Microwave Digestion Technique Research Articles

Determination of Trace Rare Earth Elements in Plant and Soil Samples by Inductively Coupled Plasma-Mass Spectrometry

Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) was employed to determine the concentration of rare earth elements (REEs) in plants and soils. Sample preparation and analytical conditions were investigated to set up a simple routine procedure for measuring rare earth elements. For prompt sample decomposition, a microwave digestion technique was successfully used with an acid mixture of HCl+HNO3+HF. Detection limits, reproducibility, accuracy and possible interference were also studied. ICP-MS provided extremely low detection limits for REEs (0.6–6ng/l). Precision was typically better than 6% RSD (relative standard deviation) for soil and 10% for plant. The potential of the method was evaluated by analysis of standard reference materials of soils and plants. A good agreement between the experimental results and certified values was observed. The spectroscopic interference of Ba with Eu and light REEs(LREEs, La-Eu) with heavy REEs(HREEs, Gd-Lu) were eliminated by the algebra correction. The results suggested that REEs in soil samples existed mainly as light REEs, and the same concentration distribution patterns of Oddo-Hakins law were observed, showing negative gradient from La to Lu concentrations. The REE contents in plants were very low, less than 20μg/g and varied with plant species. Apart from rape leaf(Brassica juncea), the REE distribution patterns in other plant leaves were consistent with soils, indicating that these plants generally absorbed REEs from soil without selectivity. Rape leaf showed selective absorption for LREEs, especially for La. The REE concentration distribution in parts of hot pepper(Capsicum annuum) was characteriaed by root>leaf>stem>fruit. The REEs absorbed by hot pepper concentrated mainly in roots and leaves, very little migrated into fruit. Transfer factors(TFs) of REEs in plants were very low. Although the contents of LREEs were relatively more than those of HREEs, no distinct difference of TFs between LREEs and HREEs was observed, meaning that LREEs and HREEs have the same abilities of transportation. However, for rape leaf, the TFs of LREEs were one or two orders of magnitude higher than those of HREEs.

Trace Metals in Fish and Sediments from Lake Boeuf, Southeastern Louisiana

The trace metals Cr, Cu, Pb, and Zn were measured in fish and sediment samples taken from Lake Boeuf, located in southeastern Louisiana. Lake Boeuf is a popular recreational fishing lake from which the following sunfish are caught and consumed: bluegill sunfish ( Lepomis macrochirus); largemouth bass ( Micropterus salmoides); and black crappie ( Poxomis nigromaculatus). Metals were extracted from the fish and sediment samples using microwave digestion techniques. The metal concentrations were quantified using standard flame atomic absorption spectroscopic methods. The concentrations of trace metals in fish did not vary significantly between species or weight of fish; however, a seasonal trend in metal concentration was observed. Concentrations of Cr varied from 2 to 15 μg/g, Cu from 0.2 to 4 μg/g, Pb from 0.5 to 9 μg/g, and Zn from 10 to 20 μg/g. Concentrations of the studied metals in the core samples did not vary with depth in the core, suggesting that no pollutant metals have been input to the lake.

Microwave digestion of organic substances, a useful tool for dissolved organic nitrogen measurements

According to Valderrama (1981) aquatic samples are successfully digested with peroxodisulphate prior to total nitrogen determination. This study compares the utilization of a microwave oven and an autoclave for the preparation of liquid samples in terms of precision and accuracy of the obtained recovery. The comparison encompasses both reference solutions such as urea, amino acids, nucleic acids and recalcitrant compounds as well as natural water samples. Although the observed differences are small, the microwave digestion technique proofs significantly more precise. On the other hand, biases introduced by each of the techniques are similar. The slightly but significantly better precision and its easy utilization on board research vessels make the microwave digestion technique highly recommendable.

Stabilizing chlorinated solvents under conditions of extreme use

Quantifying metal concentration in a hazardous solid waste is critical in evaluating techniques for metal removal or recovery from the waste. Numerous protocols have been published on the digestion of hazardous waste, with diverse methods yielding dissimilar extraction efficiencies for different metals, due to differences in composition of the wastes and chemical forms of the metals. The lack of standard methods (or failure to state the method used) has resulted in inconsistencies in data reported by different laboratories, leading to variations in metal recoveries. Using fly ash as an example, this study compares 11 metal extraction methods including ASTM, USEPA, ultrasonic-assisted and microwave digestion methods as well as a modified Tessier’s sequential extraction procedure for the extraction of metals (Al, Cd, Cr, Cu, Fe, Ni, Pb and Zn). The efficacy of acid digestion was metal dependent. ASTM method D 6357-11 was found to be an effective digestion method for most metals primarily due to the dissolution of metals bound in silicate matrices, while a microwave digestion technique (which hastened the digestion process significantly) was effective for Cd and Pb. This study highlights the importance in the selection of the most appropriate protocol for the digestion of hazardous solid waste.

