Natchanun Leepipatpiboon

Rapid determination of phenoxy acid residues in rice by modified QuEChERS extraction and liquid chromatography–tandem mass spectrometry

A new method for the analysis of phenoxy acid herbicide residues in rice, based on the use of liquid extraction/partition and dispersive solid phase extraction (dispersive-SPE) followed by ultra-performance liquid chromatography-electrospray ionization tandem mass spectrometry (UPLC-ESI-MS/MS), is reported. 5% (v/v) formic acid in acetonitrile as the extraction solvent and inclusion of citrate buffer helped partitioning of all the analytes into the acetonitrile phase. The extract was then cleaned up by dispersive-SPE using C18 and alumina neutral as selective sorbents. Further optimization of sample preparation and determination allowed recoveries of between 45 and 104% for all 13 phenoxy acid herbicides with RSD values lower than 13.3% at 5.0microgkg(-1) concentration level. Limit of detections (LODs) of 0.5microgkg(-1) or below were attained for all 13 phenoxy acids. Quantitative analysis was done in the multiple-reaction monitoring (MRM) mode using two combinations of selected precursor ion and product ion transition for each compound. This developed method produced relatively higher recoveries of the acid herbicides with a smaller range of variation and less susceptibility to matrix effects, than the original QuEChERS (Quick, Easy, Cheap, Effective, Rugged, and Safe) method.

Extension of the QuEChERS Method for Pesticide Residues in Cereals to Flaxseeds, Peanuts, and Doughs †

A simple method was evaluated for the determination of pesticide residues in flaxseeds, doughs, and peanuts using gas chromatography-time-of-flight mass spectrometry (GC-TOF) for analysis. A modified QuEChERS (quick, easy, cheap, effective, rugged, and safe) method, which was previously optimized for cereal grain samples, was evaluated in these fatty matrices. This extraction method involves first mixing the sample with 1:1 water/acetonitrile for an hour to swell the matrix and permit the salt-out liquid-liquid partitioning step using anhydrous MgSO(4) and NaCl. After shaking and centrifugation, cleanup is done by dispersive solid-phase extraction (d-SPE) using 150 mg of anhydrous MgSO(4), 150 mg of PSA, and 50 mg of C-18 per milliliter of extract. This method gave efficient separation of pesticides from fat and removal of coextracted substances better than gel permeation chromatography or use of a freeze-out step, which involved excessive use of solvent and/or time. The optimized analytical conditions were evaluated in terms of recoveries, reproducibilities, limits of detection, and matrix effects for 34 representative pesticides using different types of flaxseeds, peanuts, and doughs. Use of matrix-matched standards provided acceptable results for most pesticides with overall average recoveries between 70 and 120% and consistent RSDs <20% for semipolar pesticides and <26% for lipophilic pesticides. The recoveries of these latter types of pesticides depended on the fat content in the matrices and partitioning factor between the lipids and acetonitrile. We believe that the consistency of the pesticide recoveries for different samples in multiple experiments and the physicochemical partitioning explanation for <70% recoveries of lipophilic pesticides justify compensation of results for the empirically determined recovery values. In any case, this method still meets 10 ng/g detection limit needs for lipophilic pesticides and may be used for qualitative screening applications, in which any identified pesticides can be quantified and confirmed by a more intensive method that achieves >70% recoveries for lipophilic pesticides.

Efficient hydrophilic interaction liquid chromatography-tandem mass spectrometry for the multiclass analysis of veterinary drugs in chicken muscle.

A simple and sensitive method has been developed for multiresidue analysis of 24 important veterinary drugs (including 3 aminoglycosides, 3 β-lactams, 2 lincosamides, 4 macrolides, 4 quinolones, 4 sulfonamides, 3 tetracyclines, and amprolium) in chicken muscle. The method involved a simple extraction using (1:1, v/v) of 2% trichloroacetic acid in water-acetonitrile, followed by removing fat with hexane, dilution of sample extract, and filtration prior to liquid chromatography-tandem mass spectrometric (LC-MS/MS) analysis. Hydrophilic interaction liquid chromatography (HILIC) proved to be very effective for separation of a wide range of polar and hydrophilic compounds (providing high sensitivity and good peak shape) compared to reversed phase and ion-pair separation. The method was successfully validated according to the European Decision 2002/657/EC. Average recoveries were 53-99% at 0.5-MRL, MRL, and 1.5-MRL spiking levels, with satisfactory precision ≤15% RSD. The limit of detection of the method was 0.1-10 μgkg(-1) for 22 analytes and 20 μgkg(-1) for aminoglycosides. These values were lower than the maximum residue limits (MRLs) established by the European Union. The evaluated method provides reliable screening, quantification, and identification of 24 veterinary drug residues in foods of animal origin. It has been successfully tested in real samples (such as chicken muscle, shrimp, and egg).

