Maarten Honing

Determination of ten carbamate pesticides in aquatic and sediment samples by liquid chromatography-ionspray and thermospray mass spectrometry.

Abstract Ten carbamate pesticides which exhibit large differences in polarity were determined simultaneously in various environmental samples, using both column liquid chromatography (LC)-thermospray (TSP) mass spectrometry (MS) and LC-ionspray (ISP) MS. For sample clean-up, column chromatography with three stationary phases, neutral aluminium oxide, Florisil and aminopropyl-bonded modified silica, were tested. The aminopropyl stationary phase showed the best results, with acetone-dichloromethane (25:75) as eluent; analyte recoveries were 76–100% for all compounds with a relative standard deviation of 2–8%. In the ISP mass spectra of eight of the ten carbamates, the sodium adduct ion, [M + Na] + , was the base peak, while the protonated molecule, [M + H] + , was the most abundant ion with carbendazim and aminocarb. An eluent flow-rate between 100 and 300 μl/min was found to be optimum, with optimized nebulizer and drying gas flow-rates of 350 and 15 l/h, respectively. A capillary voltage of 3.5 kV resulted in the largest total ion current. The optimum extraction voltage with regard to analyte detectability and confirmation purposes was between 15 and 35 V. The detection limits obtained with the LC-ISP-MS system were typically in the 10–60 pg range (10 μl of 10 μg/l standard solutions), which is 10–150-fold better than obtained with LC-TSP-MS (selected-ion monitoring mode used in both instances). Large-volume injections of tap water spiked with selected carbamates at a level of 0.1 μg/l illustrated the potential of LC-ISP-MS with respect to analyte detectability. Furthermore, carbofuran was identified at a concentration level of ca. 5 μg/l in water samples from the Ebro delta. LC-TSP-MS of oxamyl and methomyl in a sediment sample containing a high percentage of organic matter was adversely affected by the presence of co-extractives. This problem did not occur with LC-ISP-MS.

On-line solid-phase extraction–liquid chromatography–particle beam mass spectrometry and gas chromatography–mass spectrometry of carbamate pesticides

On-line solid-phase extraction–liquid chromatography–particle beam mass spectrometry (SPE–LC–PB-MS) was used to study 32 carbamates and 11 of their transformation products in environmental water samples. The analytes were enriched from 100 ml samples on Bondesil-C18/OH, packed in a 10 mm × 3.0 mm id precolumn, eluted on-line with a gradient of methanol–0.1 mol l–1 ammonium acetate to a C18 analytical column and detected by PB-MS. Detection limits of 12 carbamates and five degradation products were 0.1–8 µg l–1 in surface water, using full-scan electron impact mode detection. The RSDs of the retention times were 0.05–0.2% and those of peak areas 5–35%. Twenty-eight analytes proved to be amenable to GC with detection limits of 0.05–3 ng injected on-column. When using the same mass spectrometer, the spectra obtained by LC–PB-MS and GC–MS were identical.

Ion formation of N-Methyl carbamate pesticides in thermospray mass spectrometry: The effects of additives to the liquid chromatographic eluent and of the vaporizer temperature

The effects of three additives—ammonium acetate, ammonium formate, and nicotinic acid—to the liquid chromatographic (LC) eluent and of the vaporizer temperature on the ion formation of N-methyl carbamate pesticides in thermospray (TSP) mass spectrometry was investigated by using filament- or discharge-assisted ionization. Nineteen carbamates and 12 of their known environmental degradation products were used as model compounds. The additives cause a strong reduction in the abundance of the characteristic fragment ions [M + H − CH3NCO]+ and [M − H − CH3NCO]− for some of the carbamates. The addition of nicotinic acid reduces the quasimolecular ion intensity and, in most cases, produces nicotinic acid adduct ions. The addition of ammonium acetate or ammonium formate increases the intensity of the quasimolecular ion and in most cases produces a base peak for the ammonium adduct ion. The combination of a suppression of fragmentation and an enhancement of quasimolecular ion formation produces an overall gain in sensitivity. As to more specific effects, the addition of the ammonium salts reduces the intensity of M−• with the chlorinated carbamate barban and suppresses the formation of “odd” adduct ions in the TSP mass spectra of most other carbamates. Monitoring the intensity of the fragment and the quasimolecular ion signal as a function of the probe stem temperature, and the related probe tip temperature, proved to be an easy method to study the thermal degradation of the carbamates. This monitoring procedure showed that methiocarb and its sulfone already suffer from thermal degradation at a stem temperature of 90°C and that these compounds will therefore present problems in quantitation with LC/TSP mass spectrometry.