A Comparison of Cadmium Concentrations in Tissues of Different Categories of Cattle

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Interlaboratory and Intralaboratory Variabilities in the Environmental Lead Proficiency Analytical Testing (ELPAT) Program

The Environmental Lead Proficiency Analytical Testing (ELPAT) Program evaluates over 400 laboratories that perform lead measurements in paints, soils, and dusts. A previous National Institute for Occupational Safety and Health study, based on the ELPAT data over a 3-year period (1992–1995), found no large biases among common hotplate and microwave digestion techniques, but did detect small consistent bias between two common instrumental methods. This study expands on the earlier study by examining the total sample variability and its variation components (interlaboratory and intralaboratory). A correlation model was used to separate the variation components by estimating a variation ratio. The correlation model leads to a more general approach than a sample pairing technique developed by Youden. This study found no significant evidence that the relative contribution of intralaboratory and interlaboratory variability to total variability changes with lead loading levels. There were no significant differences in the relative contribution of variation components among three most commonly used analytical methods (combinations of sample preparation techniques and instrumental methods). The interlaboratory relative standard deviation is about 1.7 times the intralaboratory relative standard deviation. Both variation components are important parts of total variation although the laboratory-to-laboratory (including analyst-to-analyst) difference is greater than the within laboratory (including sample-to-sample) variation.

Analysis of Antarctic Marine Sediment by Inductively Coupled Plasma Atomic Emission and Total Reflection X-Ray Fluorescence Spectrometry

Microwave digestion and extraction techniques were developed for elemental analysis of Antarctic marine sediment by inductively coupled plasma atomic emission spectrometry (ICP-AES) and total reflection X-ray fluorescence (TXRF) spectrometry. These sample preparation techniques were tested by analyzing river sediment certified reference material (BCR-320). Concentrations of Al, Fe, Mn, Zn, Cr, Co, and Cu were determined by ICP-AES after microwave digestion of sediment in a mixture of HF + HNO3+ HCl + H3BO3with acceptable accuracy. Due to the strong matrix effect and spectral interference, Cd, Sn, Pb, Ni, and As cannot be determined using ICP-AES; however, the proposed microwave extraction procedure appears to be suitable for measurement of Zn, Cu, Pb, Ni, and As using TXRF spectrometry.

Soil Lead and Other Metal Levels in Industrial, Residential and Nature Reserve Areas in Singapore

The use of pressure feedback microwave digestion technique has permitted rapid and efficient digestion of soil and sediment samples. The evaluation of different acid mixtures to digest soil samples were studied by mixed-level orthogonal array design. The selected acid mixture of HCl-HNO3-HF was employed in the survey of Pb, Zn, Cu, Cr and Mn in soil samples. Surface soil samples were collected from industrial, residential and nature reserve areas in Singapore. The five metal concentrations were determined by flame atomic absorption spectrometry and graphite furnace atomic absorption spectrometry. The lead and other metal contents in NBS SRM 1645, NIES CRM No. 2 and NRCC BCSS-1 sediment standard references were determined concurrently with the survey samples. Five measured metal loading on the surface soils was in the order: industrial area > residential area > nature reserve area. The trace metal concentrations in surface soil from areas of heavy traffic are higher than those from residential areas. The main sources of trace metal pollution are vehicular exhaust and industrial activities.

Determination of Major and Trace Elements in Japanese Rock Reference Samples by ICP-MS

Abstract Analysis were made, using inductively coupled plasma-mass spectrometry (ICP-MS), to measure 59 major and trace elements in 6 rock reference samples, JB-1, JB-3. JG-1, JR-2, JGb-1 and JA-2, prepared and distributed by the Geological Survey of Japan (GSJ). Sample preparation and analytical conditions were investigated to set up a simple routine procedure for measuring a large range of elements. Detection limits, reproducibility. accuracy, dilution factors, possible interferences, and stability of standard solutions were also studied. For a prompt sample decomposition, a microwave digestion technique was successfully used with an acid mixture of HF, HCIO4 and HNO3. Low background counts and the high sensitivity of ICP-MS provided extremely low detection limits for most elements (0.2–2 ng/l). Precisions were typically better than 5% RSD (relative standard deviation). Generally, the ICP-MS data presented here agreed well with the published GSJ consensus values. In about 40 elements, errors of measured...

