Direct Determination Of Selenium Research Articles

Direct Determination of Selenium in Serum Matrix by Electrothermal Atomic Absorption Spectrometry: Application on Healthy Individuals from Algeria

Selenium is a trace element implicated significantly in oxidative stress in biological systems. In this work, a direct method for selenium determination in serum samples by electrothermal atomic absorption spectrometry with Zeeman background correction is proposed.Serum samples were five-fold diluted in a 0.14% HNO3 and 0.2% Triton X-100 solution. Aliquots of 20 µL of the diluted serum samples were directly introduced into transversely heated graphite tubes. A total of 5 µg Pd and 3 µg Mg(NO3)2 was used as chemical modifier. Optimization of heating program was conducted by varying pyrolysis and atomization characteristic values. The optimal conditions were found to be 1400 and 2000 °C for pyrolysis and atomization temperatures respectively and 11 seconds for pyrolysis hold time.The standard additions method was employed for calibration. Intra-day and inter-day validation using quality control samples at each point of the addition calibration curve were performed. Good accuracy, precision and recovery were achieved with the proposed method (less than 5% for accuracy and precision). A characteristic mass of 92.550 pg, a limit of detection of 4.010 ppb and a limit of quantification of 13.375 ppb in undiluted serum samples were obtained.Several reference values of serum selenium concentrations were reported. As an application of the present method, selenium levels were determined in serum samples collected from 20 healthy individuals from Northern-Center of Algeria. Selenium concentrations ranged from 86.883 to 133.955 ppb with a mean value of 110.824±11.898 ppb.

Evaluation of internal standardization for the determination of semivolatile analytes in difficult matrices by simultaneous multielement atomic absorption spectrometry

The aim of the present work is to investigate the use of the internal standardization technique combined with permanent chemical modification for the determination of two semivolatile analytes, such as As and Se, in difficult matrices by electrothermal atomic absorption spectrometry. Bismuth and tellurium have been evaluated as internal standards to minimize matrix effects on the direct determination of selenium and arsenic in sediments, by simultaneous electrothermal atomic absorption spectrometry using graphite tubes with integrated platform, pre-treated with different masses of Zr and Ir as permanent modifier. A Perkin-Elmer SIMAA 6000 simultaneous multielement spectrometer was used to study the correlation between two integrated absorbance signals. Matrix effects were evaluated by calculating the slope ratio between the analytical curve obtained from reference solutions prepared in 1.0% (v/v) HNO3 and analytical curve obtained from IS additions in matrix solutions. The results showed that Te was the optimal internal standard and 200μg Zr and 20μg Ir was the optimal permanent chemical modifier for both analytes. The instrumental limits of detection for As and Se were 1.48 and 1.96μgL−1 without the use of an internal standard and 0.59 and 0.35μgL−1 when Te was used as an internal standard, respectively. Relative standard deviations for a sample with matrix effect containing 100μgL−1 As and 200μgL−1 Se were 1.3% and 2.3% (n=20) using 100μgL−1 Te, respectively, and for a standard solution sample containing 100μgL−1 As and 200μgL−1 Se were 3.0% and 1.2% (n=20) using 100μgL−1 Te, respectively. The accuracy of the proposed method was evaluated by an addition-recovery experiment and by the analysis of different certified reference materials. The recovered values were in the 95–100% range for both analytes.

Low volume microwave digestion and direct determination of selenium in biological samples by hydride generation-atomic fluorescence spectrometry

A low volume microwave digestion (LVMWD) procedure has been developed to have all forms of selenium (Se) compounds in biological samples decomposed to Se (IV) and allow total Se be directly determined by hydride generation-atomic fluorescence spectrometry (HG-AFS), or voltammetrically. Between 0.3 and 0.4 mL of mixed digestion reagents consisting of concentrated (15.4 M) HNO 3–(18.5 M) H 2SO 4 (v:v = 10:1) and >5 to <40 mg sample were found ideal systems with an optimized MW digestion program. Total Se in five certified reference materials was accurately determined. The results obtained by the conventional and LVMWD techniques agreed well. By avoiding pre-reduction step, this method, suitable for a wide range of biological samples, fully takes the advantages of HG-AFS or voltammetric techniques for their high sensitivity, high tolerance to matrix-related interference and accessibility in instrumentation. LVMWD not only enhances the sample output by 3 times and reduces the operational cost and acid wastes, but also makes the small sample analysis possible for many environmental and medical related research objectives. The digestion pathways of Se containing organic samples are also discussed based on the experimental results.