Effect of ion source pressure on ion formation of carbamates in particle-beam chemical-ionisation mass spectrometry

Abstract In this study the mass spectra of fourteen carbamate pesticides, obtained with desorption chemical ionisation (DCI) and flow injection (FIA)-particle beam (PB)-ammonia positive chemical ionisation (PCI)-mass spectrometry (MS), are compared. The mass spectra from the FIA-PB-PCI-MS experiments exhibit higher relative abundances for fragment ions. The influence of the ion source pressure and temperature on the ion abundances under ammonia positive chemical ionisation conditions was studied. The results indicate that thermal degradation of the carbamate pesticides takes place in the FIA-PB-MS system. In addition, the [M + NH3 + H]+ and [M + NH3 + H - CH3NCO]+ ion intensities are strongly dependent on the ion source pressure, especially for carbofuran as an extreme. Both the ion source pressure and the temperature cause irreproducibility of the ammonia PCI mass spectra of carbamates under liquid chromatography PB-PCI-MS conditions and it is therefore of utmost importance to use well defined experimental conditions for the quantitative determination of carbamates.

Comparative study of different thermospray interfaces with carbamate pesticides: Influence of the ion source geometry.

Sixteen carbamate pesticides that belong to four chemical classes (oxime-N-methylcarbamates, aryl N-methylcarbamates, N-phenylcarbamates, and methyl esters of substituted carbamic acids) were investigated via three different commercially available thermospray interfaces and ion sources that exhibit wide differences in source geometry. Comparisons were made between the three interfaces with respect to ion formation and sensitivity of detection. Experimental parameters were standardized to obtain comparable experimental conditions. Very similar mass spectra for most carbamates were obtained that illustrate independence from the geometry of the ionization and desolvation chambers of the interfaces. These findings are in sharp contrast to several literature reports. However, thermally labile carbamates gave unsatisfactory results with regard to spectral compatibility between the interfaces. Such differences were due to thermally assisted hydrolysis reactions that occur in the vaporizer probe prior to ionization and reflect differences in the vaporizer designs. The study proves conclusively that comparable spectra can be obtained under thermospray with different interfaces and mass spectrometers.

Identification of carbamates by particle beam/mass spectrometry.

The possibility of analysing 33 carbamate pesticides and 14 of their transformation products was investigated utilizing flow injection particle beam/mass spectrometry (PBMS) with electron impact (EI) ionization and ammonia and methane positive and negative chemical ionization (CI). Optimum operating conditions of the interface and mass spectrometer in each mode were determined, with special attention given to spectrum quality; variables investigated included ion source temperature and ion source pressure in CI experiments. Ammonia, as a reagent gas, provided less fragmentation and better quantitative results than methane. The CI response was generally higher with positive ion detection (PCI) than with negative ion detection (NCI), but NCI was found to be highly selective for compounds such as aminocarb, asulam and thiophanate-methyl. As regards analyte detectability, EI performed best for most compounds, with the spectra providing relevant structure information. The response of more polar degradation products is generally larger by 2–3 orders of magnitude compared with the parent compounds. When analysing real samples, the combined use of CI for molecular mass determination and EI for structure elucidation is required. The spectral information from this study and additional chromatographic data were used for the determination of low- and sub-μg l-1levels of the test carbamates in surface water.

Limitations and perspectives in the determination of carbofuran with various liquid chromatography-mass spectrometry interfacing systems

Abstract Column liquid chromatography with mass spectrometric detection (LC-MS) has been widely accepted as the preferred technique for the identification and quantification of polar and thermally labile compounds at trace levels. Over the last decade many different types of LC-MS interfacing techniques have been used for the determination of carbamate pesticides and especially for the N-methylcarbamate carbofuran. This article addresses the difficulties encountered with the various types of LC-MS interface and discusses recent alternatives for the determination of carbofuran. With thermospray and particle beam interfaces the quantification of carbofuran is affected by both the ion source pressure and temperature, whereas quantification using the recently developed atmospheric pressure ionization interfaces, atmospheric pressure chemical ionization, electrospray, and ionspray, is less dependent on these parameters.

Adduct ion formation by aromatic amines in thermospray mass spectrometry.

The formation of solvent adduct ions in thermospray and ionspray mass spectrometry was studied for twelve aromatic amines : aniline, N-methylaniline, N,N-dimethylaniline, 3-aminophenol, 3-methylaminophenol, 3-dimethylaminophenol, 2-aminopyridine, 2-methylaminopyridine and 2-dimethylaminopyridine, 2-amino-5,6-dimethyl-4-hydroxypyrimidine, 2-methylamino-5,6-dimethyl-4- hydroxypyrimidine and 2-dimethyl-amino-5,6-dimethyl-4-hydroxypyrimidine. For all compounds, adduct ions, [M + H + A n ] + , with A being methanol or acetonitrile, were observed in the thermospray mass spectra ; water adduct ions were observed for a few compounds. No adduct ions with ammonia were formed when ammonium acetate was added to the liquid chromatographic carrier stream. These observations cannot be explained on the basis of gas-phase ion-molecule reactions of the neutral analyte and protonated solvent or solvent additive molecules. Comparative experiments, changing the pH of the carrier stream in both thermospray and ionspray ionization, showed that the solvent adduct ions present in the thermospray mass spectra are not likely to be formed by ion evaporation processes. Incomplete evaporation of droplets or cluster ions is proposed to be responsible for the observations. With this hypothesis, both the absence of ammonium adduct ions and the dependence of the adduct ion abundances on the N-methylation can be related to the adduct-analyte bond strengths.

