Electron Capture Negative Ionization Research Articles

Structural determination of zinc dithiophosphates in lubricating oils by gas chromatography–mass spectrometry with electron impact and electron-capture negative ion chemical ionization

Pentafluorobenzyl ester derivatives were used to identify zinc dialkyldithiophosphates and diaryldithiophosphates anti-wear engine oil additives by GC–electron impact ionization (EI) MS and GC–electron-capture negative ion chemical ionization (ECNCI) MS analysis. GC–EI-MS of the dialkyldithiophosphate–pentafluorobenzyl derivatives afforded characteristic fragment ions corresponding to the cleavage of one and two alkyl radicals. In most cases, information was only obtained on one alkyl chain. Additional and complete information was obtained with retention time indices using synthetic derivatives and with GC–ECNCI-MS analysis. ECNCI afforded characteristic dithiophosphate anions which allowed the determination of the total number of carbon atoms in the alkyl radicals. The diastereoisomer mixtures of 2-hydroxy- sec.-alkyl radicals were completely separated on GC analysis.

A novel and sensitive method for the quantification of N-3-oxoacyl homoserine lactones using gas chromatography-mass spectrometry: application to a model bacterial biofilm.

A method is reported for the quantification of 3-oxoacyl homoserine lactones (3-oxo AHLs), a major class of quorum-sensing signals found in Gram-negative bacteria. It is based on the conversion of 3-oxo AHLs to their pentafluorobenzyloxime derivatives followed by gas chromatography-mass spectrometry (electron capture-negative ion). The method used [13C16]-N-3-oxo-dodecanoyl homoserine lactone ([13C16]-OdDHL) as the internal standard, and its validity was tested by spiking the supernatant and cell fractions with three levels of 3-oxo AHLs, i.e. 1, 10 and 100 ng per sample. These showed the method to be both sensitive (S/N ratio >10:1 for 1 ng) and accurate. The assay was applied to the biofilm and effluent of a green fluorescent protein (GFP)-expressing strain of Pseudomonas aeruginosa (6294) culture grown in flow cells. Biofilm volume was determined for three replicate flow cells by confocal scanning laser microscopy. OdDHL was detected in the biofilm at 632 +/- 381 microM and the effluent at 14 +/- 3 nM. The biofilm concentration is the highest level so far reported for an AHL in a wild-type bacterial system. The next most abundant 3-oxo AHL in the biofilm and effluent was N-3-oxo-tetradecanoyl homoserine lactone (OtDHL) at 40 +/- 15 microM and 1.5 +/- 0.7 nM respectively. OtDHL is unreported for P. aeruginosa and has an activity equivalent to OdDHL in a lasR bioassay. Two other 3-oxo AHLs were detected at lower concentrations: N3-oxo-decanoyl homoserine lactone (ODHL) in the biofilm (3 +/- 2 microM) and effluent (1 +/- 0.1 nM); and N-3-oxo-octanoyl homoserine lactone (OOHL) in the effluent (0.1 +/- 0.1 nM).

Prominent chlorobornane residues in estuarine sediments contaminated with toxaphene

Soils and sediments contaminated with residues of technical toxaphene may require remedial action to reduce human health and ecological risks. Sediments were collected from a coastal wetland impacted by discharge from a former toxaphene production facility and analyzed by gas chromatography-electron capture detection and conventional and enantioselective gas chromatography-mass spectrometry in the electron capture negative ion mode. The prominent chlorobornanes (CHBs) in all samples were 2-exo,3-endo,6-exo,8,9,10-hexachlorobornane (B6-923 or Hx-Sed) and 2-endo,3-exo,5-endo,6-exo,8,9,10-heptachlorobornane (B7-1001 or Hp-Sed), metabolites of higher chlorinated components of technical toxaphene (CTTs). Pentachlorobornanes, toxaphene homologs not previously reported in environmental samples, and likely precursor CTTs were also detected. Several CHB congeners were enantioresolved, the majority of which exhibited racemic composition. These results indicate that the profile of CHBs persisting in estuarine sediment is highly modified relative to the technical mixture, and also provides strong evidence of in situ reductive dechlorination, a process that if enhanced could act to reduce bioaccumulation and toxicity of sediment-bound CTTs at toxaphene-contaminated sites.

