Influence of citric acid as chemical modifier for lead determination in dietary calcium supplement samples by graphite furnace atomic absorption spectrometry

Citric acid was used as a chemical modifier for Pb determination by graphite furnace atomic absorption spectrometry in dietary supplement samples (calcium carbonate, dolomite and oyster shell samples) and its efficiency was compared to the use of palladium. Pyrolysis and atomization curves were established without use of chemical modifier, with the addition of 20, 100 and 200 μg of citric acid, and with 3 μg of palladium. The citric acid modifier made possible the interference-free Pb determination in the presence of high concentrations of Ca and Mg nitrates. Acid sample digestion involving closed vessels (microwave-assisted and conventional heating) and acid attack using polypropylene vessels at room temperature were compared. All digestion procedures presented similar results for calcium carbonate and dolomite samples. However, for oyster shell samples accurate results were obtained only with the use of closed vessel systems. Analyte addition and matrix-matched standards were used for calibration. The characteristic mass for Pb using citric acid and palladium were 16 and 25 pg, respectively. The relative standard deviation (RSD) was always less than 5% when citric acid was used. The relative and absolute limits of detection were 0.02 μg g^− 1 and 8 pg with citric acid and 0.1 μg g^− 1 and 44 pg with the Pd modifier, respectively (n = 10, 3σ). The recovery of Pb in spiked calcium supplement samples (10 μg l^− 1) was between 98% and 105%. With the use of 100 μg of citric acid as chemical modifier, problems such as high background absorption and high RSD values were minimized in comparison to the addition of 3 μg of palladium.     

EDTA滴定法测定萤石中氟化钙含量的方法改进

建立了EDTA滴定法测定矿石中氟化钙的方法。引入了钙乙酸为溶解试样的溶剂,溶解样品中的碳酸钙,同时,通过同离子效应减少氟化钙的溶解度。实验中探究了钙离子的浓度与氟化钙溶解度的关系,通过对比实验确定选择了含钙乙酸的最佳浓度(10g/L)。同时,对实验中的其他条件也进行了相应的探究与优化,确定最佳实验条件为:最小称样量为0.5g,洗涤沉淀用水量为50mL左右,第二次过滤时的洗涤次数为8～10次,滴定时加入氢氧化钾的量为20mL。方法的精密度(0.10%)和准确度(0.08%)皆能满足实验要求。     

EDTA滴定法测定萤石中氟化钙含量的方法改进

建立了EDTA滴定法测定矿石中氟化钙的方法。引入了钙乙酸为溶解试样的溶剂,溶解样品中的碳酸钙,同时,通过同离子效应减少氟化钙的溶解度。实验中探究了钙离子的浓度与氟化钙溶解度的关系,通过对比实验确定选择了含钙乙酸的最佳浓度(10g/L)。同时,对实验中的其他条件也进行了相应的探究与优化,确定最佳实验条件为:最小称样量为0.5g,洗涤沉淀用水量为50mL左右,第二次过滤时的洗涤次数为8～10次,滴定时加入氢氧化钾的量为20mL。方法的精密度(0.10%)和准确度(0.08%)皆能满足实验要求。     

Direct determination of silicon in powdered aluminium oxide by use of slurry sampling with in situ fusion graphite-furnace atomic-absorption spectrometry

A direct method for determination of silicon in powdered high-purity aluminium oxide samples, by slurry sampling with in situ fusion graphite-furnace atomic-absorption spectrometry (GF-AAS), has been established. A slurry sample was prepared by 10-min ultrasonication of a powdered sample in an aqueous solution containing both sodium carbonate and boric acid as a mixed flux. An appropriate portion of the slurry was introduced into a pyrolytic graphite furnace equipped with a platform. Silicon compounds to be determined and aluminium oxide were fused by the in situ fusion process with the flux in the furnace under optimized heating conditions, and the silicon absorbance was then measured directly. The calibration curve was prepared by use of a silicon standard solution containing the same concentration of the flux as the slurry sample. The accuracy of the proposed method was confirmed by analysis of certified reference materials. The proposed method gave statistically accurate values at the 95% confidence level. The detection limit was 3.3 μg g^–1 in solid samples, when 300 mg/20 mL slurry was prepared and a 10 μL portion of the slurry was measured. The precision of the determination (RSD for more than four separate determinations) was 14% and 2%, respectively, for levels of 10 and 100 μg g^–1 silicon in aluminium oxide.     

