Biological Certified Reference Materials Research Articles

Determination of methyl- and inorganic mercury in fish using focused microwave digestion followed by Cu++ addition, sodium tetraethylborate derivatization, n-heptane extraction, and gas chromatography-mass spectrometry

The analytical procedure for analysis of methyl- and inorganic mercury in fish was developed in this study. It involved microwave-assisted digestion with alkaline solution (tetra methyl ammonium hydroxide), addition of Cu++, aqueous-phase derivatization of mercury species with sodium tetraethylborate, and subsequent extraction with n-heptane. The various mercury derivatives were desorbed in the splitless injection port of a gas chromatograph and subsequently analyzed by electron impact mass spectrometry. Optimum conditions allowed the sample throughout to be controlled by the instrumental analysis time (about 8 min per sample) but not by the sample preparation step. At the irradiation power of 15-30, 45, and 60-75 W, sample heating times were only 3.5, 2.5, and 1.5 min, respectively. The recoveries of mercury species were 92.3-96.1% and 93.6-95.5% for methyl- and inorganic mercury, respectively. The proposed method was finally validated by the analysis of three biological certified reference materials (BCR CRM 464 tuna fish, NRC DORM-2 dogfish muscle, and NRC DOLT-2 dogfish liver).

High-throughput, Multi-batch System for the Efficient Microwave Digestion of Biological Samples.

In this paper, we proposed a high-throughput microwave digestion system based on multi-batch reactors (three quartz test tubes inside commercial PTFE vessels). This original configuration was validated by ICP-MS analysis of several elements in biological certified reference materials (fish tissues and plankton). The proposed system was proved to be free from contamination showing very low LODs. The improved hardware configuration is therefore highly beneficial for the detection of trace elements in microsamples from the marine food web.

Distribution of Rare Earth Elements in Citrus Leaves and Reference Materials (NIST SRM 1515 and ERM CD281)

The present study aims to discuss the data on levels and distribution of rare earth elements, including Y, (REYs) in leaves of three different citrus species (lemon, orange, and tangerine) and provide additional information about the major, minor and trace elements in two biological certified reference materials (CRMs), Apple leave (NIST SRM 1515) and Rye grass (ERM CD281). In all samples, element concentrations were determined by High Resolution Inductively Coupled Plasma Mass Spectrometry. The obtained data display substantial variability in the distribution of REY elements, not only between different citrus species but also between different genera of plants indicating their different uptake and accumulation abilities. Measured concentrations of REYs in citrus leaves were substantially lower compared to the literature values, although the fractionation indices were comparable. The data for CRMs provide additional information for the 14 elements in NIST SRM 1515 and the 30 elements in ERM CD281, including rare earth elements.

A Method for Methylmercury and Inorganic Mercury in Biological Samples Using High Performance Liquid Chromatography-Inductively Coupled Plasma Mass Spectrometry.

A new determination method was developed for the measurement of methylmercury (Me-Hg) and inorganic mercury (i-Hg) in biological samples using high-performance liquid chromatography-inductively coupled plasma-mass spectrometry (HPLC-ICP-MS) following alkaline extraction. Mercury species in biological samples were extracted with 10% (w/w) tetramethylammonium hydroxide (TMAH) solution at 80°C for 2 h. Methylmercury was completely separated from i-Hg by adamantyl type and octadecylsilyl type columns within 6 and 4 min using isocratic elution, respectively. The detection limits (3σ) of adamantyl and octadecylsilyl columns using the proposed system were 0.08 and 0.13 ng g-1 (as Hg), respectively. Inorganic Hg completely separates from Me-Hg without tailing. The proposed determination methods were applied to several biological certified reference materials (CRMs). The measurement results of Me-Hg obtained by the present method were in good agreement within the expanded uncertainties (k = 2) with the certified values. The analytical precision (n = 3) of Me-Hg was less than 2%, and the recoveries of Me-Hg and i-Hg were 101 ± 1 and 103 ± 3%, respectively. In addition, this method enables the determination of Me-Hg and i-Hg for 20 samples in 1 h.