Optimisation of the liquid chromatographic separation of pirimicarb and its metabolites V–VII: application to a soil sample used as a candidate reference material

Abstract The simultaneous separation of the N -dimethylcarbamate pirimicarb and its metabolites V–VII was carried out by liquid chromatography (LC) using diode array detection (DAD). Two columns, a 250 × 4.6 mm i.d. column packed with 5-μm particles with a cyanopropyl modified silica stationary phase and a 150 × 4.6 mm i.d. column packed with 3-μm particles with a base deactivated C 8 modified silica stationary phase, were compared. The addition of a buffer in the eluent, for both columns, was needed to improve the peak shape of metabolite V and the resolution of the metabolites V–VII and consequently the pH dependence of the retention time was tested. Additionally chromatograms of two soil samples of different origin, spiked at a concentration level of 1 μg g −1 for pirimicarb, analysed by LC-DAD, gas chromatography (GC) with nitrogen phosphorus detection and GC-mass spectrometry are shown. Detection limits and reproducibility data of primicarb in a candidate reference sample using LC-DAD and a cyanopropyl column are reported.

Sample handling and determination of carbamate pesticides and their transformation products in various matrices.

Abstract The use of non-persistent carbamate pesticides, which often replace organochlorine and organophosphorus compounds, is increasing because of their broad spectrum of activity, high pesticide effectiveness and generally low mammalian toxicity. Suitable analytical procedures for the determination of these pesticides in a variety of environmental matrices are therefore required. Analysis of the degradation products of the carbamates is also of interest, since their toxicity may be higher than that of the parent compounds. A large variety of carbamates is currently in use. Their application as an insecticide, fungicide or herbicide is related to the molecular structure. The insecticides have the N-substituted carbamate moiety and, generally, an aromatic ester or an oxime function. The fungicides have either a benzimidazolyl ester, a pyrimidyl ester or a (bis)dithiocarbamate group. The herbicides have an N-alkylthiocarbamate or an N-phenyl carbamate group [1–3]. Figure 1 shows a general representation of these subclasses. The degradation products are generally oxidized derivatives, e.g. aldicarb sulphone (from aldicarb), or alcohols formed by saponification of the carbamic acid group, e.g. 1-naphthol (from carbaryl). The general degradation pathways of carbamate pesticides were discussed by Schlagbauer and Schlagbauer [4], while several reports deal with fate studies of specific carbamates: aryl N-methylcarbamates [5,6], benomyl [7,9] and oxime N-methylcarbamates [10,14]. The biodegradation of some carbamates in various environmental matrices has also been studied [15]. Many analytical methods have been developed for the determination of the carbamate pesticides. In addition to the currently most common analytical techniques such as gas chromatography (GC), liquid chromatography (LC), and supercritical fluid chromatography (SFC), other methods, e.g. bioassays [16], stopped flow Chromatographie techniques [17], thin layer chromatography [18] and colorimetry [19–21] have been employed. This chapter will focus on GC-, LC and SFC based analytical methods. The rapid growth of the use of carbamate pesticides over the last two decades requires that validated analytical procedures be developed. It should be possible to determine low concentration levels down to e.g. 0.1 g.l 1 for drinking water [16]. Furthermore, multiresidue analytical procedures, which comprise the carbamates and their transformation products, are of much current interest, because their use effectively reduces analysis time an expense. Amongst other, our group, with the support of the Community Bureau of Reference (BCR, Measurements and Testing Programme, Brussels) of the European Commission, has developed validated extraction, clean-up and analytical methods for the determination of carbamate (and some other) pesticides in different environmental matrices. So far, several review papers concerning the use of LC [22–24] and mass spectrometry (MS) [25] have been published. In the following, procedures for LC, GC and SFC analysis of some subclasses of carbamates (and their degradation products) in various matrices will be discussed. The chapter, divided into three sections, covers: (1) sample preparation from water, plant materials and soil, (2) LC, GC and SFC separations and (3) ultraviolet (UV), fluorescence, electrochemical (ECD) and mass spectrometric (MS) detection in LC.