Development of a Novel Automatic Potentiometric System for Determination of Selenium and Its Application in Pharmaceutical Formulations and Anodic Slime

AbstractPoly(vinyl chloride) polymeric membrane sensors containing Sn(IV) phthalocyanine dichloride (SnPC) and Co(II) phthalocyanine (CoPC) as novel electroactive materials dispersed in o‐nitrophenyl octylether (o‐NPOE) as a plasticizer are examined potentiometrically with respect to their response toward selenite (SeO32−) ions. Fast Nernstian response for SeO32− ions over the concentration ranges 7.0×10−6–1.0×10−3 and 8.0×10−6–1.0×10−3 mol L−l at pH 3.5–8.5 with lower detection limit of 5.0×10−6 and 8.0×10−6 mol L−1 and calibration slopes of −25.4 and −29.7 mV decade−1 are obtained with SnPC and CoPC based membrane sensors, respectively. The proposed sensors reveals by the modified separate solution method (MSSM) a good selectivity over different anions which differ significantly from the classical Hofmeister series. A segmented sandwich membrane method is used to determine complex formation constants of the ionophores in situe in the solvent polymeric sensing membranes. Membrane incorporating CoPC in a tubular flow detector is used in a two channels flow injection set up for continuous monitoring of selenite at a frequency of ca. 50 samples h−1. Direct determination of selenium in pharmaceutical formulations and anodic slime gives results in good agreement with data obtained using standard ICP method.

Rapid and Direct Determination of Selenium, Copper, and Zinc in Blood Plasma by Flow Injection-Inductively Coupled Plasma-Mass Spectrometry

A flow injection-inductively coupled plasma-mass spectrometry (FIICP- MS) with a simple sample preparation procedure was developed for the determination of selenium, copper, and zinc in blood serum/plasma. A serum/plasma sample was filtered through a 0.45-mum membrane filter and diluted with a mixture of trace elements in a standard solution (9 : 1, v/v). Measurement of the reference serum sample confirmed the accuracy of our method for selenium, copper, and zinc concentration. In the case of blood plasma samples obtained from six healthy adult males, the selenium, copper, and zinc concentrations were similar to those of a typical healthy male in Japan. These results suggest that the sample preparative procedure coupled with FI-ICP-MS can be used for the routine determination of selenium, copper, and zinc in human blood serum/plasma.

Direct determination of selenium in sub-milligram amounts of human sperm nuclei by electrothermal atomic absorption spectrometry

In the sperm nuclei selenium is present only in form of a single selenoenzyme, the sperm nuclei glutathione peroxidase (snGPx), involved in processes to secure the structural stability of the nuclear chromatin. As changes in its expression may affect sperm function, its analysis is of interest in the diagnosis of male infertility. A method has been developed which by removal of the other selenium compounds present in other sperm components and measurement of the concentration of selenium in the purified human sperm nuclei by electrothermal atomic absorption spectrometry (ETAAS) allows the quantitative analysis of this enzyme. As the purification resulted in yields in the range of only 150 μg nuclei/ml semen and the amount of purified nuclei in the sample could only be determined by weighing, the main analytical difficulty arose from the accurate determination of the sample masses. The procedure includes preparation of purified sperm nuclei, measurement of the sample mass and direct selenium analysis in the suspensions of the compact sperm nuclei without prior digestion of the matter, using a palladium matrix modifier, a spectrometer with Zeeman background correction and a graphite atomizer with L'vov platform. The detection limit for the determination of selenium was 8.4 pg. The quality control of the results by means of instrumental neutron activation analysis (INAA) showed the reliability of the selenium determination by ETAAS. The procedure proved to be suitable to analyze selenium and thus snGPx in very small amounts of purified human sperm nuclei.

Direct determination of selenium in urine samples by electrothermal atomic absorption spectrometry using a Zr plus Rh-treated graphite tube and co-injection of Rh as chemical modifier

Different chemical modifiers for use with electrothermal atomic absorption spectrometry (ET AAS) were investigated in relation to determining the selenium in human urine samples. The samples were diluted in a solution containing 1% v/v HNO3 and 0.02% m/v cetyltrimethylammonium chloride (CTAC). Studying the modifiers showed that the use of either Ru or Ir as the permanent modifier gave low sensitivity to Se and the peak shape was very noisy, while Zr or Rh gave no peak at all. The same occurred when Zr was used in solution. For mixtures of permanent modifiers, Ir plus Rh or Zr plus Rh gave very low sensitivity, Zr plus Rh with co-injection of Ir in solution was also not efficient, Zr plus Rh in solution gave good sensitivity, but the best results were obtained with a mixture of Zr and Rh as the permanent modifier and co-injection of Rh in solution. Using this last modifier, the following dilutions with the HNO3 and CTAC were studied: 1:1, 1:2, 1:3 and 1:4. The best dilution was 1:1, which promoted good sensitivity and a more defined peak shape and made it possible to correct for the background using a deuterium arc lamp. Under these conditions, a characteristic mass of 26+/-0.2 pg was obtained for Se in aqueous solution. Six certified urine samples were analyzed using matrix matching calibration and the measured concentrations were in agreement with the certified values, according to a t-test at the 95% confidence level. Recovery tests were carried out and the recoveries were in the range 100-103%, with relative standard deviation better than 9%. The limit of detection (LOD, 3 sd, n = 10) was 3.0 microg L(-1) in the sample. The treated graphite tube could be used for at least 600 atomization cycles without significant alteration of the analytical signal.

