentic sample Such a system has been applied to confirm a variety of organic pollutants [12,91,92], mcludmg chlorotrlazme herbicides [93] and organophosphorus [94,95] and carbamate [95] msectlcldes An example of daughter ion mass spectra 1s given m Fig 3 where atrazme daughter ion spectra obtained for the parent [Ml+ and [M - CHJ+ ions are shown First, it should be pointed out that the CAD spectra for atrazme under the two different parent ions, [Ml+ and [M - CHJ, are completely different When [Ml+ 1s used as the parent ion the daughter ion formed resembles the fragmentation obtained by conventional GC-MS

D Barct%/Anal

Chwn Acta 263 (1992) 1-19

m the EI mode [22,23] Thus, CH,, C,H, and [C,H,NHl+ losses are observed Daughter ions obtained when the [M - CH,l+ ion 1s used as the parent ion correspond to ring-openmg reactlons resulting m signals at m/z 132, 104 and 96, thus mdlcatmg the presence of a C,H, group The ion at m/z 158 corresponds to a loss of C,H, and CH, groups, while the fragment ion at m/z 71 confirms the presence of the C,H, group and a secondary amme structure Such addItiona structural mformatlon 1s very useful when confirmation of chlorotrlazmes m environmental matrices 1s needed In addltlon, by momtormg the transltlon correspondmg to the loss of methyl an mcrease m selectlvlty can be achieved, thus makmg the method suitable for environmental analysis 1961 In summary, GC-MS-MS offers many posslblhtles m envlromnental orgamc analysis, with two mam pomts addltlonal structural mformatlon as compared with conventional GC-MS and selectlvlty, by monitoring specific transltlons with mmmum sample clean-up, thus allowmg the use, If necessary, of direct MS-MS confrrmatlon The disadvantages of such a technique are the cost, which IS much greater than for conventtonal GCMS and dlfflcultles m use, which also are much greater than m GC-MS, and may lead to problems with reproduclblhty of spectra

FAST ATOM BOMBARDMENT (FAB) MS

FAB and field desorptlon MS are the two desorptlon methods mostly used m environmental organic analysis FAB MS is a technique that allows the Intact iomzation of non-volatile, strongly polar compounds Several mechanisms may occur m FAB, such as desorptlon of ions performed m solution, evaporation of Ions from splash droplets, as m thermospray [971, and gasphase Ion-molecule reactions, as m chemical Ionlzatlon [2] Such mechamsms are dependent on the sample, the liquid matrm (e g , glycerol or thloglycerol) and the ionization chamber FAB MS 1s suitable for the determmatlon of pollutants not readily amenable to GC-MS The technique has been apphed to the determmatlon

D Bar&o/Anal

11

Chun Acta 263 (1992) l-19

of polyethoxylated surfactants with high degrees of polyethoxylatlon (n = 12) m surface river water samples) [24] This makes the technique useful for such applications, as GC-MS only allows the determmation of a polyethoxylatlon degree of n = 7 (see Table 1) The technique, using posltlve and negative FAB MS, is very powerful for the characterlzatlon of catlomc, amomc and amphoterlc surfactants m different types of water Catlomc surfactants such as a commercial cocoarmdopropyl amldo oxide exhlblted intense [M + HI+ ion m FAB( +) mode, anionic surfactants such as alkylbenzene sulphonates and alkyl sulphates gave [M - Na]- and [M - 2Na]- ions m FAB( - ) mode and amphoterlc surfactants of the cocoamldopropylbetame type exhibited intense [M + Na]+ ions [98] The Ions obtained m the mass spectrum of such amphotenc surfactants were identified by MS-MS and could be assigned to a general structure [RCONH(CH,),]+ [99] As an example, Fig 4A shows the positive-ion FAB mass spectrum of dltallowdlmethylammomum chloride (DTDMAC) exhibiting the structure [(CH3)2NRlR2]+ Cl-, exhibiting a base peak correspondmg to [(CH,),NC,,H,,C,,H,,l+ [26] The determmatlon of polar and amphoterlc pesticides not directly amenable to GC-MS 1s also possible by FAB MS In this regard, glyphosate and its derivatives were analysed by the prior formation of N,N-dlmethylamldmo derivatives which were soluble m glycerol and then by using positme- and negative-ion FAB MS [lo01 Another important and difficult to analyse group of pesticides is the quaternary ammonium pesticides, such as paraquat, dlquat and dlbenzoquat [loll Although the use of FAB MS has been very rare m environmental analysis, with the development of contmous-flow FAB MS more apphcatlons are expected FAB MS usually gives good-quality spectra and structural mformatlon on relatively mvolatlle compounds Two critical aspects need to be mentioned the poor quantlflcation by using this technique, so only quahtatlve results can be obtained wlthout an accurate evaluation of environmental pollutants, and contmuous cleaning of the ion source due to the use of glycerol-type matrices This last point is of mterest, especially d the same ion source 1s used for

