微波消解—AAS法测定食品中铅、镉、铁、锰、铜和锌及其不确定度评估

应用微波消解溶样,原子吸收光谱法测定食品中多种元素,其中,使用石墨炉法测定铅和镉,火焰法测定铁、锰、铜和锌,并对原子吸收光谱法分析结果的不确定度作了评估。实验结果表明,铅、镉、铁、锰、铜、锌分别在5～40,0.25～3.0 μg·L-1,0.20～3.0,0.10～2.0,0.10～2.0和0.05～1.0 μg·mL-1范围内有良好的线性关系,其线性相关系数均在0.999 8以上,用标样GBW 07602(GSV-1)测定,其相对误差均在允许范围内。可见用微波溶样,AAS法同时测定食品中多种元素,具有快速、简便、节省试剂、消解完全、污染少等特点,测定结果的精密度和准确度令人满意。     

Analytical Applications of 2,6‐Diacetylpyridine‐bis‐4‐phenyl‐3‐thiosemicarbazone (2,6‐DAPBPTSC): Determination of Cd(II) in Foods and Water Samples

To the determination of trace amount of Cd(II) present in food and water samples, a selective and extractive spectrophotometric method were developed with 2,6‐diacetylpyridine‐bis‐4‐phenyl‐3‐thiosemicarbazone as a complexing agent. The yellowish orange colored metal complex, Cd(II)‐2,6‐DAPBPTSC with 1:1 (M:L) composition was extracted in to cyclohexanol at pH 9.5 and was shows maximum absorbance at λ_max 390 nm. This method obeys Beer's law in the range of 1.12‐11.25 ppm with 0.972 correlation coefficient of Cd(II)‐2,6‐DAPBPTSC complex, which is indicates linearity between the two variables. The molar absorptivity and sandell's sensitivity were found to be 6.088 × 10⁴ L mol^?1 cm^?1 and 0.0018 μg cm^?2, respectively. The instability constant calculated from Asmus' method (1.447 × 10^?4)at room temperature. The precision and accuracy of the method were checked by relative standard deviation (n = 5), 0.929 and its detection limit, 0.0060 μg mL^?1. The interfering effects of various cations and anions were also studied. The proposed method was successfully applied to the determination of Cd(II) in foods and water samples, and was evaluated its performance in terms of Student ‘t’ test and Variance ‘f’ test, which indicates the significance of present method. The inter comparison of the experimental values, using atomic absorption spectrometer (AAS), was also repoted.     

几种粮食中硒含量的测定

采用ＲＦ－５０００型荧光分光光度计测定了几种市售粮食中的硒含量，并对硒与人体健康关系等问题进行了讨论，可作为人们饮食结构中调节硒含量的参考依据。     

Automated and manual luminescent assay of antioxidant capacity: analytical features by comparison

The analytical performances of a manual and a partially automated chemiluminescent (CL) assay, of total antioxidant capacity (TAC) were assessed. In both cases the light emitting reaction involved luminol, horseradish peroxidase and hydrogen peroxyde, but the emission kinetics and the parameters taken into account to calculate TAC values were completely different. The major characteristics expressing the quality of the two analytical methods, i.e. inaccuracy, repeteability and reproducibility, sensitivity, time required for the analysis and detection limit, were estimated by using standard solutions of Trolox. The reliability of the automated method, in comparison with the more validated manual one, was demonstrated testing food samples such as honey, wine and dietary supplements and performing a statistical analysis of the results. The comparison of the two series of data by t-test resulted in p values in the range 0.1-0.01. The time required for the analysis of each sample was reduced to one third using the automated method.     

Clean-up techniques for pesticides in fatty foods

The separation of pesticides and other chemical contaminants from high-fat food samples prior to subsequent steps in the analytical process (usually gas chromatography) is a problem to which much effort in method development has been applied. Early methods involved liquid-liquid partitioning, adsorption chromatography and chemical destruction of lipids with strong base and acid. These techniques had limited applicability, especially with the advent of more polar and labile pesticides. Later developments involving sweep codistillation, gel-permeation chromatography and reversed-phase liquid chromatography on alkyl-bonded microparticulate silica are applicable to a wider range of analytes and are generally faster and more efficient and consume less reagents. Supercritical fluid extraction should prove useful in this regard. A brief overview of methods developed for isolating trace levels of environmental contaminants from lipids is presented.     

