Optimization of microwave digestion for mercury determination in marine biological samples by cold vapour atomic absorption spectrometry

Optimization of acid digestion method for mercury determination in marine biological samples (dolphin liver, fish and mussel tissues) using a closed vessel microwave sample preparation is presented. Five digestion procedures with different acid mixtures were investigated: the best results were obtained when the microwave-assisted digestion was based on sample dissolution with HNO3-H2SO4-K2Cr2O7 mixture. A comparison between microwave digestion and conventional reflux digestion shows there are considerable losses of mercury in the open digestion system. The microwave digestion method has been tested satisfactorily using two certified reference materials. Analytical results show a good agreement with certified values. The microwave digestion proved to be a reliable and rapid method for decomposition of biological samples in mercury determination.     

Electroanalytical methods for determination of the metal content and acetic-acid-available metal fractions in soils

The pseudo-total and available arsenic, cadmium, and lead content of soils have been determined by stripping voltammetry with a hanging-mercury-drop electrode and by atomic absorption spectrometry with electrothermal atomization. For determination of pseudo-total metals microwave digestion with a mixture of HNO3 and HClO4, with and without addition of HF, was investigated. The single-extraction procedure with 0.43 mol L-1 CH3COOH, proposed by BCR, was used to assess the availability of metals in soils. The results obtained were validated by analysis of a certified reference material.     

Determination of arsenic in geological samples by HG AAS

A continuous hydride generation (HG) AAS procedure for the determination of As in geological samples utilizing the SH-group containing amino-acid L-cysteine for the pre-reduction of As (V) to As (III) in HNO(3) has been optimized and compared with a method utilizing KI and ascorbic acid in HCl. The influence of some transition metals (Co, Fe, Ni) on the determination of As has been investigated. Decompositions of geological certified reference materials, sediments and soils of different origin and geochemical composition with concentrated HNO(3) have been performed in open and closed systems and the resulting As content has been compared with certified and proposed data.     

Comparison of different digestion methods for total decomposition of siliceous and organic environmental samples.

A comparison was made of different digestion methods for the total decomposition of siliceous and organically environmental samples prior to their analysis by inductively coupled plasma optical emission spectrometry (ICP-OES). In the present study, three different digestion methods, including microwave-assisted, hot plate heating and pressurized digestion (pressure bomb), were employed for the determination of nine heavy metals, i.e. Ag, Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn in sediment, soil, sludge and oil. The investigation of different combinations of acids through their analytical performance demonstrated that HCl plays a vital role in the determination of silver. The combination of HNO3 and HCl possesses more reactive ability in oxidizing organic matter. The recoveries of all elements of interest in sediment (NIST 2704) obtained by different digestion methods were found to be 86% to 113%, while microwave assisted digestion with various combinations of HNO3-HCl-HF and HNO3-HClO4-HF was considered to be a viable alternative to the conventional digestion systems because of its more intensive reaction conditions. The analytical results of four certified reference materials with different matrices, including sediment (GBW 07305), soil (GBW 07411), sludge (BCR R-143) and oil (NIST 1085a), by the microwave-assisted acid digestion method indicated that the recoveries of all elements of interest were more than 85% and the throughput of applied analytical method could be elevated significantly.     

The certified reference materials CRM 142 R light sandy soil, CRM 143 R sewage sludge amended soil and CRM 145 R sewage sludge for quality control in monitoring environmental and soil pollution

The determination of various heavy metals in soils and sludges provides an indication for their degree of contamination. Therefore the reliability of such determinations is of utmost importance. Quality assessment can be performed by using adequate certified reference materials. Because of their success, the present supplies of the BCR CRM 142, CRM 143 and CRM 145 are exhausted. The Measurement and Testing Programme (BCR) of the Commission of the European Communities decided to replace them. After a careful preparation procedure of materials sufficiently similar to the exhausted ones and a homogeneity and stability study, the new materials were certified for a series of trace elements also including their aqua regia soluble fraction. Indicative values for other elements are given as well.     

