Chemical Ionization Conditions Research Articles

Gas Chromatography/Mass Spectrometry of Chemical Warfare Agents

Gas chromatographic mass-spectrometric analysis was performed for chemical warfare agents and related compounds including sarin, soman, tabun, VX, mustard gas, lewisite 1, 2-chloroacetophenone, o-chlorobenzilidenemalononitrile and capsaicin, under electron ionization and methane chemical ionization conditions using apolar and polar capillary columns. It was possible to identify the tested compounds with respects to their retention indices and mass spectra. Under the analytical conditions of split ratio (50:1), electron ionization and scan mode data aquisition, the limit of detection ranged from 0.06 to 7 μg/ml, except for the low detection sensitivity of lewisite 1.

Quantitative determination of fluvastatin in human plasma by gas chromatography/negative ion chemical ionization mass spectrometry using [18O2]‐fluvastatin as an internal standard

A sensitive and specific method for the quantitative determination of fluvastatin in human plasma is presented. The drug was isolated from plasma by extractive alkylation with pentafluorobenzyl bromide and further derivatized to the bis-trimethylsilyl derivative. [18O2]-Fluvastatin was prepared from unlabelled fluvastatin and used as an internal standard. Gas chromatography/mass spectrometry under negative ion chemical ionization conditions was used for quantitative measurement of the drug, using m/z 554.26 and 558.26 for target and internal standard, respectively. Calibration graphs were linear within a range of 2 and 512 ng mL(-1) plasma. Intra-day precision was 0.94% (2 ng mL(-1)), 2.53% (8.2 ng mL(-1)), 2.16% (81.9 ng mL(-1)) and 3.26% (409.6 ng mL(-1)); inter-day variability was found to be 1.64% (2 ng mL(-1)), 0.97% (8.2 ng mL(-1)), 1.97% (81.9 ng mL(-1)) and 2.01% (409.6 ng mL(-1)). Intra-day accuracy showed deviations of 0.6% (2 ng mL(-1)), 0.37% (8.2 ng mL(-1)), -1.52% (81.9 ng mL(-1)) and -1.67% (409.6 ng mL(-1)); inter-day accuracy was of -1.64% (2 ng mL(-1)), -1.13% (8.2 ng mL(-1)), -2.28% (81.9 ng mL(-1)) and -0.46% (409.6 ng mL(-1)). The stable isotope labelled standard was found to be stable under the analytical conditions.

Interpretation of alkyl diselenide and selenosulfenate mass spectra

The mass spectral fragmentation of aliphatic diselenides and selenosulfenates is analyzed to gain a better understanding of the behavior of these species. The main fragmentation pathways of these species include the fragmentation along the SeC bond, fragmentation along the SeSe or SeS bonds and intra-molecular rearrangements. In general, negative ionization favors the fragmentation along the SeSe or SeS bonds while positive ionization leads to stable molecular ions. Density functional theory calculations of bond dissociation energies and molecular orbital analysis was undertaken to explain the observed trends in molecular fragmentation. Besides the analysis of molecular fragmentation, a phenomenon of molecular association in negative electron impact and positive chemical ionization conditions was observed and investigated using a high resolution time-of-flight mass spectrometer. Molecular association that occurs during the ionization of species includes the formation of symmetrical diselenides from asymmetrical selenosulfenates and formation of alkylseleno adducts from the corresponding diselenides. For species which is hard to resolve by mass analysis, such as isobars of CHSe, CH2Se, and CH3Se, the isotope pattern superimposition procedure was applied to define the overlapping clusters.

Site of alkylation of N-methyl- and N-ethylaniline in the gas phase: a tandem mass spectrometric study.

