Optimization of Headspace Single-Drop Microextraction Coupled with Gas Chromatography–Mass Spectrometry for Determining Volatile Oxidation Compounds in Mayonnaise by Response Surface Methodology

In this assay, headspace single-drop microextraction (HS-SDME) coupled with gas chromatography–mass spectrometry (GC–MS) as a simple, low-cost and rapid method has been developed and validated for determining volatile oxidation compounds including hexanal and heptanal in mayonnaise. The main microextraction variables affecting the HS-SDME procedure such as extraction temperature and time, stirring rate, and amount of NaCl were optimized by response surface methodology employing a central composite design. Obtained results demonstrated that higher yield of extracted analytes could be achieved under the following optimal conditions: extraction temperature of 45 °C, extraction time of 16 min, stirring rate at 700 rpm, and addition of 2 g NaCl. The optimized HS-SDME/GC–MS method was validated for oxidized mayonnaise samples (50 °C/48 h) by calculating analytical parameters (linearity, precision, accuracy, and sensitivity). Good linearity (R ²?>?0.99) was observed by plotting calibration curves of extracted hexanal and heptanal over the concentration range of 0.025–10 μg g^?1, and the repeatability of the method, expressed as relative standard deviation, were found to be 4.04 % for hexanal and 3.68 % for heptanal (n?=?7). After the microextraction process of spiked mayonnaise sample, high levels of relative recovery were obtained for hexanal (107.33 %) and heptanal (91.43 %). The detection limits were 0.008 ng g^?1 and 0.021 ng g^?1 for hexanal and heptanal, respectively, while quantification limits of hexanal and heptanal were calculated to be 0.027 ng g^?1 and 0.071 ng g^?1, respectively. The possibility of the HS-SDME followed GC–MS to determine and quantify volatile oxidation compounds such as hexanal and heptanal was confirmed by analyzing commercial fresh mayonnaise stored at 4 and 25 °C during 3 months.     

LC-TOF/MS determination of phthalates in edible salts from food markets in Korea

Residual quantities of 12 phthalates have been monitored in edible salts (raw salts, refined salts, refined salts with additives and baked salts) available in Korean food markets. Liquid–liquid extraction followed by liquid chromatography time-of-flight mass spectrometry (LC-TOF/MS) was used to analyse the samples. The method was validated and showed linear correlation (R ² > 0.996) in the range 0.5–100 ng g^?1 for all target analytes. Recoveries were 85.9–108.4%, except for diethyl phthalate (DEP). Relative standard deviations (RSDs) were 2.7–6.0% and the limits of detection (LODs) were 1.2–2.8 ng g^?1. Although the contamination of phthalates in salt would be trivial in comparison to those of other main foods and below the reference dose of the Chronic Oral Exposure recommended by US-EPA, the availability of reference data could be valuable for food chemists and salt manufacturers.     

Measurement of ampicillin residue levels in chicken eggs during and after medicated feed administration by LC-MS/MS

A simple and sensitive LC-MS/MS method was developed and validated for the determination of ampicillin (ABPC) in chicken eggs. Residues were extracted by reverse-phase solid-phase extraction. Chromatographic separation was performed using a reverse-phase column with an elution gradient. The limits of detection and quantification were 0.01 and 0.1 ng g^?1, respectively. For the 0.1–50 ng g^?1 concentration range, mean recovery and accuracy values were 93.9–98.5% and 100.2–118.0%, respectively. ABPC residue concentrations in eggs before, during and after 7 days of medicated feeding of maximum dosage (40 mg kg^?1 body weight day^?1) of ABPC were determined with the LC-MS/MS method. The maximum concentration of ABPC in eggs was 3.6 ± 1.7 ng g^?1 (mean ± SD) on the last day of the administration period. Residue concentrations of ABPC in eggs during and after ABPC administration were not over the Japanese maximum residue limit of 0.01 mg kg^?1.     

