Ultrasensitive flow-injection electrochemical method for determination of histamine in tuna fish samples

Histamine is a potentially hazardous compound and one of the major concerns in food chemistry. High amount of histamine may be found in food as a consequence of the use of poor quality raw materials, contamination and inappropriate conditions during food processing and storage. A novel method for the determination of histamine in flow-injection systems has been developed for use in seafood quality inspection and food quality control laboratories. The developed technique is very simple, precise, accurate, time saving and economic as compared to all of the previously reported methods. The effects of various parameters on the sensitivity of the method were investigated. The best performance was obtained with the conditions, pH value of 2.0, and sweep rate value of 40 V/s, accumulation potential of 900 mV and accumulation time of 0.4 s. In this work, we introduce a special computer based numerical method, for calculation of the analyte signal and noise reduction. The electrode response was calculated based on partial and total charge exchanges at the electrode surface after subtracting the background current from noise. The waveform potential consisting of potential steps for cleaning and accumulation of analyte, and potential ramp was applied on an Au disk microelectrode (with a radius of 12.5 μm). The method was linear over the concentration range of 1.1–5555 pg/ml (r = 0.998) with a limit of detection and quantification 0.35 and 1.16 pg/ml, respectively.     

A novel method for the determination of sodium chloride in salted fish

A novel, simple and reliable spectrophotometric method to determine sodium chloride in salted fish was developed and validated. The method was based on the reaction of chloride with silver nitrate and the determination of turbidity of silver chloride formed. The absorbance was measured at 385 nm. The method was tested under various conditions, and we confirmed an optimal operation with 2 mL 1:4 (v/v) nitric acid, 2 mL 1.5 g L^?1 gelatin, 5 mL 0.5% silver nitrate in a total volume of 50 mL, mixed and heated at 60 °C for 10 min. The range of linearity and the detection limit were 0.4–24 mg L^?1 and 0.2 mg L^?1, respectively. The relative standard deviations and the recovery were 0.83% to 2.87% and 93.74% to 103.6%, respectively. The accuracy of this method was comparable with Volhard method, and it was cheap and successfully applied to determine sodium chloride in salted fish.     

Performance evaluation of a fluorescamine-HPLC method for determination of histamine in fish and fish products

A method for the quantification of histamine in fish and fish products using tandem solid-phase extraction and fluorescence derivatization with fluorescamine was previously developed. In this study, we improved this analytical method to develop an official test method for quantification of histamine in fish and fish products, and performed a single laboratory study to validate it. Recovery tests of histamine from fillet (Thunnus obesus), and two fish products (fish sauce and salted and dried whole big-eye sardine) that were spiked at the level of 25 and 50 μg/g for T. obesus, and 50 and 100 μg/g for the two fish products, were carried out. The recoveries of histamine from the three samples tested were 88.8-99.6% with good repeatability (1.3-2.1%) and reproducibility (2.1-4.7%). Therefore, this method is acceptable for the quantification of histamine in fish and fish products. Moreover, surveillance of histamine content in food on the market was conducted using this method, and high levels of histamine were detected in some fish products.     

葡萄酒中甜蜜素含量测定方法探讨

建立毛细管气相色谱法测定葡萄酒中甜蜜素含量的分析方法.用正己烷作萃取液,并对酯化反应条件进行改进,采用HP-5毛细管柱分离,经氢火焰离子化检测器检测,外标法定量.在最佳分析条件下,样品中的甜蜜素经酯化后在0.1mg/mL～1.0mg/mL浓度范围内与峰面积呈良好线性关系(r=0.9995),回收率为89.0%～97.0%,相对标准偏差2.67%～2.83%.     

分光光度法测定鱼罐头中组胺的方法改进

在GB/T 5009.45-2003国家标准方法的基础上对样品的前处理等过程进行了新的尝试,使样品前处理过程简单、快速,同时保证了方法的准确度和精密度.结果显示,在60℃水浴、30 min条件下,三氯乙酸的提取效果最佳;正戊醇提取过程采用旋涡后离心的方式代替了分液漏斗振摇,获得了较佳的提取效果;盐酸提取液改为1.0 mL,保证了标准系列与测定系列显色体系的一致性,同时保证了实验结果的准确度.     