Evaluation of pulsed radiofrequency glow discharge time-of-flight mass spectrometry for precious metal determination in lead fire assay buttons

In this paper, an exploration of the capabilities and limitations of pulsed radiofrequency glow discharge time-of-flight mass spectrometry (GD-TOFMS) for the determination of the precious metals Ag, Au, Pd, Pt and Rh in lead buttons obtained by Pb fire assay is reported on. Since the matrix consists almost entirely of lead (>99%), the occurrence of doubly charged Pb (Pb²⁺) ions can hinder accurate determination of Rh. This problem was counteracted by relying on the time-resolved formation of different ion types over the pulse period of the glow discharge, which allows discrimination against the Pb²⁺ ions. The formation of ArCu⁺ ions as a result of the use of a copper anode was assessed to pose no threat to the accuracy of the results obtained for the set of samples analyzed as its contribution to the total signal at m/z = 103 could be adequately corrected for. The method developed was evaluated in terms of accuracy and precision using a set of Pb button standards with analyte concentrations between 5 and 100 μg g⁻¹. For the purpose of validation, a 10 μg g⁻¹ standard was considered as a sample. Overall, an acceptable accuracy was obtained with a bias of <5% between the experimental results and the corresponding reference values, except for Au, for which a larger deviation occurred. Precision values (repeatability) of typically <5% relative standard deviation (RSD) (for N = 3) were obtained and the limits of detection (LODs) vary from ∼0.020 μg g⁻¹ for Ag to ∼0.080 μg g⁻¹ for Pt.     

A direct method for the determination of carbonate and non-carbonate carbon in geological materials by infrared spectrometry

A simple and direct infrared method for determining carbonate and non-carbonate carbon in geological samples is described. To determine carbonate carbon, hydrochloric acid is added directly to the heated samples; non-carbonate carbon is determined by combustion after digesting the samples with hydrochloric acid. The limit of detection is 2 ppm for carbonate carbon and 10 ppm for non-carbonate carbon; the relative standard deviations are 4% or less for 100–1000 μg of carbonate and non-carbonate carbon. The method has been applied to standard rocks, NBS minerals and geological exploration reference samples.     

Use of paper capsules for cadmium determination in biological samples by solid sampling flame atomic absorption spectrometry

In this study, a new device was applied for direct solid sampling flame atomic absorption spectrometry. It was used for trace determination of cadmium in biological samples (bovine and chicken liver). Test samples (0.5 to 7 mg) were weighed into small paper capsules, which were introduced into a quartz cell heated by an air-acetylene flame. Operational conditions for the proposed system were evaluated. There was no significant difference between the results obtained with the proposed system and those obtained after digestion and determination by conventional graphite furnace atomic absorption spectrometry. Good agreement was also obtained with the certified values of two reference materials. Background signals were always low. The characteristic mass was 0.34 ng and relative standard deviation was less than 8%. The limit of detection for the proposed procedure was 1.6 ng or 0.23 μg g^− 1 if a sample mass of 7 mg was used. Excluding the steps for sample preparation (drying, milling and weighing), the proposed system allows the determination of 40 test samples per hour and it can be easily adapted to conventional flame atomic absorption spectrometers.     

石墨炉原子吸收分光光度法测定空气中的铍

对300余个样品进行监测,选择灵敏度高的石墨管和最佳基体,提高灰化、原子化的温度,确立了石墨炉原子吸收法测定空气中铍含量的实验条件。样品采用干灰化消解法,最佳溶剂为质量分数l％的硝酸溶液,利用仪器内置的样品浓度计算程序,绘制工作曲线直接获得样品中铍的含量。方法检出限为0．021μg／L,测定结果的相对标准偏差小于2％（n=6）,线性范围为0～6．5μg／L,加标回收率为91．6％～107％。     

Direct detection of acetaminophen in urine by liquid chromatography with electrochemical detection using dual electrodes. Preliminary application to a single-dose pharmacokinetic study

A method for the direct determination of acetaminophen in urine based on liquid chromatography with series dual-electrode detection has been developed. No sample pretreatment steps are required except for filtration. The method gives a linear range from 0.5 to 300 μg ml^?1 and a detection limit of 0.2 μg ml^?1 (10 μl). The analysis time of the assay is less than 7 min. The pharmacokinetics of acetaminophen in urine from a subject who had orally ingested 450 mg (table form) of the drug were studied and various pharmacokinetic parameters were determined.     