N-Methylaniline (NMA) was ethylated and N-ethylaniline (NEA) was methylated under chemical ionization conditions using C(2)H(5)I and CH(3)I, respectively, as reagent gases. The structures of the resulting m/z 136 adduct ions have been probed using metastable ion and collision-induced dissociation (CID) methods. From the similarity of the spectra obtained and from the presence of structure-diagnostic ions at m/z 59 (CH(3)NHC(2)H(5) (+*)) and m/z 44 (CH(3)NHCH(2) (+)), it is concluded that predominantly N-alkylation occurs in both systems. This interpretation was aided by the use of C(2)D(5)I and CD(3)I as reagents. Adduct ions of m/z 136 were also formed by ethylation of the isomeric toluidines and by methylation of the ring-ethylanilines. The resulting CID mass spectra were distinctly different from those obtained for the m/z 136 ions obtained by alkylation of NMA and NEA. Protonation of N-ethyl-N-methylaniline using CH(3)C(==O)CH(3) as Brønsted acid reagent produced an m/z 136 species whose CID mass spectrum also featured intense ion signals at m/z 59 and 44. This observation led to the conclusion that protonation with acetone as reagent results, in this case, in dominant N-protonation. However, the CID mass spectrum of the m/z 136 ion formed when CH(3)OH was the protonating agent featured a weak signal at m/z 44 and no signal at m/z 59. Hence it was concluded that the latter m/z 136 ion contains a larger contribution from the ring-protonated adduct.

Distinguishing N-oxide and hydroxyl compounds: impact of heated capillary/heated ion transfer tube in inducing atmospheric pressure ionization source decompositions.

In the pharmaceutical industry, a higher attrition rate during the drug discovery process means a lower drug failure rate in the later stages. This translates into shorter drug development time and reduced cost for bringing a drug to market. Over the past few years, analytical strategies based on liquid chromatography/mass spectrometry (LC/MS) have gone through revolutionary changes and presently accommodate most of the needs of the pharmaceutical industry. Among these LC/MS techniques, collision induced dissociation (CID) or tandem mass spectrometry (MS/MS and MS(n)) techniques have been widely used to identify unknown compounds and characterize metabolites. MS/MS methods are generally ineffective for distinguishing isomeric compounds such as metabolites involving oxygenation of carbon or nitrogen atoms. Most recently, atmospheric pressure ionization (API) source decomposition methods have been shown to aid in the mass spectral distinction of isomeric oxygenated (N-oxide vs hydroxyl) products/metabolites. In previous studies, experiments were conducted using mass spectrometers equipped with a heated capillary interface between the mass analyzer and the ionization source. In the present study, we investigated the impact of the length of a heated capillary or heated ion transfer tube (a newer version of the heated capillary designed for accommodating orthogonal API source design) in inducing for-API source deoxygenation that allows the distinction of N-oxide from hydroxyl compounds. 8-Hydroxyquinoline (HO-Q), quinoline-N-oxide (Q-NO) and 8-hydroxyquinoline-N-oxide (HO-Q-NO) were used as model compounds on three different mass spectrometers (LCQ Deca, LCQ Advantage and TSQ Quantum). Irrespective of heated capillary or ion transfer tube length, N-oxides from this class of compounds underwent predominantly deoxygenation decomposition under atmospheric pressure chemical ionization conditions and the abundance of the diagnostic [M + H - O](+) ions increased with increasing vaporizer temperature. Furthermore, the results suggest that in API source decompostion methods described in this paper can be conducted using mass spectrometers with non-heated capillary or ion transfer tube API interfaces. Because N-oxides can undergo in-source decomposition and interfere with quantitation experiments, particular attention should be paid when developing API based bioanalytical methods.

Laboratory simulations of the transformation of peas as a result of heating: the change of the molecular composition by DTMS

Peas ( Pisum sativum L.) consist mainly of cotyledons and their bulk material is starch and proteins. Their structure is rather confined. Peas were heated at temperatures ranging from 130 to 700 °C under anoxic conditions for maximum 2 h. For each temperature a separate experiment was carried out in a pre-heated oven. Direct temperature-resolved mass spectrometry (DTMS) under electron impact (EI) and chemical ionization (CI, NH 3) conditions measured the molecular composition of each solid residue. Fourier-transform infrared (FTIR) spectroscopy was carried out on residues heated at higher temperatures. The resulting solid products of the heating process still show the original markers for polysaccharides and proteins up to 270 °C. Concurrently three phases can be considered, each characterized by its own products. The first phase, from 270 up to 310 °C, shows monosaccharides, protein fragments and aromatic compounds. The second phase, from 310 °C up to a transitional stage from 400 to 440 °C, releases various aromatic and heterocyclic compounds. The third phase at higher temperatures shows a highly C-enriched product that releases CO, CO 2, HCN, SO and SO 2. The EI and CI experiments fail to discriminate between the pyrolysis products of polysaccharides and proteins between 250 and 400 °C. FTIR shows in this temperature range the development of an aromatic network. An earlier classification based on the changes of the physical and bulk chemical properties as a function of the temperature corresponds well with the classification based on the molecular changes. Residues of heated peas, usually called carbonized peas, are found in the archaeological record. Our study suggests that peas should have been heated up to least 310 °C before their residues survive natural degradation processes.

