Microwave-assisted Sample Digestion Research Articles

Rapid on-line sample dissolution assisted by focused microwave radiation for silicate analysis employing flame atomic absorption spectrometry: iron determination

An on-line automated flow injection system with microwave-assisted sample digestion was used to perform silicate rock dissolution in acid medium for iron determination. For this purpose, a continuous flow system was built up by using an automatic flow injection analysis (FIA) system coupled to a flame atomic absorption spectrometer (FAAS), including a focused microwave oven unit. Inside the microwave cavity was inserted a polytetrafluoroethylene (PTFE) reactor coil (300 cm length and 0.8 mm i.d.) where the dissolution takes place. Chemical and flow variables as well as iron determination parameters were studied. In the flow system, a slurry of the rock sample (50 mg in 200 ml of acid mixture HF+HCl+HNO 3) is pumped through the reaction coil and the microwaves are turned on. After elapsed the time required to complete the sample dissolution, the mixture is pumped again in order to fill the sampling loop (500 μl). Then, by changing the valve position, a water carrier stream pushes the sample solution through the flame atomic absorption spectrometer nebulizer. To achieve an accurate determination of the rock certified materials, the slurry sample was irradiated during 210 s at 90 W power. Working in that condition, a detection limit of 0.80 μg ml −1 (which corresponds to an Fe 2O 3 content of 0.46%) and an analytical throughput of 10 h −1 were achieved. The relative standard deviation (R.S.D.) of the method varied between 1 and 11% when applied to the rock certified materials.

Determination of As, Sb, Se, Te and Bi in milk by slurry sampling hydride generation atomic fluorescence spectrometry

A simple and fast analytical procedure has been developed for the determination of As, Sb, Se, Te and Bi in milk samples by hydride generation atomic fluorescence spectrometry (HG-AFS). Samples were treated with aqua regia for 10min in an ultrasound water bath and pre-reduced with KBr for total Se and Te determination or with KI and ascorbic acid for total As and Sb, the determination of Bi being possible in all with or without pre-reduction. Slurries of samples, in the presence of antifoam A, were treated with NaBH4 in HCl medium to obtain the corresponding hydrides, and AFS measurements were processed in front of external calibrations prepared and measured in the same way as samples. Results obtained by the developed procedure compare well with those found after microwave-assisted complete digestion of samples. The proposed method is simple and fast, and only 1ml of milk is needed. The values obtained for detection limit are 2.5, 1.6, 3, 6 and 7ngl−1 for As, Sb, Se, Te and Bi respectively in the diluted samples, with average relative standard deviation values of 3.8, 3.1, 1.9, 6.4 and 1.2% for three independent analysis of a series of commercially available samples of different origin. Data found in Spanish market samples varied from 3.2±0.3 to 11.3±0.2ngg−1 As, from 3.1±0.2 to 11.6±0.4ngg−1 Sb, from 10.7±0.5 to 25.5±0.4ngg−1 Se, from 0.9±0.2 to 9.4±0.6ngg−1 Te and from 11.5±0.1 to 27.7±0.4ngg−1 Bi.

Determination of Ultratrace Bismuth in Milk Samples by Atomic Fluorescence Spectrometry

A sensitive procedure was developed for determination of bismuth (Bi) in milk samples by hydride generation atomic fluorescence spectrometry (HG-AFS) after microwave-assisted sample digestion with HNO3 and H2O2. The method provides a sensitivity of 1832 fluorescence units (ng/mL) with a detection limit of 0.01 ng/mL, which corresponds to 20 pg absolute limit of detection, equivalent to 0.50 ng/g in the original sample. Application of the methodology to cow milk samples from the Spanish market showed the presence of Bi at a concentration of 11.8-28.8 ng/g, which compared well with data obtained after dry ashing of samples and with data obtained by inductively coupled plasma-mass spectrometry after microwave-assisted digestion.