Fast, low-pressure gas chromatography triple quadrupole tandem mass spectrometry for analysis of 150 pesticide residues in fruits and vegetables.

We developed and evaluated a new method of low-pressure gas chromatography-tandem mass spectrometry (LP-GC/MS-MS) using a triple quadrupole instrument for fast analysis of 150 relevant pesticides in four representative fruits and vegetables. This LP-GC (vacuum outlet) approach entails coupling a 10 m, 0.53 mm i.d., 1 μm film analytical column between the MS transfer line and a 3 m, 0.15 mm i.d. capillary at the inlet. The MS creates a vacuum in the 10 m analytical column, which reduces the viscosity of the He carrier gas and thereby shifts the optimal flow rate to greater velocity. By taking advantage of the H(2)-like properties of He under vacuum, the short analytical column, a rapid oven temperature ramp rate, and the high selectivity and sensitivity of MS/MS, 150 pesticides were separated in <6.5 min. The 2.5 ms dwell time and 1 ms interscan delay of the MS/MS instrument were critical for achieving >8 data points across the 2-3 s wide peaks. To keep dwell and cycle times constant across all peaks, each segment consisted of 30 analytes (60 transitions). For assessment, we injected extracts of spiked broccoli, cantaloupe, lemon, and sweet potato from the updated QuEChERS sample preparation method. Average recoveries (n=72) were 70-120% for 144 of the pesticides, and reproducibilities were <20% RSD for all but 4 analytes. Also, detection limits were <5 ng/g for all but a few pesticides, depending on the matrix. In addition to high quality performance, the method gave excellent reliability and high sample throughput, including easy peak integration to obtain rapid results.

Evaluation of a modified QuEChERS method for analysis of mycotoxins in rice.

A simple and efficient QuEChERS (Quick, Easy, Cheap, Effective, Rugged, and Safe) sample preparation method was modified to provide good analytical results for 14 mycotoxins in rice. The method involved mixing sample with acidified aqueous acetonitrile, followed by salt-out liquid partitioning using MgSO4, NaCl, and citrate buffer salts. The extract was cleaned-up by dispersive solid-phase extraction with MgSO4, PSA, C18, and alumina-neutral. The analysis was performed using ultra-high performance liquid chromatography coupled to triple-quadrupole tandem mass spectrometry (UHPLC-MS/MS). Throughout the validation experiments, 70-98% overall recoveries were achieved with RSDs ⩽ 7% for most analytes at concentrations 10-100 μg kg(-1). Limit of detections were 0.5-15 μg kg(-1). Inter-laboratory precision was performed by proficiency testing, |z|⩽ 2 was considered satisfactory. We compared our modified QuEChERS method against sample preparation using an immunoaffinity column; the recovery and specificity were comparable for the two methods, but the QuEChERS approach was more time- and cost-effective.

Characteristic fingerprint based on gingerol derivative analysis for discrimination of ginger (Zingiber officinale) according to geographical origin using HPLC-DAD combined with chemometrics

Chromatographic fingerprints of gingers from five different ginger-producing countries (China, India, Malaysia, Thailand and Vietnam) were newly established to discriminate the origin of ginger. The pungent bioactive principles of ginger, gingerols and six other gingerol-related compounds were determined and identified. Their variations in HPLC profiles create the characteristic pattern of each origin by employing similarity analysis, hierarchical cluster analysis (HCA), principal component analysis (PCA) and linear discriminant analysis (LDA). As results, the ginger profiles tended to be grouped and separated on the basis of the geographical closeness of the countries of origin. An effective mathematical model with high predictive ability was obtained and chemical markers for each origin were also identified as the characteristic active compounds to differentiate the ginger origin. The proposed method is useful for quality control of ginger in case of origin labelling and to assess food authenticity issues.

Micro-scale membrane extraction of glyphosate and aminomethylphosphonic acid in water followed by high-performance liquid chromatography and post-column derivatization with fluorescence detector.

A carrier-mediated supported liquid membrane micro-extraction using single hollow fiber membrane suitable for the determination of the herbicide glyphosate and its main metabolite aminomethylphosphonic acid in water is reported. A solution of 0.20 M Aliquat-336, a cationic carrier, in di-n-hexyl ether was selected as the supported liquid. A 20 microL of 1.0 M potassium chloride as the acceptor phase was filled in the membrane lumen. The membrane was immersed in a 20 mL of pH 9.0 sample solution. After 60-min extraction, the acceptor phase was analyzed by high-performance liquid chromatography with post-column derivatization. The enrichment factors were found to be 853 and 136 for glyphosate and aminomethylphosphonic acid, respectively. The method detection limits are 0.22 microg/L for glyphosate and 3.40 microg/L for aminomethylphosphonic acid. The procedure was validated and showed good accuracy and precision over a large linear dynamic range. The validated method was tested for the analysis of both analytes in spiked groundwater with good success.