A

“3C\+,R1 HJC/N\R2 I

mh

H

TSP

\+0 %

H,WN\R,

p I

F@ 4 Posmve-Ion mode (Al FAB and (B) thermospray mass spectra of a methanohc sediment extract of DTDMA KCHJ~NRIR,l+, where R,, R, = C,,-C,, (m/z = 466550) and [(CH,)HNR,R,l+, where R,, R, = c,,-c,, (m/t = 452-536), respectively

other purposes, e g , EI or Cl In many speaallzed laboratories it is more practical to have an extra ion source, so that the relatively “duly” FAB source 1s only used for specific applrcatlons

LIQUID CHROMATOGRAPHY-MASS TRY (LC-MS)

SPECTROME-

The on-line combmatlon of LC and MS has a promment place m environmental organic analyses and surpasses GC-MS m the analyses of polar pollutants in some respects Books [7-lo] and reviews [6,12,17] provide excellent overviews of the fundamental aspects and environmental apphcatlons of LC-MS Also good reviews on the different types of interfaces used m this context, mcludmg transport systems, direct liquid mtro-

12

D Bade/Anal

ductlon, thermospray, atmospheric pressure ionization, electrospray, particle beam, open-tubular LC and contmuous-flow FAB have been published [1,3,5,18] Of the different LC-MS methods, the thermospray (TSP) mterfacmg system IS probably the most widely used and typically mvolves reversed-phase columns and volatile buffers, with or without a filament or discharge LC-thermospray MS has been applied to the analysis of a variety of pestlcldes mcludmg carbamates [102-1051, organophosphorus compounds

Chvn Acta 263 (1992) l-19

[105-111, pyrethrolds [lO!Jl, ureas [108,111,112], chlorinated phenoxy acids 11131 and tnazmes [103,112,1131 The charactenzatlon of photolysls breakdown products of chlorotrmzme, organophosphorus, carbamate and urea pestlcldes was also feasible by drrect analysis of the degraded solutlon contammg the photolysls mixture [ 114,115] Filament-off and filament-on with posltlve- and negative-Ion modes are common choices m this context The filament-off mode 1s assoclated with thermospray loruzatlon, whereas the

1

2000:

B

IelM: 1600: 1400: :: 1200: 2

1000:

a

600: 600; 400 200 0

I 650 HarsKharge

Fig 5 Positwe-Ion thermospray MS profile of nonylphenol polyethoxylate at a concentratron of Cl5% usmg as eluent methanol-water (50 + 50) contammg 50 mM ammomum acetate obtamed Hrltha scan range of (A) m/z 180490 and (8) m/z 600-990

D Bar&o/Anal

Chm Acta 263 (1992) 1-19

process involved m the filament-on mode IS closer to chemical lomzation and discharge lomzatlon, which are apphed to LC eluents wth high water contents, and which provide further structural mformatlon with additional fragments These two procedures are applied routmely, however, the filament-on alternative is more commonly used on account of its usually higher sensltrvlty The choice between the positive- or negatrve-Ion mode depends on the compound concerned In any case, the poatlve-ion mode 1s much more frequently used and normally yields [M + HI+ and/or [M + NHJ base peaks The negative-ion mode has been shown to be much more sensltlve than the positive-ion mode to electronegative compounds such as chlonnated phenoxy acids, the former yields [M + acetate]- or [M + formate]- base peaks If ammomum acetate or ammonium formate is used as an lomzmg addltlve [6,111] Chlonde attachment, sumlarly as m conventional NC1 MS, has also been employed m LCMS, adding an eluent additive, generally chloroacetomtrde, and permlttmg the acqulsltlon of additional structural information such as for the [M + Cl]- ion In this way, direct hquld mtroductlon LC-MS has been used for the charactenzatlon of a variety of organophosphorus pestlcldes [116], chlorinated herbicides and chlorophenols [117] Both groups of pollutants were also analysed by LC-thermospray MS with the addltlon of chloroacetomtrlle to the eluent, thus leading to useful complementary structural information [118] Buffers and ion-palrmg agents present in the LC mobile phase can be removed by using an on-line post-column extraction system that transfers the organic phase to the LC-thermospray MS system while the morgamc ions remam m the aqueous layer This system has been employed m the detection of chlorinated phenoxy aads m water samples [ 1191 LC-thermospray MS has also been applied to the determmatlon of catlomc species In this way, quaternary ammonium compounds such as pyredmlum and benzyldlmethyldodecylammonlum salts were characterized by LC-thermospray MS 11201 Figure 4B shows the thermospray mass spectrum of the same catlomc species as m Frg

