Microwave-assisted extraction and determination of cyanuric acid residue in infant formula samples by liquid chromatography–tandem mass spectrometry

In the present work, microwave-assisted extraction method in combining with liquid chromatography–tandem mass spectrometry (LC–MS/MS) was proposed for the determination of cyanuric acid (CYA) in infant formula samples. The separation was performed on a MERCK ZIC HILIC column (150 × 2.1 mm i.d., 5 μm) with gradient elution of 20 mM ammonium acetate solution – acetonitrile. The method could respond linearly with cyanuric acid at concentrations from 1.0 to 50 ng mL⁻¹ with a quantification limit of 0.25 mg kg⁻¹. The intra- and inter-day precision was less than 4% and the recovery of the assay was in the range of 86.7–93.1%. In the analysis of practical spiked infant formula samples, the new method yielded satisfactory results. Due to its simplicity and accuracy the straightforward method is particularly suitable for routine cyanuric acid detection.     

Simultaneous determination of bisphenol A and bisphenol B in beverages and powdered infant formula by dispersive liquid–liquid micro-extraction and heart-cutting multidimensional gas chromatography-mass spectrometry

The purpose of this study was to establish a reliable, cost-effective, fast and simple method to quantify simultaneously both bisphenol A (BPA) and bisphenol B (BPB) in liquid food matrixes such as canned beverages (soft drinks and beers) and powdered infant formula using dispersive liquid–liquid micro-extraction (DLLME) with in-situ derivatisation coupled with heart-cutting gas chromatography-mass spectrometry (GC-MS). For the optimisation of the DLLME procedure different amounts of various extractive and dispersive solvents as well as different amounts of the derivative reagent were compared for their effects on extraction efficiency and yields. The optimised procedure consisted of the injection of a mixture containing tetrachloroethylene (extractant), acetonitrile (dispersant) and acetic anhydride (derivatising reagent) directly into an aliquot of beverage samples or into an aqueous extract of powdered milk samples obtained after a pretreatment of the samples. Given the compatibility of the solvents used, and the low volumes involved, the procedure was easily associated with GC-MS end-point determination, which was accomplished by means of an accurate GC dual column (heart-cutting) technique. Careful optimisation of heart-cutting GC-MS conditions, namely pressure of front and auxiliary inlets, have resulted in a good analytical performance. The linearity of the matrix-matched calibration curves was acceptable, with coefficients of determination (r2) always higher than 0.99. Average recoveries of the BPA and BPB spiked at two concentration levels into beverages and powdered infant formula ranged from 68% to 114% and the relative standard deviation (RSD) was <15%. The limits of detection (LOD) in canned beverages were 5.0 and 2.0?ng?l^–1 for BPA and BPB, respectively, whereas LOD in powdered infant formula were 60.0 and 30.0?ng?l^–1, respectively. The limits of quantification (LOQ) in canned beverages were 10.0 and 7.0?ng?l–1 for BPA and BPB, respectively, whereas LOQ in powdered infant formula were 200.0 and 100.0?ng?l^–1, respectively. BPA was detected in 21 of 30 canned beverages (ranging from 0.03 to 4.70?µg?l^–1) and in two of seven powdered infant formula samples (0.23 and 0.40?µg?l^–1) collected in Portugal. BPB was only detected in canned beverages being positive in 15 of 30 samples analysed (ranging from 0.06 to 0.17?µg?l^–1). This is the first report about the presence of BPA and BPB in canned beverages and powdered infant formula in the Portuguese market.     

Simultaneous determination of kasugamycin and validamycin-A residues in cereals by consecutive solid-phase extraction combined with liquid chromatography–tandem mass spectrometry

Two polar aminoglycosides, kasugamycin and validamycin-A, were determined in cereals (brown rice, wheat and corn) by high-performance liquid chromatography–tandem mass spectrometry. The analytes were extracted from samples using methanol and water (70:30, v/v) at pH 5.5, purified using both a hydrophilic–hydrophobic-balanced cartridge and a strong cation-exchange cartridge, and then analysed using multiple reaction monitoring in positive electrospray ionisation mode with a special ReproSil 100 C₁₈ high-performance liquid chromatography column. This newly proposed method yielded good sensitivity and excellent chromatographic performance. The limits of quantification for kasugamycin and validamycin-A were 4.1 µg/kg and 1.0 µg/kg, respectively. The recoveries for both compounds at three fortification levels (4, 100 and 500 µg/kg for kasugamycin; 1, 10 and 100 µg/kg for validamycin-A) ranged from 75% to 110%, and the relative standard deviations were below 15%.     