Determination of arsenic and antimony in milk by hydride generation atomic fluorescence spectrometry

A highly sensitive procedure has been developed for total arsenic and antimony determination in milk samples by hydride generation atomic fluorescence spectrometry after microwave-assisted sample digestion. The discrete introduction of 2 ml of digested sample in the automated continuous flow hydride generation system allows us to reduce drastically the sample and HCl consume and to determine several elements from a same sample digestion. The method provides detection limits of 0.006 and 0.003 ng ml −1, a sensitivity of 2390 and 2840 fluorescence units per ng ml −1 for As and Sb respectively, and average relative standard deviation of 2.3% for As and 4.8% for Sb. The analysis of cow milk samples, obtained from the Spanish market evidenced the presence of As at concentration levels from 3.4 to 11.6 ng g −1 and Sb levels from 3.5 to 11.9 ng g −1, thus in a proportion near to 1:1, which is in contrast with the 10:1 natural ratio between As and Sb and could evidence the effect of the introduction of new alloys and polymer materials in the industrial process of milk. The method was validated by the comparison of data found for commercial samples by using the proposed procedure and reference methods based on dry-ashing and AFS, and microwave-assisted digestion and inductively coupled plasma mass spectrometry determination.

Hydride generation atomic fluorescence spectrometric determination of ultratraces of selenium and tellurium in cow milk

A sensitive procedure has been developed for selenium and tellurium determination in milk by hydride generation atomic fluorescence spectrometry (HG-AFS) after microwave-assisted sample digestion. The method provides sensitivity values of 1591 and 997 fluorescence units ng −1 ml −1 with detection limits of 0.005 and 0.015 ng ml −1 for Se and Te, respectively. The application of the developed methodology to the analysis of cow milk samples of the Spanish market evidenced the presence of concentration ranges from 11.1 to 26.0 ng ml −1 for Se, and from 1.04 to 9.7 ng ml −1 for Te having found a good comparability with data obtained after dry-ashing of samples.

Microwave sample-digestion procedure for determination of arsenic in moss samples using electrothermal atomic absorption spectrometry and inductively coupled plasma mass spectrometry.

Arsenic in moss samples was determined by electrothermal atomic absorption spectrometry (ETAAS) after microwave-assisted sample digestion. Two different sample masses (500 mg and 1000 mg) and three different microwave ovens were used in the digestion. There was a slight difference in the digestion efficiency, as determined by the residual carbon concentrations of 500 mg digested samples, between the microwave ovens. The arsenic results obtained for moss reference samples were, in most cases, satisfactory. However, phosphorus was found to have a reducing influence on the arsenic peak area in the ETAAS determination. According to the results, it was not possible to reduce the phosphorus interference by increasing the amount of Mg(NO(3))(2) in the Pd-Mg chemical modifier. The arsenic results obtained by ETAAS were compared to those obtained by inductively coupled plasma mass spectrometry (ICP-MS).

An on-line flow-injection microwave-assisted mineralization and a precipitation/dissolution system for the determination of molybdenum in blood serum and whole blood by electrothermal atomic absorption spectrometry

