Study of matrix effects on the direct trace analysis of acidic pesticides in water using various liquid chromatographic modes coupled to tandem mass spectrometric detection

Feasibility of an on-line restricted access material/liquid chromatography/tandem mass spectrometry method in the rapid and sensitive determination of organophosphorus triesters in human blood plasma

A rapid on-line solid phase extraction/liquid chromatography/tandem mass spectrometry (SPE/LC/MS/MS) method using restricted access material (RAM) was developed for the simultaneous determination of eight organophosphorus triesters in untreated human blood plasma. In a process involving column-switching techniques, the analytes were enriched on the RAM column, separated using a C-18 analytical column and detected with LC/MS. Tandem mass spectrometry was used to characterize and quantify the analytes. To elucidate the fragmentation pathway of a number of the analytes, MS3 experiments using an ion trap mass spectrometer were performed. The matrix effects associated with using APCI and ESI interfaces were investigated. The recoveries obtained were in the range 60-92% (R.S.D.<6%), with estimated detection limits between 0.2 and 1.8 ng/ml of plasma, and the total analysis time was 27 min.

Matrix effects in (ultra)trace analysis of pesticide residues in food and biotic matrices

If one has to determine multiple residues of modem pesticides and/or other groups of (semi)polar and/or thermally unstable contaminants with a wide range of physico-chemical properties within a single analytical run, it can be complicated to obtain low limits of quantitation (LOQ), good precision as well as relevant trueness of results for all the target analytes. Matrix components, which are unavoidably present in analyzed samples (even after the thorough clean-up step), may be responsible for miscellaneous adverse affects impairing different stages of the GC and/or LC determinative step. In this review, the nature of various types of matrix effects are discussed together with suggestions for prevention, reduction and/or compensation of their occurrence when determining troublesome analytes in foods and other complex biotic matrices.

Liquid chromatography-(tandem) mass spectrometry of selected emerging pollutants (steroid sex hormones, drugs and alkylphenolic surfactants) in the aquatic environment

Among the various compounds considered as emerging pollutants, alkylphenolic surfactants, steroid sex hormones, and pharmaceuticals are of particular concern, both because of the volume of these substances used and because of their activity as endocrine disruptors or as causative agents of bacterial resistance, as is the case of antibiotics. Today, the technique of choice for analysis of these groups of substances is liquid-chromatography coupled to mass spectrometry (LC-MS) and tandem mass spectrometry (LC-MS-MS). In the last decades, this technique has experienced an impressive progress that has made possible the analysis of many environmental pollutants in a faster, more convenient, and more sensitive way, and, in some cases, the analysis of compounds that could not be determined before. This article reviews the LC-MS and LC-MS-MS methods published so far for the determination of alkylphenolic surfactants, steroid sex hormones and drugs in the aquatic environment. Practical considerations with regards to the analysis of these groups of substances by using different mass spectrometers (single quadrupole, ion trap and triple quadrupole instruments, etc.), interfaces and ionization and monitoring modes, are presented. Sample preparation aspects, with special focus on the application of advanced techniques, such as immunosorbents, restricted access materials and molecular imprinted materials, for extraction/purification of aquatic environmental samples and extracts are also discussed.

Liquid chromatography-mass spectrometry and strategies for trace-level analysis of polar organic pollutants

Liquid chromatography-mass spectrometry using atmospheric pressure ionization (LC-API-MS) has drastically changed the analytical methods used to detect polar pollutants in water. The present status of application of this technique to organic water constituents is reviewed. The selection of the appropriate LC conditions, whether reversed-phase liquid chromatography, ion-pair chromatography, capillary electrophoresis or ion chromatography, and of the most sensitive ionization mode, electrospray ionization (ESI) or atmospheric pressure chemical ionization (APCI), depends upon the polarity and acidity of the analytes. Strongly acidic compounds such as aromatic sulfonates, sulfonated dyes, haloacetic acids, linear alkylbenzene sulfonates, aliphatic sulfonates and sulfates and complexing agents, weakly acidic compounds such as carboxylates and phenols, neutral compound classes, namely alkylphenol ethoxylates, alcohol ethoxylates and polycyclic aromatic hydrocarbons and the basic toxins, quaternary ammonium compounds and organometallic compounds are considered. The selection of the mass spectrometer depends upon the analytical task: triple-quadrupole mass spectrometers are highly suited for sensitive quantitation and for qualitative analyses, ion traps are especially suited for structure elucidation, whereas time-of-flight mass spectrometers and quadrupole time-of-flight mass spectrometers with their higher mass resolution are ideal for the determination of molecular formulas of unknown compounds and for screening purposes. While large steps have already been made, future efforts with respect to water analysis may be directed at fine-tuning the methodical arsenal for increased sensitivity and selectivity and to extend LC-MS application to transformation products.

Determination of abamectin and azadirachtin residues in orange samples by liquid chromatography-electrospray tandem mass spectrometry

A rapid and sensitive LC-ESI-MS-MS method has been developed for the determination of azadirachtin and abamectin residues in orange samples. Samples were extracted with acetonitrile, in a high-speed blender. After the addition of sodium acetate, an aliquot of extract was directly injected into the LC-ESI-MS-MS system. The highest sensitivity of the method was achieved under MS-MS conditions using [M+Na]+ adducts as precursor ions. Recoveries for both compoundsfrom spiked orange samples at 0.01 and 0.1 mg/kg were above 80%, with good repeatability (<10%). Method detection limits achieved (<0.007 mg/kg) were adequate for the determination of these pesticides in this kind of sample from the regulatory point of view. The importance of the solvent used for extraction, as well as the addition of sodium acetate to the extracts and the selection of adequate chromatographic conditions are discussed.