Simultaneous determination of 15 components in Radix Glehniae by high performance liquid chromatography–electrospray ionization tandem mass spectrometry

A novel qualitative and quantitative method using high performance liquid chromatography coupled with tandem mass spectrometry was developed for simultaneous analysis of 15 components including 10 coumarins, four phenolic acids and adenosine in Radix Glehniae, an important traditional Chinese medicine. The separation was performed on a C₁₈ column with isocratic elution consisted of 0.1% formic acid and methanol (30:70, v/v). The identification and quantification of the analytes were achieved on a hybrid quadrupole linear ion trap mass spectrometer. Multiple-reaction monitoring (MRM) scanning was employed for quantification with switching electrospray ion source polarity between positive and negative modes in a single run. Full validation of the method was carried out (linearity, precision, accuracy, limit of detection and limit of quantification). The results indicated that the method was simple, rapid, specific and reliable. And we successfully applied it to analyze 20 Radix Glehniae samples from different sources.     

Simultaneous quantitative determination of Sudan dyes using liquid chromatography–atmospheric pressure photoionization–tandem mass spectrometry

Atmospheric pressure photoionization–tandem mass spectrometry (APPI–MS/MS) method has been developed for quantitative determination of Sudan I to IV dyes. This study demonstrates the applicability of a simple isocratic normal phase HPLC method using isopropanol (0.3%) in n-hexane as the mobile phase for the separation of these dyes. A simple extraction procedure using n-hexane has been applied for the extraction of these dyes from spiked samples of chilli powder and tomato sauce. The quantitative determination of Sudan I to IV is obtained from the spiked tomato sauce and chilli powder samples by external standard method under single reaction monitoring (SRM) mode. The study includes a detailed investigation on LOD, LOQ, linearity and recovery of Sudan I to IV dyes. The LOD ranged from 5–18 μg/l and LOQ ranged from 10–24 μg/l. The present method can be a powerful analytical tool for the simultaneous quantitative determination of Sudan dyes present in food products.     

Multiclass and multi-residue determination of antibiotics in bovine milk by liquid chromatography–tandem mass spectrometry: Combining efficiency of milk control and simplicity of routine analysis

Antibiotics are widely used in veterinary medicine and incorrect practices may lead to drug residues in food, including milk. Fast and simple sample preparation methods have been developed for determination of quinolones, fluoroquinolones, tetracyclines, sulphonamides, trimethoprim and bromexine using liquid chromatography–tandem mass spectrometry. Small volumes of sample (0.5 mL) were extracted using organic solvent followed by centrifugation and evaporation and/or dilution. Validation took into account the maximum residue limits (MRLs). Recoveries of 62–108% were obtained. Linearity (r²) above 0.96 was achieved for all compounds using concentrations in the range 0.25–2.0 × MRL. Intraday precision with coefficients of variation (n = 6) lower than 15.0% and inter-day precision lower than 17.3% were obtained for three concentration levels in the range 0.5–1.5 × MRL. Accuracy was 87–108%. Limits of detection and quantitation, as well as decision limit, detection capability, robustness and applicability, were evaluated using >600 real milk samples.     

Determination of sulbactam in raw bovine milk by isotope dilution–ultra-high-performance liquid chromatography–tandem mass spectrometry

We developed a sensitive and selective isotope dilution ultra-high-performance liquid chromatography–tandem mass spectrometry (UPLC-MS/MS) method for the determination of sulbactam residue in raw bovine milk. Sulbactam and internal standard, sulbactam-d₅, were extracted from raw bovine milk via liquid-liquid extraction and enriched with strong anion exchange solid-phase extraction cartridges and finally analyzed by using UPLC-MS/MS with multiple reaction monitoring mode. The method was validated according to European regulations. The calibration curve showed good linearity, with a correlation coefficient of 0.9998. Decision limit and detection capability of sulbactam were determined by matrix calibration curve and were 0.0445 and 0.0517 μg/L, respectively. The recoveries of sulbactam in fortified raw bovine milk ranged from 72.1 to 91.5%, with the intra- and interday relative standard deviations ranging from 3.0 to 18.9%. Furthermore, the developed method was applied to analyzing real raw bovine milk samples collected from dairy farms in Beijing, China. Sulbactam was not determined in all samples. The proposed method could ultimately serve as a methodological foundation for the determination of sulbactam in different types of raw milk and dairy products.     