Studies on the positive-ion mass spectra from atmospheric pressure chemical ionization of gases and solvents used in liquid chromatography and direct liquid injection

Detailed studies have been made using different source gases and solvents in a Micromass Quattro mass spectrometer under positive ion atmospheric pressure chemical ionization conditions. The major background ions from nitrogen, air, or carbon dioxide were investigated by tandem mass spectrometry, followed by similar studies on solvents commonly employed in normal- and reversed-phase high-performance liquid chromatography, namely, water-acetonitrile, acetonitrile, and dichloromethane, with nitrogen, air, or carbon dioxide; hydrocarbon solvents were studied using nitrogen. Spectra were interpreted in terms of the gases, solvents, and their impurities. The acetonitrile spectra provided clear evidence for both charge exchange and proton transfer, the former being facilitated by the introduction of some air into a flow of nitrogen. Radical cations of acetonitrile dimers, trimers, and tetramers were observed, as were protonated dimer and trimer species. Examination of the analytical response of four polycyclic aromatic hydrocarbons in various hydrocarbon solvents, with nitrogen gas, showed that the sensitivity of detection for an analyte and its ionization mechanism are dependent on both the analyte structure and the solvent, with pyrene showing the highest sensitivity, phenanthrene and fluorene being intermediate, and naphthalene having the lowest sensitivity. The degree of protonation followed the same trend. Signal intensity and degree of protonation were dependent on the alkane solvent used, with isooctane providing the best overall sensitivity for the sum of protonated molecules and molecular ions. The ions observed in these studies appeared to be the most stable ions formed under equilibrium conditions in the source.

Substituent effect on ion–molecule reaction of disubstituted benzenes with acetone plasma

We investigated the ion–molecule reactions of disubstituted benzenes with acetone or acetone-d 6 as reagent gases under chemical ionization conditions, and the fragmentation reactions of the adduct ions (mostly acetyl ion and protonated acetone adducts) using collision-induced dissociation (CID) technique. The CID results of [M+A dD] + ions of phenylamine derivatives suggest that the phenylamine derivatives have higher proton affinities than acetone. Our experiments also suggest: (1) electron-releasing substituents favor the adduct reactions, while electron-withdrawing groups do not; (2) the position and properties of substituting groups have an effect on the relative abundances of the adduct ions; (3) the fragmentation reaction of the acetyl adduct ion formed by the reaction of ortho-phenylenediamine with acetyl ion is similar to the reductive alkylation reaction in the liquid phase.

A theoretical study of structure and stability of various Ge 2H m− ( m=0–5) ions

Results of theoretical investigation are reported for negative ion clusters formed from GeH 4 in gas phase mass spectrometric experiments under chemical ionization conditions. Ab initio quantum chemical calculations have been performed on Ge 2H m − (m=0−5) anions. The geometrical structure and relative stability of isomeric anions have been investigated at the DFT level of calculation with a triple-ζ basis sets. Single point calculations at the CCSD(T) level were performed with a 6-311+G(3df,2p) basis set, to better evaluate the relative stability of the investigated species. Heats of formation of the anions have also been determined with the G2 method.

Identification and characterization of conjugated fatty acid methyl esters of mixed double bond geometry by acetonitrile chemical ionization tandem mass spectrometry.