Determination of Q1, an unknown organochlorine contaminant, in human milk, Antarctic air, and further environmental samples

Q1, an organochlorine component with the molecular formula C9H3Cl7N2 and of unknown origin was recently identified in seal blubber samples from the Namibian coast (southwest of Africa) and the Antarctic. In these samples, Q1 was more abundant than PCBs and on the level of DDT residues. Furthermore, Q1 was more abundant in seals from the Antarctic than the Arctic. To prove this assumption, gas chromatography–electron-capture negative ion mass spectrometry (GC/ECNI–MS), which is sensitive and selective for Q1, allowed for screening of traces of Q1 even in samples with particularly high levels of other organochlorine contaminants. Q1 was isolated by high-performance liquid chromatography (HPLC) from a skua liver sample. A 1:1 mixture with trans-nonachlor in electron-capture detectors (ECDs) was used to determine the relative response factor with ECNI–MS. The ECNI–MS response of Q1 turned out to be 4.5 times higher than that of trans-nonachlor in an ECD. With GC/ECNI–MS in the selected ion-monitoring mode, four Antarctic and four Arctic air samples were investigated for the presence of Q1. In the Antarctic air samples, Q1 levels ranged from 0.7 to 0.9 fg/m3. In Arctic air samples, however, Q1 was below the detection limit (<0.06 fg/m3 or 60 ag/m3). We also report on high Q1 levels in selected human milk samples (12–230 μg/kg lipid) and, therefore, suggested that the unknown Q1 is an environmental compound whose origin and distribution should be investigated in detail. Our data confirm that Q1 is a bioaccumulative natural organochlorine product. Detection of a highly chlorinated natural organochlorine compound in air and human milk is novel.

Vitamin A equivalence of β-carotene in a Woman as determined by a stable isotope reference method

Quantitative information on conversion of beta-carotene to vitamin A in humans is limited. Our laboratory has developed a stable isotope method for studying the conversion of beta-carotene (beta-C) to vitamin A. Two dosage levels (a pharmacological dose, 126.0 mg beta-C-d8, and a physiological dose, 6.0 mg beta-C-d8) were used 2.5 y apart in an adult female volunteer to study dose effects on the conversion of beta-C to vitamin A. Blood samples were collected over 21 d. beta-C and retinol were extracted from serum and isolated by high performance liquid chromatography. The retinol fraction was derivatized to a trimethylsilyl ether which was analyzed by gas chromatograph/mass spectrometry with electron capture negative chemical ionization. The retinol-d4 response in the circulation peaked at 24 hours after the beta-C-d8 dose, with a higher percent enrichment after the pharmacological dose than after the physiological dose. By using retinyl acetate-d8 as the vitamin A reference, the retinol-d4 formed from 6 mg of beta-C-d8 (11.2 mumol) was calculated to be equivalent to 1.6 mg of retinol (i.e., 3.8 mg of beta-C was equivalent to 1 mg of retinol). However, the retinol-d4 formed from 126 mg of beta-C-d8 (235 mumol) was equivalent to 2.3 mg of retinol (i.e., 55 mg beta-C was equivalent to 1 mg retinol). These results provide evidence that it is feasible to use stable isotope reference method to study retinol equivalence of beta-C and that there may be a dose-dependence on bioconversion of beta-carotene to retinol.

The determination of toxaphene in environmental samples by negative ion electron capture high resolution mass spectrometry

A method is described for the analysis of toxaphene in environmental samples by high resolution gas chromatography high resolution mass spectrometry in selected ion electron capture negative ion mode. Toxaphene is detected by monitoring [M–Cl] −fragments ions of chlorobornanes (Cl 6–Cl 10) and chlorobornenes (Cl 6–Cl 7) using formal ion ratio criteria. The method shows high sensitivity and excellent specificity for the detection of chlorobornanes with negligible interference from of a wide range of common environmental organochlorines including chlordanes, PCBs and PCB-oxygen adducts. The analytical scheme is applicable to sediment and biological tissue samples and typically provide sample detection limits of less than 0.2 ng/g technical toxaphene for a 10 g sample.