Determination of trichothecenes in cereals and cereal-based products by liquid chromatography–tandem mass spectrometry

A sensitive, accurate and precise method for the simultaneous determination of nivalenol (NIV), deoxynivalenol (DON), T-2 toxin (T-2) and HT-2 toxin (HT-2) in different food matrices, including wheat, maize, barley, cereal-based infant foods, snacks, biscuits and wafers, has been developed. The method, using liquid chromatography coupled with atmospheric pressure chemical ionization triple quadrupole mass spectrometry (LC–APCI–MS/MS), allowed unambiguous identification of the selected trichothecenes at low µg per kg levels in such complex food matrices. A clean-up procedure, based on reversed phase SPE Oasis® HLB columns, was used, allowing good recoveries for all studied trichothecenes. In particular, NIV recoveries significantly improved compared to those obtained by using Mycosep® #227 columns for clean-up of the extracts. Limits of detection in the various investigated matrices ranged 2.5–4.0 µg kg^?1 for NIV, 2.8–5.3 µg kg^?1 for DON, 0.4–1.7 µg kg^?1 for HT-2 and 0.4–1.0 µg kg^?1 for T-2. Mean recovery values, obtained from cereals and cereal products spiked with NIV, DON, HT-2 and T-2 toxins at levels from 10 to 1000 µg kg^?1, ranged from 72 to 110% with mean relative standard deviation lower than 10%. A systematic investigation of matrix effects in different cereals and cereal products was also carried out by statistically comparing the slopes of standard calibration curve with matrix-matched calibration curve for each of the four toxins and the eight matrices tested. For seven of the eight matrices tested, statistically significant matrix effects were observed, indicating that, for accurate quantitative analysis, matrix-matched calibration was necessary. The method was applied to the analysis of 57 samples of ground wheat originated from South Italy and nine cereal food samples collected from retail markets.     

Rapid determination of lycopene and β-carotene in tomato by liquid chromatography/electrospray tandem mass spectrometry

BACKGROUND: The tomato fruit is a dietary source of carotenoids, bioactive antioxidant compounds that play an important role in the prevention of degenerative diseases. Several extraction and detection techniques regarding carotenoids in tomatoes can be found in the literature, mainly based on high‐performance liquid chromatography separation and ultraviolet‐visible detection. RESULTS: The best extraction conditions and tandem mass spectrometry (MS) analysis were evaluated: lycopene and β‐carotene were extracted in a cyclohexane/ethyl acetate mixture without the addition of antioxidants, next separated by liquid chromatography on a C₁₈ column and then determined through electrospray tandem MS. Ionic suppression by the matrix in negative ionisation mode did not allow the analysis of extracts, hence the positive ionisation mode was chosen. Validation parameters demonstrated the suitability for purpose of the analytical method: accuracy, precision, linearity and detection limits were adequate. The method was finally applied to different tomato samples, and differences could be easily highlighted. CONCLUSION: The method was simple, fast and appropriate for the purpose of analysing lycopene and β‐carotene in tomatoes. Copyright © 2011 Society of Chemical Industry     

Elimination of matrix effects in the determination of bisphenol A in milk by solid-phase microextraction–high-performance liquid chromatography

Solid-phase microextraction coupled to high-performance liquid chromatography (SPME–HPLC) with fluorescence detection was employed to determine bisphenol A (BPA) in milk samples. The potential influence of the milk matrix on the determination of BPA by SPME–HPLC were investigated. Optimal conditions to eliminate any matrix effects were as follows: milk samples were deproteinized with trichloroacetic acid, diluted 20-fold with BPA-free Ultrapure water, dissolved in methanol, the precipitated protein was filtered out, rinsed with methanol and evaporated to remove the methanol. Then, a 40.0-ml solution was used for SPME extraction and HPLC analysis. Satisfactory recoveries (milk: 93.1–101%; soybean milk: 93.9–102%) were achieved. The proposed method was successfully applied to real samples, BPA being detected within the range 1.6–2.6 ng ml^?1 in four brands of commercial milk but not in soybean milk.     

Determination of Gibberellin A3 residue in fruit samples by liquid chromatography–tandem mass spectrometry

A fast, simple, low cost, and high throughput method has been developed for the determination of Gibberellin A3 residue in fruit samples (apple, orange, peach, pear and grape). Analysis is performed by LC–MS/MS operated in the multiple reaction monitoring (MRM) mode, acquiring two specific precursor-product ion transitions per target compound. The method has been validated showing good linearity and selectivity. Limits of quantification (LOQs) were 10 μg kg⁻¹ for apple, orange, peach, pear and grape samples. The average recoveries, measured at three concentration levels (10, 20 and 200 μg kg⁻¹) were in the range 77.8–96.2% for the compound tested with relative standard deviations below 13.7%. The proposed method is rapid, simple and could be utilised for the routine analysis of Gibberellin A3 in fruit samples.     