Development of a generic assay for the determination of total trihydroxybenzoate derivatives based on gold-luminol chemiluminescence

A selective assay for the determination of one of the most important class of phenolic compounds, namely trihydroxybenzoates (monomeric and polymeric compounds having at least one gallate moiety) based on their enhancing effect on the chemiluminogenic reaction between gold ions and luminol is described for the first time. In the presence of trihydroxybenzoate derivatives, the light emission generated when alkaline luminol is oxidized by gold ions is amplified several orders of magnitude compared to other common phenolic compounds which exhibit minor reactivity or no reactivity at all (e.g. hydroxycinnamates, flavonols, benzenediols). Based on this property, the experimental conditions were optimized in order to enable the determination of total trihydroxybenzoates in complex mixtures without resorting to separation techniques. The method was applied to samples of different composition (teas, herbal infusions and wines) with satisfactory analytical features yielding detection limits at the 10⁻⁷ mol L⁻¹ level, intra-day precision of 3.1%, inter-day precision less than 10% and recoveries between 88.7 and 97.6%. The strengths and weaknesses of the method were identified and discussed in relation to its application in real samples.     

磁性碳包铁纳米粒子在重金属元素检测分离富集中的应用

以氩电弧等离子体法制备的碳包铁纳米粒子为固相萃取材料,采用等离子体原子发射光谱法(ICP-AES)系统研究了该材料对Cr、Ni、Cd、Pb离子的吸附性能,并确定了最佳吸附和洗脱条件。实验结果表明:当pH值为8.0～9.0时,分析物均可被碳包铁纳米粒子定量吸附;采用酸性溶液(pH=1.0～2.0)可将吸附在碳包铁纳米粒子上的金属离子完全脱附。该法对Cr、Ni、Cd、Pb的检出限分别为3.6、4.1、1.1、9.8μg/L,Cr、Ni、Cd的线性范围为1～500μg.L-1,Pb的线性范围为10～1 000μg.L-1,线性相关系数均大于0.999。方法用于自来水中Cr、Ni、Cd、Pb离子的测定,回收率可达到93%～105%;碳包铁纳米粒子对Cr、Ni、Cd、Pb离子的吸附量分别为3.6、4.8、6.3、2.1 mg/g。     

气相色谱-质谱法同时测定透皮接收液中的丙胺卡因和利多卡因

建立了同时测定体外透皮接收液中丙胺卡因和利多卡因的气相色谱-质谱(GC-MS)分析方法。以罗哌卡因为内标,样品经氢氧化钠碱化、乙酸乙酯萃取后采用GC-MS分析,采用选择离子监测(SIM)模式进行定量分析。丙胺卡因和利多卡因两种药物均在0.016～50.0 mg/L范围内呈良好的线性关系;回收率为85.3%～109.7%,日内和日间测定的相对标准偏差均小于10%;检出限分别为3 μg/L和2 μg/L。该方法操作简便,选择性好,灵敏度高,适用于局部麻醉药物快速透皮吸收研究中丙胺卡因和利多卡因含量的分析。     

Studying pellet formation of a filamentous fungus Rhizopus oryzae to enhance organic acid production

Using pelletized fungal biomass can effectively improve the fermentation performance for most of fugal strains. This article studied the effects of inoculum and medium compositions such as potato dextrose broth (PDB) as carbon source, soybean peptone, calcium carbonate, and metal ions on pellet formation of Rhizopus oryzae. It has been found that metal ions had significantly negative effects on pellet formation whereas soybean peptone had positive effects. In addition PDB and calcium carbonate were beneficial to R. oryzae for growing small smooth pellets during the culture. The study also demonstrated that an inoculum size of less than 1.5x10(9) spores/L had no significant influence on pellet formation. Thus, a new approach to form pellets has been developed using only PDB, soybean peptone, and calcium carbonate. Meanwhile, palletized fungal fermentation significantly enhanced organic acid production. Lactic acid concentration reached 65.0 g/L in 30 h using pelletized R. oryzae NRRL 395, and fumeric acid concentration reached 31.0 g/L in 96 h using pelletized R. oryzae ATCC 20344.     

