Ultrasound-assisted solubilization of trace and minor metals from plant tissue using ethylenediaminetetraacetic acid in alkaline medium

A simplified and fast sample pretreatment method based on ultrasound-assisted solubilization of metals from plant tissue with ethylenediaminetetraacetic acid in alkaline medium is described. Powdered unknown and certified plant samples (particle size < 50 microns) were slurried in the solubilization medium and subjected to high intensity ultrasonication by a probe ultrasonic processor (20 kHz, 100 W). Metal solubilization can be accomplished within 3 min using a 30% vibrational amplitude and 0.1 M EDTA at pH 10, the supernatant obtained upon centrifugation being used for analysis. The method is applied to several food plants with unknown metal contents and certified plant samples such as CRM GBW07605 tea leaves, BCR CRM 61 aquatic moss and BCR CRM 482 lichen, with good trueness and precision. Intensive treatments with concentrated acids involving total matrix decomposition can be avoided. Metal determination (Ca, Cd, Mg, Mn, Pb and Zn) in the alkaline extracts was carried out by flame and electrothermal atomic absorption spectrometry.     

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.     

Consideration of the uncertainty in the CRM value with the analysis of solid materials using atomic spectrometry

 The principles of the ISO "Guide to the expression of uncertainty in measurement" are applied to the analysis of solid materials by graphite furnace atomic absorption spectrometry. Assessment of trueness is achieved by the analysis of a certified reference material (CRM) under fixed instrumental conditions. For the evaluation of the method's uncertainty (as part of the validation) a model equation is derived, considering all significant contributions, including the uncertainty in the CRM value and the uncertainty in the CRM analysis. A concrete example is presented and discussed (soya flour as an unknown sample and CRM BCR rye grass). For routine analysis a pooled estimate from the validation experiment can be used, leading to an acceptable small uncertainty range even in the case of "duplicate determination". The test for trueness (acceptance) of the result of the CRM analysis is applied and the correction for detected bias is discussed. Received: 28 June 1998 · Accepted: 13 July 1998     

Background correction in frequency modulated simultaneous atomic absorption spectrometry

Summary For a long time simultaneous multielement determination by AAS has been a subject of intensive research. In this work a simultaneous multielement atomic absorption spectrometry method is described in a special new arrangement, called frequency modulated simultaneous AAS (FremsAAS), using fiberoptics, interference filters and frequency modulation and demodulation by lock-in amplifiers as main devices. Purpose of this work was to equip the FremsAAS with a D₂-background correction and to test it with certified reference materials. Mn, Cd, Pb, Cu, Ni, Cr and Zn had been determined simultaneously (three at a time) in sewage sludge (BCR/CRM 146), estuarine sediment (BCR/CRM 277) and phosphate rock (BCR/CRM 32) with good feasibility. Frequency modulated simultaneous AAS with background correction (FremsAASUK) represents an interesting alternative to known instruments.Dedicated to Prof. Dr. V. Krivan on the occasion of his 60th birthday     

CBNM - determination of Li in BCR reference materials RM 303 and RM 304 lyophilized serum by isotope dilution mass spectrometry (IDMS)

Summary Lithium was determined in two BCR Candidate Reference Materials 303 and 304 by Isotope Dilution Mass Spectrometry using the state-of-the-art performance of isotope-specific methods gained during previous certifications of ⁶LiF reference targets used for the determination of the neutron lifetime [1]. After reconstitution of the serum, four aliquots of each of the two candidate materials from four different bottles were spiked with a previously characterized enriched ⁶Li spike [2] which is now available as CBNM IRM-615 and has a certified ⁶Li/⁷ Li ratio of 21.78±0.12 and a certified lithium concentration of 4.001±0.028 mol/g solution. The serum aliquots were digested in an HNO₃/H₂O₂ mixture and after evaporation of the acid, the lithium was separated on a cation exchange column, eluted with 0.3 mol/L HCl and used as LiCl for mass spectrometric measurement on an NBS type thermal ionization mass spectrometer. Similarly an unknown sample BCR X, provided by BCR to check the performance of the certifying laboratories, was analyzed. In addition the chemical preparation method was controlled by assaying NBS (NIST) SRM 909. The chemical blank was determined by IDMS using ⁶Li enriched CBNM IRM-615. The measurements were corrected for isotopic fractionation using the Isotopic Reference Material CBNM IRM-016 chemically prepared in the same way as the samples. The CRM samples as well as the BCR X sample and the NBS SRM 909 were also analyzed for isotopic composition to verify whether they had indeed natural isotopic composition. The final results have an overall uncertainty of 1.2 and 1.5%, respectively. This overall uncertainty (on a 2s basis or an estimate thereof) takes into account all uncertainty contributions of statistical as well as of systematic nature (uncertainties on used reference materials, density and blank determinations). The final results compare favorably with the values proposed by BCR for certification, but have a smaller (better) uncertainty: CRM 303: (0.517 4±0.005 7) mmol/L, CRM 304: (0.987±0.014) mmol/L     