Fully automated focused infrared microashing combined with use of ICP-based instruments for rapid analysis of multiple elements in biological samples.

A fully automated focused infrared microashing sample preparation system was proposed for preparation of biological samples with high organic matter content for the determination of multiple elements combined with inductively coupled plasma optical emission spectroscopy and inductively coupled plasma mass spectrometry. The whole ashing procedure, including sample transfer, carbonization and oxidation of the sample, dissolution of ash, constant volume control, and homogenization of the solution, was automatically controlled. Gold-plated infrared tubes were used to produce and focus infrared radiation to heat the sample. Ozone was used to accelerate the carbonization of samples at a lower temperature to avoid the production of large amounts of empyreumatic oil. In addition, the self-designed double-layer tube serves as a site for ashing and carbonization of the sample and as a container for dissolving ash, as well as for holding the solution. This is the only container in the entire system to reduce the risk of pollution. Eight biological certified reference materials were used as examples to evaluate the performance of the proposed device. A sample ashing pretreatment cycle, from solid sample to liquid solution, took only 40 min and simultaneously treated 12 samples. Except for individual results, the relative errors between the certified values and recorded values for 38 micro and trace elements, including Ca, Mg, Na, P, Li, Be, Sc, Ti, V, Mn, Co, Ni, Cu, Zn, Rb, Sr, Y, Mo, Ag, Cs, Ba, Tl, Th, U, and rare earth elements, were typically less than 30%. The relative standard deviations for five determinations were typically less than 15%. Graphical abstract Automated dry ashing sample preparation system. ICP inductively coupled plasma.

Speciation of Mercury in Microalgae by Isotope Dilution-inductively Coupled Plasma Mass Spectrometry

ABSTRACTSpecies-specific stable isotope dilution in combination with gold trap- or gas chromatography (GC)-inductively coupled plasma mass spectrometry (ICP-MS) is reported for the determination of inorganic mercury and methylmercury in diatoms (Chaetoceros curvisetus). The optimum conditions for the separation parameters were established. The isotope dilution analysis was performed using 199Hg-enriched Hg2+ and laboratory-synthesized 201Hg-enriched methylmercury. The absolute detection limits obtained with isotope dilution-ICP-MS were 9 pg for total mercury and 0.6 pg for methylmercury. The relative error of 7 Hg isotopic abundances based on the peak area measurements was better than 2.0% for 20 pg of methylmercury (as Hg) and 250 pg of inorganic mercury. The accuracy of the method was validated with a biological certified reference material. The developed method was then applied to investigate the uptake of inorganic mercury and methylmercury by C. curvisetus. Continuous uptake of inorganic mercury and methylmercury was observed during 5 days of incubation.

Species specific isotope dilution for the accurate and SI traceable determination of arsenobetaine and methylmercury in cuttlefish and prawn

Methods based on species specific isotope dilution were developed for the accurate and SI traceable determination of arsenobetaine (AsBet) and methylmercury (MeHg) in prawn and cuttlefish tissues by LC-MS/MS and SPME GC-ICPMS. Quantitation of AsBet and MeHg were achieved by using a 13C-enriched AsBet spike (NRC CRM CBET-1) and an enriched spike of Me198Hg (NRC CRM EMMS-1), respectively, wherein analyte mass fractions in enriched spikes were determined by reverse isotope dilution using natural abundance AsBet and MeHg primary standards. Purity of these primary standards were characterized by quantitative 1H-NMR with the use of NIST SRM 350b benzoic acid as a primary calibrator, ensuring the final measurement results traceable to SI. Validation of employed methods of ID LC-MS/MS and ID SPME GC-ICPMS was demonstrated by analysis of several biological CRMs (DORM-4, TORT-3, DOLT-5, BCR-627 and BCR-463) with satisfying results.The developed methods were applied for the determination of AsBet and MeHg in two new certified reference materials (CRMs) prawn (PRON-1) and cuttlefish (SQID-1) produced jointly by Thailand Institute of Scientific and Technological Research (TISTR) and National Research Council Canada (NRC). With additional measurements of AsBet using LC-ICPMS with standard additions calibration and external calibration at NRC and TISTR, respectively, certified values of 1.206 ± 0.058 and 13.96 ± 0.54 mg kg−1 for AsBet as As (expanded uncertainty, k = 2) were obtained for the new CRMs PRON-1 and SQID-1, respectively. The reference value of 0.324 ± 0.028 mg kg−1 as Hg (expanded uncertainty, k = 2) for MeHg was obtained for the SQID-1 based on the results obtained by ID SPME GC-ICPMS method only, whereas MeHg in PRON-1 was found to be < 0.015 mg kg−1. It was found that AsBet comprised 69.7% and 99.0% of total As in the prawn and cuttlefish, respectively, whereas MeHg comprised 94.5% of total Hg in cuttlefish.

