Method For Determination Of Selenium Research Articles

Development of a new highly sensitive and selective spectrophotometric method for the determination of selenium at nano-trace levels in various complex matrices using salicylaldehyde-orthoaminophenol

A new spectrophotometric reagent, salicylaldehyde-orthoaminophenol (Sal-OAP) has been synthesized and characterized for the determination of selenium through novel reaction techniques. Also, a new highly selective, and sensitive spectrophotometric method for the nano-trace determination of selenium using salicylaldehyde-orthoaminophenol (Sal-OAP) has been developed. Sal-OAP undergoes reaction in a slightly acidic solution (0.0001-0.0002 M H2S04) with selenium (IV) to give an orange-red chelate, which has an absorption maximum at 379 nm. The reaction is instantaneous and absorbance remains stable for over 24 h. The average molar absorption co-efficient and Sandell’s sensitivity were found to be 6.4×105 L/mol.cm and 1.0 ng/cm2 of, respectively. Linear calibration graphs were obtained for 0.001-40.000 mg/Lof Se having detection limit of 0.1 µg/L and RSD 0-2 %. The stoichiometric composition of the chelate is 1:2 (Se:Sal-OAP). A large excess of over 60 cations, anions and some common complexing agents, such as chloride, azide, tartrate, EDTA, SCN¯etc., do not interfere in the determination. The developed method was successfully used in the determination of selenium in several Certified Reference Materials (Alloys, steels, human urine, bovine liver, drinking water, tea, milk, soil, and sediments) as well as in some environmental waters (Potable and polluted), biological fluids (Human blood, urine, hair, and milk), soil samples, food samples (Vegetables, rice, and wheat) and pharmaceutical samples (Tablet and syrup) and solutions containing both selenium (IV) and selenium (VI) as well as complex synthetic mixtures. The results of the proposed method for assessing biological, food and vegetables and soil samples were comparable with ICP-OES and AAS were found to be in excellent agreement. The method has high precision and accuracy (s = ±0.01 for 0.5 mg/L).

Comparison of three digestion methods for determination of selenium in green tea samples using fluorescence spectrometry

Various digestions are available for the determination of selenium (Se) in environmental samples. This study aimed to investigate the most effective digestion method for the determination of Se in green tea samples that effective, eco-friendly, and low cost. Samples were digested with three different acid compositions, the aqua regia method (a mixture of nitric acid-hydrochloric acids HNO3-HCl) in a ratio 1:3, only nitric acid HNO3, and reverse aqua regia method (a mixture of nitric acid-hydrochloric acids HNO3-HCl) in a ratio 3:1. Analysis of Se was conducted using fluorescence spectrometry after derivation by 2,3-diamino naphthalene (DAN). The results show that the aqua regia method was the highest fluorescence intensity. It had given a significant fluorescence intensity of 9.0510 a.u. for 2 mL sample, 26.3689 a.u. for 5 mL sample, 54.4308 a.u. for 10 mL sample, respectively. In addition, the aqua regia digestion resulted in the selenium form in the sample has been converted to tetravalent selenium, and there was a silicone compound as precipitation can be found after digestion. The aqua regia method provides a highly effective digestion method for selenium in green tea samples under fluorescence spectroscopic investigation.

Determination of selenium during pathogenesis of hepatic fibrosis employing hydride generation and inductively coupled plasma mass spectrometry.

Serum and liver selenium levels were studied during the pathogenesis of N-nitrosodimethylamine (NDMA) induced hepatic fibrosis in rats. The degree of fibrosis was assessed with Masson's trichrome staining and quantifying collagen content in the liver. Lipid peroxides were measured in blood and liver samples and total glutathione and glutathione peroxidase were assayed in the liver tissue to evaluate oxidative stress. Interleukin-6 (IL-6) and transforming growth factor-β1 (TGF-β1) were measured in the serum. Selenium levels were determined using inductively coupled plasma-mass spectrometry (ICP-MS) after acid digestion and hydride generation of selenium. Serial administrations of NDMA produced well-developed fibrosis and early cirrhosis in the liver with 4-fold increase of total collagen content and deposition of collagen fibers. Blood and hepatic lipid peroxides, serum IL-6 and TGF-β1 were significantly increased. There was significant reduction in hepatic glutathione and glutathione peroxidase levels. Serum and liver selenium were remarkably decreased on all the days studied. The results suggest that decreased selenium and glutathione peroxidase contribute to the impairment of cellular antioxidant defense, which in turn results in oxidative stress and trigger pathogenesis of hepatic fibrosis. The study further demonstrated that ICP-MS with hydride generation technique is a reliable and sensitive method for determination of selenium in biological samples.