Determination and depletion of amoxicillin residues in eggs

Eggs were used to study the determination and depletion of amoxicillin (AMO) residues after oral dosing hens (25.0 mg kg^–1, 50.0 mg kg^–1 body weight), once daily for five days. A reverse-phase high-performance liquid chromatography with fluorescence detection (RP-HPLC-FLD) method was developed to determine AMO residues in albumen, yolk and whole egg. By using pre-column derivatisation, an improved liquid–liquid extraction procedure was developed for sample preparation. AMO were extracted from eggs with acetonitrile. The extract solution was extracted using saturated methylene chloride. The supernatant was reacted with salicylaldehyde under acidic and heating conditions. Limits of detection (LODs) were 1.2 ng g^–1 and limits of quantification (LOQs) were 3.9 ng g^–1 for AMO. Recoveries of AMO from samples fortified at levels of 5.0–125.0 ng g^–1 ranged from 79.1% to 88.5% in albumen, 78.6–83.6% in yolk and 78.3–85.1% in whole egg, with coefficients of variation of ≤7.3%. The maximum concentrations of AMO in albumen, yolk and whole egg were found to occur at 1.5, 2.5, 1.5 days after withdrawal of medication respectively. AMO was not detectable in albumen at 7.5 days after final administration of AMO, at 10.5–11.5 days in yolk and 10.5 days in whole egg after administration of two oral doses. The method was applied during the residue study of AMO in order to formulate a reasonable withdrawal period to ensure food safety.     

A survey of bisphenol A and other bisphenol analogues in foodstuffs from nine cities in China

Bisphenol A (BPA) is a high-production-volume chemical that is widely used in polycarbonate plastics and epoxy food-can coatings. Following several studies that have reported adverse effects of BPA over the past decade, other bisphenol analogues, such as bisphenol F (BPF), bisphenol S (BPS), bisphenol AF (BPAF), and bisphenol B (BPB), have been gradually developed as substitutes for BPA in several applications. Nevertheless, few studies have reported on the occurrence of compounds other than BPA in foodstuffs. In this study, 289 food samples (13 categories: cereals and cereal products, meat and meat products, fish and seafood, eggs, milk and milk products, bean products, fruits, vegetables, cookies/snacks, beverages, cooking oils, condiments, and others), collected from nine cities in China, were analysed for eight bisphenol analogues using high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). BPA and BPF were found widely in foodstuffs at concentrations ranging from below the limit of quantitation (LOQ) to 299 ng g^–1 (mean = 4.94 ng g^–1) and from below the LOQ to 623 ng g^–1 (mean = 2.50 ng g^–1), fresh weight, respectively. The highest total concentrations of bisphenols (∑BPs: sum of eight bisphenols) were found in the category of vegetables that included canned products (mean = 27.0 ng g^–1), followed by fish and seafood (16.5 ng g^–1) and beverages (15.6 ng g^–1). ∑BP concentrations (mean = 2–3 ng g^–1) in milk and milk products, cooking oils, and eggs were low. Food samples sold in metallic cans contained higher mean ∑BP concentrations (56.9 ng g^–1) in comparison with those packaged in glass (0.43 ng g^–1), paper (11.9 ng g^–1), or plastic (6.40 ng g^–1). The daily dietary intakes of bisphenols were estimated, based on the mean concentrations measured and daily consumption rates of foods, to be 646 and 664 ng kg^–1 bw day^–1 for men and women, respectively.     

Rapid multiresidue determination of pesticides in livestock muscle and liver tissue via modified QuEChERS sample preparation and LC-MS/MS