13

4A, where FAB MS was used The mam fragments detected were at m/z 298, 452, 480, 508 and 536, which corresponded to fragment ions mth structures [(CH&VHClsH3,]+, [(CH,)NHC,c,H&,,H,J+, [(CH,)NHC,,H,,C,,H,,l+ (CHS)NHC16H33ClsH371+ and KCH,)NHC,, H3,C18H3,1f, respectively Quaternary anunes are subjected to Hoffmann-hke reactions, with fragments that anse from the cleavage of alkyl radicals In this way the base peaks obtamed m LC-thermospray MS (Fig 4B) dtier from those obtamed m FAB MS (Fig 4A) by 14 u, corresponding to the loss of a methyl group Most of the pubhcatlons on the apphcatlon of LC-MS to surfactants relate to the characterrzatlon of non-roxuc compounds, generally up to a degree of polyethoxylatlon of 9 LC-MS with a movmg belt [121] and thermospray [122,123] mterfacmg systems have been apphed to the analysis of a vanety of non-ionic surfactants, such as those of the octylphenolate and nonylphenolate types Determmatlon of compounds with a high degree of polyethoxylatlon 1s feasible but 1s subject to specific conditions of calrbratlon m LCthermospray MS Figure 5A shows the typical LC-thermospray MS profile of a nonylphenol polyethoxylate with a degree of polyethoxylatlon up to n = 8, corresponding to a base peak at m/z 590 The base peaks always correspond to [M + NHJ+ When a compound v&h a higher degree of polyethoxylatlon needs to be determined, then the sample must be re-injected under a second mass range with m/z varymg from 600 up to 900 In this particular case, a degree of polyethoxylatlon of n = 13, corresponding to a base peak of m/z 810, can be determined This offers a clear advantage of LC-MS over GC-MS for the characterlzatlon of such surfactants, as GC-MS only allows the determmatlon of degrees of polyethoxylatlon up to n = 7 (see Table 1) LC-thermospray MS has also been applied to the charactematlon of polar PAHs that are not amenable to GC-MS, but it 1s still rarely used Examples of the determmatlon of hydroxymtro and suphoruc PAHs have been reported [82,124] More sophlstlcated equipment such as on-line LC-MS-MS or contmuous-flow FAB mstruments also permit pesticide charactenzatlon

14

D Bar&lo/Anal Chm. Acta 263 (1992) 1-19

LC-MS-MS was applied to the analysis of organophosphorus [llOl, carbamate [102,1031and trlazme [9,101 pestmdes, and was found to provlde more fragmentation than typical LC-thermospray MS With the advent of contmous-flow FAB MS it was feasible to analyse sulphonylurea herblade metabohtes from broth extracts dlrectly, with no addltlonal clean-up [8], and permitted the characterlzatlon of non-lomc detergents such as Trlton X-100 and PEG 600 [125] Coupled SFC-MS [5,17] permlts the characterization of dtfferent pesticides with EI or CI modes, which makes the techmque potentutlly useful in envlronmental analysis In most mstances carbon dloxlde 1s used as the supercrItIcal mobtle phase and, mcldently propan-2-01 as po-

larlty modtiler 11261 SFC-MS wth atmospheric pressure lomzation and chloride attachment was applied to the determmatlon of polycychc aromatic compounds 11271and non-lomc surfactants [128], respectively Another recent technique m this field IS the use of capillary zone electrophoresls (CZE)-MS [129], which pernuts the separation of ionic compounds m an open tube through the apphcatlon of a voltage gradrent Compounds rmgrate wth different velocltles through the tube as a result of their differences m electrophoresls moblhty An example of a commercially avallable CZE-MS combmatlon 1s the Saex IonSpray atmospheric pressure romzatron (API) system Advantages clalmed are that no pumping of solvent or heat-

Thus,

1

491942

BENSULFURON

Daughter Ion Spectrum

Fig 6 Ion evaporation CZE-MS and CZE-MS-MS of 40 ng of methyl bensulfuron Condrtlons 90 cm X 100 JLIII 1d fused-sdlca column, 20 kV, 15 PA, with acetomtrde-water (50 + SO) contammg 10 mM anunomum acetate (pH 5 5) as eluent (courtesy of PE Saex, Canada)

