Reasons for the decomposition of the fungicide thiram during preparation of fruit and vegetable samples and consequences for residue analysis

The concentration of thiram in aqueous solution decreases by 50–75% within 20 min in the presence of cut pieces of apple, cucumber or celeriac with a section surface area of 160 cm² each. The decomposition rate is predominantly influenced by the section surface area of the cut fruit and vegetable samples. Denaturing reaction conditions (exchange of the solvent water by methanol; boiling of sample material) will significantly slow down the decomposition rate. It was concluded that the thiram decomposition had been caused by enzymes on the section surface of the fruit and vegetable samples. For a specific determination of thiram, a simple rinsing of the intact fruit and vegetable material was appropriate as extraction method. For the screening of thiram residues, the often used Keppel method, which determines CS₂ from thiram or dithiocarbamates seems to be applicable even if samples had been coarsely cut, since decomposition of the CS₂-forming intermediates is slower than the breakdown of thiram itself. Therefore, specific determination of thiram is necessary only, if maximum residue limits for dithiocarbamates are not adhered to.     

Phenolic-compound-extraction systems for fruit and vegetable samples

This paper reviews the phenolic-compound-extraction systems used to analyse fruit and vegetable samples over the last 10 years. Phenolic compounds are naturally occurring antioxidants, usually found in fruits and vegetables. Sample preparation for analytical studies is necessary to determine the polyphenolic composition in these matrices. The most widely used extraction system is liquid-liquid extraction (LLE), which is an inexpensive method since it involves the use of organic solvents, but it requires long extraction times, giving rise to possible extract degradation. Likewise, solid-phase extraction (SPE) can be used in liquid samples. Modern techniques, which have been replacing conventional ones, include: supercritical fluid extraction (SFE), pressurized liquid extraction (PLE), microwave-assisted extraction (MAE) and ultrasound-assisted extraction (UAE). These alternative techniques reduce considerably the use of solvents and accelerate the extraction process.     

Application of comprehensive two-dimensional gas chromatography with nitrogen-selective detection for the analysis of fungicide residues in vegetable samples

Comprehensive two-dimensional gas chromatography (GCxGC) with nitrogen-phosphorus detection (NPD) has been investigated for the separation and quantitation of fungicides in vegetable samples. The detector gas flows (H(2), N(2) and air) were adjusted to achieve maximum response of signal whilst minimizing peak width. The comparison of different column sets and selection of the temperature program were carried out with a mixture of nine N-containing standard fungicides, eight of which were chlorinated. The results from GCxGC-NPD and GCxGC with micro electron-capture detection (muECD) were compared. External calibrations of fungicides were performed over a concentration range from 1 to 1,000 microgL(-1). The peak area calibration curves generally had regression coefficients of R(2)>0.9980, however for iprodione which was observed to undergo on-column degradation, an R(2) of 0.990 was found. The limit of detection (LOD) and limit of quantitation (LOQ) were less than about 74 and 246 ng L(-1), respectively. The intra-day and inter-day RSD values were measured for solutions of concentration 0.100, 0.500 and 1.50 mg L(-1). For the 0.500 mg L(-1) solution, intra- and inter-day precision of peak area and peak height for most of the pesticides were about 2% and 8%, respectively. Excellent linearity was observed for these standards, from 0.001 to 25.00 mg L(-1). The standard mixture peak positions were identified by using GCxGC with quadrupole mass spectrometry (qMS). To illustrate the potential and the versatility of both GCxGC-NPD and GCxGC-muECD, the method was applied to determination of fungicides in a vegetable extract. Decomposition of one fungicide standard (iprodione) during chromatography elution was readily observed in the two-dimensional (2D) GCxGC plot as a diagonal ridge response in the 2D chromatogram between the degrading compound and the decomposition product.     

Determination of tridemorph and other fungicide residues in fruit samples by liquid chromatography-electrospray tandem mass spectrometry

A rapid and sensitive liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS-MS) method for the determination of tridemorph and other pre- and post-harvest fungicides (carbendazim, thiabendazole, imazalil, propiconazole and bitertanol) in banana and orange samples has been developed and validated. The sample preparation was a simple extraction step with acetone using a high-speed blender prior to the injection of the five-fold diluted extract into the LC system with no other previous sample pre-treatment. Quantification was carried out using a matrix matched calibration curve which was linear in the range of 1-100 ng ml(-1) for all the compounds. The limit of quantification was 0.05 mg kg(-1) for all studied compounds, whereas limits of detection ranged between 0.005 and 0.025 mg kg(-1) (0.01 mg kg(-1) for tridemorph). Recoveries for tridemorph from spiked banana and orange samples at 0.05 and 1 mg kg(-1) were satisfactory, with values between 83 and 99% and relative standard deviations (R.S.D.s) lower than 13% (n = 5). For the other fungicides, recoveries between 75 and 95% with R.S.D.s lower than 12% were obtained. The developed method has been applied to the determination of selected fungicides in real samples of bananas and oranges from different origin. Thiabendazole and imazalil have been detected in almost all orange samples analyzed, and in around of 30% of banana samples. Bitertanol residues exceeded the maximum residue level (0.05 mg kg(-1)) in three banana samples while tridemorph was only detected in one sample.     