Amperometric determination of glucose in undiluted food samples

Glucose oxidase is immobilized onto a cellulose acetate membrane by glutaraldehyde linkage, and the membrane is used to cover the platinum electrode of a hydrogen peroxide sensor. A silanized polycarbonate membrane then covers the enzyme layer, and extends the linear calibration range to higher concentrations. The sensor, when incorporated into a flow-injection system, allows the determination of glucose at levels up to 1 M in soft drinks at a rate of 60 samples h^?1 without sample dilution.     

气质联用法测定含蛋白食品中的甜蜜素

建立了一种用于检测含蛋白食品中甜蜜素的方法.用三氯乙酸对样品进行蛋白变性,次氯酸钠作衍生剂将甜蜜素定量转化为N,N-二氯环己胺,正己烷萃取与基体分离后由气相色谱-质谱联用技术进行测定.在2～50 μg/mL范围内方法的线性良好,5,10和25mg/kg等3个添加水平下,回收率稳定在75.0%～100.0%之间,RSD≤12.1%,灵敏度高,检出限为1.0 mg/kg.     

Lead hydride generation in a lactic acid-potassium dichromate medium and its application to the determination of lead in fish,vegetable and drink samples

The effect of different acids on the efficiency of lead hydride generation in potassium dichromate oxidant medium was investigated and lactic acid-potassium dichromate was found to give optimum lead hydride generation. Various parameters affecting sensitivity and the influence of interfering ions were studied. The sensitivity of the method (0.44 ng) is greater than published values for ammonium peroxodisulphate-nitric acid (20.0 hg) and hydrogen peroxide-nitric acid (10.0 ng). This could be because lactic acid stabilizes the Pb(IV) metastable compounds more effectively, acting as intermediate species in lead hydride formation. The method was applied to the determination of lead in liquids (tap water and wine) and fish and vegetable samples. The liquids were analysed directly without preconcentration or mineralization and the solids after wet digestion or slurry formation; these two sample preparation methods gave similar results.     

Mechanism of electrochemical reduction of oxamide analytical applications

Oxamide is electrochemically reduced at mercury electrodes between pH 5.6 and 11.6. The overall mechanism proceeds by an initial 2e reduction of the 1,2-carbonyl groups of oxamide to give a dianion. This then protonates, rearranges, and loses ammonia to glyoxylamide, which is reduced in a further 2e/2H⁺ reaction giving glycolamide as the ultimate product. The reaction thus proceeds by a typical e.c.e. mechanism. The overall homogeneous rate contant for the chemical reaction(s) interposed between the two charge-transfer steps was measured by peak voltammetric, potentiostatic and d.c. polarographic methods. The d.c. polarographic wave of oxamide between pH 5.6 and 11 provides the basis for a very simple analytical method for the determination of oxamide.     

Determination of lithium in biological samples by inductively coupled plasma mass spectrometry

Lithium was determined in human serum by inductively coupled plasma mass spectrometry. Sample preparation was kept to the minimum: serum samples were diluted and beryllium was added as internal standard. Special attention was given to the choice of the internal standard and to the occurrence of memory effects. To test the accuracy of the method several biological reference materials were analysed, namely a “Second-Generation” Biological Reference Material (Freeze-Dried Human Serum) (University of Ghent), Human Serum SRM 909, Whole Egg Powder SRM 1845 and Mixed Human Diet SRM 1548 (National Institute of Standards and Technology). The results were compared with those obtained by other techniques. For the “second-generation” reference freeze-dried human serum a mean lithium concentration of 15.10 ng g^?1 with a standard deviation of 0.54 ng g^?1 dry weight was found. Analyses on serum samples from healthy individuals yielded lithium concentrations ranging from 0.22 to 0.97 μg l^?1.