Congener and Enantioselective Analysis of Toxaphene in Sediment and Food Web of a Contaminated Estuarine Wetland

Enantioselective gas chromatography with electron capture negative ion mass spectrometry (GC/ECNI-MS) was employed to investigate the fate of toxaphene residues in contaminated sediment (source) and biota (receptor) representing several levels of an aquatic food web. Samples were collected from an estuarine marsh that was impacted by discharge from a former toxaphene plant. Several penta- to nonachlorobornanes were identified and enantiomerically resolved on a chiral stationary phase. Additional peak confirmation was obtained after fine fractionation of extracts on silica. Previously identified congeners including B6-923 (Hx-Sed), B7-515 (P-32), B7-1001 (Hp-Sed), B8-806/9 (P-42), B8-1412, B8-1413 (P-26), B8-2229 (P-44), B9-1679 (P-50), and B9-2206 (P-63) were detected, as were several unknown penta- and heptachlorobornanes. The majority of prominent congeners were essentially racemic in marsh sediment (maximum deviation 15%). In contrast, several congeners as well as several unknown hepta-CTTs were enantioselectively depleted in lower food web organisms; the enantiomer ratios (ERs) for B6-923 and B7-1001 in small fish (Fundulus sp.) were ∼2 and 0.6, respectively. These significant alterations of the ERs prove that even low-trophic level biota is able to degrade toxaphene components to some degree. In higher level predators, the ERs for B7-1001 were closer to racemic. Irrespective of trophic level, little or no shift in the ERs for B8-1413 (P-26) and B9-1679 (P-50), two recalcitrant chlorobornanes in mammals, relative to sediment were observed. These results indicate that biochemical transformations within the scope of the estuarine food web studied likely act to alter the residue pattern and the ultimate fate of toxaphene.

Frozen shell approximation violation in negative ion formation from halogenated benzenes via dissociative attachment

A series of benzene derivatives (R(1)C(6)H(4)R(2)) has been studied by means of electron capture negative ion mass spectrometry (ECNI-MS), and PM3 quantum chemical calculations. The dissociation channel M(-.) --> Hal(-) + (M - Hal). is analysed from the point of view of symmetry conservation. Generally, a symmetry ban on dissociation may be avoided in at least two ways: (i) out-of-plane vibrations of the halogen atom in the molecular negative ion (MNI), mixing pi- and sigma-states of the anion; (ii) symmetrical in-plane vibration of the C-Hal bond, changing the order of the empty levels in the MNI with subsequent radiationless conversion into a sigma-state. Our analysis shows that neither of them provides a satisfactory explanation of the ECNI mass spectra for chlorobenzene, if one retains the usual assumption that an additional electron goes into the LUMO of the neutral molecule. Thus, it may be concluded that in this case electron capture causes a significant perturbation of the energy ordering of vacant orbitals, thus making the frozen shell approximation inapplicable. Copyright 2000 John Wiley & Sons, Ltd.

Synthesis, isolation and purification of C 10–C 13 polychloro- n-alkanes for use as standards in environmental analysis

Short chain (C 10–C 13) polychloro- n-alkanes ( sPCAs) mixtures were synthesized by refluxing pure n-alkane (>99%) with sulfuryl chloride (SO 2Cl 2) in the presence of UV-light (550 W). The free radical initiated reactions produced analogs containing ∼4–9 chlorine atoms on each carbon chain. Purification of reaction products was achieved by adsorption chromatography on Florisil. The products were characterized by high-resolution gas chromatography/mass spectrometry (HRGC/MS) operated in the electron capture negative ionization (ECNI) and in electron ionization (EI) modes. Individual standards can now be combined to create standards whose profiles resemble that of environmental samples. Quantification of a known amount of the newly synthesized sPCAs mixture, using an industrial formulation as an external standard, resulted in an overestimation (∼28%) in its true value.

Levels of Organochlorines (DDT, PCBs, Toxaphene, Chlordane, Dieldrin, and HCHs) in Blubber of South African Fur Seals ( Arctocephalus pusillus pusillus) from Cape Cross/Namibia

Organochlorines (DDT, toxaphene, PCBs, chlordane, HCHs, dieldrin) were quantified in the blubber of eleven fur seals of the species Arctocephalus pusillus pusillus. The sample clean-up included microwave-assisted extraction (MAE), gel-permeation chromatography (GPC), adsorption chromatography on silica gel and quantitation with GC/ECD. Compounds of technical toxaphene (CTTs) were determined after separation from the PCBs. Highest levels arose for p, p′-DDE (7–1000 μg/kg). A so far unknown compound labelled Q1 caused the second most abundant peak in the samples. Q1 was identified as a heptachloro compound by GC/MS in the electron capture negative ionisation and electron impact ionisation mode. Levels of Q1 were estimated relative to the ECD response factor of trans-nonachlor. These estimated Q1 levels ranged from 27 to 351 μg/kg being in the range or higher than the levels of PCBs (6–697 μg/kg), toxaphene (10–97 μg/kg), chlordane (3–159 μg/kg), and dieldrin (4–36 μg/kg). One sample which showed significantly higher DDT and PCB levels (but not toxaphene, dieldrin, Q1, and chlordane) than the others is most likely migrated from an area higher polluted with DDT and PCBs. Another one showed very low levels which were not explained. Except these samples, the levels determined in the blubber were among the lower levels reported for this kind of tissue. The data also confirmed that the organochlorine levels in Africa are varying from region to region, and that there is still a need for further research.

