Rapid method for determination of chlormequat residues in tomato products by ion-exchange liquid chromatography/electrospray tandem mass spectrometry

Determination of chlormequat and mepiquat residues and their dissipation rates in tomato cultivation matrices by ultra-performance liquid chromatography-tandem mass spectrometry

This study described the development and validation of a simple, rapid, specific and sensitive method for detecting chlormequat chloride (CQ) and mepiquat chloride (MQ) residues in tomato cultivation matrices covering soil, water, seedling samples. The dissipation rates of CQ and MQ in tomato cultivation matrices were also determined in this study. A Hydrophilic Interaction Liquid Chromatography (HILIC) column was used for chromatographic separation. A triple quadrupole mass spectrometer equipped with an electrospray ionisation source in positive ion mode by multiple reaction monitoring was used for detection. Soil samples were extracted with accelerated solvent extraction (ASE) and cleaned up with WCX phase extraction column; water samples were extracted with WCX phase extraction column; seedling samples were extracted with methanol-ammonium acetate solution. LODs and LOQs of CQ and MQ were 0.02μg/kg and 0.1μg/kg in soil samples, 0.005ng/mL and 0.02ng/mL in water samples, and 0.05μg/kg and 1.0μg/kg in seedling samples, respectively. The mean recovery rate of CQ in soil, water and seedling samples ranged from 76.98% to 111.60%. While the mean recovery rate of MQ in soil, water and seedling samples ranged from 96.90% to 105.40%. The fastest to the slowest metabolising rates of CQ and MQ were as follows: soil samples>seedling samples>water samples. In conclusion, this study provided a new potential method for detecting CQ and MQ in tomato cultivation matrices using ultra-performance liquid chromatography-tandem mass spectrometry.

A Novel Molecularly Imprinted Polymer for the Selective Removal of Chlorophyll from Heavily Pigmented Green Plant Extracts prior to Instrumental Analysis

A novel molecularly imprinted polymer (MIP) powder designed for the selective removal of interfering chlorophyll pigment from heavily pigmented green plant extracts during pesticide residue analysis or analysis for bioactives in natural product research is reported. The polymer powder imprinted with chlorophyllawas synthesized by copolymerizing the functional and cross-linking monomers, methacrylic acid (MAA) and ethylene glycol dimethacrylate (EGDMA), respectively. During batch rebinding experiments, the MIP effectively removed chlorophyll from neat chlorophyll standards, green medicinal plants, and spinach extracts with determined absorbance as high as 2.501 absorbance units (Au) to as low as 0.084 Au after the optimum quantity of the MIP (170 mg mL−1) was added as the adsorbent prior to instrumental analysis. The determined 0.084 Au absorbance was far below the absorbance of 2% chlorophyll (0.401 Au) regarded as the cut-off point for interfering chlorophyll. Thus the newly developed polymer presents itself as a suitable adsorbent for the selective removal of chlorophyll from heavily pigmented, chlorophyll containing extracts.

Chlormequat residues and dissipation rates in cotton crops and soil

A simple and reliable analytical method for chlormequat residues in cotton and soil was established in this study. The residual levels and dissipation rates of chlormequat in cotton crops and soil were determined by High Performance Liquid Chromatography-Mass Spectroscopy (HPLC-MS). The limit of quantification (LOQ) was 0.05, 0.1, 0.1mg/kg for soil, cotton seeds and cotton leaves, respectively. The mean half-life of chlormequat was 4.47 days in cotton plants and was 4.34 days in soil. The final residues of chlormequat in cotton seeds were below 0.5mg/kg (the MRL of China), while the chlormequat residues could not be detected in soil. Low residues in cotton seed and soil suggest that this pesticide may be safe to use under the recommended dosage.