An on-line flow injection (FI) precipitation–dissolution system with microwave-assisted sample digestion has been developed for the electrothermal atomic absorption spectrometry (ETAAS) determination of trace or ultratrace amounts of molybdenum in human blood serum and whole blood samples. After the exposure of the sample to microwave radiation, the on-line precipitation of molybdenum was achieved by the merging-zone of a 0.5-ml plug of sample with a plug of potassium ferrocyanide, which were carried downstream with a solution of 0.5 mol l −1 of HNO 3. The interfering effects of iron and copper were minimized by the introduction of a flow of a 5% (w/v) sodium potassium tartrate (for iron) and 2% (w/v) of thiourea (for copper and zinc) in a 5% (v/v) ammonia and 2% (v/v) ammonium chloride solution previous to the precipitation reaction. The reddish-brown precipitate of molybdenyl ferrocyanide was collected on the walls of a knotted reactor. The precipitate was dissolved with the introduction of 1 ml of a 3.0 mol l −1 NaOH solution and the best performance in terms of detection limit and precision was achieved when a sub-sample of 140 μl was collected in a capillary of a sampling arm assembly, to introduce 20 μl volumes into the atomizer by means of positive displacement with air through a time-based injector. A detection limit (3 σ) of 0.1 μg Mo l −1 using an aqueous standard solution was obtained. The method is quantitative and is applied over the range 0.2–20.0 μg Mo l −1. The precision of the method evaluated by ten replicate analyses of aqueous standard solutions containing 0.5 and 1.0 μg Mo l −1 was 2.8 and 3.1% (relative standard deviation, RSD) (for n=5), respectively. Whereas, the precision evaluated by five replicate analysis of a serum and a whole blood sample were 3.3 and 3.8% RSD. An enrichment factor of ca. 3.5 was achieved with the introduction of 0.5 ml aqueous standard solutions at a sample flow rate of 1.0 ml min −1. Recoveries of spiked molybdenum in blood serum and whole blood were in the ranges 96–102 and 94–98%, respectively. The results obtained for two human whole blood certified reference materials were in good agreement with the indicative values.

ICP-MS multielement determination in fly ash after microwave-assisted digestion of samples

A microwave assisted digestion procedure has been developed for dissolution of fly ash samples prior to the inductively coupled plasma-mass spectrometric determination of their elemental composition. The developed methodology was validated by carrying out the analysis of two high-silicate containing reference materials (CRM 134R sewage amended soil and NIES JR 1 rock) and by means of the comparison between results found by microwave-assisted digestion and ICP-MS of fly ash samples with those found by neutron activation analysis (NAA) for Sb, Cs, Cr, Co, Fe, U and Zn determination. The method developed can be recommended for routine multielement analysis of fly ash.

Determination of As, Sb, Se, Sn and Hg in beer and wort by direct hydride generation sample introduction−electrothermal AAS

A method is described for the hydride generation atomic absorption (HG-AAS) determination of As, Sb, Se, Sn and Hg in untreated samples of beer and wort using a batch system and in situ preconcentration of the analytes onto the Pd- (for As, Sb, Se, Sn) or Au-pretreated (for Hg) interior wall surfaces of a graphite furnace. Samples were degassed by filtration and the hydride was generated in the presence of an antifoam agent. Instrument parameters, hydride generation, transportation and trapping were selected. Determination of the total concentration of these elements was obtained after a previous reduction with thiourea. To minimize the amount of moisture from the reaction vessel reaching the graphite tube, an extra gas–liquid separator was installed in line. For 10 mL of sample, detection limits (LOD, 3σblank, peak height) of 28, 21, 10, 50 and 90 ng L−1 were obtained for As, Sb, Se, Sn and Hg, respectively, reflecting overall generation/collection efficiencies of 53, 100, 54, 57 and 66%, respectively. The detection limits were restricted by variations in the blank absorbance. Precision of replicate determination was typically 5% RSD at a concentration 50-fold above the LOD for a 10 mL sample volume. The accuracy of the method was confirmed by comparing the results obtained with those found for beer and wort using microwave-assisted digestion and by analysing five certified reference materials. Data comparable with those obtained by hydride generation after microwave-assisted digestion of samples were found for a series of natural samples, giving evidence of the applicability of the developed methodology to directly determining analytes. Calibration was achieved via the method of standard additions.