Measurement of Urinary F2-Isoprostanes as Markers of in Vivo Lipid Peroxidation—A Comparison of Enzyme Immunoassay with Gas Chromatography/Mass Spectrometry

This study aimed at comparing the two most commonly utilized methods for measuring urinary F2-isoprostanes, currently considered one of the best available markers of in vivo lipid peroxidation. The F2-isoprostanes were measured in 24-h urine samples from 14 male subjects using electron capture negative ionization gas chromatography–mass spectrometry (ECNI–GCMS) with 8-iso-PGF2α-d4 as an internal standard and compared with levels obtained using an enzyme immunoassay (EIA, 8-iso-PGF2α kit, Cayman Chemical Co.). The methods were compared using Pearson correlation coefficients, and Bland–Altman plots were constructed for the difference in F2-isoprostane against the average F2-isoprostane measured by either method. Weighted least-products regression was used to determine fixed bias (where there is a consistent difference between the methods) and proportional bias (where one method gives values higher or lower than the other method by an amount proportional to the size of the measurement). The correlation between F2-isoprostane levels obtained using EIA and GCMS methods, although significant, was poor (r = 0.628, P < 0.02). Comparison of the methods using the Bland–Altman analysis showed that there were wide limits of agreement between the two methods with only 28% of the values falling within the 95% confidence limits for the difference. The GCMS gave higher values with a mean difference of 298.1 pM (636.6, −40.2; P = 0.079), and a near significant linear association between the differences and the mean F2-isoprostane level (r = −0.559, P = 0.05). Weighted least-product regression analysis confirmed the presence of both significant fixed and proportional bias with the EIA giving lower levels of F2-isoprostanes at low concentrations and higher levels at higher concentrations. The cross-reactivity in the EIA of 8-iso-15(R)-PGF2α and 9β-PGF2α which coelute with the F2-isoprostane peak measured by GCMS was very low, 0.2 and 0.1%, respectively. The proportional bias observed between the methods may in part be due to differences in the relative amounts of 8-iso-15(R)-PGF2α, 9β-PGF2α, and 8-iso-PGF2α with increasing lipid peroxidation. This study shows that the measurements of F2-isoprostanes by EIA and GCMS are not equivalent. Therefore, comparison of levels derived using a GCMS method which estimates concentration from a peak encompassing a number of F2-isoprostane isomers, and levels derived from enzyme immunoassay measuring a specific isoprostane, may be inappropriate.

Occurrence of C10−C13 Polychlorinated n-Alkanes in Canadian Midlatitude and Arctic Lake Sediments

Sediment cores from six lakes in Canada ranging from 49°N to 81°N were analyzed for C10−C13 polychlorinated n-alkanes (PCAs) with the intent of (i) examining the depositional trends with increasing latitude, (ii) studying the historical profiles and fluxes of PCAs in dated sediment slices, and (iii) investigating possible in situ degradation. Sediment slices were dated using 210Pb and 137Cs, and extracts were analyzed for PCA concentrations by high resolution gas chromatography electron capture negative ion high resolution mass spectrometry (HRGC-ECNI/HRMS) in the selected ion monitoring (SIM) mode. Concentrations of total PCAs in surface sediments declined significantly from 135 ng/g (dry weight (dw)) in sediments from the southern basin of Lake Winnipeg (50°N/96°W, Manitoba) to 4.52 ng/g in Hazen Lake (81°N/71°W, high Arctic); corresponding surficial fluxes were 147 and 0.9 μg/m2 yr, respectively. The high flux of PCAs to the south Lake Winnipeg basin suggests local contamination. This was confirmed by ...

Shape resonances in slow electron scattering by aromatic molecules. I. Anthraquinone derivatives.