Solid-liquid extraction of copper from slurried samples using high intensity probe sonication for electrothermal atomic absorption spectrometry

A fast and simple method is proposed for determination of copper by electrothermal atomic absorption spectrometry in biological samples. Pulverized solid samples were placed in autosampler cups, slurried in an acidic diluent and subsequently treated by sonication under optimized conditions. Parameters influencing extraction such as sonication time, ultrasound amplitude, acid concentration and particle size were optimized so that quantitative copper recovery could be achieved. Quantitative recoveries for copper in mussel tissue were obtained using a 3 min sonication time, a 60% ultrasound amplitude, a 3% V/V HNO(3) concentration along with a particle size of the solid particles less than 50 microm. Under these extraction conditions, quantitative recovery of copper was also seen to be achieved for several certified reference materials such as BCR 278 mussel tissue, NRCC DORM-2 dogfish muscle and BCR CRM 60 (Lagarosiphon major) aquatic plant. The LOD of copper in the biological samples was 0.16 microg g(-1) when a sample mass of 10 mg were slurried in a volume of 1.5 ml. When comparing within- and between-batch precision values no significant differences occurred, hence indicating good homogeneity at the 10 mg mass level. Potential advantages of the method proposed over conventional slurry sampling such as an improved precision, since the representative subsample is the whole mass weighed in the autosampler cup, a decreased build-up of carbonaceous residues inside the graphite tube and the removal of volumetric and sedimentation errors can be anticipated.     

Determination of arsenic in scalp hair samples from exposed subjects using microwave-assisted digestion with and without enrichment based on cloud point extraction by electrothermal atomic absorption spectrometry

A simple and rapid cloud point extraction (CPE) procedure was applied for preconcentration of trace quantities of arsenic (As) in scalp hair samples. The samples were subjected to microwave-assisted digestion in a mixture of nitric acid and hydrogen peroxide (2 + 1, v/v) prior to preconcentration by CPE. The As in digested samples was complexed with ammonium pyrrolidine dithiocarbamate (APDC), and the resultant As-PDC complex was extracted by a nonionic surfactant, octylphenoxypolyethoxyethanol (Triton X-114). After centrifugation, the surfactant-rich phase was diluted with 0.1 M HNO3 in methanol and analyzed by electrothermal atomic absorption spectrometry. The experimental parameters, i.e., amount of APDC, concentration of Triton X-114, equilibrium temperature and time, were optimized. For validation of the proposed method, a certified reference material (CRM) of human hair (BCR 397) was used. No significant difference (P > 0.05) was observed between the experimental results and certified values of the CRM (paired t-test). The LOD and LOQ obtained under the optimal conditions were 0.025 and 0.083 microg/kg, respectively. The developed method was applied for the determination of As in scalp hair samples from male and female subjects of two villages of Khairpur Mir's, Pakistan.     

Some observations on the determination of total heavy metals in sewage sludge by atomic absorption spectrophotometry after a pressurized acid digestion

An economical and simple method for the flame atomic absorption spectrometric determination of Cd, Pb, Ni, Cu, Fe, and Zn in sewage sludges is described. Samples are treated with concentrated HNO₃ in a thermal oven using Pyrex glass tubes hermetically sealed with Bakelite screw caps. The effect of the digestion parameters, such as digestion time, acid volume, sample mass, and temperature, were studied. The precision and accuracy of this procedure were evaluated by the analysis of two BCR (Community Bureau of Reference, European Communities) certified sewage sludge samples (CRM 146 and 144).     

