Determination of Cd, Cu, Pb and Zn in environmental samples: microwave-assisted total digestion versus aqua regia and nitric acid extraction

We validated the determination of the content of Cd, Cu, Pb and Zn using two digestion protocols: a microwave-assisted total digestion and an aqua regia extraction procedure based on the International Organization for Standardisation (ISO) 11466 method. Our goal in validating these two protocols, along with a nitric acid digestion, is to propose a rapid, cheap and easily automated digestion method for monitoring heavy metal content in environmental samples. We applied the digestion protocols to samples with a wide range of organic matter such as sediments, soils, sludges and plant material.For samples with a low carbonate or organic matter contents, such as sediments and agricultural soils, aqua regia digestion in an aluminium block was revealed to be an optimum estimator for the total metal content. For samples with a high organic matter content, such as organic horizons of forest floor layers, plant material and organic soils, nitric acid digestion could substitute microwave (MW)-hydrofluoric acid (HF) digestion. Except in a few samples with high organic matter or low heavy metal content, the RSD values obtained after the application of the proposed digestion procedures were lower than 5%. Based on the obtained results, a decision flow chart for choosing the fit-for-purpose digestion procedure is suggested.     

Microwave-assisted aqua regia digestion for determining platinum,palladium, rhodium and lead in catalyst materials

This study investigated a microwave-assisted aqua regia digestion of catalyst samples prior to the determination of Pt, Pd, Rh and Pb by ICP-OES. While optimising the method, the effect of digestion temperature on the digestion efficiency was investigated. Few aqua regia digestions were also carried out using a high pressure asher, with a digestion temperature of 280 °C. In addition, XRD (X-ray diffractometry) was used to characterise digestion residue. The study showed that accurate and reliable results for Pt, Pd, Rh and Pb in a recycled monolith catalyst (NIST SRM 2557) were obtained by ICP-OES after the microwave assisted aqua regia digestion. The amounts of Pt, Pd and Rh in the prepared catalyst samples were also at the expected levels. Furthermore, the results indicated that the main part of the impurities and supporting material elements can be quantitatively extracted from the catalyst samples by using the microwave-assisted aqua regia sample pre-treatment.     

冷原子荧光光谱法测定含朱砂中成药中痕量汞的样品消解溶剂选择

目的为了测定紫金锭、复方牛黄消炎胶囊等含朱砂中成药样品中痕量汞的含量,方法比较并确定了高压密封消解法适用的消解溶剂体系。结果以y（王水）＋V（H2O2）=5＋1为消解溶剂,高压密封消解-冷原子荧光法测得紫金锭和复方牛黄消炎胶囊样品的总汞含量分别为7．22％和2．66％,样品的加标回收率为96．2％-97．8％,RSD小于2％（n=3）;结论实验表明,y（王水）＋y（H2O2）=5＋1混合溶剂适用于紫金锭、复方牛黄消炎胶囊等含朱砂中成药样品的消化,获得的样品汞含量测定结果令人满意。     

Multielement analysis of coal by ICP techniques using solution nebulization and laser ablation

The combination of inductively coupled plasma atomic emission spectrometry and high resolution inductively coupled plasma mass spectrometry for the determination of 70 elements in coal were studied. Four microwave-assisted digestion procedures with different dissolution mixtures (nitric and hydrofluoric acids, aqua regia and hydrogen peroxide), lithium metaborate fusion with and without previous sample ashing as well as direct sampling by laser ablation (LA) have been tested. Examples of spectral interferences are given and different correction procedures are discussed. Detection limits in the low ng g(-1) range were obtained for most of the elements investigated by using high-purity reagents and by taking special care to prevent sample contamination during preparation. The precision was assessed from replicate analysis (including sample preparation) of coal samples and was found to be, as average values far all elements, 4-5% RSD and 10-15% RSD for procedures including sample digestion and LA sampling, respectively. The accuracy of the overall analytical procedures was estimated by analysis of certified reference materials and of a coal sample obtained from the Interlab Trace round robin test. Among the dissolution mixtures tested, the combination of nitric and hydrofluoric acids with hydrogen peroxide provide the best agreement with certified, recommended, literature-compiled or consensus values, though fusion is necessary to obtain quantitative recoveries for Si, Cr, Hf, W, Zr, Y. In general, results obtained by LA fall within +/-20% of those obtained after digestion.     

