[Simultaneous determination of three components of sodium nitrophenolate in foodstuffs of animal origin by high performance liquid chromatography-tandem mass spectrometry using atmospheric pressure chemical ionization].

Sodium nitrophenolate (SNP) is a widely used universal growth regulator consisting of 5-nitroguaiacol sodium (5NG), 4-nitrophenol sodium (PNP), and 2-nitrophenol sodium (ONP). SNP has a positive influence on plants and animals as a feed additive that accelerates growth but is potentially hazardous to humans. SNP has been reported to be cytotoxic and mutagenic, which may increase the risk of cancer and pose a great threat to food safety. There are neither mature detection nor standard methods for the trace analysis of SNP in animal food. Therefore, the development of an accurate and precise analytical method is imperative. This innovative method has theoretical and practical significance for the control of SNP residues, offering advantages such as cost-effectiveness and time efficiency. It will be beneficial for the establishment of detection standards and management measures in foodstuffs of animal origin.In this study, a reliable method for the simultaneous determination of SNP residues in animal food (porcine muscle, chicken tissue, fish, and liver) was developed. For realizing the perfect limit of quantification, the application of back extraction coupled with high performance liquid chromatography-atmospheric pressure chemical ionization-tandem mass spectrometry (HPLC-APCI-MS/MS) was proposed to combine high sensitivity and high selectivity. The optimal method was as follows. First, 2.0 g samples were extracted with 10 mL 0.5 mol/L sodium hydroxide solution, followed by adjustment of the pH to acidity with 3 mol/L hydrochloric acid and the addition of sodium chloride (5.0 g) to saturate the inorganic phase. After back-extraction twice with 16 mL acetonitrile, the solution was merged and again saturated with 5 mL of sodium chloride solution. Second, the merged organic phase was cleaned up with 10 mL of n-hexane for defatting. The middle acetonitrile layer was then concentrated to nearly 1.5 mL at 40 ℃ in a N2 stream before dilution with the mobile phase to a volume of 3.0 mL and filtered. Finally, the analytes were separated on a C18 column (100 mm×4.6 mm, 3 µm) and subjected to gradient elution with a mixed solution of methanol and water. Mass spectrometric analysis, which was quantified using the external standard method, was carried out with an atmospheric pressure chemical ionization negative ion source and based on multiple reaction monitoring (MRM) mode. The key parameters, such as the extraction solvent, extraction steps, and purification method, were optimized.The calibration curves were linear in the ranges of 0.5-10 (5NG), 1.0-20 (PNP), and 2.5-50 µg/L (ONP) with correlation coefficients greater than 0.9999. The limit of quantification (LOQ) for 5NG was 1.0 µg/kg, double for PNP, and five times for ONP. The recoveries of the three different concentration levels in all the four matrices were in the range of 81.5%-98.4%, 81.5%-102%, and 81.4%-95.1%. The repeatability, expressed as the relative standard deviations (RSDs) of the three compounds, ranged from 1.51% to 5.98%, 1.10% to 8.85% and 0.91% to 8.61% (n=6). The developed method is characterized by an excellent purification effect, sensitivity, and accuracy. This method is suitable for the simultaneous and quantitative determination of SNP residues in foodstuffs of animal origin.

[Determination of benzimidazoles residue markers in chicken tissue by high performance liquid chromatography].

A method was developed for the simultaneous determination of 11 benzimildazoles residue markers in chicken meat, liver and kidney samples by high performance liquid chromatography (HPLC). The chicken tissue sample was extracted with acetonitrile, defatted with n-hexane, and purified with an MCX solid-phase extraction cartridge. Chromatographic separation was performed on an Atlantis T3 column with the gradient elution of methyl alcohol-1% (v/v) acetic acid aqueous solution as the mobile phases at a flow rate of 1.0 mL/min. The detection wavelength was set at 292 nm. Analytes were quantified by the external standard method. The linearities of the calibration curves were well in the range of 25-1000 µg/L, and the limit of quantification was 50 µg/kg. The recoveries at different spiked levels in all the three matrices ranged from 70.91% to 103.21%, and the relative standard deviations (RSDs) were between 1.48% and 10.08% (n=6). The developed method is characterized by an excellent purification effect, sensitivity and accuracy, and can be used for the determination of benzimidazoles residue markers in chicken tissue samples.