Determination of selenium, zinc and cadmium in antidandruff shampoos by atomic spectrometry after microwave assisted sample digestion

Microwave assisted pre-treatments for atomic spectrometric determination (inductive coupled plasma-optical emission spectrometry, ICP-OES or flame atomic absorption spectrometry, FAAS) of metallic elements, usually present in antidandruff shampoos, are proposed. They are based on the digestion of the sample with HNO 3 into a closed reactor, which is irradiated at 800 W for a few minutes. Selenium was determined by ICP-OES. The limit of detection was 0.11 mg l −1; the relative standard deviation (R.S.D.) for the selenium content in the samples was in the 0.6–3.6% range. The results obtained were in agreement with the label contents and the recovery of the proposed method was in the 100–106% range. Zinc and cadmium were determined by FAAS. The limit of detection for zinc determination was 0.078 mg l −1; the R.S.D. for zinc contents was in the 0.8–8.6% range. A limit of detection of 0.09 mg l −1 was obtained for cadmium determination; the R.S.D. for cadmium contents was in the 0.7–2.7% range. The determinations were performed after two different sample mineralization pre-treatments — dry ashing (in an electric furnace) and wet mineralization (in a microwave oven). Both methodologies provided comparable results for zinc and cadmium determination in shampoos. The proposed microwave assisted digestion procedures allow a precise and accurate determination of selenium, zinc and cadmium in commercial antidandruff shampoos, and the sample pre-treatment is less time-consuming than the classic methods.

Development of hardware and software for on-line sample preparation using sequential-injection analysis

This work describes the software and hardware developed for implementation of on-line microwave-assisted sample digestion in an automated sequential-injection analysis (SIA) system. The system was completely developed with conventional equipment available in analytical laboratories. The software and hardware allows for the acquisition and manipulation of analytical signals and also for the synchronization of the actuation of each component. The assembled system is composed of a mixing valve, three solenoid valves, a commercial microwave oven, a peristaltic pump, and an ultrasonic bath. Additionally, it is possible to program 60 different events that can be controlled by the operator according to the requirement of analysis. The operator only needs to inject the samples, and the other steps are carried out by the automated SIA system. This system was applied for direct determination of Fe in white wines and presented a sampling frequency of 10 h−1. The limit of detection was 0.6 mg L−1, and an addition-recovery experiment led to recoveries in the 98–101% range. © 2000 John Wiley & Sons, Inc. Lab Robotics and Automation 12:246–252, 2000

Determination of bismuth in biological samples using on-line flow-injection microwave-assisted mineralization and precipitation/dissolution for electrothermal atomic absorption spectrometry

An on-line automated flow injection system with microwave-assisted sample digestion for the electrothermal atomic absorption spectrometric determination of bismuth in biological materials is described. After the exposure of the sample to microwave radiation, the analyte was subject to a precipitation/dissolution process. Bismuth was precipitated with the stannite ion in basic medium and collected on the walls of a knotted coil, while the other matrix components flowed downstream to waste. The precipitate was dissolved with nitric acid and a sub-sample was collected in a capillary of a sampling arm assembly, to introduce 20 μl volumes into the graphite tube by means of positive displacement with air through a time-based injector. The analytical figures of merit were first evaluated by filling the sampling arm with a standard solution of bismuth and thereafter injecting aliquots of this solution into the atomizer. The calibration graph was linear from the detection limit (8 pg) to 1.2 ng of bismuth. The sensitivity was of 26.8 μg l −1 for 0.2 A-s and the characteristic mass ( m o) was of 11.8 pg/0.0044 A-s. The precision of the method, evaluated by replicate analyses of solutions containing 20 and 200 pg of bismuth, were 5.5 and 3.0% ( n=10), respectively. When solutions were introduced in the flow system here described, the calibration graph was linear in the range 0.04–6.0 μg l −1, which means that a preconcentration factor of 10 was obtained for bismuth. The precision slightly deteriorated, e.g. the replicate analysis of solutions containing 1 and 10 pg of bismuth were 7.1 and 5.3% ( n=10), respectively. However, the recoveries values obtained with urine and whole blood bismuth spiked samples were over 96.5% and the agreement between observed and certified values was good.