无标样X荧光分析软件UNIQUANT在标准物质定值和未知样品鉴定中的应用

采用一种新的Ｘ射线荧光ＵＮＩＱＵＡＮＴ软件分析方法,分析了土壤标准物质和未知样品,土壤标准物质的分析结果与标准值较吻合,除氧化钠和氧化镁的相对偏差较高外,其余氧化物的相对偏差在０～１０％之间。     

Method to reduce the memory effect of mercury in the analysis of fish tissue using inductively coupled plasma mass spectrometry

The routine determination of mercury (Hg) by inductively coupled plasma mass spectrometry (ICP-MS) is affected by a pronounced memory effect in the sample introduction system. This results in long washout times for the analyte, which affects the accuracy and reliability of the analytical procedure. By using a combination of flow injection sample introduction and a sulfur-containing compound in the carrier solution, it was possible to decrease the memory effect of mercury to that for the internal standard (rhodium). The carrier solution contained 2-mercaptoethanol (2-ME) and the developed method was evaluated using three different fish tissue certified reference materials: CRM 464 (BCR, Brussels); DORM-1; and DORM-2 (NRC, Canada). The samples were mineralized using a combination of concentrated nitric acid and hydrogen peroxide and heating in a closed microwave oven. The developed flow injection ICP-MS procedure gave values for total mercury in all three CRM materials in agreement with the certified concentration range. Cold vapour atomic fluorescence spectrometry (CV-AFS) confirmed the results from the developed method. The developed flow injection method had a detection limit (defined as three times the standard deviation of the blank concentration) for mercury of 5.1 μg l⁻¹.     

Determination of selenium in marine biological tissues by transverse heated electrothermal atomic absorption spectrometry with longitudinal Zeeman background correction and automated ultrasonic slurry sampling.

A fast, sensitive, and reliable method for determination of selenium in marine biological tissues by electrothermal atomic absorption spectrometry with slurry sampling was developed. Slurries were prepared from fresh and frozen seafood samples that were previously homogenized, dried, and ground; particle sizes <100 microm were taken for analysis. A 3% (v/v) HNO3 solution containing 0.01% (v/v) Triton X-100 was used as slurry diluent. Slurries were mixed on an automated ultrasonic slurry sampler at 20% amplitude for 30 s just before an aliquot was injected into the furnace. The method was successfully validated against the following certified reference materials: NRCC CRM DORM-2 (Dogfish muscle); NRCC CRM TORT-2 (Lobster hepatopancreas); NRCC CRM DOLT-2 (Dogfish liver); and BCR CRM 278 (Mussel tissue), and was subsequently applied to determination of Se in 10 marine biological samples. The influences of the drying procedure (oven-, microwave-, and freeze-drying), matrix modifier amount, mass of solid material in cup, and pipetting sequence are discussed. The limit of determination of Se was 0.16 microg/g and the repeatability, estimated as between-batch precision, was in the range of 4-8%. Se contents in the samples ranged from 0.6 to 2.8 microg/g. The proposed method should be useful for fast assessment of the daily dietary intake of Se.     

Dynamic ultrasound-assisted extraction of cadmium and lead from plants prior to electrothermal atomic absorption spectrometry

A dynamic ultrasound-assisted extraction step is proposed for the quantitative extraction of Cd and Pb from plant leaves prior to determination by electrothermal atomic absorption spectrometry (ETAAS). Beech leaves (a certified reference material—CRM 100—where the target analytes were not certified) were used for optimizing the extraction step by a multivariate approach. The samples (0.25 g) were subjected to dynamic ultrasound-assisted extraction with dilute nitric acid as extractant. The method was validated with a certified reference material BCR-062 (olive leaves) where both Cd and Pb are certified. The good agreement between the certified values and those found using the proposed method demonstrates its usefulness. The repeatability was 2.0 and 0.9% and the within-laboratory reproducibility was 7.1 and 2.8% for Cd and Pb, respectively. The precision of the method, together with its efficiency, rapidity, low cost and environmental acceptability makes it a good alternative for the determination of trace metals from plant material.     

Determination of phosphorus in small amounts of protein samples by ICP–MS

Inductively coupled plasma mass spectrometry (ICP-MS) is used for phosphorus determination in protein samples. A small amount of solid protein sample (down to 1 micro g) or digest (1-10 micro L) protein solution was denatured in nitric acid and hydrogen peroxide by closed-microvessel microwave digestion. Phosphorus determination was performed with an optimized analytical method using a double-focusing sector field inductively coupled plasma mass spectrometer (ICP-SFMS) and quadrupole-based ICP-MS (ICP-QMS). For quality control of phosphorus determination a certified reference material (CRM), single cell proteins (BCR 273) with a high phosphorus content of 26.8+/-0.4 mg g(-1), was analyzed. For studies on phosphorus determination in proteins while reducing the sample amount as low as possible the homogeneity of CRM BCR 273 was investigated. Relative standard deviation and measurement accuracy in ICP-QMS was within 2%, 3.5%, 11% and 12% when using CRM BCR 273 sample weights of 40 mg, 5 mg, 1 mg and 0.3 mg, respectively. The lowest possible sample weight for an accurate phosphorus analysis in protein samples by ICP-MS is discussed. The analytical method developed was applied for the analysis of homogeneous protein samples in very low amounts [1-100 micro g of solid protein sample, e.g. beta-casein or down to 1 micro L of protein or digest in solution (e.g., tau protein)]. A further reduction of the diluted protein solution volume was achieved by the application of flow injection in ICP-SFMS, which is discussed with reference to real protein digests after protein separation using 2D gel electrophoresis.The detection limits for phosphorus in biological samples were determined by ICP-SFMS down to the ng g(-1) level. The present work discusses the figure of merit for the determination of phosphorus in a small amount of protein sample with ICP-SFMS in comparison to ICP-QMS.     