A method for the determination of total and reduced methimazole in various biological samples

A simple, rapid, reproducible and sensitive method based on HPLC with ultraviolet detection was developed for the determination of methimazole (MMI) in animal tissues and plasma samples. Under the optimum experimental conditions, the calibration curves for MMI were linear in the tested range 0.5–20 mg kg^?1 tissue sample (mg l^?1 plasma) with correlation coefficients better than 0.99. The performance of the proposed method was tested for the determination of MMI levels in brain, liver, thyroid gland and plasma of MMI-treated hens, as well as in their eggs and embryos. The proposed method reduces time and simplifies the sample preparation procedure.     

A simplified method for the determination of several fish drugs in edible fish and shrimp by high-performance liquid chromatography

A simplified HPLC method was used to recover antibiotic and antibacterial agents from 11 cultured fish and one shrimp. The average recoveries of oxytetracycline, oxolinic acid, miloxacin, and sulfamonomethoxine were 77, 92, 89 and 80%, respectively. The detection limit was 0.02–0.04 μg/g. We also examined the recovery of oxytetracycline and oxolinic acid used for cultured black tiger shrimp, which is a popular imported shrimp in Japan. To demonstrate the usefulness of this technique for detecting drug residues in cultured fish, the method was used to examine the muscle tissues of 12 commercial fish and shrimp obtained from several fish shops. No agents were found in any of the fish tested.     

Kinetic-spectrophotometry method for determination of ultra trace amounts of aluminum in food samples

A simple and sensitive kinetic-spectrophotometry method is developed for the determination of trace amounts of aluminum in food samples based on its catalytic effect on the oxidation of Nile Blue A by potassium bromate in sulfuric acid medium. The absorbance is measured at 595.5 nm with the fixed-time method. The optimization of the operating conditions regarding concentrations of the reagents, temperature and interferences are also investigated. The calibration curve is linear over the concentration range 0.07–0.9 μg ml⁻¹ of aluminum with good precision and accuracy and the detection limit was down to 0.034 μg ml⁻¹. The relative standard deviation for a standard solution of 0.4 μg ml⁻¹ of aluminum is 1.73% (n = 10). The proposed method proved highly sensitive, selective and relatively rapid for the assay of aluminum at ultra trace level without any pre-concentration and separation step. The method was applied to the determination of aluminum in food samples (rice, tea and potato). The analytical results of the real samples were in good agreement with the standard method.     

A simple and rapid screening method for the determination of protein and tryptophan in kernel halves and small samples of barley meal

The protein of distal halves of barley kernels or small meal samples was extracted with ethanolic sodium hydroxide solution. After dilution, the protein content was estimated with a spectrophotometer by measurements at 215 and 225 nm. The tryptophan content was estimated from the same extract by a spectrophotofluorimeter. The methods showed high correlations with those used for control. The presented methods can be used in screening kernels in segregating ears or selecting single plants.     

一种快速测定蛋白质含量的新方法

研究了用电位滴定法测定蛋白质含量的一种新方法。与凯氏法相比,该方法具有操作简便、结果准确、快速、节能等特点。经ｔ检验法进行显著性检验,该方法与凯氏法无显著性差异。适用于酿酒及食品行业中蛋白质含量的分析。     

鲜奶中蛋白质含量的快速测定

目的建立一种鲜奶中蛋白质含量快速消化的简便测定方法。方法改用8.8mol/L过氧化氢,浓硫酸混合液(4:1,V:V)为消化试剂,消化好的试样以甲醛法测定。结果该方法的消化时间由原来的6h缩至30min,测定结果和凯氏定氮法(国家标准方法)的测定结果无显著性差异。结论该方法分析速度快,操作简便,可用于鲜奶中蛋白质的测定。     

A fluorometric method for the micro-quantitative determination of haemoglobin and myoglobin concentrations in fish muscle

A fluorometric procedure based upon conversion of the haem moiety of haemoproteins to the free porphyrin by incubation with oxalic acid was employed to determine haemoglobin and myoglobin contents of fish extracts. The haemoproteins were extracted with 0.05M Tris buffer, pH 8.6, and the haemoglobin and myoglobin were separated with DEAE cellulose. Quenching or interference by unidentified substances resulted in low apparent recoveries of added haemoprotein but this could be partially overcome by the addition of potassium ferricyanide or by dialysis or ultra-filtration.     