A series of anthraquinone (C(14)O(2)H(8)) derivatives has been studied by means of electron capture negative ion mass spectrometry (ECNI-MS), photoelectron spectroscopy (PES), and AM1 quantum chemical calculations. Mean lifetimes of molecular negative ions M(-.) (MNI) have been measured. The mechanism of long-lived MNI formation in the epithermal energy region of incident electrons has been investigated. A simple model of a molecule (a spherical potential well with the repulsive centrifugal term) has been applied for the analysis of the energy dependence of cross sections at the first stage of the electron capture process. It has been shown that a temporary resonance of MNI at the energy approximately 0.5 eV corresponds to a shape resonance with lifetime 1-2.10(-13) s in the f-partial wave (l = 3) of the incident electron. The next resonant state of MNI at the energy approximately 1.7 eV has been associated with the electron excited Feshbach resonance (whose parent state is a triplet npi* transition). In all cases the initial electron state of the MNI relaxes into the ground state by means of a radiationless transition, and the final state of the MNI is a nuclear excited resonance with a lifetime measurable on the mass spectrometry timescale. Copyright 1999 John Wiley & Sons, Ltd.

Shape resonances in slow electron scattering by aromatic molecules. I. Anthraquinone derivatives

A series of anthraquinone (C14O2H8) derivatives has been studied by means of electron capture negative ion mass spectrometry (ECNI-MS), photoelectron spectroscopy (PES), and AM1 quantum chemical calculations. Mean lifetimes of molecular negative ions M−· (MNI) have been measured. The mechanism of long-lived MNI formation in the epithermal energy region of incident electrons has been investigated. A simple model of a molecule (a spherical potential well with the repulsive centrifugal term) has been applied for the analysis of the energy dependence of cross sections at the first stage of the electron capture process. It has been shown that a temporary resonance of MNI at the energy ∼0.5 eV corresponds to a shape resonance with lifetime 1–2·10−13 s in the f-partial wave (ℓ = 3) of the incident electron. The next resonant state of MNI at the energy ∼1.7 eV has been associated with the electron excited Feshbach resonance (whose parent state is a triplet nπ* transition). In all cases the initial electron state of the MNI relaxes into the ground state by means of a radiationless transition, and the final state of the MNI is a nuclear excited resonance with a lifetime measurable on the mass spectrometry timescale. Copyright © 1999 John Wiley & Sons, Ltd.

Mass spectrometric analysis of arachidonyl-containing phospholipids in human U937 cells.

The human histiocytic lymphoma U937 cell line contains a rich source of the 85 kDa cytosolic phospholipase A2 (cPLA2). DMSO-differentiated U937 cells were used as a model to investigate the free arachidonic acid release, the arachidonate distribution and the phospholipid source of arachidonate upon Ca2+ ionophore stimulation. A combination of several chromatographic and mass spectrometric techniques was employed in this study. The amount of free arachidonic acid (AA) released upon stimulation, the arachidonate content in total lipids and in each of the phospholipid classes were determined by gas chromatography/mass spectrometry (GC/MS). Glycerophosphoethanolamine (GPE) was found to be the major pool of arachidonate in differentiated human U937 cells (55%) and glycerophosphocholine (GPC) and glycerophosphoinositol (GPI) contributed 22 and 8%, respectively. Upon Ca2+ ionophore stimulation, GPE class lost the largest amount of arachidonate, followed by GPC class. GPI class, however, gained a substantial amount of arachidonate. Most of the arachidonate depleted from GPE and GPC was recovered as free AA, some of which was rapidly esterified into GPI species. GC/MS with electron capture negative chemical ionization provided excellent sensitivity for the measurement of arachidonic acid which was derivatized to its pentafluorobenzyl ester. Intact phospholipid molecular species including the arachidonyl-containing phospholipid species were identified using capillary high-performance liquid chromatography/continuous-flow liquid secondary ion mass spectrometry (CF-LSIMS). No specificity was found for releasing free AA among the arachidonyl-containing GPE and GPC species upon Ca2+ ionophore stimulation. CF-LSIMS provided a sensitive and effective means of detecting intact phospholipid species.

Automated Toxaphene Quantitation by GC/MS

Toxaphene is a complex mixture of at least 600 hexa- to decachlorinated bornanes and bornenes, which was used as an insecticide from the late 1950s to the early 1980s. Like PCBs and other environmentally persistent organochlorine pesticides, toxaphene is ubiquitous in the environment. Toxaphene's complex composition makes its accurate quantitation difficult. We report here an automatic, gas chromatographic mass spectrometry method (using electron capture negative ionization) that is precise and fast. This method is implemented by a small QBasic program that compares peak area ratios to the predicted chlorine isotopic ion ratios. This method decreases the time required for analysis while maintaining precise quantitation. The method is verified with standard and unknown samples contaminated with various amounts of other organochlorine pesticide interferents.