Comparison of open digestion methods and selection of internal standards for the determination of Rh,Pd and Pt in plant samples by ICP-MS

An analytical procedure for the reliable determination of Pd, Pt and Rh in plant samples by inductively coupled plasma-mass spectrometry (ICP-MS) was developed. An ultrasonic nebulizer (USN) was used for sample introduction to improve sensitivity. Under various synthetic plant sample matrix compositions, it was established experimentally that moderate amounts (0.2–2%) of dissolved solids decreased the analyte signals significantly. Internal standardisation with In (for Pd and Rh) and Ir (for Pt) proved to be essential for obtaining correct results. Five open digestion approaches, used for converting solid plant samples to aqueous solution, were also tested for the purpose, namely dry-ashing, dry-ashing followed by HF attack, wet digestion with H₂O₂–HNO₃, wet digestion followed by HF attack and aqua regia digestion. Recovery tests in two spiked plant materials showed that only wet digestions must be used. With these ways, all PGEs could be reliably quantified by USN-ICP-MS without applying a separation or preconcentration step with a good precision (below 10% RSD). The aqua regia procedure was applied to the determination of PGEs in various plant matrices collected along a highway. Results showed that mosses were probably the best choice of samples to monitor the bioaccumulation of PGEs in time.     

Comparison of wet microwave digestion methods of plant materials for the determination of metals by flame atomic absorption spectrometry

Microwave closed-system wet digestion procedures for plant samples were examined. Each procedure was tested with samples of tobacco and cabbage, and included digestion by the use of different acids composition, almost complete evaporation of the digest, and then dissolution of the residue in 1% nitric acid. Three microwave digestion programs that varied power, duration, and temperature were used. Closed-vessel reactions followed open-vessel reaction-delay time. Using flame atomic absorption spectrometry on the digests, four or five elements were determined to evaluate effectiveness, precision and accuracy of analytes extraction into solution. After a preliminary study of tobacco digests, the four most effective procedures were chosen, and detailed investigations were carried out on both tobacco and cabbage reference materials. Although all four of the final procedures were accurate, the most precise procedure, with the lowest errors of determination, was using reverse ‘aqua regia’ for tobacco and ‘aqua regia’ for cabbage.     

土壤中铅的分析方法比对

对不同的样品消解方法及电感耦合等离子体质谱、电感耦合等离子体原子发射光谱、石墨炉原子吸收光谱法测定土壤中铅的测定结果进行比对。采用电热板、微波及水浴3种加热方式,选择硝酸、氢氟酸、双氧水、王水、高氯酸、盐酸的不同组合进行土壤样品消解,通过分析测定值的精密度和准确度,考察消解体系对电感耦合等离子体质谱、电感耦合等离子体发射光谱、石墨炉原子吸收光谱法测定结果的影响。结果表明采用电感耦合等离子体质谱法测定土壤中的铅,最适宜的消解体系是硝酸-氢氟酸-高氯酸(微波加热),采用电感耦合等离子体原子发射光谱法测定最适宜的消解体系是硝酸(电热板加热),采用石墨炉原子吸收光谱法测定最适宜的消解体系是硝酸-盐酸-高氯酸(微波加热)。电感耦合等离子体质谱法的精密度和准确度优于另外两种方法。     

Influence of sample pre-treatment on the determination of trace silver and cadmium in geological and environmental samples by quadrupole inductively coupled plasma mass spectrometry

The suitability of three different digestion procedures has been evaluated with regard to the quantitative determination of trace amounts of silver and cadmium in geological and environmental samples. Procedure A: extraction with aqua regia in an open vessel system; Procedure B: extraction with aqua regia in a closed pressurized vessel system; Procedure C: digestion with HF + HNO₃ in a closed pressurized vessel system. It was found that procedure A represented an effective way of extracting analytes from different types of geological samples while the effect of extracting interfering metals is low. Because it is interference-free, poses a low risk of contamination and is time-saving, sample treatment procedure A was preferred. For this digestion procedure, a series of Chinese geological reference materials was determined by ICP-MS, the results of which were found to be in reasonable agreement with the certified values.     

不同消解方式对土壤中锑的原子荧光法检测影响

氢化物发生-原子荧光光谱法是土壤环境中锑检测所广泛使用的方法．土壤的消解前处理分别采用王水微波消解（半消解）、混酸全消解（硝酸＋高氯酸＋氢氟酸）方式．研究结果表明王水微波消解对锑的检测效果较好,标准土壤9次测定值的相对标准偏差为3．6％,实际样品的回收率为96％-102％．而采用混酸全消解的方式测定值偏低,实际样品的回收率为78％～86％,而且精密度超过5％,这是由于在赶酸过程中样品易被蒸干而造成痕量锑元素的损失．     

Focused microwave-assisted digestion of vegetal materials for the determination of essential mineral nutrients

