Optimization and evaluation of low-pressure gas chromatography-mass spectrometry for the fast analysis of multiple pesticide residues in a food commodity

Potentiality of Gas Chromatography−Triple Quadrupole Mass Spectrometry in Vanguard and Rearguard Methods of Pesticide Residues in Vegetables

A new analytical strategy for the screening and confirmation/quantification of multiclass pesticide residues in vegetables has been established and validated. No complicated sample preparation was needed, but only a simple and rapid extraction using ethyl acetate and sodium sulfate, which required no cleanup. The approach is based on the use of the triple quadrupole (QqQ) mass spectrometry (MS) as detection system in gas chromatography (GC). In a first step, a GC-QqQ-MS screening method, which monitors only one MS/MS transition by compound, allows the identification of approximately 130 pesticides in 11.6 min. In this way, the differentiation between negative and potentially nonnegative samples is carried out. In the second step, the nonnegative samples are reanalyzed by the GC-QqQ-MS confirmation/quantification method, which monitors two or three MS/MS transitions by compound. Confirmation of pesticides was based on the comparison of intensity ratios for the main ions in samples with those obtained on the same day from the standard in a matrix containing the pesticides at a preestablished concentration level. Quantification of the identified and confirmed pesticides was based on the addition standard method, which avoids matrix effect. The proposed analytical strategy allowed a reliable identification and confirmation of the target pesticides at trace levels, reducing analysis time and increasing sample throughput in routine analytical laboratories.

Rapid determination of benzo(a)pyrene in olive oil samples with solid-phase extraction and low-pressure, wide-bore gas chromatography–mass spectrometry and fast liquid chromatography with fluorescence detection

Benzo(a)pyrene (B(a)P) was extracted from olive oil using solid-phase extraction on columns filled with Florisil and Nucleoprep C18. The extracts were analyzed with GC-MS, using standard capillary column and low-pressure wide-bore column (LP-GC-MS), as well as with HPLC on standard column and short donor-acceptor complex chromatography (DACC) column. Quantitation was done with isotope dilution method (GC-MS and LP-GC-MS) or with internal standard benzo(k)fluoranthene (HPLC). Limits of detection were 1 ng/g for GC-MS on standard column, 1.6 ng/g on LP-column, 0.5 ng/g for HPLC on standard column, and 0.3 ng/g on DACC column, respectively. The applied extraction method allowed handling over 50 samples per day and assured recovery over 80%. Matrix solid-phase dispersion, tried as an alternative isolation method, appeared less advantageous. Fast chromatographic methods (LP-GC-MS and HPLC on DACC) made it possible to reduce analysis time to 8 and 5 min, respectively. The method was applied to routine analysis of B(a)P in olive oil samples.

Determination of polar organophosphorus pesticides in vegetables and fruits using liquid chromatography with tandem mass spectrometry: selection of extraction solvent

A method based on liquid chromatography (LC)-mass spectrometry (MS)/MS was developed for sensitive determination of a number of less gas chromatography (GC)-amenable organophosphorus pesticides (OPs; acephate, methamidophos, monocrotophos, omethoate, oxydemeton-methyl and vamidothion) in cabbage and grapes. For extraction, several solvents were evaluated with respect to the possibility of direct injection, matrix-induced suppression or enhancement of response, and extraction efficiency. Overall, ethyl acetate was the most favourable solvent for extraction, although a solvent switch was required. For some pesticide/matrix combinations, reconstitution of the residue after evaporation required special attention. Extracts were analysed on a C18 column with polar endcapping. The pesticides were ionised using atmospheric pressure chemical ionisation on a tandem mass spectrometer in multiple reaction monitoring mode. The final method is straightforward and involves extraction with ethyl acetate and a solvent switch to 0.1% acetic acid/water without further cleanup. The method was validated at the 0.01 and 0.5 mg/kg level, for both cabbage and grapes. Recoveries were between 80 and 101% with R.S.D. < 11% (n = 5). The limit of quantification was 0.01 mg/kg and limits of detection were between 0.001 and 0.004 mg/kg.