ABSTRACT

Many multiresidue methods for the determination of pesticides in vegetables and fruits have been reported to date. However, few such methods have been employed to investigate pesticide residues in animal tissue. In this study, an LC-MS/MS multiresidue method coupled with modified QuEChERS extraction was developed and validated for the investigation of eight pesticide residues: prallethrin (PR), resmethrin (RMT), imidacloprid (IMC), diflubenzuron (DFB), cyromazine (CYR), etofenprox (EFP), dinotefuran (DNT) and phthalthrin (PTLT). This method involves initial extraction in a water/acetone system, the addition of salts and a subsequent extraction/partitioning step and, finally, a clean-up step utilising dispersive solid-phase extraction (SPE). The mean recoveries of seven of the pesticides (the exception being CYR) ranged between 74.7% and 113.5%, and the CVs of the livestock tissue – bovine, swine, and chicken muscle and liver tissue spiked at 10 ng g^–1 (50 ng g^–1 for RMT and DNT) and 100 ng g^–1 – were < 13.8%. The recoveries of CYR in all muscle and liver spiked samples ranged from 56.9% to 78.3%, while those of RMT in swine liver were > 120%. Therefore, this method was considered as being unsuitable for the investigation of these samples. The limits of quantitation (LOQs) of seven of the investigated pesticides (the exception being swine liver) in the tissue samples ranged from 0.9 to 15.2 ng g^–1. We therefore concluded that this LC-MS/MS multiresidue method is a valid and suitable for the investigation of seven pesticides in animal tissue, but it is unsuitable for the analysis of CYR in all animal tissues and RMT in swine liver tissue.     

Simultaneous quantitative determination,identification and qualitative screening of pesticides in fruits and vegetables using LC-Q-Orbitrap™-MS

A method based on QuEChERS extraction and LC-quadrupole-Orbitrap? MS detection was established utilising an improved fully non-targeted way of data acquisition with and without fragmentation. A full-scan acquisition event without fragmentation (resolving power 70 000) was followed by five consecutive fragmentation events (variable data independent acquisition – vDIA; resolving power 35 000) where all ions from the full-scan range are fragmented. Compared with fragmentation in a single event (all-ion fragmentation – AIF), this improves both selectivity and sensitivity for the fragment ions, which is beneficial for screening performance and identification capability. The method was validated, using the data from the same measurements, for two types of analysis: quantitation/identification and qualitative screening. The quantitative validation, performed according to the guidelines in SANCO/12571/2013, tested the performance of the method for 184 compounds in lettuce and orange at two spiking levels: 10 and 50 ng g^?1. The validation showed that the vast majority of the compounds met the criteria for trueness and precision set in the SANCO guidance document. In the qualitative validation the same 184 compounds were used to test the untargeted screening capabilities of the method. In this validation the compounds were spiked at three levels into 11 different fruit and vegetable matrices, which were measured twice on separate days. Taking all data from the qualitative validation together, an overall detection rate of 92% was achieved at the 10 ng g^?1 level, increasing to 98% at 200 ng g^?1. A screening detection limit (as defined in the SANCO guidelines) of 10 ng g^?1 could be achieved for 134 compounds. For 39 and two pesticides the SDL was 50 and 200 ng g^?1, respectively. For the other nine compounds no SDL could be established. The identification (ion ratio) criteria as recommended in the SANCO document could be met for 93% of the detected pesticide/matrix/concentration combinations. The outcome of both validations shows that the described method can be used to combine quantitative analysis and the identification of frequently detected pesticides (so far typically done using triple quadrupole MS/MS) with a qualitative screening to be used for a wide range of less frequent detected compounds in one measurement.     

Monitoring by LC-MS/MS of 48 compounds of sildenafil,tadalafil, vardenafil and their analogues in illicit health food products in the Korean market advertised as enhancing male sexual performance

More than 46 phosphodiesterase type 5 (PDE5) inhibitor analogues have been found to be present as illegal adulterants in various forms of health food products (powder, tablet, capsule, etc.), thereby placing the health of consumers at risk through product intake. In this study, 164 samples advertised to be effective at enhancing male sexual performance were collected over a 4-year period (2009–2012) from the Korean on-line or off-line market and screened. An LC-MS/MS method was employed to screen for the presence of 48 compounds including sildenafil, tadalafil, vardenafil and their analogues. Method validation established LOQs (0.30–10.00 ng ml^?1 or ng g^?1) and recoveries (spiked in liquid sample, 84–112%; spiked in solid sample, 83–110%). Most of the illicit products screened were adulterated with 14 of the PDE5 derivatives under examination, including considerable amounts of sildenafil and tadalafil; of the 48 compounds, tadalafil was the most frequent adulterant (42.6%), followed by sildenafil (27.9%). Specifically, tadalafil concentration ranges (mg g^?1) in the samples collected over the 4-year period were determined as follows: 2.91–52.20 (2009), 4.50–108.10 (2010), 0.37–101.40 (2011), and 0.08–138.69 mg g^?1 (2012). The concentration ranges (mg g^?1) of sildenafil were also at high levels: 4.90–117.96 (2009), 1.30–369.93 (2010), 0.03–241.77 (2011), and 18.34–297.91 mg g^?1 (2012). The results of screening for PDE5 inhibitor pharmaceuticals as adulterants in illicit health food products are of great significance with respect to the protection of public health and consumer safety.     

