Slurry-electrothermal atomic absorption spectrometric determination of aluminium and chromium in vegetables using hydrogen peroxide as a matrix modifier

Fast heating programmes for determining aluminium and chromium in vegetables using electrothermal atomic absorption spectrometry with slurry sampling are developed using wall atomization. The build-up of carbonaceous residues inside the atomizer is avoided by adding 4% hydrogen peroxide and 1% nitric acid to the slurries instead of using an air-ashing stage. In accordance with fast-programme methodology, the conventional drying and charring steps are replaced by a modified drying stage. simplifying the heating programmes. For suspensions containing 0.1% m/V of ground vegetables, the relative standard deviation (RSD) is about +/-5% for aluminium. For chromium determination, the use of 0.5-1% m/V suspensions leads to RSDs close to +/-4%. Calibration is carried out using aqueous standards. The aluminium and chromium contents of a number of vegetable samples obtained by using the slurry approach agree with those obtained by means of a conventional procedure based on the total dissolution of the samples. The reliability of the procedures is also confirmed by analysing two certified reference materials.     

Fast determination of phosphorus in honey,milk and infant formulas by electrothermal atomic absorption spectrometry using a slurry sampling procedure

A procedure for the electrothermal atomic absorption spectrometric determination of phosphorus in honey, milk and infant formulas using slurried samples is described. Suspensions prepared in a medium containing 50% v/v concentrated hydrogen peroxide, 1% v/v concentrated nitric acid, 10% m/v glucose, 5% m/v sucrose and 100 mg l^− 1 of potassium were introduced directly into the furnace. For the honey samples, multiple injection of the sample was necessary. The modifier selected was a mixture of 20 μg palladium and 5 μg magnesium nitrate, which was injected after the sample and before proceeding with the drying and calcination steps. Calibration was performed using aqueous standards prepared in the same suspension medium and the graph was linear between 5 and 80 mg l^− 1 of phosphorus. The reliability of the procedure was checked by comparing the results obtained by the new developed method with those found when using a reference spectrophotometric method after a mineralization step, and by analyzing several certified reference materials.     

Enzymatic determination of choline in milk using a FIA system with potentiometric detection

The development of a FIA system for the determination of total choline content in several types of milk is described. The samples were submitted to hydrochloric acid digestion before injection into the system and passed through an enzymatic reactor containing choline oxidase immobilised on glass beads. This enzymatic reaction releases hydrogen peroxide which then reacts with a solution of iodide. The decrease in the concentration of iodide ion is quantified using an iodide ion selective tubular electrode based on a homogeneous crystalline membrane. Validation of the results obtained with this system was performed by comparison with results from a method described in the literature and applied to the determination of total choline in milks. The relative deviation was always < 5%. The repeatability of the method developed was assessed by calculation of the relative standard deviation (RSD) for 12 consecutive injections of one sample. The RSD obtained was < 0.6%.     

Rapid determination of lead and cadmium in biological fluids by electrothermal atomic absorption spectrometry using Zeeman correction

Procedures for the electrothermal atomic absorption spectrometric determination of lead and cadmium in urine, serum and blood are developed. For serum and blood, the samples are diluted by incorporating 0.015% (w/v) Triton X-100 and 0.1% (w/v) ammonium dihydrogenphosphate to the solutions, which are then introduced directly into the furnace. A solution containing 15% (w/v) hydrogen peroxide and 0.65% (w/v) nitric acid is also introduced into the atomizer by means of a separate injection. Zeeman-based correction is recommended. Both conventional and fast-heating programs are discussed. Calibration is carried out using the standard additions method. The reliability of the procedures is checked by analyzing three certified reference materials and by recovery studies.     

Determination of arsenic in biological fluids by electrothermal atomic absorption spectrometry

A procedure for the determination of the total content of arsenic in urine, serum and blood by electrothermal atomic absorption spectrometry (ETAAS) is described. Zeeman correction is used to compensate the high background signals. The samples are diluted (1 + 1 for urine and 1 + 3 for both serum and blood samples) in a medium containing 0.1% w/v Triton X-100 before being introduced directly into the furnace. A solution containing 15% w/v hydrogen peroxide, 0.65% w/v nitric acid and 0.5% w/v nickel is also introduced into the atomizer by means of a separate injection. Calibration is carried out against aqueous standards for blood and serum samples and using the standard additions method for urine samples. The detection limit is 20 pg (2 ng ml-1). The reliability of the procedure is checked by analyzing three certified reference materials and by recovery studies.     