[Determination of three tranquillizer residues in animal foods by QuEChERS-high performance liquid chromatography-tandem mass spectrometry].

A method for simultaneous determination of chlorpromazine, diazepam and metolazone residues in porcine muscle, fish, liver and kidney was developed using QuEChERS and HPLC-MS/MS technique. The samples were extracted with ethyl acetate and cleaned up with C18, N-propylethylendiamine (PSA) and NH2 sorbents after using Na2SO4 as dehydrating agent. The analytes were separated by a special C18 column, Atlantis T3, and gradiently eluted with a mixed solution of 5 mmol/L formic acid and acetonitrile at a flow rate of 0.35 mL/min. The mass spectrometric analysis that quantified using isotope internal standard, was carried out with electrospray positive ion source (ESI+) and multiple reaction monitoring mode (MRM). The linearity of the calibration curves was good in the range of 0.2-5.0 µ g/L. The recoveries at three different spiked levels (0.5, 1 and 5 µ g/kg) in four matrices were in the range of 92.5%-117.8%. The repeatability expressed as relative standard deviations (RSDs) ranged from 0.7% to 11.6% (n=6). The method, with wide matrix range of application, is highly effective and sensitive and suitable for the rapid analysis of large quantities of samples.

[Determination of antibiotics in oral hygiene products by high performance liquid chromatography-tandem mass spectrometry].

A high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/ MS) method was developed for simultaneous determination of 13 antibiotics in oral hygiene products, including five tetracyclines, three macrolides, two quinolones, one beta-lactam and two lincosamides. The sample was extracted with 0.1% (volume percentage, same hereinafter) formic acid-acetonitrile (95:5, v/v), then centrifuged, filtered and diluted. The target compounds were separated on a C18 column (150 mm x 2.1 mm, 5 microm) with a gradient elution of 0. 1% formic acid and acetonitrile as the mobile phases, and detected by tandem mass spectrometry in positive electrospray ionization and multiple reaction monitoring (MRM) mode. The quantification of 13 antibiotics was performed by the external standard method. The calibration curves showed good linearity in the range of 5.0-50.0 microg/L with detection limits of 10.0 mg/kg. The recoveries of antibiotics in mouthwash and toothpaste samples at the three spiked levels of 10, 20 and 100 mg/kg were in the range of 80.1%-115% with the relative standard deviations in the range of 0.94%-8.69%. This method is accurate, reliable, simple, and suitable for the analysis of antibiotics in oral hygiene products.

[Determination of nitroimidazoles in oral hygiene by ultra-performance liquid chromatography-tandem mass spectrometry].

A method for the simultaneous determination of metronidazole, tinidazole, ornidazole, ronidazole and dimetridazole in oral hygiene by ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) has been developed. The sample was diluted with 0.1% formic acid/acetonitrile (95:5, v/v), then centrifuged and filtered with a membrane. The separation was carried out on a Cloversil C18 column (100 mm x 2.1 mm, 3.5 microm) with the gradient elution of 0.1% formic acid and acetonitrile as the mobile phases. The analytes were determined by UPLC-MS/MS and quantified by external standard method. The calibration curves showed good linearity in the range of 1.0-60.0 microg/L with r > or = 0.9992. The recoveries were 91.5%-108% at the three spiked levels of 10.0, 20.0 and 100 mg/kg, and the relative standard deviations were 1.14%-5.22%. This method is easy, sensitive and suitable for the determination of nitroimidazoles in oral hygiene.