On-line UV photochemical generation of volatile copper species and its analytical application

Volatile Cu species were on-line generated by photochemical reduction in a formic acid medium utilizing a unique flow-through photochemical reactor. Digests of biological samples in 18% formic were introduced to the photochemical vapor generation (PVG) reactor under conditions wherein copper-containing species were initially retained on the reactor wall following a purge of the line with air and desorbed in the presence of a plug of 60% formic acid to yield volatile species which were transported to a gas–liquid separator and introduced to multi-collector inductively coupled plasma spectrometry (MC-ICPMS). Sensitivity of the proposed method could be further improved if a sample solution is repeatedly introduced using several cycles comprising loading and drying steps. However, the unstable volatile Cu species generated by PVG together with the early release of Cu during drying step resulted in a poor measurement precision of near 30% (n=4, RSD) and a non-linear correlation between the signal intensity and the Cu2+ concentration. Despite the above shortcomings, the accurate and precise determination of Cu concentrations in biological samples was achieved by applying isotope dilution (ID) calibration. A method detection limit of 8ngg−1 normalized to a nominal test mass of 0.25g of sample was obtained based on ID quantification. Method validation was demonstrated by analysis of three biological certified reference materials of TORT-3, SRM 1566b and DOLT-5 with satisfying results. Concentrations of 490.8±0.6, 71.88±0.06 and 34.95±0.04μgg−1 (1SD, n=4) with precisions of 0.12, 0.08 and 0.13% RSD for Cu were obtained in TORT-3, SRM 1566b and DOLT-5, respectively, in good agreement with certified values.

Feasibility of halogen determination in noncombustible inorganic matrices by ion chromatography after a novel volatilization method using microwave-induced combustion

A microwave-induced combustion (MIC) system based on the volatilization process was applied for subsequent halogen determination from noncombustible inorganic matrices. Portland cement samples were selected to demonstrate the feasibility of the proposed method, allowing the subsequent determination of Cl and F by ion chromatography (IC). Samples were mixed with high-purity microcrystalline cellulose, wrapped with a polyethylene film and combusted in quartz closed vessels pressurized with oxygen (20bar). Water and NH4OH (10, 25 or 50mmolL−1) were evaluated for Cl and F absorption, but water was selected, using 5min of reflux after volatilization. Final solutions were also suitable for analysis by pontentiometry with ion-selective electrode (ISE) for both analytes, and no difference was found when comparing the results with IC. The accuracy of the proposed method for Cl was evaluated by analysis of certified reference materials (CRMs), and agreement with certified values ranged from 98% to 103%. Results were also compared to those using the procedure recommended by the American Society of Testing and Materials (ASTM) for the determination of total chlorides (C114-13), and no difference was found. Volatilization by MIC using a mixture of cement, cellulose and a biological CRM was carried out in order to evaluate the accuracy for F, and recovery was about 96%. The proposed method allowed suitable limits of detection for Cl and F by IC (99 and 18mgkg−1, respectively) for routine analysis of cement. Using the proposed method, a relatively low standard deviation (<7%), high throughput (up to eight samples can be processed in less than 30min) and lower generation of laboratory effluents, when compared to the ASTM method, were obtained. Therefore, the method for volatilization of Cl and F by MIC and subsequent determination by IC can be proposed as a suitable alternative for cement analysis.