Fast determination of lead and copper in dairy products by graphite furnace atomic absorption spectrometry

A rapid and direct procedure for determining lead and copper in dairy products by electrothermal atomic absorption spectrometry (ETAAS) is described. Samples are slurried in a medium containing 50% v/v hydrogen peroxide, 1% v/v nitric acid, 0.5% w/v dihydrogen phosphate, and 20% v/v ethanol and directly injected into the furnace with no previous mineralization. Calibration is performed with aqueous standards. Limits of determination were 0.4 and 2.4 ng/mL for copper and lead, respectively. The reliability of the procedure was checked by comparison with the acid mineralization procedure and by analyzing 3 certified reference milk samples.     

MPT-AES测定奶粉中的Ca和Fe

用微波等离子体(MPT)为激发光源,氩气为等离子体工作气体,用气动雾化进样,采用标准曲线法研究了微波等离子体炬原子发射光谱法(MPT-AES)测定奶粉中Ca、Fe的方法。详细考察了溶液中HCl浓度、HNO3浓度、微波前向功率、载气流量、工作气流量等实验参数对测定的影响,同时考察了共存元素钠、镁、锌对钙和铁发射强度的影响。     

Determination of aluminium and chromium in slurried baby food samples by electrothermal atomic absorption spectrometry

Electrothermal atomic absorption spectrometry was used to determine aluminium and chromium in different types of baby foods. Samples without previous treatment were introduced into the atomizer as suspensions, which were prepared in a medium containing 0.1% (w/v) Triton X-100 (for chromium) or 10% (v/v) ethanol (for aluminium), 5% (v/v) concentrated hydrogen peroxide, and 0.5% (v/v) concentrated nitric acid. The slurries were homogenized with a potter and introduced directly into the furnace. The presence of nitric acid allowed a substantial amount of analyte to be extracted to the liquid phase. No matrix effect was observed and aqueous standard solutions were used for calibration. The detection limits were 4 and 50 pg for chromium and aluminium, respectively; characteristic masses were 3.8 pg for chromium and 18 pg for aluminium. Reliability of the procedures was checked by statistically comparing the results with those obtained with a previous microwave oven mineralization stage and by analyis of several certified reference materials. Values for the aluminium content ranged between 0.4 and 3.0 microg/g, and for chromium between 0.003 and 0.06 microg/g.     

Microwave heated vapor-phase digestion method for biological sample materials

A microwave heated, vapor-phase nitric acid-hydrogen peroxide digestion method for pulverized, biological sample materials was developed. Sample masses up to 200 mg were digested using calibrated quartz inserts inside first generation type, low-pressure, Teflon-PFA microwave vessels. In the first step, samples were digested in the vapor-phase for 80 min using a progressive heating pattern. Three mL of 70% nitric acid and 0.5 mL of 30% hydrogen peroxide were used as digestion reagents. In the second step, the small residue left after first step digestion was dissolved in 1.4% nitric acid or additionally with 0.5% hydrofluoric acid by heating for 15 min. The digestion method was optimized using pike (Esox lucius) muscle as a test material. The method was further optimized using three certified reference materials. Ca, Cu, Fe, Mg and Zn were determined from NIST-SRM 1577a bovine liver by ICP-AES. Cr and Ni were determined from NIST-SRM 8433 corn bran and NRCC DOLT-2 dogfish liver by GFAAS. For all elements the values obtained were close or within certified limits. Spike recoveries were between 96 to 107%. Digestion efficiency ranged from 91 to 99%.     

Microwave heated vapor-phase digestion method for biological sample materials

A microwave heated, vapor-phase nitric acid-hydrogen peroxide digestion method for pulverized, biological sample materials was developed. Sample masses up to 200 mg were digested using calibrated quartz inserts inside first generation type, low-pressure, Teflon-PFA microwave vessels. In the first step, samples were digested in the vapor-phase for 80 min using a progressive heating pattern. Three mL of 70% nitric acid and 0.5 mL of 30% hydrogen peroxide were used as digestion reagents. In the second step, the small residue left after first step digestion was dissolved in 1.4% nitric acid or additionally with 0.5% hydrofluoric acid by heating for 15 min. The digestion method was optimized using pike (Esox lucius) muscle as a test material. The method was further optimized using three certified reference materials. Ca, Cu, Fe, Mg and ¶Zn were determined from NIST-SRM 1577a bovine liver by ICP-AES. Cr and Ni were determined from NIST-SRM 8433 corn bran and NRCC DOLT-2 dogfish liver by GFAAS. For all elements the values obtained were close or within certified limits. Spike recoveries were between 96 to 107%. Digestion efficiency ranged from 91 to 99%.     