体外模拟法测定婴儿奶粉中蛋白质的消化率

采用体外模拟的方法测定了婴儿奶粉中蛋白质的消化率。此法的重现性试验的相对标准偏差为1．73％，表明重现性较好。测定结果表明：各种不同原料间蛋白质的消化率差异显差。此法快速，简便，重现性好，可应用于婴儿食品质量的评定。     

荧光猝灭法测定鱼肉中苯胺绿含量

以水热法制备巯基乙酸修饰的Cd Te量子点,发现Cd Te量子点溶液中加入苯胺绿可使其荧光强度降低,据此建立一种测定苯胺绿含量的荧光分光光度法。在最佳实验条件下,苯胺绿浓度在1.0~10.0μmol/L与Cd Te量子点的荧光猝灭强度呈良好线性关系,相关系数r为0.999 3,检出限为0.018μmol/L。该方法用于鱼肉中苯胺绿含量的测定,回收率在97.6%~103.2%。     

高选择性的菜籽蛋白含量测定方法

为解决菜籽蛋白原料及制品中真蛋白含量难以测定的问题,建立了一种基于分级和定量2步完成的高选择性菜籽蛋白含量测定方法。通过酸化丙酮溶液和沸水萃取实施分级处理,可将样品中的非蛋白氮分离;结合应用可溶性蛋白的染色法测定和不溶性蛋白的凯氏定氮法测定,可获得样品的真蛋白含量。该方法变异系数不大于2.83%,回收率95%~96%,并可排除本源性非蛋白氮(包括芥子碱和硫甙)及外源性非蛋白氮(包括硝酸盐、铵盐、三聚氰胺和尿素)的干扰。该方法具备良好的抗干扰能力且不受蛋白质溶解性的影响,可推广到更多的植物蛋白制品及原料的真蛋白含量测定中,并可为相关行业的掺杂辨识或品质评价提供可靠手段。     

Zinc determination in samples fish by GFAAS using acid digestion in an ultrasound bath

The aim of this paper was to determine the zinc concentrations in muscle samples of Nile tilapia (Oreochromis niloticus) produced in aquaculture and fed diets containing inorganic and organic zinc sources. In the sample preparation step, the samples were lyophilized and ground cryogenically to produce particles smaller than 60 µm. The zinc extraction was conducted by acid mineralization using concentrated nitric acid and hydrogen peroxide in a thermostatically controlled ultrasonic batch reactor. The zinc determinations were performed by Graphite Furnace Atomic Absorption Spectrometry at a drying temperature of 90–250 °C, pyrolysis temperature of 1400 °C, atomization temperature of 2400 °C, and cleaning temperature of 2800 °C. Niobium nitrate was used as a chemical modifier co-injected with the samples, and tungsten was employed as a permanent modifier. Among the muscle tissue samples of Nile tilapia that were analyzed, zinc concentrations were determined in the range of 3.70–19.00 mg kg^?1 (LOD 0.012 µg L^?1 and LOQ 0.041 µg L^?1). The accuracy and precision of the proposed method of zinc determination was validated using the DORM-certified standard Fish Protein 4 NRC.     

离子选择电极法测定高氟样品中氟的方法改进

将GB/T 5009.18-2003《食品中氟的测定》氟离子选择电极法进行改进,将线性范围扩展至0.04～50.0μg/mL,建立了氟离子选择电极法测定南极磷虾和茶叶等高氟样品中氟含量的方法,通过精密度及回收率实验,南极磷虾中氟的回收率为88.7％ ～98.2％,茶叶标物的回收率为91.2％～105.3％,紧压茶的回收率为89.7％ ～ 104.0％,RSD为1.1％～2.5％.结果表明该方法的稳定性好、精密度高、操作简便、检测结果准确可靠,该方法的建立将为高氟样品中氟含量的监测和食用安全性评价提供科学依据.     

Development of a fast MECK method for determination of 5-HMF in honey samples

In this study, 5-hydroxymethylfurfural (5-HMF) determination was carried out by a micellar electrokinetic capillary chromatography (MEKC) methodology, using caffeine as the internal standard (IS). The optimisation of the electrolyte composition was approached using a 3² full factorial design with a central point to study the MEKC electrolyte components. Inspection of the response surface indicated that the optimal electrolyte composition was 5 mmol L⁻¹ sodium tetraborate (STB, pH 9.3) containing 120 mmol L⁻¹ sodium dodecyl sulphate (SDS). Under optimal CE conditions, separation of the investigated substance was achieved in less than 0.7 min. Quality parameters, such as linearity (R² > 0.99), precision (RSD < 5.41%), detection and quantification limits (3.37 and 11.24 mg kg⁻¹ for honey samples) and recovery (96.37–99.56%). The proposed methodology was successfully applied to the analysis of 5-HMF in honey samples. The analytical performance of this method makes it suitable for implementation in food laboratories for the routine determination of 5-HMF in honey samples.