Dissipation and residues of chlormequat in wheat and soil

A specific, sensitive method was developed for the analysis of chlormequat in wheat and soil by high performance chromatography/mass spectrometry. The fortified recoveries of soil were from 75.08% to 96.55%, with RSD 3.34%-15.18%, the limit of detection of the analytical method was 0.05 ng at a signal-to-noise ratio of 3, and the limit of quantification was 0.05, 0.1, 0.5 mg/kg for soil, wheat plants and wheat grain, respectively. The degradation dynamics and final residues of chlormequat in Beijing and Changchun were investigated. The half-life of chlormequat in wheat plants were 3.15 days in Beijing and 4.56 days in Changchun, while the half-life in soil was 3.88 days in Beijing and 4.51 days in Changchun. The final residues of chlormequat in soil were not detectable, and the final residues of chlormequat in wheat grain were below 0.50 mg/kg except for 3.51 mg/kg from high dosage plot of Changchun. The fact that all the final residues were below 5 mg/kg (GB2763 in National standards of the People's Republic of China, maximum residue limits for pesticide in food, Beijing, 2005) suggested that chlormequat could be safely used in wheat crops with the suitable dosage and application.

Gradient chromatofocusing-mass spectrometry: a new technique in protein analysis

A new analytical technique, gradient chromatofocusing-mass spectrometry (gCF-MS), was developed employing ion-exchange high-performance liquid chromatography (HPLC) interfaced to an electrospray-quadrupole mass spectrometer in the determination of proteins. There have been few reports, if any, of a HPLC-MS technique for proteins in which the ion-exchange column is directly interfaced to the mass spectrometer. The employment of a linear pH gradient elution scheme directly interfaced to mass spectrometry is also unique in the present work. The technique was demonstrated by the separation of six proteins (carbonic anhydrase II, enolase, beta-lactoglobulin A, lactoglobulin B, soybean trypsin inhibitor, and amyloglucosidase) employing a descending linear pH gradient from pH 9 to 2.6 on a 50 mm x 2.1 mm DEAE HPLC column using volatile buffer components. A signal enhancement solution consisting of 8% formic acid in acetonitrile was pumped post-column and was mixed 1:1 with column effluent and then directed on-line into the mass spectrometer. Molecular masses of the proteins were determined within +/-0.010% to 0.033% (+/-100 to 330 ppm) with peak height total ion current detection limits of 4 to 78 pmol of injected amounts (S/N = 3). This technique is applicable to the analysis of proteins and other charged molecules.

Evaluation of pesticide residue in grape juices and the effect of natural antioxidants on their degradation rate

Various studies have been drawn toward the beneficial properties of fruit juices because they have several components, such as phenols, vitamins, and flavonoids, with antioxidant effects. However, fruit juices can also contain residues of pesticides used as standard pest control methods in crops. Many of these pesticides are degraded through oxidative mechanisms, and their persistence in juices can be enhanced by antioxidants. This study covers the degradation of four pesticides, aldicarb, demeton-S-methyl, fenamiphos, and methiocarb, to their respective sulfoxide and sulfone in grape juices, water (pH 3.5) and water (pH 3.5) with quercetin (one of the most important flavonoids of grape) added in an attempt to establish whether the presence of antioxidants can affect the degradation rate of pesticides. For this purpose, a multiresidue method based on solid-phase extraction (SPE) was developed for the simultaneous determination of these pesticides and their metabolites in commercial juices. The extraction procedure was carried out in C(18) columns. The subsequent elution of pesticides was performed with dichloromethane prior to the determination by liquid chromatography-tandem mass spectrometry (LC-MS/MS), using two precursor-product ion transitions. Average recoveries for all the pesticides studied were higher than 80%, with relative standard deviations lower than 15% in the concentration range 0.005-0.05 microg/mL, and the quantification limits achieved ranged from 0.1 to 4.6 microg/L. The results demonstrated that degradation was slower in fruit juices and aqueous solutions with quercetin than in water. Several commercial grape juices were also analyzed to establish the levels of these pesticides. Methiocarb, fenamiphos, and demeton-S-methyl were found at low levels in some samples.

