Pascal Mottier

Determination of the antibiotic chloramphenicol in meat and seafood products by liquid chromatography-electrospray ionization tandem mass spectrometry.

A confirmatory method based on isotope dilution liquid chromatography-electrospray ionization tandem mass spectrometry is described for the determination of the antibiotic chloramphenicol (CAP) in foods. The method is quantitative and entails liquid-liquid extraction followed by a clean-up step on a silica gel solid-phase extraction cartridge. Mass spectral acquisition is done in the negative ion mode applying multiple reaction monitoring of two diagnostic transition reactions for CAP (m/z 321 --> 257 and m/z 321--> 152). In addition, the presence of two chlorine atoms in the CAP molecule provides further analyte certainty by assessing the 37Cl/35Cl ratio using the transition reactions m/z 323 --> 257 and m/z 323 --> 152. Validation of the method in chicken meat is conducted according to the latest European Union criteria for the analysis of veterinary drug residues at levels of 0.05, 0.10, and 0.20 microg/kg, employing [2H5]-chloramphenicol as internal standard. The decision limit and the detection capability were calculated at 0.01 microg/kg and 0.02 microg/kg, respectively. At the lowest fortification level (i.e. 0.05 microg/kg), precision values below 14 and 17% were achieved under repeatability and within-laboratory reproducibility conditions, respectively. The accuracy of the method was within 20, 15, and 5% of the target values at the 0.05, 0.10, and 0.20 microg/kg fortification levels, respectively. The applicability of this procedure was demonstrated by the analysis of other meat (turkey, pork, beef) and seafood (fish, shrimps) products. The method is robust and suitable for routine quality control operations, and more than 200 sample injections were performed without excessive pollution of the mass spectrometer or loss of LC column performance.

Development and comparison of two multiresidue methods for the analysis of 17 mycotoxins in cereals by liquid chromatography electrospray ionization tandem mass spectrometry.

Two multiresidue methods based on different extraction procedures have been developed and compared for the liquid chromatography electrospray ionization tandem mass spectrometry analysis of 17 mycotoxins including ochratoxin A, aflatoxins (B(1), B(2), G(1), and G(2)), zearalenone, fumonisins (B(1) and B(2)), T-2 toxin, HT-2 toxin, nivalenol, deoxynivalenol, 3- and 15-acetyldeoxynivalenol, fusarenon-X, diacetoxyscirpenol, and neosolaniol in cereal-based commodities. The extraction procedures considered were a QuEChERS-like method and one using accelerated solvent extraction (ASE). Both extraction procedures gave similar performances in terms of linearity (r(2) > 0.98) and precision (both RSD(r) and RSD(iR) < 20%). Trueness was evaluated through participation in four proficiency tests and by the analysis of two certified reference materials and one quality control material. Satisfactory Z scores (|Z| < 2) and trueness values (73-130%) were obtained by the proposed procedures. Limits of quantification were similar by both methods and were within the 1.0-2.0 microg/kg range for aflatoxins, 0.5 microg/kg for ochratoxin A, and the 5-100 microg/kg range for all other mycotoxins tested. The QuEChERS-like method was found to be easier to handle and allowed a higher sample throughput as compared to the ASE method.

Comparison of analytical techniques to quantify malondialdehyde in milk powders

Several analytical methods were compared to quantify malondialdehyde (MDA) in milk powders. Modified thiobarbituric acid (TBA) methods, using either visible spectrophotometry (direct absorbance reading or after third derivative transformation of the spectrum) or HPLC, required derivatisation at elevated temperature, which appeared to catalyse artefactual MDA formation and thus overestimate the MDA content. In contrast to the TBA derivatisation method, the measurement of MDA as the dinitrophenylhydrazone derivative by HPLC or as the phenylhydrazone product by GC-MS with a deuterated internal standard resulted in lower estimates in the ranges of 2-17- and 3-30-fold, respectively; apparently due to the milder derivatisation conditions. The estimates of MDA determined by both HPLC-UV and GC-MS techniques result in lower values which are similar in magnitude even though the GC-MS technique is more sensitive.

Simultaneous quantitative determination of melamine and cyanuric acid in cow's milk and milk-based infant formula by liquid chromatography-electrospray ionization tandem mass spectrometry.