Determination of impurities in micro-amounts of silver alloys by electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS) after in-situ-digestion in the graphite furnace

Forgeries of antique silver objects can be identified by their fingerprints of impurities. The dissolution of the samples causes severe problems since Au and Ag have to be dissolved simultaneously. In order to overcome that difficulty and to minimize the amount of sample, an ETV-ICP-MS method is presented based on solid sampling and an in-situ-digestion with nitric acid in a graphite tube. Determinations of Au, Bi, Cd, Pb, Sb, Sn and Zn were performed in a range of 10 μg/g–1% and with an accuracy of 10%–50%. Less than 1 mg sample material is required.     

电感耦合等离子体质谱法同时测定地质样品中镉、锗、钴

建立电感耦合等离子体质谱法同时测定地质样品中镉、锗、钴含量的分析方法。样品用氢氟酸-硝酸混合溶液加热溶解,然后加热浓缩驱酸,再用硝酸溶液(1+1)复溶提取,在选定的仪器工作条件下进行测定。镉、锗、钴的含量分别在0.00~0.10,0.00~5.00,0.00~50.00 μg/g范围内与质谱峰强度呈良好的线性关系,相关系数均大于0.999,方法检出限分别为0.01,0.02,0.02 μg/g。用该方法对国家一级标准物质进行测定,测定值的相对误差均小于10%,测定结果的相对标准偏差为0.79%~8.45%(n=12)。该方法样品处理过程简便,检测效率高,适用于批量地质样品中镉、锗、钴的测定。     

Application of NaClO-treated multiwalled carbon nanotubes as solid phase extraction sorbents for preconcentration of trace 2,4-dichlorophenoxyacetic acid in aqueous samples

Multiwalled carbon nanotubes functionalized by oxidation of original multiwalled carbon nanotubes with NaClO were prepared and their application as solid phase extraction sorbent for 2,4-dichlorophenoxyacetic acid (2,4-D) was investigated systemically, and a new method was developed for the determination of trace 2,4-D in water samples based on extraction and preconcentration of 2,4-D with solid phase extraction columns packed with NaClO-treated multiwalled carbon nanotubes prior to its determination by HPLC. The optimum experimental parameters for preconcentration of 2,4-D, including the column activating conditions, the amount of the sorbent, pH of the sample, elution composition, and elution volume, were investigated. The results indicated 2,4-D could be quantitatively retained by 100 mg NaClO-treated multiwalled carbon nanotubes at pH 5, and then eluted completely with 10 mL 3:1 (v/v) methanol-ammonium acetate solution (0.3 mol/L). The detection limit of this method for 2,4-D was 0.15 μg/L, and the relative standard deviation was 2.3% for fortified tap water samples and 2.5% for fortified riverine water sample at the 10 μg/L level. The method was validated using fortified tap water and riverine water samples with known amount of 2,4-D at the 0.4, 10, and 30 μg/L levels, respectively.     

Synergy of glutathione, dithiothreitol and N-acetyl-L-cysteine self-assembled monolayers for electrochemical assay: sensitive determination of arsenic(III) in environmental and drinking water

A simple and efficient electrochemical assay based on self-assembled monolayers (SAMs) was developed for the highly sensitive determination of arsenic(III) in water samples. The synergy of glutathione (GSH), dithiothreitol (DTT) and N-acetyl-L-cysteine (NAC) mixed SAMs enhanced the detection specificity and sensitivity of As(III) in water samples, resulting from the immobilization of a large number of As(III) moieties on the gold electrode surface via As-O and As-S linkages. After accumulating As(III), anodic stripping voltammetry (ASV) was performed, and linear sweep voltammetry (LSV) was employed for signal recording. Several main voltammetric parameters were optimized as follows: supporting electrolyte, 1 mol L(-1) HCl; deposition potential, -0.35 V; deposition time, 150 s. A good linear relationship (R = 0.9980) was attained between the concentration of the As(III) standard and peak current, in the range of 3-100 μg L(-1). The limit of detection (LOD) of this sensing system was determined to be 0.5 μg L(-1) at a signal-to-noise ratio of 3. A variety of common coexistent ions in water samples were examined, showing no obvious interferences on the As(III) determination. The amenability of this method to the analyses of water samples was also investigated. High recovery of 90.5% with the precision of 5.1% at spiked 10 μg L(-1), and low LOD of 0.3 μg L(-1) were obtained in seawater. The synergy effect of GSH, DTT and NAC provided the possibility for the rapid and sensitive LSV determination of As(III) in complicated water samples.     