Fatty acids with conjugated double bonds have attracted great interest because of their reported potent bioactivities. However, there are currently no rapid methods for their structural characterization. We report here a convenient mass spectrometry-based strategy to establish double bond geometry by analysis of collisional dissociation products of cis/trans and trans/cis conjugated linoleic acids (CLAs), as methyl esters, and to distinguish CLAs from homoallylic (methylene-interrupted) fatty acids in a single-stage mass spectrum. A series of CLA standards with double bond positions 6,8; 7,9; 8,10; 9,11; 10,12; 11,13; 12,14; and 13,15, with all four possible geometries (cis/trans; trans/cis; cis/cis; trans/trans) were analyzed. The m/z 54 (1-methyleneimino)-1-ethenylium ion, generated by self-reaction of acetonitrile under chemical ionization conditions, reacts with unsaturated fatty acids to yield an [M + 54]+ ion, which decomposes in the single-stage mass spectrum by loss of neutral methanol to form [M + 54 - 32]+. The ratio of [M + 54]+/[M + 54 - 32]+ in the single-stage mass spectra of CLA isomers is 1 order of magnitude less than for homoallylic diene FAME. Collisional dissociation of the [M + 54]+ ion yields two diagnostic ions that contain the alpha- and omega-carbon atoms and is characteristic of double bond position in the analyte. The fragment vinylic to the trans double bond is significantly more abundant than that for the cis double bond, revealing double bond geometry. The ratio of alpha to we diagnostic ion abundances is >4.8 for cis/trans isomers, <0.5 for trans/cis isomers, and 0.7-3.2 for cis/cis and trans/trans isomers. This method provides a rapid alternative to conventional conjugated fatty acid analysis and, together with complementary elution time information provided by gas chromatography, enables rapid, positive identification of double bond position and geometry in most CLA FAME.

Unusual atmospheric pressure chemical ionization conditions for detection of organic peroxides.

Organic peroxides such as the cumene hydroperoxide I (M(r) = 152 u), the di-tert-butyl peroxide II (M(r) = 146 u) and the tert-butyl peroxybenzoate III (M(r) = 194 u) were analyzed by atmospheric pressure chemical ionization mass spectrometry using a water-methanol mixture as solvent with a low flow-rate of mobile phase and unusual conditions of the source temperature (< or =50 degrees C) and probe temperature (70-200 degrees C). The mass spectra of these compounds show the formation of (i) an [M + H](+) ion (m/z 153) for the hydroperoxide I, (ii) a stable adduct [M + CH(3)OH(2)](+) ion (m/z 179) for the dialkyl peroxide II and (iii) several protonated adduct species such as protonated molecules (m/z 195) and different protonated adduct ions (m/z 227, 389 and 421) for the peroxyester III. Tandem mass spectrometric experiments, exact mass measurements and theoretical calculations were performed for characterize these gas-phase ionic species. Using the double-well energy potential model illustrating a gas-phase bimolecular reaction, three important factors are taken into account to propose a qualitative interpretation of peroxide behavior toward the CH(3)OH(2) (+), i.e. thermochemical parameters (DeltaHdegrees(reaction)) and two kinetic factors such as the capture constant of the initial stable ion-dipole and the magnitude of the rate constant of proton transfer reaction into the loose proton bond cluster.

Sensitive liquid chromatographic/tandem mass spectrometric method for the determination of beclomethasone dipropionate and its metabolites in equine plasma and urine.

Beclomethasone dipropionate (BDP) is a potent pro-drug to beclomethasone (BOH) and is used in the treatment of chronic and acute respiratory disorders in the horse. The therapeutic dose of BDP (325 microg per horse) by inhalation results in very low plasma and urinary concentrations of BDP and its metabolites that pose a challenge to detection and confirmation by equine forensic laboratories. To solve this problem, a method involving the use of a liquid chromatography coupled with tandem mass spectrometry (LC/MS/MS) was developed for the detection, confirmation and quantification of the analytes in equine samples. Ammonium formate or acetate buffer added to LC mobile phase favored the formation of [M + H](+) ions from BDP and its metabolites, whereas formic acid led to the formation of sodium and potassium adduct ions ([M + Na](+), [M + K](+)) together with [M + H](+) ions. Acetonitrile, on the other hand, favored the formation of abundant solvent adduct ions [M + H + CH(3)CN](+) with the analytes under electrospray ionization (ESI) and atmospheric pressure chemical ionization conditions. In contrast, methanol formed much less solvent adduct ions than acetonitrile. The solvent adduct ions were thermally stable and could not be completely desolvated under the experimental conditions, but they were very fragile to collision-induced dissociation (CID). Interestingly, these solvent adduct ions were observed on a triple-quadrupole mass spectrometry but not on an ion trap instrument where helium used as a damping gas in the ion trap might cause the solvent adduct ions desolvated by collision. By CID studies on the [M + H](+) ions of BDP and its metabolites, their fragmentation paths were proposed. In equine plasma at ambient temperature over 2 h, BDP and B21P were hydrolyzed in part to B17P and BOH, respectively, but B17P was not hydrolyzed. Sodium fluoride added to equine plasma inhibited the hydrolysis of BDP and B21P. The matrix effect in ESI was evaluated in equine plasma and urine samples. The method involved the extraction of BDP and its metabolites from equine plasma and urine samples by methyl tert-butyl ether, resolution on a C(8) column with a mobile phase gradient consisting of methanol and ammonium formate (2 mmol l(-1), pH 3.4) and multiple reaction monitoring for the analytes on a triple-quadrupole mass spectrometer. The detection limit was 13 pg ml(-1) for BDP and B17P, 25 pg ml(-1) for BOH and 50 pg ml(-1) for B21P in plasma and 25 pg ml(-1) for BOH in urine. The method was successfully applied to the analysis of equine plasma and urine samples for the analytes following administration of BDP to horses by inhalation. B17P, the major and active metabolite of BDP, was detected and quantified in equine plasma up to 4 h post-administration by inhalation of a very low therapeutic dose (325 microg per horse) of BDP.