Determination of Mineral Elements in Milk Products by Inductively Coupled Plasma-Optical Emission Spectrometry

The determination of mineral elements in milk products is of great importance since their excess or deficiency may affect human health. In this study, calcium, magnesium, potassium, sodium, phosphorus, and iron were determined in milk products from South Korea. The samples were wet-digested by microwave-assisted combustion using nitric acid and hydrogen peroxide, and analyzed by inductively coupled plasma-optical emission spectrometry. The method was validated by sensitivity, linearity, precision, recovery checks, and the analysis of a milk powder certified reference material. The elemental concentrations were similar in the milk products. Calcium and potassium were the most abundant, followed by phosphorus, sodium, magnesium, and iron. All concentrations were comparable to previous values and were within the limits of recommended dietary allowances and tolerable upper levels.     

Evaluation of oxidant media for the determination of lead in food slurries by hydride generation atomic absorption spectrometry

Several oxidant media were evaluated for the generation of lead hydride from slurry samples and their application to the determination of lead in vegetables and fish by hydride generation atomic absorption spectrometry. Three oxidant - acid media were compared: hydrogen peroxide - nitric acid, ammonium persulphate - nitric acid and potassium dichromate - lactic acid. The powdered samples were suspended in Triton X-100 and shaken with 10.0 g of blown zirconia spheres until a slurry was formed. The potassium dichromate - lactic acid medium was the most satisfactory for the determination of lead in fish and vegetables, providing the lowest detection limits as a result of its high sensitivity and low blank values. The ammonium persulphate - nitric acid medium gave good accuracy, precision and selectivity for vegetables (1-2 p.p.m. of lead); however, with fish (0.1-1 p.p.m. of lead) it was only a semi-quantitative medium for the determination of lead owing to its lack of sensitivity and selectivity. The hydrogen peroxide - nitric acid medium was unsatisfactory for the generation of lead hydride from slurry samples because of decomposition of hydrogen peroxide by the organic matter in the sample.     

Determination of lead in vinegar by ICP-MS and GFAAS: evaluation of different sample preparation procedures

Lead concentrations of 59 different types of vinegars (15-307 μg l⁻¹ in balsamic vinegars and 36-50 μg l⁻¹ in wine vinegars) were determined using both inductively coupled plasma mass spectrometry (ICP-MS) and graphite furnace atomic absorption spectrometry (GFAAS). Although the precision of direct analyses, following simple aqueous dilutions, with either instrumental method was poor; that precision, following nitric acid and/or hydrogen peroxide digestions, markedly improved with either instrument and the values obtained with the two instruments were in good agreement. The efficacy of different digestions, including (1) nitric acid using a heating block, with or without addition of hydrogen peroxide and (2) mixtures of nitric acid and hydrogen peroxide using ultraviolet (UV) photolysis, were then assessed. The latter procedure was found to be much faster and more efficient, but it was limited by the relatively high levels of contaminant lead in hydrogen peroxide. Consequently, it is recommended that lead concentrations in vinegar be measured following a nitric acid digestion and UV photolysis to oxidize all organic matter before ICP-MS or GFAAS analysis; and it is further recommend that the thermal settings for the latter analyses be adjusted to account for the apparent presence of relatively volatile organolead compounds in vinegar digests.     

Determination of 90 Sr in milk by solvent extraction of 90Y (author's transl)

In order to replace the conventional method using violent fuming nitric acid, a new method for the determination of 90 Sr in milk has been developed by using the solvent extraction with bis (2-ethylhexyl) phosphoric acid (HDEHP). The daughter nuclide 90Y in a radiochemical equilibrium with its parent 90Sr was extracted with 2:1 HDEHP-toluene from the acid solution (1M HCL) of milk ash sample prepared by dry-ashing. After stripping with 8M HCL, 90Y, together with stable yttrium added as carrier, was precipated as oxalate to prepare beta-counting source. The radiochemical purity was confirmed by decay curve. The decontamination of strontium was checked by applying non-dispersive fluorescence X-ray analysis using 133Ba as irradiating source. Bone samples of cow were also analyzed by the same method and the results were compared with those obtained by other methods. The duplicate crosschecking analyses of finely ground bone samples were carried out to examine the effectiveness of this method. This simple new method was found to be very effective for the routine analysis of 90Sr in these samples.     

In-line determination of metabolites and milk components with electrochemical biosensors

Electrochemical biosensors for lactate, pyruvate and β-hydroxybutyrate based on oxygen, hydrogen peroxide, and NADH sensors coupled with oxidase and dehydrogenase enzymes were developed and used in conjunction with an artificial pancreas in experiments with extracorporeal circulation. Such procedures allow the fate of these species involved in glucose metabolism to be clarified during insulin treatment of diabetic patients. Studies with a glucose oxidase electrode for in-line determination of glucose produced by hydrolysis of cellobiose in a bioreactor are reported; for the determination of glucose in the presence of high concentrations of cellobiose, the purity of glucose oxidase is important in obtaining linear calibration plots. Impurities like amylase, maltase, invertase, and galactose oxidase, which are usually present in commercial preparations of glucose oxidase, must be absent. Another application is the amperometric determination of lactose, lactate and glucose in milk samples by using a hydrogen peroxide sensor coupled with β-galactosidase, lactate oxidase and glucose oxidase. The procedures outlined are simple and the short response times enable milk to be monitored during processing.     