Single vessel procedure for acid-vapour partial digestion in a focused microwave: Fe and Co determination in biological samples by ETAAS

A single vessel procedure using a focused microwave oven is proposed for biological sample preparation with nitric acid vapour under atmospheric pressure. A laboratory-made PTFE support vessel equipped with four cups that received the samples was adapted to fit on the microwave glass vessel. Biological samples (30 mg) were directly weighed into these PTFE cups followed by the addition of 150 microliters of water or H2O2. The mixture was exposed to acid vapour stemming from 15 ml of concentrated HNO3 placed in the bottom of the glass vessel. The acid vapour was formed at 115 degrees C and brought about the Co and Fe extraction in 10 and 60 min, respectively. The resulting suspension was diluted with 0.14 mol l-1 HNO3 to a final volume of 1.0 ml, shaken and centrifuged. The supernatant was analysed by electrothermal atomic absorption spectrometry (ETAAS) by placing the cups directly in the autosampler of the spectrometer. This system minimised contamination, and reagent and time consumption and was suitable for Co and Fe determination in biological materials. The accuracy of the proposed method was assessed by using certified reference materials and by comparison with the closed vessel microwave as a comparative technique. Cobalt and Fe recovery was around 82-99%. As an additional advantage, up to 6 samples can be simultaneously prepared in each vessel, thereby improving the sample throughput from 6 to 24, when a 6-cavity focused microwave is used.     

Comparison of microwave-assisted acid leaching techniques for the determination of heavy metals in sediments, soils, and sludges

Microwave-assisted EPA method 3051 for nitric acid leaching of environmentally key elements from sediments, soils, and sludges was tested, and the influence of leaching temperature and time on element recovery for an estuarine sediment (CRM 277) was investigated. The extraction efficiencies for four certified reference materials applying EPA method 3051, an optimized nitric acid procedure, and an aqua regia (HCl/HNO₃ 3:1) procedure were compared. Digestions were carried out in a high-pressure microwave system offering simultaneous temperature and pressure control for all digestion vessels employed. Eight elements (Cd, Co, Cr, Cu, Hg, Ni, Pb, and Zn) were determined by ICP-AES and ICP-MS. Extraction efficiency strongly depended on the applied leaching parameters and varied for certain elements among different materials when a nitric acid procedure was applied. In general, element recoveries obtained from the aqua regia procedure were superior to those obtained from nitric acid procedures and showed good agreement with the 95% confidence interval of the certified value for most of the elements investigated. Received: 27 March 1998 / Revised: 29 June 1998 / Accepted: 3 July 1998     

Elimination of hydrofluoric acid interference in the determination of antimony by the hydride generation technique

For the determination of antimony by hydride generation techniques a pretreatment procedure has been developed for the reduction of Sb(V) to Sb(III) in order to remove the effect of hydrofluoric acid which strongly interferes with the reduction of pentavalent antimony to the trivalent state. It is based on the combined action of l-cysteine and boric acid at 80 degrees C. The pretreatment is effective in both nitric and hydrochloric acid media. Quantitative recoveries are obtained in less than 60 min. Under these conditions antimony is reduced to the trivalent state in acid media containing both nitric and hydrochloric acid. The method has been applied to the determination of total antimony in certified reference materials of sediments after pressurized microwave digestion with HNO(3)-HCl-HF. Good agreement is obtained by using both analytical techniques: continuous flow hydride generation atomic fluorescence spectrometry and flow injection electrothermal atomic absorption spectrometry with in-situ trapping of stibine in a graphite atomizer.     

Comparison of microwave digestion procedures for the determination of some elements in asphaltite ash using ICP-AES

A microwave digestion procedure for asphaltite ash was developed in an attempt to facilitate routine analysis and obtain reproducible conditions or comparable results. The conditions of the most effective procedure for 0.1 g asphaltite ash samples are 1 ml of HNO3 + 3 ml of HCl + 1 ml of HF + 1 ml of deionized water as acid mixture and 15 min for digestion time. The digestion was accomplished in five stages applying continuously 90% to 20% of the microwave power and 20 to 100 psi of the pressure for 10 min of total time. Concentrations of selected elements, Cr, Co, Fe, Mn, Ni and Zn were measured using inductively coupled plasma-atomic emission spectroscopy. The proposed method of digestion provided precise results with relative standard deviations generally less than 3% for investigated elements. Results for fly ash as standard reference material was in good agreement with certified values.     