An isotope dilution liquid chromatography-electrospray ionization tandem mass spectrometry method for the simultaneous determination of melamine and cyanuric acid in cows milk (range of 0-0.3 mg/kg) and milk-based infant formulas (ranges of 0-0.3 and 0-2.0 mg/kg) is described. This quantitative method entails simple sample preparation, limited to a protein precipitation in acetonitrile/water followed by a centrifugation and direct injection of the supernatant. Selected reaction monitoring of two diagnostic transition reactions for each analyte and each corresponding ((13)C(3),(15)N(3))-labeled compound enables selective and confirmatory detection. Acquisition was performed sequentially in the negative ion mode for cyanuric acid, while in the positive mode for melamine within the same run. Validation of the method was conducted according to European Union criteria (CD 2002/657/EC). Internal standard-corrected recoveries were within the 99-116% range for both analytes in the two matrix types, along with repeatability and intermediate reproducibility values of <or=12.3 and <or=31.2%, respectively. LODs were 0.025 and 0.050 mg/kg for melamine and cyanuric acid, respectively, whereas LOQs, set arbitrarily at the lowest fortification level, were 0.05 and 0.10 mg/kg for melamine and cyanuric acid, respectively. CCalpha and CCbeta, at the 1 mg/kg maximum limit (ML) for infant formula powder endorsed by WHO, were respectively 1.03 and 1.05 mg/kg for melamine and 1.04 and 1.09 mg/kg for cyanuric acid.

Use of molecularly imprinted solid-phase extraction sorbent for the determination of four 5-nitroimidazoles and three of their metabolites from egg-based samples before tandem LC-ESIMS/MS analysis.

A nitroimidazole, molecularly imprinted polymer (MIP) was tested to extract four 5-nitroimidazoles (i.e., dimetridazole (DMZ), ipronidazole (IPZ), metronidazole (MNZ), and ronidazole (RNZ)) and three of their metabolites (i.e., DMZOH, IPZOH, and MNZOH) from egg powder samples. Various MIP templates were produced, and their selectivity was assessed on nitroimidazole standard solutions using liquid chromatography coupled with ultraviolet detection. The optimal cleanup was then used for the extraction of nitroimidazole in egg powder samples, and their quantification was achieved by isotope dilution LC-ESIMS/MS. The sample preparation entails a solubilization of the samples with water and acetonitrile followed by a MISPE cleanup step before LC-ESIMS/MS analysis. Data acquisition was achieved using selected reaction monitoring, and quantification was done with five deuterated analogues (i.e., DMZ- d(3), RNZ- d(3), IPZ- d(3), DMZOH- d(3), and IPZOH- d(3)). DMZOH- d(3) was used to quantify MNZ and MNZOH since they do not have their corresponding internal standards. The method was validated according to the European Union criteria by spiking experiments at concentration levels of 1, 2, and 3 microg/kg. At these three levels and for compounds having their own internal standards, acceptable performance data were obtained, with internal standard corrected recoveries ranging from 91 to 111%, and decision limits (CCalpha) and detection capabilities (CCbeta) were below 0.34 and 0.39 microg/kg, respectively.

Combining the quick, easy, cheap, effective, rugged and safe approach and clean-up by immunoaffinity column for the analysis of 15 mycotoxins by isotope dilution liquid chromatography tandem mass spectrometry

Optimization and validation of a multi-mycotoxin method by LC-MS/MS is presented. The method covers the EU-regulated mycotoxins (aflatoxins, fumonisins, ochratoxin A, deoxynivalenol, zearalenone, T-2 and HT-2), as well as nivalenol and 3- and 15-acetyldeoxynivalenol for analysis of cereals, cocoa, oil, spices, infant formula, coffee and nuts. The proposed procedure combines two clean-up strategies: First, a generic preparation suitable for all mycotoxins based on the QuEChERS (for quick, easy, cheap, effective, rugged and safe) protocol. Second, a specific clean-up devoted to aflatoxins and ochratoxin A using immunoaffinity column (IAC) clean-up. Positive identification of mycotoxins in matrix was conducted according to the confirmation criteria defined in EU Commission Decision 2002/657/EC while quantification was performed by isotopic dilution using (13)C-labeled mycotoxins as internal standards. Limits of quantification were at or below the maximum levels set in the EC/1886/2006 document for all mycotoxin/matrix combinations under regulation. In particular, the inclusion of an IAC step allowed achieving LOQs as low as 0.05 and 0.25μg/kg in cereals for aflatoxins and ochratoxin A, respectively. Other performance parameters like linearity [(r)(2)>0.99], recovery [71-118%], precision [(RSDr and RSDiR)<33%], and trueness [78-117%] were all compliant with the analytical requirements stipulated in the CEN/TR/16059 document. Method ruggedness was proved by a verification process conducted by another laboratory.

Analysis of chloramphenicol in honeys of different geographical origin by liquid chromatography coupled to electrospray ionization tandem mass spectrometry.

A sensitive liquid chromatography tandem mass spectrometry (LC-MS/MS) method was developed to detect trace amounts of the antibiotic chloramphenicol (CAP) in honey. The methodology entailed a solid-phase extraction of aqueous honey solutions followed by liquid-liquid partitioning, filtration and direct injection onto the LC-MS/MS system. Honey extracts were spiked with an isotopically labelled internal standard (d5-CAP) to compensate for analyte loss and potential ion suppression during the MS stage. Detection of the analyte was achieved by negative ionization electrospray in the selected reaction monitoring (SAM) mode. For confirmation, four characteristic mass transitions were monitored each for the analyte and the surrogate standard. The method was validated according to the latest European Union criteria for the analyses of veterinary drug residues in food. At all three fortification levels studied (0.1, 0.2, 0.5 μg kg-1) the method was accurate to within 15%. The repeatability and within-laboratory reproducibilities were <12 and 18%, respectively. The decision limit (CCα) and detection capability (CCβ) were both <0.1 μg kg-1. The procedure provides a sensitive and reliable method for the determination of residues of chloramphenicol in honey. Numerous raw honeys of various geographical origins were analysed, showing extensive contamination particularly those of Chinese origin.