Rapid trace analysis of alachlor in water and vegetable samples

The use of a rapid and specific (cross-reactivity<4%) enzyme-linked immunosorbent assay (ELISA) for the determination of alachlor residues in water and vegetable samples is addressed. The analytical method consists of a fast extraction procedure followed by an optimised ELISA. The detection limit was 0.44 microg l(-1), with a linear range from 0.89 to 143.2 microg l(-1). For alachlor extraction from water samples, different solid-phase cartridges (C, Ph, C8 and C2) were assayed using MeOH as eluent. Extracts were diluted (1:4) with distilled water before ELISA. This procedure gave recoveries close to 100% with RSDs<14%. For vegetable samples, alachlor was extracted directly with MeOH and the extracts diluted 1:40 (v/v) with saline buffer prior to ELISA. The results obtained by the proposed procedure correlate well with the reference method (multiresidue extraction-GC-MS) for vegetable samples (r>0.85).     

Application of dual counter-current chromatography for rapid sample preparation of N-methylcarbamate pesticides in vegetable oil and citrus fruit

Dual counter-current chromatography (dual CCC) has been successfully applied to rapid sample preparation for the simultaneous determination of residual carbaryl, fenobucarb and methomyl in vegetable oil and citrus fruit. The citrus fruit samples were extracted with n-hexane solution containing stable isotopically labeled internal standards (methomyl-d3, fenobucarb-d3 and carbaryl-d9), and applied to dual CCC using a two-phase solvent system of n-hexane-acetonitrile to purify the carbamate pesticides from aliphatic sample matrix. The coiled column was rotated at 420 rpm, the lower mobile phase was introduced through the head toward the tail, and the upper mobile phase in the opposite direction. Due to the high partition efficiency of dual CCC, the lower phase fraction collected from 2 to 5 min after injection could be subjected to flow-injection tandem mass spectrometry directly after concentration. Repetitive sample injection can be performed at high reproducibility without a risk of contamination from the compounds retained in the column.     

Extraction as a method for preparation of vegetable samples for the determination of trace metals by atomic absorption spectrometry

An alternative, simple and rapid technique was developed for a quantitative isolation of the group of eight elements: Al, Ca, Cd, Cu, Fe, Mg, Pb and Zn from vegetable material samples in an open system with the use of acids: conc. HCl, dil. HNO₃ and hydrofluoric acids. Equivalence of both the extractants, HCl and HNO₃, was found suitable for a quantitative isolation of Ca, Cu, Mg, Zn, Pb and Cd. For lead and cadmium, however, dil. HNO₃ proved to be more suitable because these elements are determined by the graphite furnace atomic absorption spectrometry (GF-AAS) technique. A quantitative dissolution of Al and Fe requires hydrofluoric acid as an additional extractant. The proposed method allows to obviate the organic matrix destruction stage, shorten the analyte dissolution time, reduce cost, and minimize hazards of loss and contamination. Validity and versatility of the method developed was verified by the analysis of standard reference materials.     

A review of sample preparation methods for the pesticide residue analysis in foods

The pesticide residues in foods have received increasing attention as one of the most important food safety issues. Therefore, more strict regulations on the maximum residue limits (MRLs) for pesticides in foods have been established in many countries and health organizations, based on the sensitive and reliable analysis methods of pesticide residues. However, the analysis of pesticide residues is a continuing challenge mainly because of the small quantities of analytes as well as the large amounts of interfering substances which can be co-extracted with them, often leading to experimental errors and damage to the analytical instruments. Thus, extensive sample preparation is often required for the pesticide residue analysis for the effective extraction of the analytes and removal of the interferences. This paper focuses on reviewing the recent development in the sample preparation methods for the pesticide residue analysis in foods since 2006. The methods include: liquid-liquid extraction (LLE), supercritical-fluid extraction (SFE), pressurized-liquid extraction (PLE), microwave-assisted extraction (MAE), ultrasound-assisted extraction (UAE), gel permeation chromatography (GPC), solid-phase extraction (SPE), molecularly imprinted polymers (MIPs), matrix solid-phase dispersion (MSPD), solid-phase micro-extraction (SPME), QuEChERS, cloud point extraction (CPE) and liquid phase micro-extraction (LPME), etc. Particularly their advantages, disadvantages and future perspectives will be discussed.     