Reduction of analysis time in gas chromatography. Application of low-pressure gas chromatography-tandem mass spectrometry to the determination of pesticide residues in vegetables

An alternative to conventional capillary gas chromatography (GC) is evaluated as a new approach to determine pesticide residues in vegetables. Low-pressure gas chromatography-tandem mass spectrometry (LP-GC-MS-MS) is proposed after a fast and simple extraction of the vegetable samples with dichloromethane and without clean up. The use of the above-mentioned GC technique reduced the total time required to determine 72 pesticides to less than half the present time (31 min), increasing the capability of a monitoring routine laboratory. The use of guard column and plug of carbofrit into the glass liner in combination with LP-GC was evaluated. The method was validated with limits of quantitation low enough to determine the pesticide residues at concentrations below the maximum residue levels stated by legislation. In order to assess its applicability to the analysis of real samples, 25 vegetable samples previously determined using conventional-capillary GC-MS-MS were analysed by LP-GC-MS-MS. The results obtained with the compared techniques showed differences lower than 0.01 mg kg(-1).

Development of an enzyme-linked immunosorbent assay for the detection of the organophosphorus insecticide acephate

A competitive indirect enzyme-linked immunosorbent assay (ciELISA) for the organophosphorus insecticide acephate, O,S-dimethyl acetylphosphoramidothioate, was developed using a polyclonal antibody. Five different haptens mimicking the analyte were synthesized and conjugated with the carrier proteins bovine serum albumin (BSA) and keyhole limpet hemocyanin (KLH) by the N-hydroxysuccinimide active ester and diazotization methods. Polyclonal antibodies raised against hapten-KLH conjugates in rabbits and hapten-BSA conjugates as coating antigens were screened and selected for the assay in the homologous and heterologous ELISA systems. The effects of various assay conditions such as detergent, organic solvents, pH, and preincubation of the mixture of the polyclonal antibody and the analyte on the sensitivity were evaluated. The IC(50) value for acephate was 25 ng/mL in an optimized heterologous system using hapten-4-BSA as a coating antigen and a polyclonal antibody no. 8377 against hapten-1-KLH, showing the detection range of 5-140 ng/mL and the lowest detection limit of 2 ng/mL. The cross-reactivities of the structurally related organophosphorus insecticides, including the major metabolite of the analyte, methamidophos, were less than 1%. Recoveries from the analyte-fortified tap water, mulberry leaves, and lettuce samples in the assay were in the range of 72-121% by simple extraction, concentration, and dilution. These results indicate that the ELISA could be a convenient and supplemental analytical tool for monitoring acephate residues in environmental and agricultural samples.

Practical approaches to fast gas chromatography-mass spectrometry

Fast gas chromatography-mass spectrometry (GC-MS) has the potential to be a powerful tool in routine analytical laboratories by increasing sample throughput and improving laboratory efficiency. However, this potential has rarely been met in practice because other laboratory operations and sample preparation typically limit sample throughput, not the GC-MS analysis. The intent of this article is to critically review current approaches to fast analysis using GC-MS and to discuss practical considerations in addressing their advantages and disadvantages to meet particular application needs. The practical ways to speed the analytical process in GC and MS individually and in combination are presented, and the trade-offs and compromises in terms of sensitivity and/or selectivity are discussed. Also, the five main current approaches to fast GC-MS are described, which involve the use of: (1) short, microbore capillary GC columns; (2) fast temperature programming; (3) low-pressure GC-MS; (4) supersonic molecular beam for MS at high GC carrier gas flow; and (5) pressure-tunable GC-GC. Aspects of the different fast GC-MS approaches can be combined in some cases, and different mass analyzers may be used depending on the analytical needs. Thus, the capabilities and costs of quadrupole, ion trap, time-of-flight, and magnetic sector instruments are discussed with emphasis placed on speed. Furthermore, applications of fast GC-MS that appear in the literature are compiled and reviewed. At this time, the future usefulness of fast GC-MS depends to some extent upon improvement of existing approaches and commercialization of interesting new techniques, but moreover, a greater emphasis is needed to streamline overall laboratory operations and sample preparation procedures if fast GC-MS is to become implemented in routine applications.

Fast gas chromatography and its use in trace analysis

There is revived interest in the development and implementation of methods of faster GC. The paper summarises the advantages of faster GC analysis, general approaches to faster GC method development and practical aspects of fast gas chromatography with the utilisation of open tubular capillary columns with the stress on trace analysis. There are a number of ways to take the advantage of the improved speed of analysis by faster GC. Numerous options exist for pushing the speed of capillary gas chromatography (CGC) analysis. The scope of this paper is also to give an overview of the present state of faster GC instrumentation which is already available for trace analysis. The practicality of fast CGC is a function of sample preparation and the matrix interferences and how they affect the resultant resolution that may be achieved. Researchers have demonstrated the applicability of fast GC to trace and ultratrace analysis of volatile and semivolatile compounds also with narrow bore columns and difficult sample matrices (such as food, and soil extract). The main development of faster GC methods has been observed in the field of environmental analysis. Practical applications are presented. Both optimised sample preparation and experimental conditions for faster GC are the future perspective of trace analysis.