D Bar&lo/Anal Chun Acta 263 (1992) 1-19

15

TABLE 2

Compansoaof relatnreabundancesbetweenGC-MS wth NCI, thermospray MS and FAB MS for organophosphorus and quaternary amme pestwdes [23,101,106,118] Compound

m/z

Orgarwphosphorus pest&es Femtrothlon 168 211 Parathion-ethyl 154 291

Tentatwe Identticafion

GC-MS

Thermospray MS

FAR MS

W,H,NO,lWIKjH,NOJ-

100

15 100 7 100

nl

84 30 100

[Ml-

Quatemary ammepest&es Dlfenzoquat 118 235 249 Dlquat 91 157 184 Paraquat 171 186

[C,H&NCHJ+ [c~,H~~N~-cH~+ HI+

[W-W&l+ [W-M+

nl

ni ’

15

100 100 100

10 nl

[C,pH,,Nz - HW+ [C,,H,,Nzl+ &H,~,Nz -(&I+ [C,,H,,Nzl+

20 35 15 100

100 10 100

nl

a n 1 = Not mveshgated

many slmdantles with conventional GC-chemical lomzatlon MS In addition, the thermospray ionization has also sumlarltles Hrltha solutrondependent lomzatlon techmque, such as FAB MS The snmlarlty m the lomzatlon processes of LC-thermospray MS with GC-MS m the NC1 mode and FAB MS for organophosphorus pesticides and quaternary amme pesticides which are not amenable for GC analysis, respectively, 1s shown m Table 2 Such slmllantles m fragmentation facilitate the interpretation of new thermospray mass spectra by matchmg with more conventional lomzatlon techniques and supports the argument that LC-thermospray MS 1s mfluenced by both gas-phase and solution-phase chemistry [97,131] Drawbacks are that the sensrtlwty is lower than that of GC-MS m all instances (see Table 31, which 1s a serious hmltatlon m environmental

mg 1s reqmred, mdd ambient temperature lomzatlon 1s used, thus makmg the process surtable for labile analytes, mstrumental slmphclty and the use of MS-MS, thus provldmg additional structural mformatlon As an example, Fig 6 shows the spectra of the sulphonylurea herbicide methyl bensulfuron obtained by ion evaporation CZEMS-MS The structurally useful fragment ion ldentlfled m the daughter ion spectrum matches the expected fragment ion obtamed using a movmg belt interface m LC-MS for several sulphonylurea herbicides of similar type [130] The mcreasmg use of LC-MS m the last few years indicates the need for this technique m many environmental analytical applications An advantage of this technique is that the lomzatlon, when using the direct-liquid mtroductlon mterface or filament on thermospray LC-MS, has

TABLE 3 Detection lumts (ng) for certam polar pestwdes usmg GC-MS and LC-thermospray MS under full-scan condltlons ’ Pesticides

Organophosphorus Chlorotnazmes

GC-MS

LC-MS

References

EI

PC1

NC1

PI

NI

1 1

5-10 1

01 20

20 10

50 100

a Full-scan conditions for GC-MS from m/z 40 to 600 and for LC-MS Tom m/z 140 to 600

23,106 23,118

16

D Bar&/Anal

trace analysis unless a greater amount of sample 1s extracted, difficult quanufication, due to vanatlons in sensitwity m day-to-day use, unless careful calibration and cleamng of the different parts, e g , the interface, are done, hence it can mostly be recommended for confnmatlon purposes, and poor structural mformatlon, which 1s particularly true for LC-thermospray MS, one of the most commonly used mterfaces at present The development of LC-particle beam MS, with the pomblhty of producmg EI spectra, has partly overcome these problems, but m this instance polar compounds are more difficult to analyse than with the LC-thermospray MS interface The problem of analysmg polar compounds and collecting structural mformatlon m LC-MS can be better solved by using tandem systems, either LC-thermospray MS-MS or CZE-MS-MS Concluswm

The use and development of MS techniques for the detection of environmentally important compounds has increased m the last few years GC-MS with El and CI can be of great help for confirmation and/or analysis of pollutants at the low kg kg- ’ level m waters, sediments and blota samples GC-MS provides the most desirable aspects m an analytical technique selectlwty which can be enhanced by the use of SIM and NCI, sensltlvlty and reproduclblhty With mcreasmg needs m confirmation and quantlflcatlon, momtormg programmes are incorporating GCMS m bench-top instruments usmg EI to confirm unambiguously the different pollutants The main characterlstrcs of GC-MS with EI are its convenience, easy use for routme work, day-to-day reproduclb&y, posslblhty of library searches and sufficient posslblhtles of structural elucldatlon In the last few years, GC-MS benchtop instruments have expanded the range of optlons, and many of them are now available with PC1 and NC1 The applications of GC-MS with NCI, offering good selectivity and sensitmlty for specific apphcatlons, will undoubted grow m the near future This option will be even more used after the new generation of EPA analytical methods dlscussed by Hates and Budde [1321 It 1s evident that most laboratories involved m this field follow the EPA methods