Microwave-assisted double insert vapour-phase digestion of organic samples

A microwave-assisted double insert multimode vapour-phase digestion method was developed for the digestion of organic samples. The experimental set-up was based on a third generation-type teflon microwave vessel, equipped with an automatic pressure regulating type vessel cover. A borosilicate glass holder insert, containing a smaller quartz sample insert, was fitted inside the vessel. Sulphuric acid was added to the holder insert as a microwave absorbing and temperature transferring liquid, which transferred heat to the sample insert (into which the sample was weighed) and charred the sample material. Oxidation of the sample material was carried out simultaneously with charring using nitric acid vapour, which was generated by the 1:1 (v/v) sulphuric acid-nitric acid mixture located in the bottom of the microwave vessel. This set-up generated high digestion efficiency, without any of the interferences normally associated with direct sulphuric acid usage. The method was used for determining the concentrations of Cd, Cr, Cu, Mn, Mo, Zn and Fe in certified organic reference materials using ICP-OES instrumentation. The certified organic reference materials were NRCC DOLT-2 dogfish liver, NIST-SRM 1577b bovine liver and IRMM VDA cadmium in polyethylene No. 001 and No. 004. The results were in good agreement with the certified values, forepart from Cd. For Cd the results were lower than the certified values due to volatilization losses. Sample materials that could not be digested by an earlier procedure were completely digested during a single-step, 30 min digestion. The tested sample materials included certified reference materials, 3-nitrobenzoic acid (3-NBA) and pike (Esox lucius) muscle. The residual carbon concentrations in the digestion solutions were below the detection limit of the TOC instrument. This type of digestion method is described here for the first time in the literature.     

Comparison of some newly synthesized chemically modified Amberlite XAD-4 resins for the preconcentration and determination of trace elements by flow injection inductively coupled plasma-mass spectrometry (ICP-MS)

XAD copolymer resins may be functionalized with heavy metal ion-selective ligands either by covalent linkage to the polymer backbone or by impregnation. These resins may be tailored to be specific for certain heavy metals by adjusting the retention and elution parameters. For the synthesis of immobilized Amberlite XAD-4 copolymer resins that are expected to preconcentrate a number of transition and heavy metals, the Schiff base method was chosen. For this purpose the copolymer was nitrated, reduced to the corresponding amine and converted to the imine compounds via a Schiff base reaction using different organic aldehyde compounds. The interactions of 8 elements (Cd, Co, Cu, Mn, Ni, Pb, U and Zn) with the resins were qualitatively investigated. Optimal pH for retention was typically 6-8 for most resins although one could be used at pH 5 and elution was achieved using 0.1 M HNO3. The resins were characterized by FTIR, SEM and elemental analysis. It was demonstrated that the resins could be used to preconcentrate ultra-trace analytes from natural waters, and analysis of environmental certified reference materials using FI-ICP-MS showed good agreement with the certified values. Metal retention capacities were also calculated using a batch system and were found to compare favorably with other resins reported in the literature.     

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.     

Determination of noble metals in silicate rocks, ores and metallurgical samples by simultaneous multi-element graphite furnace atomic absorption spectrometry with Zeeman background correction

A new method has been developed for rapid determination of mug/g and ng/g amounts of noble metals in silicate rocks, ores and metallurgical samples by attacking with hydrofluoric acid and aqua regia, preconcentration by ion-exchange chromatography and measuring in a simultaneous multi-element graphite furnace atomic absorption spectrometer equipped with a polarized Zeeman background correction device which eliminated interferences from any incompletely separated common elements. The method was tested for Ru, Rh, Pt, Ir, Pd, Ag and Au with three Canadian certified reference materials, and then applied to the determination of ng/g amounts of these elements in four new Canadian candidate reference materials.     

Digestion of titanium bearing geologic materials involving microwaves

An environmentally friendly and rapid digestion procedure involving 10 mL of acid mixture (HNO3 : HCl : HF = 2:2:1) for 0.1 g of sample in closed vessel microwave digester following heating program : 250W for 10 min., hold time 2 min., 600 W for 17 min, and Ventilation time 10 min was developed. The operating parameters were varied and optimized by factorial design approach using "Steepest Ascent" method. The validity of the recommended digestion procedure were examined by analyzing several well characterized standard reference materials such as diabase (W2), basalt (BIR-1, JB-3, BHVO-1), granite (G2), gabbro (JGb-1), Mn-nodule (Nod-A-1, Nod-P-1), sediment (STSD-4, LKSD-2), limestone (KH-2), soil (SAu-1), ilmenite (IGS-31), rutile (IGS-32), Zircon (IGS-35) and titanium dioxide (SRM-154b) employing both inductively coupled plasma-atomic emission spectrometry (ICP-AES) and well known spectrophotometric method. An excellent agreement between the methods and the certified values of standard reference materials suggest that the digestion procedure can be used for quality control and allied purposes.     