Multielement analysis of lichen samples using XRF methods. Comparison with ICP‐AES and FAAS

This research presents the contents of Ca, Fe, Zn, Br, Rb, Sr and Pb in lichen samples used as biomonitors of air pollution collected in Havana. Statistical comparisons were made among the results obtained in three campaigns during three years. Two X‐Ray Fluorescence (XRF) methods were used, employing for excitation an annular 109Cd source and a Mo X‐ray tube with a molybdenum secondary target. In both cases, matrix effects were corrected by the use of normalization for the Compton scattered peak; in this way the determination is more efficient. For quality control of the results, biological Certified Reference Materials were analyzed and were made comparisons between XRF, Inductively Coupled Plasma‐Atomic Emission Spectrometry and Flame Atomic Absorption Spectrophotometry. No significant differences were found between the different techniques. The elemental distribution patterns obtained for each metal were associated with different pollution sources, thus contributing to the assessment of air pollution in Havana. Copyright © 2015 John Wiley &amp; Sons, Ltd.

Electrospray Ionization Mass Spectrometry for the Quantification of Inorganic Cations and Anions

Recent studies from our laboratory on electrospray ionization mass spectrometry (ESI-MS) for the quantification of inorganic cations and anions are reviewed. Metal ions were determined by ESI-MS in negative-ion mode as monovalent negative ions of their aminopolycarboxylate (APC) complexes, where excess amounts of the APC agents were added to sample solutions. Among the APCs studied, we found trans-1,2-diaminocyclohexane-N,N,N',N'-tetraacetic acid (CyDTA, the chemical forms in a complex were expressed as H(n)cydta(n-4)) as the best chelating agent. A size exclusion column was used for on-line separation of the metal-APC complexes from matrix salts in samples. Total amounts of Al, Ni, Cu, Zn, and Pb in the biological certified reference materials (CRM), Olive Leaves (BCR-062) and Plankton (BCR-414), and in a soil CRM (JSAC-0401) were successfully determined by the proposed method. Halide ions (X(-) = F(-), Cl(-), Br(-) and I(-)) and cyanide (CN(-)) were determined by ESI-MS based on the formation of ternary complexes of metals, chelating agents and the analyte anions. Negative ions of the ternary complexes of group 13 elements, nitrilotriacetic acid (NTA, H(n)nta(n-3)), and halides, i.e., [AlF(nta)](-) for F(-), and [InX(nta)](-) for other halides, were measured; the limits of detection (LODs) were 10 nmol dm(-3) for F(-), 0.31 μmol dm(-3) for Cl(-), 3.8 nmol dm(-3) for Br(-), and 1.6 nmol dm(-3) for I(-), respectively. In the case of CN(-), an LOD of 20 nmol dm(-3) was obtained based on measurements of the ternary complex of Cu(II), CN(-) and 4-(2-pyridylazo)resorcinol (PAR, Hnpar(n-2)), i.e., [(63)Cu(II)(CN)(par)](-) (m/z 302). Moreover, quantitative methods for Cr(VI) and Cr(III) by ESI-MS were developed, where HCrO4(-) (m/z 117) for Cr(VI) and [Cr(III)(cydta)](-) for Cr(III) were used for measurements.

Оценка возможности применения прямого анализа образцов биотканей малой массы методом рентгенфлуоресцентного анализа с синхротронным возбуждением