Studies of skeletal cadmium assay and toxicity

Flameless Atomic Absorption Spectrophotometry was found to be a sensitive (2·10^–12 g detection limit), accurate but destructive method for cadmium assay in bone biopsy samples (about 30 mg dry weight). The inductively coupled plasma emission technique was poorer in sensitivity (1.2·10^–9 g) and is also a destructive method. Activation Analysis is still less sensitive (2·10^–8 g detection limit) but a nondestructive one. Cadmium was found to accumulate in bone of rats fed, for 5 weeks, 0, 50, and 100 mg Cd/l in drinking water and the bone concentrations were 0.16, 1.09, and 2.6 mg Cd/kg bone (dry wt). Histological examination of the bones showed that cadmium induced increased osteoid surface in the bone with no evidence of accompanying kidney damage. This suggests a primary effect of cadmium on bone rather than secondary effect due to kidney damage.     

The impact of nitrogen fertilizers on degradation and leaching of chlorotoluron in soil

Abstract

This study presents the developed and applied methods for the determination of carbendazim in environmental samples originating from several field studies.

For water samples sample pretreatment consisted of a solid phase extraction (SPE) on cartridges packed with 200 mg SDB-1. In case of solid samples the performance of microwave assisted solvent extraction (MASE) and classical ultrasonic extraction with acetone-ethyl acetate were studied. The latter technique was selected because of the reduced time of manual operations. Instrumental analysis of extracts of water samples was performed on-line with coupled column reversed phase liquid chromatography (LC/LC) and UV detection (280 nm) allowing to assay carbendazim to a level of at least 0.1 μg/l. Improved column life time was obtained by performing the favorable LC separation of carbendazim at high pH on newly developed 5 μm Extend-pH bidentate C18 material.

The combination of a short column packed with 5 μm Inertsil ODS-5 and a mobile phase at low pH material was most adequate as the regards the robust and fast processing of extracts of solid samples and allowed in most cases the screening of carbendazim in soils and sediments to a level of 10μg/kg.

The developed procedures yield overall recoveries for carbendazim of 101, 80 and 71 % in water (levels, 0.1—1.2 μg/l: n=12), soil (levels, 10 and 100 μg/kg; n=22) and sediments (levels, 10 and 100 μg/kg; n=11), respectively, with a repeatability and reproducibility below 7 % for all method/matrix combinations. Soil samples with aged residues (level, 100 μg/kg; n=10) provided an overall recovery of 71% and no significant decrease of carbendazim was observed during nine weeks of storage in the refrigerator.     

Multielemental analysis in small amounts of environmental reference materials with inductively coupled plasma mass spectrometry

The lowest possible sample weight for performing multielemental trace element analysis on environmental and biological samples by ICP-MS has been investigated. The certified reference materials Bovine Liver NIST SRM 1577b, Human Hair NCS DC 73347 and Oriental Tobacco Leaves CTA-OTL-1 were applied at sample weights (1, 5, 20 and 50 mg aliquots, n = 10) which were significantly lower than those recommended with most recoveries in the range of 95–110%. Samples were digested in a mixture of nitric acid, hydrogen peroxide and hydrogen fluoride by closed-vessel microwave digestion. Multielemental analysis was performed with an optimized ICP-QMS method. Aqueous standard solutions were applied for external calibration with rhodium as the internal standard element. The detection limits varied between 0.02–¶0.38 μg/g for Li, Na, Cr, Mn, Ni, Cu, Zn, Sr, Cd, Ba and Pb, and up to 1.92 μg/g for Mg, Al, Ca, Fe and Ni. Digested human plasma samples were spiked with multielemental solution (0.5–10 μg/L) to test the analytical method and the recoveries were 95–105% for most analytes. Our results show that in the case of homogeneous SRMs it is possible to use them in very low amounts (1–5 mg) for method development and quality control.