Internal standardization in graphite furnace atomic absorption spectrometry: Comparative use of As and Ge to minimize matrix effects on Se determination in milk

Arsenic and germanium have been evaluated as internal standards to minimize matrix effects on the direct determination of selenium in milk by graphite furnace atomic absorption spectrometry (GFAAS) using tubes with integrated platform, pre-treated with W together with Pd as chemical modifier. The efficiency of As and Ge as internal standards for 25 μg L − 1 Se plus 500 μg L − 1 As or Ge in diluted (1 + 9 v/v) milk plus 1.0% (v/v) HNO 3 was evaluated by means of correlation graphs plotted from the normalized absorbance signals ( n = 20) of internal standard (axis y) versus analyte (axis x). The equations that describe the linear regression were: A As = − 0.004 ± 0.019 + 1.02 ± 0.019 A Se ( r = 0.9967 ± 0.005); A Ge = − 0.017 ± 0.015 + 1.01 ± 0.015 A Se ( r = 0.9978 ± 0.004). Samples and reference solutions were automatically spiked with 500 μg L − 1 Ge or As and 1.0% (v/v) HNO 3 by the autosampler. For 20 μL of aqueous standard solutions, analytical curves in the 5.00–40.0 μg L − 1 Se range were established using the ratio of Se absorbance to internal standard absorbance ( A Se / A IS) versus analyte concentration, and good linear correlations were obtained. The characteristic mass was 40 pg Se. Limits of detection were 0.55 and 0.40 μg L − 1 with As and Ge as the internal standard, respectively. Relative standard deviations (RSD) for a sample containing 25 μg L − 1 Se were 1.2% and 1.0% ( n = 12) using As and Ge, respectively. The RSD without internal standardization was about 6%. The accuracy of the proposed method was evaluated by an addition-recovery experiment and all recovered values were in the 99–105% range with IS and in the 70–80% range without IS. Using Ge as the internal standard, results of analysis of standard reference materials were in agreement with certified values at a 95% confidence level. The selenium concentration for 10 analyzed milk samples varied from 5.0 to 20 μg L − 1 .

Direct Determination of Selenium and other Trace Elements in Serum Samples by ICP-MS

Selenium belongs to a group of trace elements of special interest in biological samples for clinical diagnosis. Selenium has antioxidizing functions and is essential for providing the organism with triiodothyronine produced from thyroxine. Among several analytical techniques used to determine the Se concentration in serum, Inductively Coupled Plasma Mass Spectrometry (ICP-MS) has been used in the past because of its high sensitivity. Interference problems originating from different ions on the major Se isotopes have been described to be a limiting factor for the direct determination of Se in these matrices. Standard addition calibration or isotope dilution is often required to overcome carbon-enhanced ionisation effects in biological sample matrices. In most cases, the typical serum sample volume which is available for the analysis is limited to 0.5 ml or less, making multiple sample preparation for standard addition calibration impractical. Isotope dilution requires enriched isotopes and substantial sample preparation. Furthermore, the approximate Se concentration in every sample has to be known to adjust the appropriate amount of spike to each sample. Matrix matching with methanol has been described to overcome ionisation effects but we found limiting factors of this application when other trace elements are also determined within one sample run. This paper describes an effective sample preparation method which allows the direct determination of Se in serum without limiting the analytical capabilities for the additional determination of Al, Cu, Ni, Co, Cd, Mn and Zn in a single sample run by ICP-MS. Optimization procedures are presented and results of the analysis of reference samples are discussed, with a comparison of more than 150 serum data with those obtained by the GF-AAS method.