The direct analysis of the biological tissue samples is a great advantage of the X-ray Fluorescent Technique with Synchrotron Radiation (SRXRF). SRXRF method is realized on the basis of INP SB RAS in Siberian Synchrotron and Terahertz Radiation Centre. In the present work, the whole liver tissue samples were dried under weight and analyzed in the form of parallel-plane fragments. The minimization of sample preparation procedures is known to significantly reduce the risks of the sample contamination and loss of analyte. The preparation procedure, which was used in the present work, was carried out without lyophilization, grinding and pelletizing of liver tissue samples. Elemental concentrations in the samples were calculated using the calibration and constructed on the basis of biological certified reference materials. It was found that there weren’t any significant differences between elemental concentrations in the case of the direct analysis of parallel-plane liver fragments and concentrations obtained for the same liver samples after grinding and pelletizing. Two unbroken samples and one grinded sample were measured 5 times to assess the reproducibility. The relative standard deviation for each sample was calculated, and it included both the assessment of the reproducibility and the heterogeneity of the elemental distribution in the sample. The validation of the results obtained by SRXRF method was estimated by the comparison with the results obtained by another method, namely by Two-Jet Plasma Atomic Emission Spectrometry (TJP-AES). Thereby the offered way of sample preparation procedure using external standard method for calculation of elemental concentrations can be applied for SRXRF analysis of biological samples. Keywords : x-ray fluorescent analysis, synchrotron radiation, sample preparation, biological tissue, liver (Russian) DOI: http://dx.doi.org/10.15826/analitika.2015.19.2.008 V.A. Trunova 1,2 , A.V. Sidorina 1 , V.V. Zvereva 1 1 A.V. Nikolaev Institute of Inorganic С hemistry SB RAS, Novosibirsk, Russian Federation 2 Novosibirsk State University , Novosibirsk, Russian Federation

Strontium mono-chloride — A new molecule for the determination of chlorine using high-resolution graphite furnace molecular absorption spectrometry and direct solid sample analysis

A new method has been developed for the determination of chlorine in biological reference materials using high-resolution continuum source graphite furnace molecular absorption spectrometry (HR-CS GF MAS) of the strontium mono-chloride (SrCl) molecule and direct solid sample analysis. The use of the SrCl molecule for high-temperature MAS was not described up to now in the literature. Preliminary time-dependent density functional theory calculations of the SrCl structure were carried out in order to obtain reasonable estimates of the absorption spectrum of the target molecule. The calculations, which were carried out at BHandHLyp/def2-QZVP level of theory, proved a very accurate and inexpensive way to get information about the spectrum of the SrCl molecule, which enabled us to perform the Cl determination with good sensitivity and specificity. The molecular absorption of the SrCl molecule has been measured using the wavelength at 635.862nm, and zirconium and palladium have been evaluated as the chemical modifiers in order to increase the sensitivity of the gaseous SrCl molecule generated in the graphite furnace. The pyrolysis and vaporization temperatures were 600°C and 2300°C, respectively. Accuracy and precision of the method have been evaluated using biological certified reference materials of both animal and plant origins, showing good agreement with the informed and certified values. Limit of detection and characteristic mass were 1.0 and 2.2ng, respectively. The results found using HR-CS GF MAS were in agreement (95% confidence level) compared to those obtained by electrothermal vaporization-inductively coupled plasma mass spectrometry.

Determination of sulfur in food by high resolution continuum source flame molecular absorption spectrometry

In the present work, a fast, simple and sensitive analytical method for determination of sulfur in food and beverages by high resolution continuum source flame molecular absorption spectrometry was developed. The determination was performed via molecular absorption of carbon monosulfide, CS. Different CS rotational lines (257.959nm, 258.033nm, 258.055nm), number of pixels and types of standard solution of sulfur, namely: sulfuric acid, sodium sulfate, ammonium sulfate, sodium sulfite, sodium sulfide, dl-cysteine, and l-cystine, were studied in terms of sensitivity, repeatability of results as well as limit of detection and limit of quantification. The best results were obtained for measurements of absorption of the CS molecule at 258.055nm at the wavelength range covering 3pixels and dl-cysteine in 0.2molL−1 HNO3 solution as a calibration standard. Under optimized conditions the limit of detection and the limit of quantification achieved for sulfur were 10.9mgL−1 and 36.4mgL−1, respectively. The repeatability of the results expressed as relative standard deviation was typically <5%.The accuracy of the method was tested by analysis of digested biological certified reference materials (soya bean flour, corn flour and herbs) and recovery experiment for beverage samples with added known amount of sulfur standard. The recovery of analyte from such samples was in the range of 93–105% with the repeatability in the range of 4.1–5.0%. The developed method was applied for the determination of sulfur in milk (194±10mgkg−1), egg white (2188±29mgkg−1), mineral water (31.0±0.9mgL−1), white wine (260±4mgL−1) and red wine (82±2mgL−1), as well as in sample rich in ions, such as bitter mineral water (6900±100mgL−1).