Trace analysis of heavy metals in groundwater samples by ion chromatography with post-column reaction and ultraviolet-visible detection

A rapid and automated method for the analysis of alpha-, gamma- and delta-tocopherols in vegetable oils is reported. Continuous extraction of vitamin E isomers from oil samples dissolved in Triton X-114 in the presence of methanol-hexane is achieved and coupled on-line with the chromatographic system. Using an acetic acid/sodium acetate buffer in a methanol-water (97:3) solution as the mobile phase, a C18 stationary phase and electrochemical detection in the coulometric mode, alpha-, gamma- and delta-tocopherol isomers can be successfully analyzed within 17 min. Thirteen commercially available oils of olive, sunflower, corn and seed mixtures were analyzed using 2,2,5,7,8-pentamethyl-6-chromanol as internal standard. The results obtained using three methodologies, one of them including classical sample treatment for liposoluble vitamin analysis, were in good agreement. To validate the proposed method, analysis of the only BCR Reference Material available, with a certified content of alpha-tocopherol (margarine CRM 122), was carried out using the automated methodology, the results found being in agreement with the certified value.     

Element fingerprinting of marine organisms by dynamic reaction cell inductively coupled plasma mass spectrometry

A method for the determination of sixteen elements (Al, As, Cd, Co, Cr, Cu, Fe, Hg, Mn, Mo, Ni, Pb, Se, Sn, V, Zn) in seafood by dynamic reaction cell inductively coupled plasma mass spectrometry (ICP–DRC–MS) is presented. A preliminary study of polyatomic interferences was carried out in relation to the chemical composition of marine organisms belonging to different taxa. Acid effects and other matrix effects in marine organisms submitted to closed-vessel microwave digestion were investigated as well. Ammonia was the reactive gas used in the DRC to remove polyatomic ions interfering with ²⁷Al, ⁵²Cr, ⁵⁶Fe and ⁵¹V. Optimal conditions for the simultaneous determination of analytes were identified in order to develop a fast multielement method. A suite of real samples (mussels and various fish species) were used during method development along with three certified reference materials: BCR CRM 278R (mussel tissue), BCR CRM 422 (cod muscle) and DORM-2 (dogfish muscle). The proposed analytical approach can be used in conjunction with suitable chemometric procedures to address quality and safety issues in aquaculture and fisheries. As an example, a case study is described in which mussels from three farming sites in the Venice Lagoon were distinguished by multivariate analysis of element fingerprints.      

Fractionation of heavy metals in sediment by using microwave assisted sequential extraction procedure and determination by inductively coupled plasma mass spectrometry

In this work, a fast microwave assisted extraction procedure was developed and optimized for the heavy metals (Cu, Ni, Cr, Pb and Cd) partitioning in the three-stage sequential extraction procedure proposed by the European Standards, Measurements and Testing (SM&;T) Program, formerly the Community Bureau of Reference (BCR). The microwave oven procedure was optimized to obtain extraction efficiencies similar to the conventional BCR procedure, in less time, while using smaller volumes of reagents. In the optimization process, three variables (extraction time, ramping time and microwave power) were considered as factors and as a response the concentration of different metal ions in each individual BCR fraction. Interactions between analytical factors and their optimized levels were investigated using a central composite design. Extractable metals obtained by both comparable methodologies were measured by inductively coupled plasma mass spectrometry. With the use of optimal microwave conditions, steps 1–3 of the sequential extraction (including the hydrogen peroxide digestion in step 3) could be completed between 21 and 22 min. Detection limits were between 1 and 18 ng l^{− 1}. The accuracy of the proposed method was checked with a certified reference material (CRM) of Lake Sediment BCR 701. Values obtained were in accordance with those reported for the certified material with only a few exceptions. Different origin sediments (river and marine) were analyzed by both BCR and MW procedures, and the results obtained were comparable according to the t-paired-test for a 95% confidence level.     