Cadmium Determination in Human Whole Blood by Electrothermal Atomic Absorption Spectrometry with Magnesium Chloride and Sodium Hydroxide as a Combined Chemical Modifier

AbstractIn this work, we propose a method to determine trace amounts of Cd in human whole blood samples by electrothermal atomic absorption spectrometry (ETAAS) with the combined chemical modifier including magnesium chloride and sodium hydroxide. Prior to the ETAAS analysis, dissolution of the blood samples is accomplished using a HNO3‐HClO4double closed‐vessel microwave digestion technique followed by drying of the dissolved blood samples by means of an infrared lamp. In using this approach, a MgCl2 chemical modifier is added to the digested samples, then they are injected into the graphite furnace for detecting the Cd level via atomic absorption spectrometer. Besides we used a NaOH chemical modifier, which removed the matrix major elements through prior ashing at 1200 ° C for 30 s, and the Cd is subsequently volatilized at 2200 °C and determined by AAS. However, the proposed method can be employed to determine the of Cd level in whole blood samples by the calibration technique and the standard‐additions method. Its validity is confirmed with two certified reference whole blood materials (Seronorm Trace Elements Whole Blood Batch no. 205052 and Batch no. 203056). By using 10 μL injections, a detection limit of 0.052 ng mL−1 is achieved.

Direct ICP-MS determination of trace and ultratrace elements in geological materials after decomposition in a microwave oven. I. Quantitation of Y, Th, U and the lanthanides

A microwave digestion technique using a mixture of HF + HNO 3 + HCl + H 3BO 3 was found to be effective for the rapid dissolution of various silicate rock and sediment reference samples. From the solutions thus prepared, it was possible to determine quantitatively trace and ultratrace amounts of yttrium, thorium, uranium and the lanthanides by inductively coupled plasma-mass spectrometry (ICP-MS) without any separation of matrix elements or preconcentration. In the ICP-MS determinations, oxide and non-spectral interferences on individual masses of the rare earth element ions were corrected by the method of algebraic approach of elimination and dilution, respectively, and measurement drift was controlled by ruthenium and rhenium internal standards. The method yielded excellent results comparable with “recommended”, “consensus” and “working” values of the literature for the specified elements on various well-known international reference materials such as andesite (AGV-1), basalts (BCR-1, BHVO-1, BIR-1 and BE-N), granites (G-2 and NIM-G), syenite (SY-2), gabbro (MRG-1), diabase (W-2 and DNC-1), marine mud (MAG-1), river sediment (NBS 1645), lake sediments (LKSD-1-LKSD-4) and stream sediment (GSD-1, GSD-5, GSD-6 and STSD-1-STSD-4)). New values for Er, Gd, Ho, Pr and Tm in LKSD-1-LKSD-4 and STSD-1-STSD-4, and Er, Ho, Lu, Nd, Pr, Tb, Tm and Yb in NBS 1645 are first reported in this work.

Microwave digestion technique for the determination of total cadmium in soils

Abstract A rapid method is described for the determination of total cadmium (Cd) in soils. The soil samples and standard sediment samples were digested in a microwave oven using concentrated HNO3 and also by the conventional HF‐HC1O4 digestion in platinum crucibles. The Cd content in the extracts was determined using graphite furnace atomic absorption spectro‐photometry (GFAAS). Both digestion methods produced comparable quantitative values for total Cd of standard reference materials obtained from the National Institute of Standards and Technology and a series of surface and subsurface soil samples. Thus, the microwave digestion technique was shown to be an accurate and rapid method for digesting soil samples prior to total Cd analysis.

Boron analysis in biological material: microwave digestion procedure and determination by different methods

Investigations were made on the determination of boron in biological material. A procedure using the microwave digestion technique was optimised. The analyses were performed by photometry with azomethine-H, fluorimetry with carminic acid, inductively coupled plasma atomic emission spectrometry and inductively coupled plasma mass spectrometry. The matrix interferences, the interferences caused by iron and the detection limits were investigated for these methods. Determinations were performed for plant material, wheat, milk, meat and blood plasma. Recoveries and precision of all methods were studied. To test accuracy and precision, four NBS reference materials were analysed and the results compared with the values in literature. Good recoveries were found with all methods, except the fluorimetric technique. The boron content found in the NBS standard reference materials agreed well with data reported before. Best precision was obtained for the two ICP methods. The azomethine-H method gave good results when material of high boron content was analysed. With the carminic acid method no reliable results were achieved.

Kinetic spectrophotometric determination of iron oxidation states in geological materials

A kinetic spectrophotometric approach is applied to the determination of iron oxidation states in geological materials. Silicate rock samples were sealed in a Teflon vial under argon atmosphere and were decomposed with a mixture of hydrofluoric acid and sulphuric acid by the microwave digestion technique. The absorbance of iron(III)-Tiron complex was followed at 560 nm and the absorbance/time relation was analyzed by non-linear least squares fitting. The FeO and Fe2O3 determinations in silicate rocks by the proposed kinetic method agree with those done by the static o-phenanthroline method. The analytical results for standard igneous rock samples are compared with published data.