Chm Acta 263 (1992) 1-19

Although it 1s dticult to predict the future of GC-MS 111environmental organic analysis, the combmatlon of GC with atomic enusslon detection (GC-AED) [133-1351, which allows element-specific chromatograms to be obtained, should be taken mto consideration because it appears to be a powerful competitor to GC-MS GC-AED has been successfully applied for the determmatlon of pesticide residues m agricultural commodltles by using carbon, phosphorus, chlorme, nitrogen and sulfur selective analysis Only m the nitrogen mode were poor selectlvlty and sensitivity observed [135] Future MS apphcatlons m environmental analysis can be expected m different directIons (1) The use of MS-MS techmques, although avallable m many laboratories, especially the tnplestage quadrupole, appear to be reluctantly used Recently, the direct analysis of agricultural residues without clean-up was reported by using thermolysis-MS-MS [136] and secondary ion MS [137], and the characterization of polyethoxylated surfactants of the alcohol and alkylphenol type, together with then acidic metabohtes was feasible by FAB MS-MS [138] (11)FAB MS IS of great important for the ldentlficatlon of organic pollutants and IS a good alternative for the determmatlon of cationic, anionic and non-lomc surfactants exhlbltmg a high polyethoxylatlon degree By the combination of different LC fracttonatlon methods, FAB MS appears to be a very powerful technique thus allowmg the characterlsatlon of surfactants with molecular weights > 2100, with n = 30 [139] (111)The on-lme combination of LC-UV-MS can be useful for the quantltatlon and confumatlon of pollutants m environmental samples such as polar pesticides and polycychc aromatic compounds [140,141] This approach 1s particularly interesting 111LC-MS, since many problems arise during quantification and so it is safer to use an on-line UV detector The quantltatlon problems m usmg different LC-MS approaches have been recently reported m an mterlaboratory comparison between thermospray and particle beam LC-MS thus showing statlstlcally significant differences between interfaces m the quantitative data of acidic herbicides [1421 (IV> The use of the new generation of GC quadrupole ion trap MS (GC-QITMS) systems allows the

D Bar&/Anal

Chm Acta 263 (1992) l-19

characterlzatlon of higher molecular weight compounds wrth the posslblllty of using MS-MS or LC-MS wth the electrospray mterface and colhslonally activated decomposition (CAD) This will form a direct competitor to the triple quadrupole MS instruments, so far the most used tandem MS instruments m environmental analysis (VI The charactensatlon of chelating compounds, such as Cu-EDTA complexes m mnced hazardous wastes, by LC-MS opens up a new field of analytical apphcatlons for this already established technique [1431 h) The development of computerlzed mterpretative methods such as MASSPEC that allow a mass spectrum to be correlated with a proposed structure and which have recently been developed for FAB MS, LC-MS and MS-MS, should open up novel posslbllltles for solvmg the problems of elucldatlon of mass spectra and hbrary searches 11441,and (vu) the use of more sophisticated analytical techniques which at present are used only as research instruments, such as laser desorptlon Fourier transform ion cyclotron resonance MS This technique has been applied to the characterlzatlon of the Trlton surfactant molecular weight distribution up to a molecular weight of 3500 Tbe ldentlflcatlon of this surfactant was feasible without the need for prior chromatographlc separation At present, no other analytical techmque has been able to resolve such a high molecular weight dlstrlbutlon [I451 REFERENCES 1 M Lmscheld, Fresemus J Anal Chem , 337 (1990) 648 2 C Fenselau and R J Cotter, Chem Rev, 87 (1987) 501 3 T R - Covey, E D Lee, A P Brums and J D Hemon, Anal Chem , 58 (1986) 1451A 4 S J Gaskell and E M H Fmlay, Trends Anal Chem , 1 (1988) 202 5 P Arpmo, Fresemus’ J Anal Chem , 337 (1990) 667 6 P Arpmo, Mass Spectrom Rev, 9 (1990) 631 7 AL Yergey, CG Edmonds, I AS Lewe and ML Vestal, Llquld Chromatography/Mass Spectrometry Techmques and Appbcatlons, Plenum, New York, 1990, pp l-306 8 R M Capnoh, Contmuous-Flow Fast Atom Bombardment Mass Spectrometry, Wdey, ChIchester, 1990, pp l-208 9 J D Rosen, Apphcatlons of New Mass Spcctrometry

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