Determination of arsenic in traditional Chinese medicine by microwave digestion with flow injection-inductively coupled plasma mass spectrometry (FI-ICP-MS).

A simple, rapid, and sensitive method with high sample throughput was developed for determining arsenic in traditional Chinese medicine (TCM) in the form of uncoated tablets, sugar-coated tablets, black pills, capsules, powders, and syrups. The method involves microwave digestion with flow injection-inductively coupled plasma mass spectrometry (FI-ICP-MS). Method precision was 2.7-10.1% (relative standard deviation, n = 6) for different concentrations of arsenic in different TCM samples analyzed by different analysts on different days. Method accuracy was checked with a certified reference material (sea lettuce, Ulva lactuca, BCR CRM 279) for external calibration and by spiking arsenic standard into different TCMs. Recoveries of 89-92% were obtained for the certified reference material and higher than 95% for spiked TCMs. Matrix interference was insignificant for samples analyzed by the method of standard addition. Hence, no correction equation was used in the analysis of arsenic in the samples studied. Sample preparation using microwave digestion gave results that were very similar to those obtained by conventional wet acid digestion using nitric acid.     

Simultaneous determination of trimethyl-and triethyllead in urban dust by species-specific isotope dilution/gas chromatography-inductively coupled plasma mass spectrometry

Both (206)Pb-labeled trimethyllead (TML) and triethyllead (TEL) were synthesized from (206)Pb-enriched metallic Pb certified reference material (NIST SRM 983) and iodomethane or iodoethane through a one-process reaction in a closed system using centrifuge tubes, respectively. Organolead compounds in an urban dust reference material (BCR CRM 605) were extracted with an acetic acid/methanol (1:1) solution, which was mechanically shaken for 24 h. After adjusting the pH of the extracted solution to pH 5, the extracted organolead compounds were derivatized by tetrabutylammonium tetrabutylborate (TATB) and measured with GC-ICPMS. The analytical results of TML and TEL for BCR CRM 605 were 8.22 +/- 0.04 microg kg(-1) (mean +/- standard deviation, n = 3) and 1.12 +/- 0.06 microg kg(-1), respectively. The analytical results of TML agreed well with the certified value (7.9 +/- 1.2 microg kg(-1)).     

Micro-heterogeneity study of trace elements in BCR CRM 680 by means of synchrotron micro-XRF

BCR CRM 680 is a newly released reference material (RM) with a polyolefinic matrix, doped with various metallic compounds in trace concentrations, to be used for calibration of multi-element trace analytical methods. The micro-heterogeneity of this new CRM was investigated to evaluate the suitability as a RM for trace-level micro analytical techniques. Synchrotron micro-XRF, a trace-level micro analytical method, allows to quantitatively measure the degree of heterogeneity of inorganic trace constituents in solid materials with a homogeneous matrix. The procedure for calculating the minimal sampling mass for homogeneous measurements was employed for BCR CRM 680. By repeating the entire procedure on several samples of the same material, the repeatability of the micro-heterogeneity characterization based on micro-XRF was investigated. Afterwards, the micro-heterogeneity results from the BCR CRM 680 material were used to evaluate the suitability of the micro-heterogeneity procedure by means of a Monte Carlo simulation model. Also the existence of nuggets in the polymer material is looked into.     

Micro-heterogeneity study of trace elements in BCR CRM 680 by means of synchrotron micro-XRF

BCR CRM 680 is a newly released reference material (RM) with a polyolefinic matrix, doped with various metallic compounds in trace concentrations, to be used for calibration of multi-element trace analytical methods. The micro-heterogeneity of this new CRM was investigated to evaluate the suitability as a RM for trace-level micro analytical techniques. Synchrotron μ-XRF, a trace-level micro analytical method, allows to quantitatively measure the degree of heterogeneity of inorganic trace constituents in solid materials with a homogeneous matrix. The procedure for calculating the minimal sampling mass for homogeneous measurements was employed for BCR CRM 680. By repeating the entire procedure on several samples of the same material, the repeatability of the micro-heterogeneity characterization based on μ-XRF was investigated. Afterwards, the micro-heterogeneity results from the BCR CRM 680 material were used to evaluate the suitability of the micro-heterogeneity procedure by means of a Monte Carlo simulation model. Also the existence of nuggets in the polymer material is looked into.