Simultaneous Determination of Seven Polycyclic Aromatic Hydrocarbons in Coffee Samples Using Effective Microwave-Assisted Extraction and Microextraction Method Followed by Gas Chromatography-Mass Spectrometry and Method Optimization Using Central Composite Design

In this research, for the first attempt, we successfully determined seven polycyclic aromatic hydrocarbons (PAHs) in various coffee samples using microwave-assisted extraction and dispersive liquid-liquid microextraction (MAE-DLLME) coupled with gas chromatography-mass spectrometry (GC-MS). The effects of most important variables in microextraction step were investigated and optimized using response surface methodology (RSM) based on central composite design. The calibration curves were linear in the range of 1–200 ng g^?1, with a correlation coefficient (R ²) higher than 0.989. Limits of detection were obtained between 0.1 and 0.3 ng g^?1. The relative standard deviations (RSD%) for seven repeated analysis were less than 8% for all PAH compounds at a concentration of 10 ng g^?1. Relative recoveries were obtained 88.1–101.3%. The satisfactory results obtained by the proposed method and the comparison of these results with previous methods demonstrated that the MAE-DLLME-GC-MS is an accurate, rapid, and reliable sample-pretreatment method with low consumption of the organic solvent.     

Simultaneous determination of sorbic and benzoic acids in milk products using an optimised microextraction technique followed by gas chromatography

A rapid and reliable method for direct determination of sorbic and benzoic acids in milk products was developed by dispersive liquid–liquid microextraction (DLLME) and gas chromatography with flame ionisation detector (GC-FID). A response surface methodology (RSM) based on a central composite design (CCD) was applied for optimisation of the main variables, such as volume of extraction and dispersive solvents, pH and salt effect. The primary extraction of sorbic and benzoic acids were performed in 8 mL NaOH (0.1 M) in a closed-vessel system. Carrez solutions (potassium hexaferrocyanide and zinc acetate) were used for protein sedimentation. The best simultaneous extraction efficiency was identified using acetone and 1-octanal as dispersive and extraction solvents, respectively. For DLLME, central composite design resulted in the optimised values of microextraction parameters as follows: 475 µL of dispersive and 60 µL of extraction solvents, 2 g NaCl at pH 2.5. Under optimum conditions, the calibration curve was linear over the range 0.1–50 μg mL^?1 and the square of correlation coefficient (R²) was 0.9992 for sorbic acid and 0.9994 for benzoic acid. Relative standard deviation (RSD %) was 6.1% and 3.1% (n = 5) for sorbic and benzoic acids, respectively. Limits of detection were 150 ng g^?1 for sorbic acid and 140 ng g^?1 for benzoic acid and recoveries were 88% and 103.7% respectively. Good reproducibility (RSD %), short extraction time and no matrix interference were advantages of the proposed method which was successfully applied to the determination of sorbic and benzoic acids in milk products.     

Determination of Phthalates into Vegetable Oils by Isotopic Dilution Gas Chromatography Mass Spectrometry

The presented method for the determination of a number of phthalic acid esters into oily media is based on their extraction by acetonitrile with precipitation under freezing and subsequent solid-phase extraction using alumina. This technique was checked as the best procedure to separate lipophilic phthalates from fatty media achieving elimination of contamination by excess use of solvents. Extracted phthalates are determined in acetonitrile solutions with gas chromatography in conjunction to isotopic dilution mass spectrometry using D4 isotopic labeled derivatives. Full validation of the method was carried out and background effect was examined. Method calibration for extraction from oil resulted in limit of detection (LOD) of 7–10 ng g^?1 and limit of quantification (LOQ) of 20–50 ng g^?1 for DMP, DEP, DiBP, DBP, DEHP, and BBP and in LOD 500 ng g^?1 and LOQ of 1,500 ng g^?1 for DiNP and DiDP. Real samples of virgin olive oil from olive press establishments from three different areas were analyzed and the phthalates content was below detection limit for all phthalic esters under consideration for nonindustrial areas and in measurable concentrations for industrial areas specifically with regard to DiBP.     