An open focused microwave-assisted digestion procedure has been developed to decompose and dissolve vegetal matrices for subsequent macro- and micronutrients analysis. The parameters of the microwave oven were evaluated using an experimental design. Sulfuric acid (5 mL) and hydrogen peroxide (3 mL) were found to be suitable for quantitative determination of Ca, Cu, Fe, K, Mg, Mn, N, P, and Zn in 0.100-0.500 g of vegetal sample. The precision was better than 6% for all elements at different concentrations. Results for reference and laboratory control materials are in agreement with certified and indicative values. In addition, the sample digest could be used for ICP-OES of all the elements mentioned. The proposed microwave-assisted digestion procedure offers the ability to determine the most important essential plant nutrients in one unique solution by means of analytical techniques usually found in most laboratories.     

Comparative determination of Ba, Cu, Fe, Pb and Zn in tea leaves by slurry sampling electrothermal atomic absorption and liquid sampling inductively coupled plasma atomic emission spectrometry

The comparative determination of barium, copper, iron, lead and zinc in tea leaf samples by two atomic spectrometric techniques is reported. At first, slurry sampling electrothermal atomization atomic absorption spectrometry (ETAAS) was applied. The results of Ba and Pb determination were calculated using the method of standard additions, and results of Cu, Fe and Zn from the calibration graphs based on aqueous standards. These results were compared with the results obtained after microwave-assisted wet (nitric+hydrochloric+hydrofluoric acids) digestion in closed vessels followed by inductively coupled plasma-atomic emission spectrometric (ICP-AES) determination with the calibration by means of aqueous standards. The exception was lead determined after a wet digestion procedure by ETAAS. The accuracy of the studied methods was checked by the use of the certified reference material Tea GBW-07605. The recoveries of the analytes varied in the range from 91 to 99% for slurry sampling ETAAS, and from 92.5 to 102% for liquid sampling ICP-AES. The advantages of slurry sampling ETAAS method are simplicity of sample preparation and very good sensitivity. Slurry sampling ETAAS method is relatively fast but if several elements must be determined in one sample, the time of the whole microwave-assisted digestion procedure and ICP-AES determination will be shorter. However, worse detection limits of ICP-AES must also be taken into the consideration in a case of some analytes.     

Analysis of eco-relevant elements and noble metals in printed wiring boards using AAS,ICP–AES and EDXRF

Different analytical procedures were developed to investigate the chemical composition of printed wiring boards. A set of 11 samples from different electronic devices were ground and prepared for ICP-AES and AAS analyses by extraction with aqua regia and microwave digestion. Several sample preparation techniques were used for the analyses by EDXRF; the best results were obtained by embedding the samples in Vaseline. Since no standard reference material is available for printed wiring boards, a model reference material was created to compare the applicability and limitations of the employed analytical techniques.     

微波王水消解不赶酸原子荧光光谱法测定土壤中的砷

采用微波消解土壤样品不赶酸的情况下利用原子荧光光谱法测定土壤中的砷.结果表明:微波王水消解土壤样品不赶酸情况下,砷的测定值均在国家标准物质ESS-1的推荐值范围内.砷的线性范围分别为0.0～50.0μg/L,相关系数为r=0.9995.按称取0.2 g样品,定容至50 mL,求出砷检出限为0.5 mg/kg.砷回收率为93.4%～100.9%之间,相对标准偏差(n=4)为0.39～4.56%.结果表明:微波王水消解不赶酸原子荧光光谱法测定土壤中的砷,灵敏度高,操作简便快速,结果准确可靠.     

Determination of four additives in aluminum electrolyte by ICP-OES with wet digestion

A method to quantify K, Ca, Mg and Li in aluminum electrolyte by ICP-OES with wet digestion was developed. The samples were digested using aqua regia in PTFE beakers and heated by electric hot plate. The levels of four additives, namely KF, CaF₂, MgF₂ and LiF in aluminum electrolyte were determined simultaneously by ICP-OES. The recovery rate of this method was 93.27%–103.51%. Accuracy was also proven through the measurement of standard sample of aluminum electrolyte. The developed method was applied to relative standard deviations for three digestion replicates of ten samples were in the range from 0.51% to 8.33%.     

Determination of four additives in aluminum electrolyte by ICP-OES with wet digestion

A method to quantify K, Ca, Mg and Li in aluminum electrolyte by ICP-OES with wet digestion was developed. The samples were digested using aqua regia in PTFE beakers and heated by electric hot plate. The levels of four additives, namely KF, CaF₂, MgF₂ and LiF in aluminum electrolyte were determined simultaneously by ICP-OES. The recovery rate of this method was 93.27%–103.51%. Accuracy was also proven through the measurement of standard sample of aluminum electrolyte. The developed method was applied to relative standard deviations for three digestion replicates of ten samples were in the range from 0.51% to 8.33%.     