Direct determination of selenium in serum by electrothermal atomization laser-induced fluorescence spectrometry

A technique for the determination of serum selenium by electrothermal atomization laser-induced fluorescence (ETA-LIF) spectrometry is discussed. Far-UV radiation used for Se excitation at 196.026 nm was generated as the second anti-Stokes stimulated Raman shift of the output of a frequency doubled dye laser operating near 234 nm. Owing to the high spectral selectivity and high sensitivity of the ETA-LIF technique, direct determination is possible by using a simple aqueous dilution (1:10 or 1:20) of the serum samples and a Pd-Mg chemical modifier to reduce pre-atomization losses of the analyte. The accuracy of the method was demonstrated by analysis of NIST SRM 1598 Inorganic Constituents in Bovine Serum (experimental value 42±3 ng g –1 ; certified value 42.4±3.5 ng g –1 ). Analysis of 128 serum samples drawn from bone marrow transplant patients yielded values of 89±20 and 92±23 ng g –1 for pre- and post-operative samples, respectively.

Direct determination of selenium in human blood plasma and seminal plasma by graphite furnace atomic absorption spectrophotometry and clinical application.

Direct determination of selenium (Se) in body fluids by graphite furnace atomic absorption spectrophotometry (GFAAS) may suffer from problems like severe background, matrix effects, preatomization losses, and spectral interferences. In this study we evaluate critically the influence on the accuracy of the direct determination of Se in blood plasma and seminal plasma by GFAAS, and propose a simple, rapid, and accurate method, suitable for routine clinical analysis. The method for blood plasma is mainly based on studies by the use of matched matrix and a Pd-Ni modifier, but for seminal plasma only a Pd modifier is required. The method developed was also applied to study the Se distribution in plasma protein fractions of patients with hepatocellular carcinoma. The Se in plasma of patients was significantly lower than that of the controls. The distribution pattern of Se in blood plasma fractions of patients was also different from that of the controls.

Direct determination of selenium in serum by electrothermal atomic absorption spectrometry using automated ultrasonic slurry sampling

Selenium concentration in body fluids is a good index to establish human selenium status. This work discusses the determination of selenium in serum by ETAAS using longitudinal Zeeman-effect background correction and combining the use of automated slurry sampling. The standard reference materials bovine serum (NIST, SRM 1598) and second-generation biological freeze-dried human serum are analyzed to verify the accuracy and precision of this technique. The direct method proposed in this study is used for the determination of selenium in human serum collected from healthy people of 19–25 years. The average accuracy values of certified reference serum samples and the recovery values of spiked samples indicate this method to be an efficient and rapid technique for determining selenium in biological samples.

Direct determination of selenium in whole blood by anodic stripping voltammetry

Trace quantities of selenium can be determined in the presence of iron, copper and lead using anodic stripping voltammetry, depositing at −0.60 V in 0.1M HClO4 and stripping in the anodic direction. Two separate peaks are observed at −0.25 V and −0.10 V belonging to copper and selenium, respectively. Sometimes one peak may be observed for both copper and selenium. In this case one more stripping (without deposition) must be done to obtain separate peaks. After standard addition, two strippings have to be done also. With this proposed method, 10−7M selenium could be determined as (1.09±0.03) × 10−7M with a 90% confidence interval in blood samples without any separation.

Cathodic stripping potentiometric determination of selenium in biological and environmental materials on a combined electrode with a rotating sample platform

The use of a combined working(glassy carbon mercury film electrode)-counter-reference electrode and a rotating sample platform for the reliable determination of selenium in biological and environmental materials by cathodic stripping potentiometry is described. The optimum conditions for the determination of selenium by this method include an electrolyte consisting of 2 M HCl and 1 M CaCl 2, an electrolysis potential of −200 mV and a stripping current of −5 μA. Under these conditions, as little as 0.1 μg/l of selenium can be detected with an electrolysis time of 120 s, and the precision at this level was within 1–3% rsd. The interferences of organic and inorganic substances on the cathodic stripping potentiometric determination of selenium were minimal, except for copper which gave an additional peak when present at >2 mg/ l. Even in this case, the copper interference can be overcome or reduced by sample dilution. The use of a dry ashing method with the technique enabled the reliable determination of selenium in biological and environmental materials. The direct determination of selenium in water samples by cathodic stripping potentiometry on the combined electrode is demonstrated.

Direct determination of selenium in a wild fruit juice by electrothermal atomic absorption spectrometry

A matrix modifier composed of platinum and nickel is proposed for the determination of selenium in a wild fruit juice made from Lantingguo (Vuccinium uliginosam). Five matrix modifiers (copper/nickel, palladium/magnesium, platinum/magnesium, platinum/nickel and platinum/copper) for suppressing the interference effects of seven co-existing elements (potassium, phosphorus, calcium, magnesium, manganese, zinc and iron) in a wild juice were studied and a matrix modifier composed fro`m 10 μg of platinum and 200 μg of nickel was found to give the best performance. Selenium in three juices was determined by electrothermal atomic absorption spectrometry employing the proposed matrix modifier without matrix preseparation. The relative standard deviation was 14% for 0.20 mg l −1 of selenium. The recoveries were 95–110%. A characteristic mass was 28 pg.