Determination of caramel colorants’ by-products in liquid foods by ultra-high-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS)

2-Methylimidazole, 4-methylimidazole (2-MI and 4-MI), 2-acetyl-4-(1,2,3,4-tetrahydroxybutyl) imidazole (THI) and 5-hydroxymethylfurfural (5-HMF) are neo-formed compounds generated during the manufacture of caramel colours and are transferred to the processed food. These contaminants are known to have a toxicological profile that may pose health risks. Hence, to characterise THI, 2- and 4-MI and 5-HMF levels in liquid foods, an ultra-high-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method was developed and sample preparation was divided into two analytical strategies depending on the concentration range expected in the type of foods targeted. For the determination of the imidazole substitutes (THI, 2- and 4-MI), a sample enrichment and clean-up step by strong cation solid-phase extraction was developed. This method is capable of quantifying over a range of 5 ng ml^–1 (LOQ) to 500 ng ml^–1 with recoveries of 75.4–112.4% and RSDs of 1.5–15%. For determination of 5-HMF, a standard addition method was applied covering the linear range of 0.25–30 µg ml^–1 with RSDs from 2.8% (for intraday precision) to 9.2% (for intermediate precision). The validated analytical methods were applied to 28 liquid food samples purchased from local markets. THI was found only in the beer samples at levels up to 141.2 ng ml^–1. For 2-MI, non-quantifiable traces were observed for all samples, while 4-MI was observed in all samples with large concentration variations (from < LOQ to 563.9 ng ml^–1). 5-HMF was found at expected concentrations, except for a sherry vinegar sample (113 µg ml^–1), which required a high level of dilution before following the standard addition protocol.     

Are Chileans exposed to dietary furan?

Chilean consumer preferences include foods that may contain considerable amounts of furan, a potential human carcinogen. However, there is no information regarding dietary exposure to furan in Chile. Thus, the objective of this work was to determine the Chilean exposure to dietary furan. To accomplish this objective, the furan concentration of 14 types of commercial foods processed at high temperature were analysed based on a modified headspace-GC/MS (HS-GC/MS) method in which the limits of detection for different food matrices ranged from 0.01 to 0.6 ng g^?1. In addition, a risk assessment was made with exposure estimates based on dietary data from national studies on different age groups (9-month-old babies, school children, adults and elderly people). Of the food items surveyed “American”-type coffee (espresso coffee plus hot water) obtained from automatic coffee machine (936 ng g^?1) and low moisture starchy products like crisps and “soda”-type crackers showed the highest furan concentrations (259 and 91 ng g^?1, respectively). Furthermore, furan was also found in samples of breakfast cereals (approximately 20 ng g^?1), jarred fruit baby foods (8.5 ng g^?1) and orange juice (7.0 ng g^?1). School children (aged 9–13 years) represented the highest intake of furan (about 500 ng kg^?1_bw day^?1), with margins of exposure of 2479 and 2411, respectively, which points to a possible public health risk.     

Determination of oxytetracycline residue in shrimp using a portable time-resolved analyzer and HPLC�CMS/MS validation

Oxytetracycline residue in shrimp muscle was determined using a portable time-resolved analyzer. After extraction in EDTA-metaphosphoric acid and filtration, the analyte was cleaned up using hydrophilic-lipophilic balance cartridges. Europium-sensitized luminescence (ESL) was measured at ??_ex = 385 nm and ??_em = 620 nm. Recoveries were 80.3 and 79.7% at 100 ng g^?1 and 2 ??g g^?1, respectively. The signal intensity was linear (r ² ?? 0.996) in each decade in the 5?C5,000 ng g^?1 range. Averaged relative standard deviation was ~2% and limit of detection was 8.3 ng g^?1. This instrument-method combination enabled sensitive in-situ quantification of OTC residue in shrimp. The ESL results were validated by HPLC?CMS/MS.     