Low-temperature cleanup with solid-phase extraction for the determination of polycyclic aromatic hydrocarbons in edible oils by reversed phase liquid chromatography with fluorescence detection

Low-temperature cleanup, which is a simple and cost-efficient sample preparation technique that allows the convenient treatment of multiple samples simultaneously, was developed in conjunction with solid-phase extraction (SPE) cleanup for the determination of 16 polycyclic aromatic hydrocarbons (PAHs) in refined and used edible oil samples by high-performance liquid chromatography with fluorescence detection (HPLC-FLD). Samples are extracted with a small amount of organic solvent and most of lipids in the extract were removed by low-temperature cleanup. SPE cartridge was used to further cleanup prior to HPLC-FLD analysis. Optimum extraction of low-temperature cleanup was achieved when using two extractions with a 4:1 (v/v) mixture of acetonitrile: acetone as the extraction solvent, freezing at between -18 °C and -25 °C for 24 h and then cleanup with an Alumina-N SPE cartridge. The PAH recoveries were 45.9-118.5%, with limit of detection (LOD) and limit of quantitation (LOQ) values of 0.13-3.13 μg/kg and 0.25-6.25 μg/kg across the 16 tested PAHs, respectively. The validated method was successfully applied for the determination of PAHs in reference materials of olive oil and real refined and used edible oil samples.

Evaluation of dilute-acid pretreated bagasse, corn cob and rice straw for ethanol fermentation bySaccharomyces cerevisiae

Bagasse, corn cob, and rice straw agricultural wastes were found to consist of 37, 39 and 34% cellulose and 24, 41 and 22% hemicellulose, respectively, on a dry solid (w/w) basis and thus have the potential to serve as a low cost foodstock for ethanol production. Hydrolysates produced by dilute-acid pretreatment followed by cellulase digestion were evaluated as substrates for ethanol fermentation bySaccharomyces cerevisiae. After pretreatment by 141 mM sulphuric acid, bagasse waste released glucose (134 mg/g) at a higher level than that from corn cob (75 mg/g) and rice straw (8 mg/g). Hydroxymethylfurfural (HMF) levels derived from acid pretreatment of bagasse (1.5 g/l), but not corn cob (0.8 g/l) or rice straw (0.1 g/l) attained levels likely to be toxic (1.5 g/l) forS. cerevisiae growth and ethanol fermentation rates. All three agricultural wastes released likely non-toxic levels of furfural (<0.5 g/l) and lactic acid (negligible for bagasse and rice straw and 0.7 g/l for corn cob). After cellulase saccharification of the dilute-acid pretreated agricultural wastes, the glucose content of corn cob hydrolysates (13 ± 0.17 g/l) was marginally higher than that of bagasse (12 ±0.27 g/l) or rice straw (11 ± 0.07 g/l), yet the ethanol conversion yield byS. cerevisiae on corn cob hydrolysate (0.45 ± 0.006 g/g) was lower than that attained with bagasse hydrolysate (0.49 ± 0.007 g/g). Synergistic adverse effects between furfural and HMF with weak acids, or other lignin derived products in the corn cob hydrolysate are proposed as the effective inhibitor (s) for ethanol fermentation byS. cerevisiae.

Separation of Co(II) and Ni(II) from thiocyanate media by hollow fiber supported liquid membrane containing Alamine300 as carrier — investigation on polarity of diluent and membrane stability

The separation of cobalt(II) and nickel(II) ions by HFSLM has been presented. The feed solution is 0.5M thiocyanate containing 300 ppm each of cobalt(II) and nickel(II) ions, whereas extractant is Alamine300 and the stripping solution is ammonia. Cobalt(II) is more preferable with Alamine300 than nickel(II). The effects of pH, Alamine300 concentration and ammonia concentration were investigated. Seven diluents were used: hexane, decanol, chlorobenzene, benzene, dichloromethane, ethylene dichloride and chloroform with different polarity indexes, from 0.1–4.1. Nickel(II) ion which is unpreferable with Alamine300 was used as a tracer to determine the membrane stability. The polarity of the diluents was found to be the main factor influencing the extraction performance and stability of a liquid membrane. The decreasing of polarity of the diluent can prolong the membrane stability, but the percentages of extraction and stripping decreased. The longest lifetime, 200 minutes, was obtained by using hexane as a diluent with the polarity index of 0.1.