Determination of elements by atomic absorption spectrometry in medicinal plants employed to alleviate common cold symptoms.

Eleven important medicinal plants generally used by the people of Turkey for the treatment of common cold have been studied for their mineral contents. Eleven minor and major elements (essential, non-essential and toxic) were identified in the Asplenium adiantum-nigrum L. , Althaea officinalis L. , Verbascum phlomoides L., Euphorbia chamaesyce L., Zizyphus jujube Miller, Peganum harmala L., Arum dioscoridis Sm., Sambucus nigra L., Piperlongum L., Tussilago farfara L. and Elettaria cardamomum Maton by employing flame atomic absorption and emission spectrometry and electro-thermal atomic absorption spectrometry. Microwave digestion procedure for total concentration was applied under optimized conditions for dissolution of medicinal plants. Plant based biological certified reference materials (CRMs) served as standards for quantification. These elements are found to be present in varying concentrations in the studied plants. The baseline data presented in this work can be used in understanding the role of essential, non-essential and toxic elements in nutritive, preventive and therapeutic properties of medicinal plants.

Interaction Between Selenium and Mercury in Biological Samples of Pakistani Myocardial Infarction Patients at Different Stages as Related to Controls

It has been speculated that trace elements may a play role in the pathogenesis of heart diseases. In the present study, we aimed to assess the levels of selenium (Se) and mercury (Hg) in biological samples (whole blood, urine, and scalp hair) of myocardial infarction (MI) patients of both genders (age range 45-60 years) at the first, second, and third heart attack (n = 130), hospitalized in a cardiac ward of a civil hospital of Hyderabad City (Pakistan). For comparison, healthy age-matched referent subjects (n = 61) of both genders were also selected. Se and Hg in biological samples were measured by electrothermal atomic absorption spectrometry and cold vapor atomic absorption spectrometry, prior to microwave acid digestion, respectively. The validity of the methodology was checked by biological certified reference materials. During this study, 78 % of the 32 registered patients of third MI attack (aged >50 years) died. The concentration of Se was decreased in scalp hair and blood samples of MI patients, while Hg was higher in all biological samples as compared to referent subjects. Se concentration was inversely associated with the risk of MI attacks in both genders. These results add to an increasing body of evidence that Se is a protective element for cardiovascular health.

Silver nanoparticle-assisted preconcentration of selenium and mercury on quartz reflectors for total reflection X-ray fluorescence analysis

In this work, a new analytical approach based on the trapping of Se and Hg vapours using silver nanoparticles (Ag NPs) immobilized on quartz reflectors, prior to their determination by total reflection X-ray fluorescence (TXRF), is proposed. Ag NPs were synthesized by reduction of the metal precursor with a reducing agent in aqueous solution. Silanization with 3-mercaptopropyltrimethoxysilane (MPTMS) was used in order to modify the quartz reflectors and immobilize Ag NPs by interaction between the organosilane compound and Ag NPs. A comprehensive characterization of synthesized Ag NPs was carried out by Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). SeH2 and Hg(0) vapours were generated by means of a continuous flow vapour generation system and trapped onto the quartz reflector containing immobilized Ag NPs. Different parameters involved in both the Ag NP synthesis and the continuous flow system for vapour generation and preconcentration were optimized in order to obtain the best results. Detection limits were 0.18 and 0.55 μg L−1 for selenium and mercury, respectively. Enrichment factors of 265 and 175 were obtained for Se and Hg, respectively. The new method was successfully validated against three biological certified reference materials and applied to several seafood samples. Recoveries carried out on three certified reference materials were in the range 94–106% with a relative standard deviation of 5% (N = 5).