Magnetic three-dimensional graphene solid-phase extraction of chlorophenols from honey samples

A novel magnetic three-dimensional graphene nano-composite (3D-G@Fe₃O₄) with a high surface area was synthesised by a vacuum freeze-dried method. Due to its high surface area, specific 3D nanoporous structure and excellent magnetic properties, it can be used as a magnetic solid-phase extraction adsorbent. Some chlorophenols in a honey samples were enriched by this nanocomposite prior to their determination by HPLC with ultraviolet detection. Factors that affect the extraction efficiency, such as the amount of 3D-G@Fe₃O₄, extraction time, sample pH, ionic strength and desorption conditions, were investigated and optimised. Under the optimum conditions, good linearity existed in the range of 10.0–1000.0 ng g^–1. The enrichment factors of the method for the analytes were in the range from 101 to 248. The limits of detection of the method (S/N = 3) were 1.0–1.5 ng g^–1. The recoveries of the method for the analytes at spiking levels of 100.0 and 400.0 ng g^–1 were in the range of 93.2–98.9%. The results showed that the proposed method is simple, reliable and sensitive. It will be a useful tool for the routine monitoring of chlorophenols in honey products.     

Vortex-Assisted Liquid–Liquid Microextraction Combined with HPLC for the Simultaneous Determination of Five Phthalate Esters in Liquor Samples

A vortex-assisted liquid–liquid microextraction (VALLME) method using hexanoic acid as extractant followed by high-performance liquid chromatography–diode array detection was developed for the extraction and determination of five phthalate esters (PAEs) including bis-methylglycol ester (DMEP), benzyl butyl phthalate (BBP), dicyclohexyl phthalate (DCHP), di-n-butyl phthalate (DBP), and di-n-octyl phthalate (DNOP) from liquor samples. In this method, hexanoic acid was employed as extraction solvent, because its density is lower than water. And vortex mixing was utilized as a mild emulsification procedure to reduce emulsification time and improve the effect of extraction. Under the studied conditions, five phthalate esters were successfully separated within 20 min and the limits of detection were 2.3 ng mL^?1 for DMEP, 1.1 ng mL^?1 for BBP, 1.9 ng mL^?1 for DCHP, 1.2 ng mL^?1 for DBP, and 1.5 ng mL^?1 for DNOP, respectively. Recoveries of the PAEs spiked into liquor samples were ranged from 89 to 93 %. The precisions of the proposed method were varied from 1.6 to 2.6 % (RSD). The VALLME method has been proved to have the potential to be applied to the preconcentration of the target analytes. Moreover, the method is simple, high sensitivity, consumes much less solvent than traditional methods and environmental friendly.     

Development of an ultra-high-performance liquid chromatography coupled to high-resolution quadrupole-Orbitrap mass spectrometry method for the rapid detection and confirmation of illegal adulterated sedative-hypnotics in dietary supplements

A novel method using ultra-high performance liquid chromatography coupled to hybrid quadrupole-Orbitrap high-resolution mass spectrometry (UHPLC-Q-Orbitrap) was developed and validated for the simultaneous screening, identification and quantification of sedative-hypnotics in dietary supplements. Chromatographic conditions were optimised and a full data-dependent MS² scan (MS/dd-MS²) in positive and negative ion mode was used. A single injection was sufficient to perform the simultaneous screening and identification/quantification of samples. The response showed a good linear relationship with analyte concentrations over wide ranges (e.g., 1.0–1000 ng g^–1 for diazepam) with all the determination coefficients (r²) > 0.9985. The method was validated, obtaining accuracy (intra- and inter-day) in the range of 94.5–105.3% and precision (intra- and inter-day) in the range of 0.4–8.9%, respectively. The detection limits (LODs) were in the range of 0.3–1.0 ng g^–1 for different analytes. Recoveries were performed and ranged from 74.1% to 90.2%, while all matrix effects were over the range of 85.4–93.6%. Finally, this method was used to detect sedative-hypnotics in commercial dietary supplements. Of a total of 45 batches of dietary supplements, only three batches were found to be positive samples with concentrations of diazepam, clonazepam and alprazolam at high levels (≥ 8.22 mg g^–1).     