酸水解-气相色谱法测定奶粉中的二十二碳六烯酸

建立了盐酸水解,索氏提取总脂肪酸,氢氧化钾甲醇溶液甲酯化,硫酸氢钠处理,气相色谱测定奶粉中二十二碳六烯酸(DHA)含量的方法。采用三因素三水平正交试验对氢氧化钾甲醇溶液甲酯化条件进行了优化,得到最优反应条件为:1 mol/L氢氧化钾在25 ℃反应5 min。甲酯化衍生液经硫酸氢钠处理,在SP-2560气相色谱柱(100 m×0.25 mm×0.20 μ m)上进行55 min程序升温测定DHA含量。DHA在5.0~300 mg/L范围内呈良好线性,相关系数为0.9999。DHA质量浓度为10、50、100 mg/L时目标峰峰面积的相对标准偏差(RSD)分别为3.4%、1.2%和1.1%。方法检出限为2 mg/kg,回收率为90.4%~93.5%。该法用于实际样品的检测,结果令人满意。     

Decomposition of vegetables for determination of Zn,Cd, Pb and Cu by stripping voltammetry

A simple and accurate digestion method using nitric acid, perchloric acid and hydrogen peroxide has been developed for use in trace analysis for heavy metals in vegetables by differential pulse anodic stripping voltammetry. The recovery of the metals from the samples is lower if the hydrogen peroxide is omitted from the digestion mixture. Standard reference materials have been analysed satisfactorily by this method.     

Quantification of total chromium and hexavalent chromium in UHT milk by ETAAS

Procedures for the quantification of total chromium and hexavalent chromium in UHT milk samples are presented. Total chromium was determined directly in milk with the addition of a surfactant and a mixture of Pd and Mg as a chemical modifier. For the selective separation of hexavalent chromium, the sample pre-treatment consisted in precipitation of proteins and elution of the supernatant through a Chromabond NH2 column. The metal was eluted with nitric acid. Both total chromium and hexavalent chromium were evaluated by atomic absorption spectrometry with electrothermal atomization using the same instrumental conditions. The detection limits were 0.2 and 0.15 microgram l-1 for total chromium and hexavalent chromium, respectively. The linearity ranges under the optimized conditions were 0.2-20 and 0.15-50 micrograms l-1. For total chromium the precision was 4.9 and 5.7% for the analytical and the over-all procedure, respectively, and for hexavalent chromium 4.3 and 4.9%, respectively. The validation of both procedures was performed by the standard additions method and the recoveries were higher than 93% in all cases. For total chromium, a certified reference material was also used to validate the methodology. The methods were applied to the determination of total chromium and hexavalent chromium in 60 UHT milk samples.     

微波消解-火焰原子吸收光谱法测定玉米面中的铜、锌和铁

实验采用微波消解系统消解玉米面样品,将样品置于密闭容器内,加入一定量的硝酸和过氧化氢,放在微波炉内进行消解。详细考察了微波消解溶剂、消解时间、消解功率和消解压力对消解效果的影响,采用正交实验设计确定了微波消解的最佳工作参数。用火焰原子吸收光谱法测定玉米面中铜、锌和铁的含量,其相对标准偏差分别为1．99％、0．92％和2．10％（n=6）,平均加标回收率分别为97．5％、102．9％和98．7％。与常压消解法的测定结果进行比较,测定值吻合,准确度和精密度均优于传统方法。     

Rapid determination of lead and cadmium in sewage sludge samples using electrothermal atomic absorption spectrometry with slurry sample introduction

Lead and cadmium concentrations in sewage sludge samples are determined by suspending the ground samples in a solution containing 10% (v/v) concentrated hydrofluoric acid, 1% (v/v) concentrated nitric acid, 0.5% (m/v) dihydrogen ammonium phosphate and 0.1% (m/v) sodium hexametaphosphate. Aliquots of 20 microL of these suspensions (4 mg/mL) are diluted to 1000 microL with the same solution and then injected into the electrothermal atomizer. The drying stage is performed by programming a 400 degrees C temperature, a ramp time of 20 s and a hold time of 15 s on the power supply of the atomizer. No ashing step is used. Platform atomization is carried out at 1600 and 1800 degrees C for Pb and Cd, respectively. Calibration is performed using aqueous standards in the 5-75 and 0.2-5 microg/L Pb and Cd ranges, respectively. Results obtained for three certified reference materials and four samples demonstrate the reliability of the procedures described.