Liquid chromatography–mass spectrometry and liquid chromatography–tandem mass spectrometry of the Alternaria mycotoxins alternariol and alternariol monomethyl ether in fruit juices and beverages

Alternariol (AOH) and alternariol monomethyl ether (AME) are among the main mycotoxins formed in apples and other fruits infected by Alternaria alternata. For determination of AOH and AME by LC, apple juice and other fruit beverages were cleaned up on C 18 and aminopropyl solid-phase extraction columns. Positive and negative ion mass spectra of AOH and AME under electrospray (ESI) and atmospheric pressure chemical ionization (APCI) conditions were obtained. Collision-induced dissociation of the [M+H] + and [M–H] − ions for both compounds were also studied. The phenolic anions of both compounds are more stable with less fragmentation. In quantitative analysis, negative ion detection also offers lower background and better sensitivity. Sensitive LC–MS and LC–MS–MS confirmatory procedures based on APCI with negative ion detection were applied to confirm the natural occurrence of AOH in nine samples of apple juice and in single samples of some other clear fruit beverages—grape juice, cranberry nectar, raspberry juice, red wine, and prune nectar (which also contained 1.4 ng AME/ml)—at levels of up to 6 ng AOH/ml. Electrospray LC–MS–MS with negative ion detection and in multiple reaction monitoring mode offers higher sensitivity and specificity. Absolute detection was better than 4 pg per injection for both compounds.

Detection of thiopental and pentobarbital in head and pubic hair in a case of drug-facilitated sexual assault

The quali-quantitative determination of two barbiturates, thiopental and its metabolite pentobarbital, in head and pubic hair samples of a woman who had been sexually assaulted during hospitalisation, is reported. Hair was analysed by means of solid-phase microextraction (SPME) and gas chromatography-multiple mass spectrometry (GC–MS-MS), in chemical ionisation conditions. Thiopental and pentobarbital were found in three proximal head hair segments (sample 1A: 0.30 and 0.40 ng/mg; sample 1B: 0.20 and 0.20 ng/mg; sample 3: 0.15 and 0.20 ng/mg) and pubic hair sample. Two distal head hair segments were negative for both barbiturates. Despite the lack of collection and toxicological analysis of blood or urine samples within the hospital setting, analytical findings from hair revealed the use of the anaesthetic agent thiopental to sedate the victim quickly and deeply and commit sexual assault.

Liquid chromatography/mass spectrometric analysis of explosives: RDX adduct ions.

In liquid chromatography/mass spectrometry (LC/MS) of 1,3,5-trinitro-1,3,5-triazacyclohexane (RDX), attachment of an anion to the analyte molecule is the major way of producing characteristic ions under electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) conditions. The formation of RDX cluster ions in LC/MS and the origin of the clustering agents have been studied. In order to determine whether the clustering anions originate from self-decomposition of RDX in the source or from impurities in the mobile phase, isotopically labeled RDX ((13)C(3)-RDX and (15)N(6)-RDX) and isotopically labeled glycolic acid, acetic acid, ammonium formate and formaldehyde have been used in order to establish the composition and formation route of RDX adduct ions produced in ESI and APCI sources. The results showed that, in ESI, self-decomposition of RDX plays no role in adduct ion formation; rather, RDX clusters with formate, acetate, hydroxyacetate, and chloride anions present in the mobile phase as impurities at ppm levels. In APCI, part of the RDX molecules decompose yielding NO(2) (-) species which in turn cluster with a second RDX molecule producing abundant [M+NO(2)](-) cluster ions.