Electron Energy Dependence of Regioselective Chloride Ion Loss from Polychlorodibenzo-p-dioxins. Relationship between Resonance Electron Energies and Virtual Orbital Energies

Regiospecifically chlorine-37-labeled polychlorodibenzo-p-dioxins (PCDDs) undergo electron energy-dependent regioselective chloride ion loss when analyzed by electron capture negative ion mass spectrometry using an electron monochromator to supply the slow monoenergetic electrons. Three negative ion resonances, produced with electrons of energies <0.5, ∼1, and ∼4 eV are associated with the production of chloride ions from PCDDs. Negative ion resonances for the production of molecular ions of higher PCDDs were recorded with electrons of energies <0.2 eV. Dichlorodibenzo-p-dioxins and some trichlordibenzo-p-dioxins showed no molecular ions. A correlation was found between the experimental electron attachment energies and the virtual orbital energies calculated by modified density functional theory methods using the B3LYP/D95//B3LYP/D95 level of theory. The results from these correlations strongly suggest that all negative ion-forming processes for this class of compounds are initiated from π* states. The loss of chloride ion from transient negative PCDD ions requires π*−σ* orbital mixing.

Interlaboratory Study on Quantitative Methods of Analysis of C10−C13 Polychloro-n-alkanes

Seven laboratories participated in an international interlaboratory comparison exercise to compare the quantitative methods used for measuring C10−C13 polychloro-n-alkanes (PCAs). Participants were supplied with two solutions (PCA-1, PCA-70) containing PCAs of “known” but unstated concentrations, and two real world samples (fish extracts FE1 and FE2) each consisting of a cleaned up extract (lipid-free) of a fish tissue known to contain PCAs. A well-characterized commercial formulation, PCA-60, of stated concentration was also supplied and was used as the external standard for the exercise. Participants having other commercially available C10−C13 PCA mixtures were encouraged to use them as external standards for the study, and the choice of the quantitative method employed was left to participants, though all were based on high-resolution gas chromatography with detection by electron capture negative ion mass spectrometry (plus electron capture detection in one case). The results of the study met with mixe...

Microwave-Assisted Extraction Coupled with Gas Chromatography with Nitrogen-Phosphorus Detection or Electron Capture Negative Chemical Ionization Mass Spectrometry for Determination of Dimethomorph Residues in Soil

Abstract Dimethomorph, a cinnamic acid derivative, is a crop protection product for the control of fungi in grapes, tomatoes, potatoes, and tobacco. Of the extraction techniques evaluated, microwave-assisted extraction (MAE) gave the best extractability of the analyte at trace levels from soil. After an appropriate cleanup, dimethomorph residues could be determined by gas chromatography (GC) with either nitrogen-phosphorus detection (NPD) or mass spectrometry with electron capture negative chemical ionization (ECNCI). The sensitivity and specificity of the latter detection technique made it possible to use a greatly simplified cleanup procedure. The limit of quantitation of both procedures was 10 ppb. Soils fortified over a range of 10 to 500 ppb gave an average recovery of 88%, with a standard deviation of 11% by GC-NPD and an average recovery of 99%, with a standard deviation of 8.8% by GC/ECNCI. Control soils generally showed apparent residues of less than 1 ppb

Effects of temperature and sample amount on the electron capture negative ion mass spectra of polychloro- n-alkanes

Ion source temperature, sample amount and the positions of the chlorine atoms attached to the neutral molecule all had profound effects on the appearance of the ECNI mass spectra of a number of synthesized polychloro- n-alkanes (PCAs). Increases in the ion source temperature resulted in a decrease in the abundances of both the [M + Cl] − and [M − Cl] − ions, while the abundances of the structurally non-characteristic ions, HCl 2 − and Cl 2 −•, increased. An increase in the amount of the injected PCA resulted in an increase in the abundance of the [M + Cl] − ion, most notably for congeners containing chlorine atoms only 1,2-substituted at both ends of the alkane chain. The abundance of the [M − Cl] − ion increases with decreasing ion source temperature down to 120°C, the lowest temperature easily maintained with our instrument. For analytical purposes we recommend that this source temperature be used.