Trace determination of organotin compounds in water, sediment and mussel samples by low-pressure gas chromatography coupled to tandem mass spectrometry

A fast method for the determination of eight organotin compounds (OTs), monobutyltin (MBT), dibutyltin (DBT), tributyltin (TBT), tetrabutyltin (TeBT), monophenyltin (MPhT), diphenyltin (DPhT), triphenyltin (TPhT) and tetraphenyltin (TePhT), in water, sediments and mussels, was developed using low-pressure gas chromatography/tandem mass spectrometry (LPGC/MS/MS). The method is based on sodium diethyldithiocarbamate (DDTC) complexation of the ionic organotins, followed by extraction of the target matrices and derivatization by a Grignard reagent, as described in a previously published method for water samples. Solid-phase extraction was selected as extraction method from water samples after comparison with liquid-liquid extraction, but extraction of the OTs from sediment and mussel samples was performed using toluene. Matrix-matched calibration standards were used to minimize matrix effects. The analytical process was validated by the analysis of spiked blank samples. Performance characteristics such as linearity, detection limit (LOD), quantitation limit (LOQ), precision, and recovery were determined. Recoveries of OTs in spiked matrices ranged from 86-108% in water and from 78-110% in sediments and mussels, with precision values lower than 18%. Detection limits ranged from 0.1-9.6 ng L(-1) in water, and 0.03-6.10 microg kg(-1) in the other matrices. The present implementation of LPGC rather than conventional capillary GC permitted use of large-volume injection and reduced analysis time by a factor of two. The proposed methodology was applied to the determination of OTs in real samples of water, marine sediments and mussels from the west coast of the Mediterranean Sea (Spain).

Recent advances in the application of mass spectrometry in food-related analysis

A review is presented on recent applications of mass spectrometry (MS)-based techniques for the analysis of compounds of food concern. Substances discussed are naturally occurring compounds in food products such as lipids, oligosaccharides, proteins, vitamins, flavonoids and related substances, phenolic compounds and aroma compounds. Among xenobiotics, applications of MS techniques for the analysis of pesticides, drug residues, toxins, amines and migrants from packaging are overviewed. Advances in the analysis of trace metals of nutritional and toxicological interest by MS with inductively coupled plasma (ICP) source are presented. The main features of mass spectrometry combined with separation instruments are discussed in food-related analysis. Examples of mass spectrometry and tandem MS (MS-MS) are provided. The development and application of matrix-assisted laser desorption ionization (MALDI) and electrospray (ESI) to the analysis of peptides and proteins in food is discussed. This survey will attempt to cover the state-of-the-art up from 1999 to 2001.

Evaluation of low-pressure gas chromatography linked to ion-trap tandem mass spectrometry for the fast trace analysis of multiclass pesticide residues

A rapid multiresidue method for the analysis of 72 pesticides has been developed using a single injection with low-pressure gas chromatography/tandem mass spectrometry (LP-GC/MS/MS). The LP-GC/MS/MS method used a short capillary column of 10 m x 0.53 mm i.d. x 0.25 microm film thickness coupled with a 0.6 m x 0.10 mm i.d. restriction at the inlet end. Optimal LP-GC conditions were determined which achieved the fastest separation in MS/MS detection mode. Also MS/MS conditions were optimized in order to increase sensitivity and selectivity. The analytical parameters of the LP-GC/MS/MS method were compared with those obtained by GC/MS/MS using a conventional capillary column (30 m x 0.25 mm i.d. x 0.25 microm film thickness). Better precision and sensitivity values were obtained with the LP-GC/MS/MS approach. The limits of detection (LOD) of the compounds ranged from 0.1 to 14.1 microg L(-1) for LP-GC/MS/MS, lower than those obtained for conventional GC/MS/MS that ranged from 0.1 to 17.5 microg L(-1). The peak widths obtained with the short column in LP-GC are similar to those obtained using conventional capillary GC columns, and the peaks can be successfully identified by MS/MS detection with the conventional scan speed of ion-trap instruments. In addition, the analysis time was significantly reduced with LP-GC/MS/MS (32 min) versus GC/MS/MS (72 min), allowing the number of samples analyzed per day in a routine laboratory to be doubled.