Automated on-line solid-phase extraction coupled to liquid chromatography–tandem mass spectrometry for determination of lipophilic marine toxins in shellfish

Automated on-line solid-phase extraction (SPE) coupled to liquid chromatography–tandem mass spectrometry (LC–MS/MS) has been developed for fast determination of lipophilic marine toxins in shellfish samples. The direct coupling of an on-line SPE column to LC–MS/MS was accomplished using column switching techniques. Suitable chromatographic separation was performed on a reversed-phase C18 column under alkaline conditions (pH 11).     

Determination of alkylphenol residues in breast and commercial milk by solid-phase extraction and gas chromatography–mass spectrometry

This study presents a feasible and sensitive method to determine alkylphenol residues (i.e., 4-t-octylphenol (4-t-OP) and the isomers of 4-nonylphenols (4-NPs)) in breast milk samples and commercial cow milk products. The matrix interference associated with the constituents in the milk was reduced by extraction with n-hexane and dilution with 50% methanolic solution (v/v, methanol/water), then followed by the Oasis-HLB SPE extraction. The analytes were determined by a GC–MS system in full-scan and selected ion monitoring modes simultaneously. Limit of quantitation was less than 0.05 ng/g in a 20 g (wet weight) milk sample. The 4-NPs were detected in 19 of the 20 breast milk samples at concentrations ranging from 1.7 to 11.6 ng/g, while 4-t-OP was detected in 8 samples at concentrations ranging from 0.4 to 1.1 ng/g. The 4-NPs were detected in all the testing commercial cow milk products at concentrations ranging from 2.9 to 8.8 ng/g.     

Sensitive determination of domoic acid in shellfish by on-line coupling of weak anion exchange solid-phase extraction and liquid chromatography–diode array detection–tandem mass spectrometry

An automated method based on the use of on-line solid-phase extraction (SPE) coupled to liquid chromatography with diode array detection and tandem mass spectrometry (LC–DAD–MS/MS) has been developed for the determination of domoic acid in shellfish. The on-line coupling of SPE and liquid chromatography was accomplished by a column switching approach. A weak anion exchange (WAX) sorbent was selected for the SPE procedure, allowing a selective cleanup of shellfish extracts. High sensitivity was achieved by on-line pre-concentration of large volume injections (50–1000 μL). A simple protein precipitation cleanup with acetone was used to efficiently remove proteins from shellfish extracts, preventing possible column clogging during chromatographic separation.     

Simultaneous determination of 10 mycotoxins in grain by ultra-high-performance liquid chromatography–tandem mass spectrometry using 13C15-deoxynivalenol as internal standard

An ultra-high-performance liquid chromatography–tandem mass spectrometry (UHPLC–MS/MS) method for simultaneous determination of 10 mycotoxins in grain was developed. The selected mycotoxins were: deoxynivalenol, 3-acetyldeoxynivalenol, 15-acetyldeoxynivalenol, nivalenol, fusarenon X, moniliformin, zearalenone, zearalanone, ochratoxin A and ochratoxin B. The samples were extracted with aqueous acetonitrile (84?:?16,?v/v) and purified by reliable laboratory-made mixed cartridges. The analytes were separated on an Acquity UPLC HSS T3 column (100?×?2.1?mm,?1.8?µm) and eluted with a mobile phase of water containing 0.2% aqueous ammonia and acetonitrile/methanol (90?:?10,?v/v). All mycotoxins were detected with a Waters Micromass Quattro Ultima Pt tandem quadrupole mass spectrometer operating in negative electrospray ionization using multiple reaction monitoring mode. Accurate determination was achieved by employing commercial ¹³C₁₅-deoxynivalenol as internal standard, which compensated for target loss and eliminated matrix effects. The established method was further validated by determining the linearity (R ^2?>?0.9990), average recovery (75.8–106.5%), sensitivity (limit of quantitation 0.09–8.48?µg?kg^?1) and precision (relative standard deviation?≤?6.9%). It was shown to be a suitable method for simultaneous determination of 10 mycotoxins in grain. Finally, a total of 69 corn samples randomly collected from eastern and northern China were analyzed. The results showed that deoxynivalenol was the most frequently detected contaminant, whilst 3-acetyldeoxynivalenol, 15-acetyldeoxynivalenol, nivalenol, zearalenone, zearalanone, fusarenon X and moniliformin also occurred frequently. Ochratoxin A and ochratoxin B were present only in trace amounts in a small number of samples.     