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.

A New Spectrophotometric Method for Determination of Selenium in Cosmetic and Pharmaceutical Preparations after Preconcentration with Cloud Point Extraction

A simple, rapid, and sensitive spectrophotometric method for the determination of trace amounts of selenium (IV) was described. In this method, all selenium spices reduced to selenium (IV) using 6 M HCl. Cloud point extraction was applied as a preconcentration method for spectrophotometric determination of selenium (IV) in aqueous solution. The proposed method is based on the complexation of Selenium (IV) with dithizone at pH < 1 in micellar medium (Triton X-100). After complexation with dithizone, the analyte was quantitatively extracted to the surfactant-rich phase by centrifugation and diluted to 5 mL with methanol. Since the absorption maxima of the complex (424 nm) and dithizone (434 nm) overlap, hence, the corrected absorbance, Acorr, was used to overcome the problem. With regard to the preconcentration, the tested parameters were the pH of the extraction, the concentration of the surfactant, the concentration of dithizone, and equilibration temperature and time. The detection limit is 4.4 ng mL−1; the relative standard deviation for six replicate measurements is 2.18% for 50 ng mL−1 of selenium. The procedure was applied successfully to the determination of selenium in two kinds of pharmaceutical samples.

Development of surfactant assisted spectrophotometric method for determination of selenium in waste water samples

A new, simple and highly selective method for spectrophotometric determination of selenium in waste water samples is described. Selenium(IV) oxidizes I − ions into I 2 which subsequently reacts with excess of I − ion in the acidic media to give tri-iodide ions (I 3 −), and it further reacts with cetylpyridinium cation (CP +) to give a violet colored species. The value of molar absorptivity of the ion-associate species in terms of selenium is 1.80 × 10 4 L mol −1 cm −1 at λ max 510 nm. The detection limit of the method is 10 ng mL −1 Se. The calibration curve is linear over 50–1000 ng mL −1 Se with slope, intercept and co-relation coefficient of 0.23, −4.0 × 10 −4 and +0.99, respectively. None of the tested diverse ions interfered in the present method. The method has been tested for the determination of selenium in waste water samples.

A definitive RNAA method for determination of selenium in biological samples: uncertainty evaluation and assessment of degree of accuracy

This article describes work on the development of a highly accurate RNAA method for determination of selenium in biological samples. The analytical post-irradiation procedure is based on a combination of cation-exchange and extraction chromatography with final selective and quantitative fixation of selenium on a column packed with 3,3′-diaminobenzidine (DAB) supported on Amberlite XAD4, followed by gamma-ray spectrometric measurement. The suitability and accuracy of the method was demonstrated by analysing CRMs with certified selenium content. The uncertainty budget for Se determination in standard reference material Peach Leaves NBS 1547 was estimated; the combined standard uncertainty was calculated as 1.7%. The described method fulfils all the criteria for definitive methods. It was subsequently used for determination of selenium in biological materials intended as new CRMs and proficiency test samples.

A Method for Determination of Selenium in Organic Tissues Using Microwave Digestion and Liquid Chromatography

An existing laboratory procedure for selenium analysis using open-vessel wet digestion and liquid chromatographic fluorescence determination was modified for use with microwave digestion. The proposed microwave digestion method eliminated the hazards associated with the use of HClO4 while maintaining excellent recoveries of selenium. A 2-step HNO3/H2O2 digestion procedure was developed. Digested samples were derivatized with 2,3-diaminonaphthalene, and the resultant piazselenol complex was measured fluorometrically using a liquid chromatograph. Measured values were in agreement with 9 different certified reference materials. The detection limit for this method was 0.54 ng Se/g tissue (3 sigma), and the calibration curve remained linear (r2 = 0.9968) up to 2 microg Se/g.