Control of pesticide residues by liquid chromatography-mass spectrometry to ensure food safety

Liquid chromatography-mass spectrometry (LC-MS) has become an invaluable technique for the control of pesticide residues to ensure food safety. After an introduction about the regulations that highlights its importance to meet the official requirements on analytical performance, the different mass spectrometers used in this field of research, as well as the LC-MS interfaces and the difficulties associated with quantitative LC-MS determination, are discussed. The ability to use practical data for quantifying pesticides together with the option of obtaining structural information to identify target and non-target parent compounds and metabolites are discussed. Special attention is paid to the impact of sample preparation and chromatography on the ionization efficiency of pesticides from food. The last section is devoted to applications from a food safety point of view. (c) 2006 Wiley Periodicals, Inc.

Matrix effects in quantitative pesticide analysis using liquid chromatography-mass spectrometry

Combined liquid chromatography-mass spectrometry using electrospray or atmospheric-pressure chemical ionization has become an important tool in the quantitative analysis of pesticide residues in various matrices in relation to environmental analysis, food safety, and biological exposure monitoring. One of the major problems in the quantitative analysis using LC-MS is that compound and matrix-dependent response suppression or enhancement may occur, the so-called matrix effect. This article reviews issues related to matrix effects, focusing on quantitative pesticide analysis, but also paying attention to expertise with respect to matrix effects acquired in other application areas of LC-MS, especially quantitative bioanalysis in the course of drug development.

Validation and qualification: the fitness for purpose of mass spectrometry-based analytical methods and analytical systems

The context of validation for mass spectrometry (MS)-based methods is critically analysed. The focus is on the fitness for purpose depending on the task of the method. Information is given on commonly accepted procedures for the implementation and acceptance of analytical methods as 'confirmatory methods' according to EU criteria, and strategies for measurement. Attention is paid to the problem of matrix effects in the case of liquid chromatography-mass spectrometry-based procedures, since according to recent guidelines for bioanalytical method validations, there is a need to evaluate matrix effects during development and validation of LC-MS methods "to ensure that precision, selectivity and sensitivity will not be compromised". Beneficial aspects of the qualification process to ensure the suitability of the MS analytical system are also evaluated and discussed.

Environmental and food applications of LC-tandem mass spectrometry in pesticide-residue analysis: an overview

An overview is given on pesticide-residue determination in environmental and food samples by liquid chromatography/mass spectrometry/mass spectrometry (LC/MS/MS). Pesticides comprise a large number of substances that belong to many completely different chemical groups, the only common characteristic is that they are effective against pests. They still constitute a challenge in MS because there is no collective pathway for fragmentation. A brief introduction to the theory of tandem MS permits a discussion of which parameters influence the ionization efficiency when the ions are subjected to different actions. Emphasis is placed on the different tandem MS instruments: triple and ion-trap quadrupoles, and hybrid quadrupole time-of-flight (Q-TOF), including advantages and drawbacks, typical detection limits, and ion signals at low concentrations. The instrumental setup, as well as LC and mass spectrometric experimental conditions, must be carefully selected to increase the performance of the analytical system. The capacity of each instrument to provide useful data for the identification of pesticides, and the possibility to obtain structural information for the identification of target and non-target compounds, are discussed. Finally, sample preparation techniques and examples of applications are debated to reveal the potential of the current state-of-the-art technology, and to further promote the usefulness of tandem MS.

Multidimensional nano-HPLC for analysis of protein complexes

The analysis of macromolecular protein complexes is an important factor in understanding most cellular processes, e.g., protein transport into cell organells, signal transduction via biological membranes, apoptosis, energy metabolism, directed motion of cells, and cell division. These complexes are not only built of various numbers of different proteins but also of prosthetic groups and RNA molecules. To understand the role each protein plays in a complex, a complete analysis of all protein compounds is necessary. Therefore, several separation steps have to be coupled to mass spectrometry to identify the proteins. In this work, we describe the application of multidimensional liquid chromatography, SCX-RP-LC as well as SAX-RP-LC, coupled to electrospray ion trap mass spectrometry. Tryptic digested ribosomes were separated by ion exchange chromatography manually collected and prepared for reversed phase chromatography to analyze the peptides via nano-ESI mass spectrometry. The total numbers of identified proteins are compared in consideration of the separation method (SCX-RP versus SAX-RP).