Development of a new method for direct determination of selenium associated with atmospheric particulate matter using chemical modifiers and graphite probe furnace atomic absorption spectrometry

Direct determination of selenium on or in atmospheric particulate matter (APM) has been achieved using an integrated filtration and analysis system developed in our laboratories. The filtration (sampling) and analysis system consists of a porous electrographite plate which is used initially for the purpose of collecting APM and subsequently as a probe in graphite probe furnace atomic absorption spectrometry. Selenium produced a double peak when it was atomized from such an electrographite probe. Palladium nitrate+magnesium nitrate, as a mixed chemical modifier or ascorbic acid as a chemical modifier, eliminated the double peak. The addition of the chemical modifier(s) also removed the unpredictable changes in the peak-height and the peak-area absorbance which occurred from one atomization cycle to the next if the chemical modifier was not used. Precision of 5% RSD (peak-area absorbance) was obtained for an aqueous solution of selenium standard containing 1.25 ng of selenium with palladium nitrate+magnesium nitrate mixed chemical modifier, or ascorbic acid chemical modifer. The characteristic masses and the limits of detection for the aqueous solution of selenium standard with palladium nitrate+magnesium nitrate mixed chemical modifier are 27 and 41 pg (peak-area absorbance), respectively, and with ascorbic acid chemial modifier are 29 and 36 pg, respectively (peak-area absorbance). The results of analysis of the NIST (formerly National Bureau of Standards) Standard Reference Material No. 1648, Urban Particulate Matter, for selenium with palladium nitrate+magnesium nitrate mixed chemical modifier gave a recovery of 92%, and a precision of 10% RSD, and characteristic mass and the limit of detection of 20 and 37 pg, respectively.

Direct Determination of Selenium In Horse Blood By Graphite Furnace Atomic Absorption Spectroscopy

Abstract Results on a direct determination of selenium in horse blood are presented. A 10 mg/L solution of nickel was added to the blood after the blood was treated with Triton X. This provides a means of direct determination of selenium in horse blood and cuts out the time consuming digestion step. the accuracy of the method was good and the precision of greater than 10 percent was considered acceptable.

Determination of selenium in blood serum by XRF

Direct determination of selenium in biological tissues by X-ray emission spectroscopy is not possible due to the limited sensitivity of all modes of sample excitation. Therefore, it is necessary to develop a preconcentration procedure to bring selenium to detectable level. In this paper a rapid and simple chemical preparation procedure including coprecipitation with APDC for the analysis of selenium in blood serum by X-ray emission spectroscopy is described.

Direct determination of selenium in serum by graphite-furnace atomic absorption spectrometry with deuterium background correction and a reduced palladium modifier: age-specific reference ranges.

We describe the development of a direct method for determination of selenium in serum by graphite-furnace atomic absorption spectrophotometry with deuterium background correction. We include palladium modifier to stabilize selenium in the presence of a strong reducing agent. Spectral interferences from iron are not evident in this system. Because an analysis requires only 20 microL of serum or plasma, the method is applicable to neonatal populations. At a selenium concentration of 0.75 mumol/L (approximately the mean found in our pre-term infants), the within-run CV is 5.3%. For a concentration of 1.83 mumol/L, which approximates our normal adult mean, within-run and between-run CVs are 2.7% and 3.4%. Accuracy is demonstrated by analytical recoveries ranging from 96% to 102%. We present reference values for pre-term and term infants, and age-specific ranges for infants to adults.

Percutaneous absorption of selenium sulfide

The purpose of this study was to determine selenium levels in the urine of Tinea patients before and after overnight application of a 2.5% selenium sulfide lotion. Selenium was measured by atomic absorption spectroscopy (AAS). Hydride generation and carbon rod atomization were studied. It was concluded from this study that selenium is absorbed through intact skin. Selenium is then excreted, at least partially, in urine, for at least a week following treatment. The data show that absorption and excretion of selenium vary on an individual basis. Selenium levels in urine following a single application of selenium sulfide lotion do not indicate that toxic amounts of selenium are being absorbed. Repeated treatments with SeS/sub 2/ result in selenium concentrations in urine which are significantly higher than normal. Significant matrix effects are observed in the carbon rod atomization of urine samples for selenium determinations, even in the presence of a matrix modifier such as nickel. The method of standard additions is required to obtain accurate results in the direct determination of selenium in urine by carbon rod AAS.