Determination of Melatonin and Its Metabolites in Biological Fluids and Eggs Using High-Performance Liquid Chromatography with Fluorescence and Quadrupole-Orbitrap High-Resolution Mass Spectrometry

Melatonin is a hormone found in animals, plants, fungi, and bacteria, which can be used as a sleep aid and in the treatment of sleep disorders. Here, a rapid and accurate method was developed for the determination of melatonin in plasma, milk, and egg using high-performance liquid chromatography with fluorimetric detection (HPLC-FLD) and ultra high performance liquid chromatography–quadrupole-orbitrap high-resolution mass spectrometry (UHPLC-Q-Orbitrap HRMS). Sample was extracted with methanol and cleaned by passing through hydrophilic–lipophilic balanced (HLB) solid phase extraction cartridge. The method validation results showed that recovery for melatonin was between 80.3 and 105.1 % with relative standard deviations less than 9.8 %. UHPLC-Q-Orbitrap HRMS was employed as a further means of confirmation to assure accuracy of the results. Limits of detection for melatonin were 0.13 ng g^?1 and 0.14 ng mL^?1 for solid and liquid samples, respectively. Thus, the proposed method can be applied to detect melatonin in milk, plasma, and egg samples. Meanwhile, the metabolites of melatonin were identified using Q-Orbitrap HRMS. The approach identified five metabolites; among them, a novel metabolite, named mono-oxygenation-demethylation-melatonin, was found in plasma.     

Determination of free and total bisphenol A in human milk samples from Canadian women using a sensitive and selective GC-MS method

A sensitive and selective GC-MS method was developed and used to analyse human milk samples for both free and total bisphenol A (BPA). Total BPA was detected in 72 of the 278 human milk samples (25.9%) at concentrations from < 0.036 to 2.5 ng g^–1 with a geometric mean (GM) of 0.13 ng g^–1 and median of 0.11 ng g^–1, while free BPA was detected in fewer samples, 46 of the 278 samples (16.5%) at concentrations ranging from < 0.036 to 2.3 ng g^–1 with a GM of 0.11 ng g^–1 and median of 0.10 ng g^–1. Ratios of [free BPA]/[total BPA] for the positive samples ranged from 7.9% to 100% with a GM of 57.2% and median of 70.3%. Concentrations of free and total BPA in most samples were low with 0.39 and 0.65 ng g^–1 at the 95th percentile for free and total BPA, respectively, and they are also lower than those reported in other countries. Based on the low frequency of detection of free BPA in human milk samples, in general, dietary exposure to BPA for Canadian breast-fed infants is expected to be somewhat lower compared with exposure among formula-fed infants.     

A novel method to determine valnemulin in feedingstuffs for several animal species by liquid chromatography-electrospray tandem mass spectrometry

A new method specific for the determination and unambiguous confirmation of the antibiotic valnemulin in feed for all animal species is described. Simple clean-up based on solvent extraction and liquid partition is carried out prior to determination by liquid chromatography coupled to electrospray tandem mass spectrometry on a hybrid QTRAP 4000 system, in multiple reaction monitoring mode. Valnemulin is licensed in the European Union as a veterinary drug for use in feed for pigs and rabbits, but unavoidable carryover in feed for non-target species should be monitored. The method is rapid and reliable, and was validated in-house at 10, 100 and 750 ng g^–1, evaluating the analytical performances according to Commission Regulation (EC) No. 882/2004. Good mean recoveries from 79.7% to 92.6%, and within-laboratory reproducibility RSDs, ranging from 6.2% to 12.1%, were measured; the limit of quantification at 10.0 ng g^–1 also allows for sensitive evaluation of undesirable carryover in feed for non-target species. The results of monitoring 24 compound feeds for several animal species are also reported.