Is the atmospheric pressure chemical ionisation and collisionally induced methanol loss from protonated dehydroamino acids a retrosynthetic process?

Unsaturated 5(4H)-oxazolones lead, by methanolysis, to the corresponding dehydroamino acid derivatives. Interestingly, under atmospheric pressure chemical ionisation (APCI) conditions, the latter give rise, aside from abundant [M+H](+) ions, to [MHbondCH(3)OH](+) species, formally corresponding to the protonated oxazolones employed for their synthesis. Retrosynthetic processes have often been described as energetically favoured decompositions of odd-electron molecular ions but never invoked in APCI-activated fragmentations. To investigate this possible retrosynthetic process, occurring also under collisional conditions, some experiments on the deuterated analogues have been undertaken. The breakdown curves of [M+H](+) of oxazolones and [MHbondCH(3)OH](+) of the dehydroamino acid derivatives are superimposable, proving their structural identity and giving experimental evidence of the occurrence of a real retrosynthetic process from even-electron protonated molecules.

Chemical ionization of amino and hydroxy group containing arylalkyl compounds with ions in a nitromethane plasma

The gas-phase ion/molecule reactions of organic molecules containing several functional groups, including amino, hydroxy and carboxy groups, have been investigated under nitromethane chemical ionization conditions. Three main reaction channels are observed in the ion source: (a) proton transfer, (b) electron transfer and (c) hydride abstraction. The product ion [M+NO] + is also formed, but in a very low abundance. Initial electrophilic attack of the nitrosonium ion on the aromatic ring is postulated to explain the elimination of HNO from the [M+NO] + adduct ions, observed for all substrates studied. Elimination of water is a characteristic fragmentation pathway for all substrates possessing a benzylic hydroxy group. Fragment ions resulting from cleavage of the molecular ions of the amines, formed by charge transfer, react with the neutral molecules forming two types of adduct ions: [M+immonium] + and [M+C 7H 7] +, which have been characterized through the study of their unimolecular decompositions. The latter provide strong evidence for the existence of two types of structures: a covalent and an ion/molecule complex, that is a non-covalent structure.

Mass Spectrometry Study of Acylthioureas and Acylthiocarbamates

A variety of acylthiocarbamates and acylthioureas have been investigated under electron impact ionization (EI), chemical ionization (CI) and electrospray ionization (ESI) conditions. Sequential product-ion fragmentation (MSn) was performed to elucidate the degradation pathways for these compounds. Comparisons are made between positive and negative even-electron ions from ESI and CI and the odd-electron ions obtained under EI conditions. The data collected in this paper provide information on the strong differences found in the fragmentation process of these compounds.

Attachment of neutrals during tandem mass spectrometry of sulfonic acid dyes and intermediates in an ion trap.

Several positional isomers of 2-(2-quinolinyl)-1H-indene-1,3(2H)-dione mono- and disulfonic acids prepared as reference materials for development of analytical methods involved in FDA certification of D&C Yellow No. 10 (Quinoline Yellow) were found consistently to show [MH + 14](+) ions when their electrospray- or atmospheric pressure chemical ionization-prepared MH(+) ions were subjected to collisional activation. The source of these ions was found to be the methanol used as solvent in these procedures which combined with their [MH - H(2)O](+) ions under chemical ionization conditions. The reaction was found to be sensitive to their isomeric and chemical structures and other examples of this process are reviewed.

A rapid and efficient mass spectrometric method for the analysis of explosives.

The high explosives trinitrotoluene, nitroglycerine, pentaerythritol tetranitrate and hexahydro-1,3,5-trinitro-1,3,5-triazine are efficiently ionised under negative ion atmospheric pressure chemical ionisation (APCI) conditions. The limit of detection is improved, in some cases by several orders of magnitude, by complexation with chlorine demonstrating this to be a highly suitable method for enhancing the detection capabilities for explosives. The spectra produced from introduction of the analytes in a liquid matrix, with and without chlorine present, contain a number of ions that arise through secondary processes including breakdown and adduct formation. Sample introduction into an APCI source in air, via a heated-plate inlet with a supplementary feed of dichloromethane, produces improved response for the chloride adducts of the analytes and minimises their decomposition during analysis. The tandem mass spectra produced from the chloride adducts are simple. Optimisation of the trapping parameters of the ion trap detector enhances selected transitions, yields highly reproducible spectra and improves the limits of detection for MS/MS analysis.