Development of QuEChERS-based extraction and liquid chromatography–tandem mass spectrometry method for quantifying flumethasone residues in beef muscle

A rapid, specific, and sensitive method based on liquid chromatography–electrospray ionization tandem mass spectrometry (LC–ESI–MS/MS) in the positive ion mode using multiple reaction monitoring (MRM) was developed and validated to quantify flumethasone residues in beef muscle. Methods were compared between the original as well as the EN quick, easy, cheap, effective, rugged, and safe (QuEChERS)-based extraction. Good linearity was achieved at concentration levels of 5–30 μg/kg. Estimated recovery rates at spiking levels of 5 and 10 μg/kg ranged from 72.1 to 84.6%, with relative standard deviations (RSDs) < 7%. The results of the inter-day study, which was performed by fortifying beef muscle samples (n = 18) on 3 separate days, showed an accuracy of 93.4–94.4%. The precision (expressed as relative standard deviation values) for the inter-day variation at two levels of fortification (10 and 20 μg/kg) was 1.9–5.2%. The limit of detection (LOD) and limit of quantitation (LOQ) were 1.7 and 5 μg/kg, at signal-to-noise ratios (S/Ns) of 3 and 10, respectively. The method was successfully applied to analyze real samples obtained from large markets throughout the Korean Peninsula. The method proved to be sensitive and reliable and, thus, rendered an appropriate means for residue analysis studies.     

Quantification of staphylococcal enterotoxin type A in cow milk by using a stable isotope-labelled peptide via liquid chromatography–tandem mass spectrometry

ABSTRACT

In this study, the staphylococcal enterotoxin type A (SEA) contaminant was quantified in cow milk by liquid chromatography–tandem mass spectrometry (LC–MS/MS) with the use of a stable isotope-labelled peptide of SEA as an internal standard. SEA was cleaned up in a two-step process that included pH control and trichloroacetic acid (TCA) precipitation. The pH control phase eliminated other proteins. TCA precipitation cleaned up SEA without special equipment. An appropriate enzyme-to-protein ratio maximised tryptic digestion. A desalting process guaranteed the stable retention of SEA-digested peptides. The coverage of amino-acid sequences (>10%) clearly identified the toxin’s presence. SEA was accurately quantified using LC-MS/MS based on a multiple-reaction monitoring mode. The developed method was validated based on spiked recovery tests at 50 and 100 µg kg^?1 conducted with two samples collected on a daily basis for five days based on Japanese validation guidelines. The new method exhibited good accuracy which ranged from 80% to 82%. The relative standard deviations of repeatability were 13–14% and the relative standard deviations of within-laboratory reproducibility were 13–18%. These standard deviations satisfied the criteria of the Japanese validation guidelines. The quantification limit was estimated to be 10 µg kg^?1.     

Confirmatory analysis of steroids in muscle using liquid chromatography–tandem mass spectrometry

A method is described for screening and confirmation of synthetic and endogenous steroids in muscle tissue. The method is sensitive, selective, and rapid and the consumption of organic solvents is low, compared to previously published methods. The procedure involves hydrolysis, defattening with heptane and final clean up with SPE using C₁₈ cartridge. After filtration, the analytes are analysed by LC/MS/MS and quantification is performed using deuterated internal standards. Decision limits (CCα) varied from 0.02 to 0.33?µg?kg^?1 and the detection capabilities (CCβ) were <0.50?µg?kg^?1. The mean within-laboratory reproducibility ranged 5–22% (%RSD_IR). Endogenous steroids (e.g. testosterone, epitestosterone and androstenedione) have been included in the method, to provide an insight into their levels, as the presence of these steroids was detected several times during analysis of imported meat.     

Determination of selected pesticides in fruit juices by matrix solid-phase dispersion and liquid chromatography–tandem mass spectrometry

A rapid and sensitive liquid chromatography–tandem mass spectrometry method has been developed for the analysis of acephate, monocrotophos, carbendazim, acetamiprid, dimethoate, simazine, carbofuran, atrazine, diuron, DNOC (4,6-dinitro-o-cresol), malathion and tebufenozide in fruit juices. Extracts were obtained by matrix solid-phase dispersion using diatomaceous earth as dispersant and dichloromethane as eluent. Significant matrix effects observed for most of the pesticides tested were eliminated using matrix-matched standards. The quantification of the analytes was carried out using the most sensitive transition. The confirmation of residues detected in real samples was performed by repeated injection and acquiring additional transitions to that used for quantification. Recoveries were in the range 71–118%. Repeatability of the method, expressed as the relative standard deviation, was in general between 5–15%. Low limits of detection (0.01–0.94 ng ml⁻¹) and quantification (0.03–3.12 ng ml⁻¹) were readily achieved with this method for all tested pesticides.