Ion suppression in the determination of clenbuterol in urine by solid-phase extraction atmospheric pressure chemical ionisation ion-trap mass spectrometry

Ion suppression effects were observed during the determination of clenbuterol in urine with solid-phase extraction/multiple-stage ion-trap mass spectrometry (SPE/MS(3)), despite the use of atmospheric pressure chemical ionisation. During SPE, a polymeric stationary phase (polydivinylbenzene) was applied. Post-cartridge infusion of analyte to the SPE eluate after the extraction of blank urine was performed to obtain a profile of the suppression. Single and multiple-stage MS were performed to provide insight in the suppressing compounds. The ion suppression was mainly ascribed to two m/z values, but still no identification of the compounds was achieved from the multiple-stage MS data. No ionisable and non-ionisable complexes and/or precipitation of clenbuterol with matrix compounds were observed. A concentration dependence of the percentage of suppression was observed. Up to 70% of the signal was suppressed upon post-cartridge infusion of 0.22 microg/mL (at 5 microL/min) clenbuterol into the eluate, and this decreased to about 4% at infusion of 22 microg/mL clenbuterol. Molecularly imprinted polymers were used to enhance the selectivity of the extraction. Although matrix components were still present after extraction, no interference of these compounds with the analyte was observed. However, the bleeding of the imprint from the polymer (brombuterol) caused significant ion suppression.

Identification and quantification of polar naphthalene derivatives in contaminated groundwater of a former gas plant site by liquid chromatography-electrospray ionization tandem mass spectrometry

A liquid chromatography (LC) method followed by electrospray ionization (ESI) and tandem mass spectrometry (MS-MS) was developed for the quantification of acidic naphthalene derivatives in the concentration range 0.1 to 100 microg/l without excessive sample preparation. For optimal sensitivity the LC-MS-MS measurements were performed recording mass fragmentation by collision induced dissociation in the multiple reaction mode. The collision energy was optimized for every analyte. The matrix effects of the sample were investigated by spiking standards of 1-naphthoic acid with humic acid (HA) and with calcium chloride. While HA decreased the signal intensity an increase was observed in the presence of calcium chloride. For the investigated groundwater samples of a tar oil contaminated site a complete separation of the analytes from the sample matrix by reversed-phase separation could be obtained. The absence of matrix effects on quantification results was confirmed by comparison of results based on external calibration with those based on standard addition of the analytes to a groundwater sample. In four groundwater samples of the contaminated site naphthalene derivatives like 1-naphthoic acid, 2-naphthoic acid, 1-naphthylacetic acid, 2-naphthylacetic acid, 1-hydroxy-2-naphthoic acid, 2-hydroxy-3-naphthoic acid, and naphthyl-2-methylenesuccinic acid have been detected.

Different quantitation approaches for xenobiotics in human urine samples by liquid chromatography/electrospray tandem mass spectrometry

The potential of liquid chromatography combined with tandem mass spectrometry (LC/MS/MS) for the determination of pesticide metabolites in human urine at the sub-ppb level is explored. Metabolites from two organophosphorous pesticides, 4-nitrophenol (from parathion and parathion-methyl) and 3-methyl-4-nitrophenol (from fenitrothion), are taken as model analytes to conduct this study. After direct injection of the urine sample (10 microL), different approaches were evaluated in order to achieve correct quantitation of analytes using an electrospray ionisation (ESI) interface. Thus, the feasibility of using external calibration was checked versus the use of different isotope-labeled internal standards. The advantages of applying coupled-column liquid chromatography (LC/LC) as an efficient clean-up without any type of sample manipulation are also discussed. The combination of LC/LC with ESI-MS/MS allows the direct analysis of free metabolites in urine, as the automated clean-up performed by the coupled-column technique is sufficient for the removal of interferences that suppress the ionisation of analytes in the ESI source. Using this procedure with external calibration, good precision and recoveries, and detection limits below 1 ng/mL are reached with analysis run times of around 8 min. The hyphenated technique LC/LC/ESI-MS/MS is proved to be a powerful analytical tool, allowing the rapid, sensitive and selective determination of 4-nitrophenol and 3-methyl-4-nitrophenol in human urine without any sample treatment.

Rapid direct determination of pesticides and metabolites in environmental water samples at sub-microg/l level by on-line solid-phase extraction-liquid chromatography-electrospray tandem mass spectrometry

A very rapid, multi-residual, sensitive and specific procedure for determining 35 pesticides in environmental ground and surface water in proposed. It is based on the use of solid-phase extraction (SPE) combined on-line with liquid chromatography (LC) electrospray (ESI) tandem mass spectrometry (MS-MS). Simultaneous target analysis of 29 pesticides (1 fungicide, 16 insecticides, 10 herbicides and 2 acaricides) and 6 metabolites with positive or negative ionization was reached by the direct injection of only 1.3 ml of filtered water sample, with a total analysis time of 18 min. The SPE-LC-MS-MS method was validated, obtaining good results for all compounds at 0.5 and 0.1 microg/l. Most of them could be correctly quantified at a concentration level as low as 25 ng/l. Efficiency and applicability of this method was evaluated by the analysis of several samples included in a monitoring program.