Fourth derivative spectrophotometric determination of fungicide thiram (tetramethyldithiocarbamate) using sodium molybdate and its application

A procedure has been developed for the direct fourth derivative spectrophotometric determination of tetramethyldithiocarbamate by converting it into its molybdenum complex, which is then extracted in to methyl isobutyl ketone (MIBK). Beer’s law is obeyed over the concentration range 24 μg mL⁻¹ in the final solution. The analytical sensitivity is calculated to be 0.004(d⁴A/dλ⁴) μg⁻¹ mL⁻¹ from the slope of the calibration curve. The detection limit is 0.3 μg mL⁻¹ for thiram (signal to noise ratio = 2). Various parameters, such as effect of acid concentration, interference of a large number of ions in the determination of thiram have been studied in detail. The method is sensitive, highly selective and can be used for the determination of thiram in a commercial sample, in mixtures with various dithiocarbamates (zineb, maneb, etc.) and from wheat grains.     

Current trends in sample preparation for growth promoter and veterinary drug residue analysis

A comprehensive review is presented on the current trends in sample preparation for the isolation of veterinary drugs and growth promoters from foods. The objective of the review is to firstly give an overview of the sample preparation techniques that are applied in field. The review will focus on new techniques and technologies, which improve efficiency and coverage of residues. The underlying theme to the paper is the developments that have been made in multi-residue methods and particularly multi-class methods for residues of licensed animal health products, which have been developed in the last couple of years. The role of multi-class methods is discussed and how they can be accommodated in future residue surveillance.     

Robotic preparation of metal samples for analysis by plasma emission spectrometry

Summary A method utilizing a laboratory robotic system to automate sample preparation for the chemical analysis of metals was developed. Anticipated elemental concentration values for samples are entered into the robotic system, and the system determines the needed sample weights and calibration solution concentrations. The robot then weighs, dissolves, and dilutes the samples and prepares calibration solutions prior to multi-elemental analyses by inductively-coupled plasma — atomic-emission spectrometry. Zinc-base alloy standard reference materials were used to evaluate this method. For a batch of ten samples, operator times compared with a similar manual method were reduced by about 5-fold. Precision and accuracy data for samples prepared by robotic and manual methods were equivalent.

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Automatische Probenvorbereitung für die Analyse durch Plasma-Emissions-Spektrometrie mit Hilfe eines Laborroboters

     

An installation for the preparation of foraminifera micro samples for the isotopic analysis of carbon and oxygen

A technical modification of the traditional method of decomposition of carbonates in phosphoric acid was proposed for the determination of δ¹³C and δ¹⁸O in organogenic carbonate samples weighing 10–30 μg with an accuracy of 0.05%. The extraction of CO₂ was carried out under a vacuum at 95°C in 105% phosphoric acid. The isotopic composition of CO₂ was measured by CG-IRMS. The used feed-motion of samples to the reactor provides a consecutive delivery of the samples from the sample holders to the acid. This sample feeding method prevents the contamination of the acid with impurities from the surface of the sample, obviates the necessity of removing the sample holders from the acid, and allows the use of the same acid for performing a very large numbers of analyses. The accuracy and reproducibility of the δ¹³C and δ¹⁸O values was estimated by measuring international standards and comparing with the δ¹³C and δ¹⁸O values for organogenic carbonate samples obtained by the proposed method of analysis at a microgram level and the traditional method at a milligram level. The proposed technology was successfully used to study the isotopic composition of oxygen and carbon in the plankton and benthos foraminifers in order to reconstruct the Okhotsk Sea palaeotemperatures.     