Slurry sampling combined with ultrasonic pretreatment for total mercury determination in samples containing inorganic and methylmercury by flow injection-cold vapor-atomic absorption spectrometry

A method for the determination of total mercury in solid biological and environmental samples by slurry sampling combined with flow injection-cold vapor-atomic absorption spectrometry (FI-CV-AAS) was developed. The slurries were prepared in 15% m/m nitric acid (mussel tissue, aquatic plant) or a (9 + 1) 15% m/m nitric acid–15% m/m hydrochloric acid mixture (river sediment, sewage sludge) containing 0.02% v/v Triton X-100 as dispersing agent, and subjected to ultrasonic pretreatment before being injected into the FI manifold. Ultrasonic pretreatment of slurries was proved to be necessary in order to improve the low mercury recoveries obtained. The effect of several FI parameters on the effectiveness of cold vapor generation for total mercury determination in slurries of mussel tissue was investigated. Mercury concentrations obtained by the proposed method were compared with those obtained after microwave-assisted digestion of mussel tissue samples. The method was validated against CRM BCR 278 mussel tissue, CRM BCR 60 aquatic plant, CRM BCR 320 river sediment and CRM BCR 145R sewage sludge. LODs were 3, 26, 28 and 8 ng g–1 for mussel tissue, river sediment, sewage sludge and aquatic plant, respectively. The precision, expressed as relative standard deviation [RSD (%)], ranged from 4 to 7% for three replicates of each sample analysed by the standard additions method.

Microwave-Assisted Vapor-Phase Nitric Acid Digestion of Small Biological Samples for Inductively Coupled Plasma Spectrometry

The applicability of microwave-assisted, vapor-phase nitric acid digestion of small biological samples in closed-vessel microwave systems is examined for the inductively coupled plasma atomic emission spectroscopy (ICP-AES) determination of 10 elements (Al, As, Ca, Cu, Cd, Fe, Mn, Mo, Pb, and Zn). A 1.8 mL quartz sample container geometry was optimized for the successful decomposition of 50 to 90 mg of powdered biological samples. Microwave energy was efficiently coupled by addition of 250 μL of distilled deionized water to the sample. A single microwave-assisted, vapor-phase acid sample digestion was accomplished within 30 min (including cooling time) at ∼1200 psi pressure and 450 W microwave power in a commercial pressurized microwave decomposition (PMD) system. Multiple microwave-assisted, vapor-phase acid digestions were achieved at moderately high pressure (400 to 480 psi) and 230 °C with a second closed-vessel microwave apparatus. The results for 10 elements in biological standard reference materials agree well with the certified values.

Clean laboratory chemistry for the microwave-assisted digestion of botanical samples

Download options Please wait... Article information DOI https://doi.org/10.1039/JA9961100751 Article type Paper Download Citation J. Anal. At. Spectrom., 1996,11, 751-757 BibTex EndNote MEDLINE ProCite ReferenceManager RefWorks RIS Permissions Request permissions Clean laboratory chemistry for the microwave-assisted digestion of botanical samples C. B. Rhoades, J. Anal. At. Spectrom., 1996, 11, 751 DOI: 10.1039/JA9961100751 To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page. If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given. If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page. Read more about how to correctly acknowledge RSC content. Social activity Tweet Share Search articles by author Charles B. Rhoades, Jr.

Hydride Generation Graphite Furnace Atomic Absorption Determination of Bismuth in Clinical Samples with in Situ Preconcentration

A sensitive method for the determination of bismuth in clinical samples using hydride generation/trapping and atomization in a graphite furnace is described. Addition of Pd-Ir to the furnace tube surface before hydride trapping leads to great improvement in the sensitivity of the method. Calibration is achieved with simple aqueous standards carried through this same procedure. An absolute detection limit (3σ) of 100 pg and a concentration detection limit of 20 ng/liter are obtained using 5-ml sample volumes. Corresponding precisions of 8-12% are typical for analyses of these samples. Microwave-assisted sample digestion procedures using HNO 3 and H 2O 2 were used to decompose clinical materials. The method was used to determine Bi in human blood, serum, urine, and tissue before and after intake of therapeutic doses of colloidal bismuth citrate.