Quantitative determination of sodium monofluoroacetate “1080” in infant formulas and dairy products by isotope dilution LC-MS/MS

A fast and easy-to-use confirmatory liquid-chromatography tandem mass-spectrometry (LC-MS/MS) based-method was developed for the analysis of the pesticide sodium monofluoroacetate (MFA, also called “1080”) in infant formulas and related dairy products. Extraction of the compound encompassed sample reconstitution and liquid–liquid extraction under acidic conditions. Time-consuming solid-phase extraction steps for clean-up and enrichment and tedious derivatisation were thus avoided. Resulting sample extracts were analysed by electrospray ionisation (ESI) in negative mode. Quantification was performed by the isotopic dilution approach using 13C-labelled MFA as internal standard. The procedure was validated according to the European document SANCO/12571/2013 and performance parameters such as linearity (r2 > 0.99), precision (RSD(r) ≤ 9%, RSD(iR) ≤ 11%) and recovery (96–117%) fulfilled its requirements. Limit of quantifications (LOQ) was 1 µg kg−1 for infant formulas and related dairy products except for whey proteins powders with a LOQ of 5 µg kg−1. Method ruggedness was further assessed in another laboratory devoted to routine testing for quality control.

Determination of polyadipates migrating from lid gaskets of glass jars. Hydrolysis to adipic acid and measurement by LC-MS/MS.

Polyadipate plasticizers can be present in the polyvinylchloride (PVC) gaskets used to seal the lids of glass jars. As the gaskets can come into direct contact with the foodstuffs inside the jar, the potential exists for polyadipate migration into the food. The procedure and performance characteristics of a test method for the analysis of polyadipates in food simulants (3% aqueous acetic acid and 10% aqueous ethanol) and the volatile test media used in substitute fat tests (isooctane and 95% aqueous ethanol) are described. The PVC gaskets were exposed to the food simulants or their substitutes under standard test conditions. Studies were initially carried out using direct measurement of the polyadipate oligomers by liquid chromatography with time-of-flight mass spectrometric detection (LC-TOF-MS) but this was not practical due to the number of peaks detected. Instead, the migrating polyadipates were hydrolysed to adipic acid and measured by liquid chromatography with tandem mass spectrometric detection (LC–MS/MS). The amount of polyadipate that this measurement of adipic acid represents was then calculated. Method performance was assessed by analysis of gaskets from two types of jar lids by single-laboratory validation. Linearity, sensitivity, repeatability, intermediate reproducibility and recovery were determined to be suitable for checking compliance with the 30 mg/kg specific migration limits for polyesters of 1,2-propane diol and/or 1,3- and/or 1,4-butanediol and/or polypropylene-glycol with adipic acid, which may be end-capped with acetic acid or fatty acids C12–C18 or n-octanol and/or n-decanol. The method was found to be much quicker than previous methods involving extraction, clean-up, hydrolysis, esterification, derivatisation and GC measurement, consequently saving time and money.

LC-MS/MS analytical procedure to quantify tris(nonylphenyl)phosphite, as a source of the endocrine disruptors 4-nonylphenols, in food packaging materials

Tris(nonylphenyl)phosphite, an antioxidant used in polyethylene resins for food applications, is problematic since it is a source of the endocrine-disrupting chemicals 4-nonylphenols (4NP) upon migration into packaged foods. As a response to concerns surrounding the presence of 4NP-based compounds in packaging materials, some resin producers and additive suppliers have decided to eliminate TNPP from formulations. This paper describes an analytical procedure to verify the “TNPP-free” statement in multilayer laminates used for bag-in-box packaging. The method involves extraction of TNPP from laminates with organic solvents followed by detection/quantification by LC-MS/MS using the atmospheric pressure chemical ionisation (APCI) mode. A further acidic treatment of the latter extract allows the release of 4NP from potentially extracted TNPP. 4NP is then analysed by LC-MS/MS using electrospray ionisation (ESI) mode. This two-step analytical procedure ensures not only TNPP quantification in laminates, but also allows the flagging of other possible sources of 4NP in such packaging materials, typically as non-intentionally added substances (NIAS). The limits of quantification were 0.50 and 0.48 µg dm–2 for TNPP and 4NP in laminates, respectively, with recoveries ranging between 87% and 114%. Usage of such analytical methodologies in quality control operations has pointed to a lack of traceability at the packaging supplier level and cross-contamination of extrusion equipment at the converter level, when TNPP-containing laminates are processed on the same machine beforehand.