Simultaneous determination of arsenic, selenium and mercury in foodstuffs by chemical vapour generation inductively coupled plasma optical emission spectroscopy

A procedure for the simultaneous determination of arsenic, selenium and mercury in foodstuffs has been developed. After a two-step microwave-assisted wet digestion in closed vessels, using concentrated nitric acid and hydrogen peroxide, the solution was analysed by inductively coupled plasma multichannel-based emission spectrometry using chemical vapour generation as the sample introduction system. All steps of the procedure, such as solid sample dissolution, pre-reduction to the suitable oxidation state, vapor generation, transport and atomization have been designed and optimised taking into account the concomitant presence of all the analytes considered. Temporal variation of analytical signals as well as interfering effects due to transition elements were also studied. Under the optimised operating conditions, the achieved detection limits for the simultaneous determination of arsenic, selenium and mercury in foodstuffs were 0.006, 0.023 and 0.018 microg g(-1), respectively, allowing their determination in real samples. Precision of the analytical procedure was 6.8% for arsenic, 5.2% for selenium and 7.7% for mercury (n=7). The accuracy and reliability of the method was verified by the analysis of both standard reference materials (rice flour and spinach leaves) and real samples (natural and Se-enriched rice).     

The homogeneity of heavy metal deposition on glass fibre filters collected using a high-volume sampler in the vicinity of an opencast chrome mine complex at Kemi,Northern Finland

The homogeneity of heavy metal (Cr, Ni, Cu, Fe and Cd) distribution on glass fibre filters (Munktell MG 160, 203 x 254 mm, 75 g m(-2)) collected using a high-volume sampler (Wedding & Associates) at an opencast chrome mine complex at Kemi, Northern Finland was studied. The heavy metals in the total suspended particulate (TSP) material were analysed by inductively coupled plasma atomic emission spectrometry (ICP-AES) or graphite furnace atomic absorption spectrometry (GFAAS). The glass fibre filters were digested in a microwave oven using a mixture of aqua regia+HF acids. There was significant non-uniform distribution of heavy metals on glass fibre filters. The TSP material containing chromite was very difficult to dissolve by acid digestion. The results from X-ray fluorescence spectrometry (XRF), and from energy filtering transmission electron microscope (EFTEM) equipped with energy dispersive X-ray spectrometer (EDS), showed that insoluble residue left after microwave oven digestion with aqua regia+HF acids was probably partly due to chemical reactions occurring during microwave heating.     

电感耦合等离子体质谱法测定地球化学样品中的银、砷、锑、铋

建立了王水分解样品,电感耦合等离子体质谱法测定地球化学样品中的银、砷、锑、铋的方法,采用王水-水浴分解试样,电感耦合等离子体质谱仪测定新疆和田策勒恰哈地球化学样品中的银、砷、锑、铋,确立了最佳的溶样时间、测定酸度、干扰元素的校正方法,结果令人满意。各元素的方法检出限为0.003 8~0.041g/g;相对标准偏差RSD(n=12)为0.52%~2.8%;方法灵敏度较好、简便、快速,且结果准确,适用于大批量地球化学样品的快速测定。     

Analysis of PCBs in soils and sediments by microwave-assisted extraction,headspace-SPME and high resolution gas chromatography with ion-trap tandem mass spectrometry

A procedure for the determination of seven indicator PCBs in soils and sediments using microwave-assisted extraction (MAE) and headspace solid-phase microextraction (HS-SPME) prior to GC-MS/MS is described. Optimization of the HS-SPME was carried out for the most important parameters such as extraction time, sample volume and temperature. The adopted methodology has reduced consumption of organic solvents and analysis runtime. Under the optimized conditions, the method detection limit ranged from 0.6 to 1?ng/g when 5?g of sample was extracted, the precision on real samples ranged from 4 to 21% and the recovery from 69 to 104%. The proposed method, which included the analysis of a certified reference material in its validation procedure, can be extended to several other PCBs and used in the monitoring of soil or sediments for the presence of PCBs.     

Determination of tin in poly(vinyl chloride) by atomic-absorption spectroscopy

A simple procedure is described for the determination of tin in PVC by atomic-absorption spectroscopy with an air-hydrogen flame, after wet digestion of the sample with sulphuric acid and hydrogen peroxide.