Comparison of sample preparation procedures for the determination of trace heavy metals in house dust, tobacco and tea samples by atomic absorption spectrometry

The effect of wet ashing, dry ashing and microwave procedure for the determination of trace metal levels was investigated in house dust, tobacco and tea samples by atomic absorption spectrometry. The study of sample preparation procedures showed that the microwave method was the best. The recovery of trace metals was very good and precision and accuracy were compatible with standard reference material. The relative standard deviations for all measured metal concentrations were lower than 10%. The digestions of HNO3/H2SO4/HClO4 (4: 1: 1) mixture for house dust, HNO3/H2SO4/H2O2 (2: 2: 2) mixture for tea and HNO3/H2O2 (4: 2) mixture for tobacco were very efficient.     

测定土壤中重金属元素时前处理方法的改进

建立了一种微波消解前处理技术的半消解法消解样品,采用原子吸收光谱法和原子荧光光谱法同时测定土壤中主要重金属元素铜、锌、镉、砷、汞的方法,检测土壤标准物质GSS-3、GSS-5、GSS-20,结果显示测定均值在标准差允许范围内,相对标准偏差小于8.5%(n=4),是土壤重金属元素快速检测的可选方法。     

Microwave digestion of sediment, soils and urban particulate matter for trace metal analysis

A microwave digestion technique was developed to determine the content of nine heavy metals in sediments and soils. The digests were subsequently analysed by inductively coupled plasma-atomic emission spectroscopy (ICP-AES). The metals determined were Ca, Mg, Fe, Mn, Zn, Cr, Cd, Cu, Pb and V. The digestion was achieved by using an acid mixture of HNO₃, HF and distilled H₂O. The experimental study was conducted using four standard reference materials (SRMs): sewage sludge (LGC6136), marine sediment (PACS-1), urban particulate matter (NIST 1648) and coal carbonisation site soil (LGC6138). Two different programs were examined to determine which was optimal for the digestion of real environmental samples. The accuracy and precision of the two digestion programs for the analysis of the SRMs were compared. From the results obtained, the microwave program providing a maximum of power of 650 W and a cycle time of 51 min resulted in the best analytical performance. The experimental results obtained were in good agreement with the certified values and demonstrated that the proposed method is precise and accurate.     

210Pb and210Po analysis in sediments and soils by microwave acid digestion

A microwave acid digestion method prior to the determination of²¹⁰Pb and²¹⁰Po in sediments and soils is described. It involves an acid (HNO₃, HCl, HF and H₃BO₃ mixture) digestion with microwave heating in closed vessels at high pressures. Analyses carried out for various reference materials showed that the results were statistically equal to certified values and reproducibility was also assured. The advantage of the microwave technique compared to the traditional leaching procedures is that the solid materials are completely dissolved and, therefore, ca. 100% efficiency is achieved in the extraction of²¹⁰Po and²¹⁰Pb, even though a fraction is associated to the silica net. Moreover, time of analysis is drastically reduced, as are the risks associated to vapour inhalation and material corrosion.     

微波消解电感耦合等离子体发射光谱法测定塑料中铅和镉

采用微波消解技术溶样，ICP-AES法测定了塑料中的铅和镉。通过对消解试剂和微波温度程序的研究，建立了塑料样品的微波消解方法。该方法与传统马弗炉高温灰化消解方法比较，具有准确、简便、快速、省试剂、污染少、消解完全等优点。方法回收率为93％～106％，相对标准偏差(n=7)均小于2％。实际样品对比分析结果表明，方法具有良好的准确度，适于多种塑料材料中铅和镉的快速分析。     

Teflon bomb decomposition of silicate materials in a microwave oven

A method is described for the decomposition of silicate materials in 20-tal Tefion- TFE bombs by using a domestic microwave oven. A domestic pressure cooker was used as a precautionary device to contain acid fumes. Total decomposition of the reference materials, marine sediment MESS-1 and granite G-2, was achieved in 60 s with a mixture of hydrofluoric acid and aqua regia. By using flame or graphite-furnace atomic absorption spectrometry, recoveries greater than 97% were obtained for aluminium, chromium and zinc and greater than 93% for silicon in the samples and for silicon in a pure quartz rod.