Determination of osmium abundance in molybdenite mineral by isotope dilution mass spectrometry with microwave digestion using potassium dichromate as oxidizing agent

An efficient and reliable method was developed for the accurate determination of osmium abundance in molybdenite (MoS2) by isotope dilution mass spectrometry. The sample solution of molybdenite was prepared by acid decomposition using the microwave digestion technique with addition of potassium dichromate (K2Cr2O7) as oxidizing agent and osmium in the sample solution was purified by distillation. There was no change in the ratios of 187Os derived from molybdenite relative to 192Os of an osmium standard with progress of distillation, indicating that isotopes of osmium derived from the two sources were completely homogenized. The precision of the osmium abundance obtained in the developed method was 1%(1σ). The technique was applied to a natural molybdenite sample for Re—Os age determination and the result was in good agreement with that obtained by the U—Pb method for zircon.

Applications of microwave digestion technique for elemental analyses

The acceptance of microwave digestion technique is based on procedures successfully carried out for most different kinds of samples. It is not only the knowledge of the mechanisms how microwaves interact with the material scientists deal with but more the experimental procedures for the most efficiently reagents attack. The goals of this paper are to gather all informations concerning applications of microwave digestion methods for elemental analysis and to review the results obtained by selecting several groups of materials digested.

Comparison of a microwave digestion system to other digestion methods for plant tissue analysis

Abstract Most digestion procedures for the preparation for plant tissue for elemental analysis are often very laborious. Elemental contents of plant tissue prepared by microwave digestion were compared to those obtained by conventional dry ashing and sulfuric acid‐hydrogen peroxide wet digestion. All three digestion methods produced comparable quantitative values for the elements P, K, Ca, Mg, Fe, Mn, Zn, and Cu for all plant materials used. Thus, the microwave digestion technique was shown to be a viable rapid method for digesting relatively small numbers of samples prior to elemental analysis.

Microwave digestion technique for the extraction of minerals from environmental marine sediments for analysis by inductively coupled plasma atomic emission spectrometry and atomic absorption spectrometry

A microwave digestion sample preparation technique for the determination of environmentally significant elements in marine sediments is discussed. Samples were digested with nitric and hydrochloric acids in unvented PFA vessels for periods of up to 20 min. The digestion time compared favourably with the 3 h required for a conventional hot-plate procedure. Recoveries of metals (using inductively coupled plasma atomic emission spectrometry and graphite furnace atomic absorption spectrometry) from an in-house reference sediment and National Research Council of Canada reference materials MESS-1 and BCSS-1 were comparable or superior to those attained by the conventional procedure (89–140%). Significant improvements in precision at the 95 and 99% confidence levels and a reduction in analytical blank levels were noted. Elements with the poorest precision by the conventional method showed the greatest improvement. Diluting the concentrated acids for digestion increased recoveries by 20–30%. The PFA vessels have been found to be resilient to repeated (>100) digestions of a wide variety of samples if properly annealed before use.

Clean Room and Microwave Digestion Techniques: Improvement in Detection Limits for Aluminum Determination by GF-AAS

A rapid, precise, and accurate method for the determination of aluminum in part-per-billion concentrations in biological materials using graphite-furnace atomic absorption spectroscopy has been developed. In order that the necessary accuracy and precision for the analysis of aluminum in bone and brain tissue could be obtained, reduction of laboratory environmental contributions to the aluminum blank was required. Use of a closed-vessel microwave digestion system and a clean room for sample preparation accomplished this goal by reducing Al concentrations in the digestion blanks from 10 ppb to 1 ppb. Digestion time was decreased from many hours to several minutes, and the amount of acid required for digestion was reduced by 70%. Using less nitric acid improved precision in the analyzed solutions by significantly extending the lifetime and consistency in performance of the graphite tube atomizer.

Microwave digestion techniques in the sequential extraction of calcium, iron, chromium, manganese, lead, and zinc in sediments.

The sequential extraction scheme of Tessier partitions metals in sediments into exchangeable, carbonate bound iron-manganese oxide bound, organic bound, and residual binding fractions. Extraction rate experiments using conventional and microwave heating showed that microwave heating produces results comparable to the conventional procedure. Sequential microwave extraction procedures were established from the results of the extraction rate experiments. Recoveries of total metals from NBS SRM 1645 ranged from 76% to 120% for the conventional procedure and 62% to 120% for the microwave procedure. Recoveries of total metals using the microwave and conventional techniques were reasonably comparable except for iron (62% by microwave vs. 76% by conventional). Substitution of an aqua regia/HF extraction for total/residual metals results in essentially complete recovery of metals. Precision obtained from 31 replicate samples of the California Gulch, Colorado, sediment yielded about an average 11% relative standard deviation excluding the exchangeable fraction which was more variable.