Determination of chromium by electrothermal atomic absorption spectrometry after rapid microwave-assisted digestion of sediment and botanical samples

Determination of chromium by electrothermal atomization atomic absorption spectrometry with normal electrographite tube has been investigated after microwave-assisted digestion of sediment and botanical samples. Microwave oven-assisted procedures involve digestion with aqua regia, HF (for sediments) and H2O2 in a poly (tetrafluoroethylene)(PTFE) reactor followed by treatment with saturated H3BO3(where HF is used in the earlier step). Comparative studies on the determination of chromium using three previously reported chemical modifiers, Mg(NO3)2, Pd(NO3)2 and Triton X-100, and a new modifier NaVO3, have been made. Sodium vanadate was identified as an effective chemical modifier for chromium in botanical samples such as tomato leaves and citrus leaves. Whereas, for river sediment and sewage sludge, chromium has been determined accurately without the need of any chemical modifier. The advantages of the present method are its simplicity, low cost, high speed of sample attack and rapid calibration.

Continuous-flow microwave-assisted digestion of environmental samples using atomic spectrometric detection

A continuous-flow microwave-assisted digestion technique was tested with a view to the evaluation of its effectiveness for decomposition of environmental samples. A CEM SpectroPrep system was used at moderate powers and pressures of up to 2413 kPa to perform on-line digestion of slurried samples of biological tissues (0.5% m/v) and marine sediment (1% m/v). The efficiency of oxidation of biological matrices, as characterized by the residual carbon content of the solutions, was 64%. Recovery of trace elements averaged 90±1% and was accommodated with the use of suitable internal standards. Accuracy was verified by analysis of certified reference materials from the National Research Council of Canada, marine sediment BCSS-1 and lobster hepatopancreas tissue LUTS-1. Precision of measurement, as reflected in the determination of the trace metal content in replicate solutions, using a variety of atomic spectrometric techniques, was better than 1% RSD (relative standard deviation).

On-line microwave-assisted digestion of solid samples for their flame atomic spectrometric analysis

A new procedure has been developed for the on-line digestion of solids in a microwave oven. The direct injection in a water carrier flow of dispersions of solid samples in concentrated nitric acid, the merging of these slurries with 30% (v/v) H 2O 2 and the microwave-assisted digestion in a Teflon coil of 100 cm permit a fast and quantitative extraction of Cu and Mn from different solid matrices, such as vegetables, powdered dietary products and sewage sludges. The development of an appropriate interphase, in which digested samples are cooled and degassified, previous to their introduction into the nebulizer of a flame atomic absorption spectrometer, makes possible the full automatization of the digestion and measurement steps of the elemental analysis of solids and it provides a sample frequency of 180 injections per hour. The developed procedure has also been applied for Pb and Zn determination in certified sewage sludge samples, with accurate results obtained for Pb but low results found for Zn.

Atomic absorption spectrometric analysis of solids with on-line microwave-assisted digestion

A procedure was developed for the on-line microwave-assisted digestion of solid samples and their analysis by flame atomic absorption spectrometry. The method involves the transport of a slurry of the sample in a 1 + 1 mixture of concentrated HNO3 and H2O2, which provides quantitative extraction of Cu and Mn in a few minutes. Real samples of sewage sludges dispersed in 20 cm3 of HNO3 and H2O2 can be digested in 4 min and other matrices, such as artichoke and diet samples dispersed in 10 cm3 of HNO3 and H2O2 are digested in only 2 min. A closed flow injection system permits the on-line digestion to be carried out; the use of two interconnected injection valves allows the measurement of standards during the digestion of samples. The method permits the analysis of more than 15 samples per hour and provides accurate results, as demonstrated by the analysis of certified samples of sewage sludges ad tomato leaves.