Mercury speciation in Cuban commercial edible fish by HPLC-ICP-MS using the double spike isotope dilution analysis strategy

A sensitive and accurate quantitative method for the speciation of inorganic Hg2+ and methyl-mercury by ID-HPLC–ICP-MS has been optimised and implemented for marine fish samples. Quantitative extraction of Hg species was achieved using a 0.1% (v/v) 2-mercaptoethanol, 0.05% (w/v) L-cysteine and 0.10% (v/v) HCl solution by sonication for 30 min. Chromatographic separation of mercury species was carried out on a C8 reverse phase column with 0.05% (v/v) 2-mercaptoethanol, 0.075% (w/v) L-cysteine and 0.06 mol L−1 ammonium acetate as the mobile phase. A species specific isotope dilution analysis approach, using 201CH3Hg+ and 200Hg2+ was employed for the quantification of both species. Two biological Certified Reference Materials (DOLT-2, DORM-2) were analysed to assess the analytical performance. No significant differences were found between the obtained concentrations and the certified reference values for total Hg and CH3Hg+. The results indicate that no species interconversion reactions occurred during the used extraction and chromatographic separation procedures. The detection limits for CH3Hg+ and Hg2+ species were 7.7 and 5.2 ng g−1, respectively. The method recovery (expressed as the sum of both species contents in relation to total Hg concentration analysed by ICP-MS) was about 97 ± 5%. The procedure was applied to speciation of mercury in 12 species of the most commonly consumed commercial fish in Cuba.

Trace Rare Earth Element Detection in Food and Agricultural Products Based on Flow Injection Walnut Shell Packed Microcolumn Preconcentration Coupled with Inductively Coupled Plasma Mass Spectrometry

With the extensive use of rare earth elements (REEs) in agriculture as fertilizer and feed additives, the concentration of REEs has increased in environmental and biological samples and finally impaired human health by food chain accumulation. The determination of trace REEs has gained considerable importance because of their toxicity and increasing occurrence. In this work, walnut shell has been used as the green adsorbent in online preconcentration and detection of REEs in food and agricultural products coupled with inductively coupled plasma mass spectrometry (ICP-MS). Because of the porous surface and abundant -COO(-) groups on the walnut shell surface, the walnut shell-packed microcolumn provides high adsorption efficiency and high tolerable capacity for coexisting ions. Under the optimized conditions, the adsorption efficiency of the walnut shell packed microcolumn was as high as 98.9% for 15 REEs, and the tolerable concentration ratios were between 2000 and 80,000,000 for 37 kinds of coexisting interfering ions. The enhancement factors achieved were 79-102 for 15 REEs with a sample loading volume of 4.7 mL. The detection limits were in the range of 2-34 pg g(-1). The relative standard deviation for 11 replicate preconcentrations of 2.5 ng L(-1) REEs solution ranged from 0.5 to 2.0%. The present method was successfully applied to selective determination of REEs in 4 environmental and biological certified reference materials and 18 locally collected food and agricultural products.

Microwave-enhanced cold vapor generation for speciation analysis of mercury by atomic fluorescence spectrometry

A new and simple cold vapor generation technique utilizing microwave irradiation coupled with atomic fluorescence spectrometry is developed for the speciation analysis of mercury in biological and geological samples. In the presence of formic acid, inorganic mercury (Hg2+) and total mercury (both Hg2+ and methylmercury (MeHg)) can be converted to mercury cold vapor (Hg0) by microwave irradiation without and with H2O2, respectively. The cold vapor was subsequently released from the liquid phase and rapidly transported to an atomic fluorescence spectrometer for the mercury detection. Optimum conditions for vapor generation as well as interferences from concomitant ions were carefully investigated. The conventionally required evaporation of the remnants of acid or oxidants was avoided because no significant interferences from these substances were observed, and thus analyte loss and potential contamination were minimized. A limit of detection of 0.005ngmL−1 for total mercury or inorganic mercury was obtained. A precision of less than 3% (RSD) at 2μgL−1 of mercury species was typical. The accuracy of the method was validated by determination of mercury in geological and biological certified reference materials. The speciation analysis of Hg2+ and MeHg was achieved by controlling the conditions of microwave-enhanced cold vapor generation and validated via determination of Certified Reference Materials DORM-2, DORM-3 and a real river water sample.