Combined approach for high-throughput preparation and analysis of plasma samples from exposure studies

In drug discovery today, drug exposure is determined in preclinical efficacy and safety studies and drug effects are related to measured concentrations rather than to the administered dose. This leads to a strong increase in the number of bioanalytical samples, demanding the development of higher throughput methods to cope with the increased workload. Here, a combined approach is described for the high-throughput preparation and liquid chromatography/tandem mass spectrometry (LC/MS/MS) analysis of drug levels in plasma samples from the preclinical efficacy and safety studies, i.e. exposure studies. Appropriate pharmacokinetic (PK) compartmental models were fitted to data from PK screening studies in the rat, which were subsequently used to simulate the expected plasma concentrations of the respective exposure studies. Information on the estimated drug concentrations was used to dilute the samples to appropriate concentration levels. A Tecan Genesis RSP liquid handling system was utilized to perform automated plasma sample preparation including serial dilution of standard solutions, dilution of plasma samples, addition of internal standard solution and precipitation with acetonitrile. This robotic sample preparation process permitted two studies of 1-96 samples each to be run simultaneously. To ensure the performance of this method the accuracy and precision for diazepam were examined. Two novel drugs were used to illustrate the suggested approach. In conclusion, our method for sample preparation of exposure samples, based on the combined use of PK simulations, a liquid handling system and a fast LC/MS/MS method, increased the throughput more than three times and minimized the errors, while maintaining the required accuracy and precision.     

Target preparation of biological samples for trace element analysis using nuclear techniques

An easy and rapid method for preparing biological targets for trace element analysis using nuclear techniques involving charged particle beams is described. The targets are thin, homogeneous and uniform. They withstand 100 nA of 1–2 MeV proton beams and of 5–10 MeV alpha beams for about 10 hrs.     

Chlorotrimethylsilane, a reagent for the direct quantitative analysis of fats and oils present in vegetable and meat samples

Acylglycerides present in oil seeds and meat can be transformed into volatile fatty esters using chlorotrimethylsilane (CTMS) and 1-pentanol as reagents. The volatile esters can then be analysed by GC. The method is quantitative and involves only minor sample manipulation. It often permits major recoveries of the total saponifiable lipids present in solid samples. A 40 min reaction time is enough to ensure the total conversion of saponifiable lipids to the corresponding FAPEs.     

The use of FT-IR as a screening technique for organic residue analysis of archaeological samples

A range of archaeological samples have been examined using FT-IR spectroscopy. These include suspected coprolite samples from the Neolithic site of Catalh?yük in Turkey, pottery samples from the Roman site of Silchester, UK and the Bronze Age site of Gatas, Spain and unidentified black residues on pottery sherds from the Roman sites of Springhead and Cambourne, UK. For coprolite samples the aim of FT-IR analysis is identification. Identification of coprolites in the field is based on their distinct orange colour; however, such visual identifications can often be misleading due to their similarity with deposits such as ochre and clay. For pottery the aim is to screen those samples that might contain high levels of organic residues which would be suitable for GC-MS analysis. The experiments have shown coprolites to have distinctive spectra, containing strong peaks from calcite, phosphate and quartz; the presence of phosphorus may be confirmed by SEM-EDX analysis. Pottery containing organic residues of plant and animal origin has also been shown to generally display strong phosphate peaks. FT-IR has distinguished between organic resin and non-organic compositions for the black residues, with differences also being seen between organic samples that have the same physical appearance. Further analysis by GC-MS has confirmed the identification of the coprolites through the presence of coprostanol and bile acids, and shows that the majority of organic pottery residues are either fatty acids or mono- or di-acylglycerols from foodstuffs, or triterpenoid resin compounds exposed to high temperatures. One suspected resin sample was shown to contain no organic residues, and it is seen that resin samples with similar physical appearances have different chemical compositions. FT-IR is proposed as a quick and cheap method of screening archaeological samples before subjecting them to the more expensive and time-consuming method of GC-MS. This will eliminate inorganic samples such as clays and ochre from GC-MS analysis, and will screen those samples which are most likely to have a high concentration of preserved organic residues.     

Gel-free sample preparation for the nanoscale LC-MS/MS analysis and identification of low-nanogram protein samples

Protein identification at the low nanogram level could in principle be obtained by most nanoscale LC-MS/MS systems. Nevertheless, the complex sample preparation procedures generally required in biological applications, and the consequent high risk of sample losses, very often hamper practical achievement of such low levels. In fact, the minimal amount of protein required for the identification from a gel band or spot, in general, largely exceeds the theoretical limit of identification reachable by nanoscale LC-MS/MS systems. A method for the identification of low levels of purified proteins, allowing limits of identification down to 1 ng when using standard bore, 75 microm id nanoscale LC-MS/MS systems is here reported. The method comprises an offline two-step sample cleanup, subsequent to protein digestion, which is designed to minimize sample losses, allows high flexibility in the choice of digestion conditions and delivers a highly purified peptide mixture even from "real world" digestion conditions, thus allowing the subsequent nanoscale LC-MS/MS analysis to be performed in automated, unattended operation for long series. The method can be applied to the characterization of low levels of affinity purified proteins.