Method for Determination of Selenium and Arsenic in Human Urine by Atomic Fluorescence Spectrometry

The study presents the method for simultaneous determination of selenium and arsenic in human urine by atomic fluorescence spectrometry (AFS). According to the procedure developed, a sample is first digested in the microwave system, then chemically treated in the flow through a hydride generation system, and finally exposed to measurements in a double‐channel atomic fluorescence spectrometer. It has been revealed that selenium and arsenic can be accurately determined with detection limit of 0.13 and 0.16 µg/L and repeatability (RSD) of 1.0 and 1.2%, respectively. The urine samples taken from a control group and from persons subjected to a special diet were analyzed. The obtained results proved that the method developed was capable of controlling reliably even slight changes of both elements in a wide range of their concentrations, and, as such, that it can be recommended to be used for clinical and toxicological purposes.

Hydride generation-headspace single-drop microextraction-electrothermal atomic absorption spectrometry method for determination of selenium in waters after photoassisted prereduction

A headspace single-drop microextraction (SDME) method has been developed in combination with electrothermal atomic absorption spectrometry for determination of total inorganic Se and Se(IV). SeH 2 is generated in a 40 mL volume closed-vial and trapped onto a Pd(II)-aqueous containing drop that is supported at the needle tip of a high-precision chromatographic syringe. Sample pre-treatment by UV irradiation prior to hydride generation allowed converting Se(VI) into Se(IV), hence, facilitating total Se determination. A 2 IV 6-2 fractional factorial design was employed for characterising the effect of relevant variables over SeH 2 trapping. The variables showing the most significant effect were Pd(II) concentration in the drop and extraction time. A preconcentration factor of about 25 is achieved. The limit of detection of Se was 0.15 ng/mL using trapping onto a 3-μL drop and the precision expressed as relative standard deviation was about 3%. The limit of detection could be improved further using repeated sampling of the headspace.

Development and application of a simple routine method for the determination of selenium in serum by octopole reaction system ICPMS

The aim of the study was to develop an inductively coupled plasma mass spectrometry (ICPMS) method for robust and simple routine determination of selenium in serum. Polyatomic interferences on 76Se, 77Se, and 78Se were removed by applying an octopole reaction system ICPMS with the reaction cell pressurized with H2 gas. We developed a novel simple optimization routine for the H2 gas flow based on a signal-to-noise ratio (SNR) calculation of the selenium signal measured in a single selenium standard. The optimum H2 flow was 2.9 mL min-1. The selenium content in serum was determined after a 50-fold dilution with 0.16 M HNO3 and quantified by using addition calibration and gallium as an internal standard. The method detection limit was 0.10 microg L-1 for 76Se and 78Se and 0.13 microg L-1 for 77Se. Human serum samples from a case-control study investigating if selenium was associated with risk of colorectal adenoma were analyzed. The average selenium concentration for the control group (n=768) was 137.1 microg L-1 and the range was 73.4-305.5 microg L-1. The within-batch repeatability (a batch is ten samples) estimated from 182 replicate analyses was 6.3% coefficient of variation (CV), whereas the between-batch repeatability was 7.4% CV estimated from 361 replicates between batches. The method accuracy was evaluated by analysis of a human serum certified reference material (Seronorm Serum level II, Sero A/S, Norway). There was a fairly good agreement between the measured average of 145+/-3 microg L-1 (n=36) and the certified value of 136+/-9 microg L-1. In addition the method was successfully applied for analysis of zinc serum concentrations without further optimization. For the Seronorm certified reference material a value of 911+/-75 microg L-1 (n=31) for zinc was obtained, which corresponds well to the certified zinc value of 920+/-60 microg L-1.

Determination of selenium in infant foods using electrothermal atomic absorption spectrometry with direct slurry sample introduction

Abstract Slurry sampling electrothermal atomic absorption (SS ETAAS) was applied to the development of a sensitive and precise method for selenium determination in infant foods without sample pretreatment. Suspensions prepared in a medium containing 0.1% Triton X-100, 0.5 or 5% v/v concentrated HNO3 were directly introduced into the furnace. The accuracy of the procedure was confirmed by analysis of a standard reference material and comparison with hydride generation atomic absorption spectrometric (HGAAS) procedure. The characteristic mass is 44 pg and detection limit 0.43 μg·l−1.

Simple and Rapid Method for Determination of Selenium in Breast Milk by HG-AFS

A digestion procedure using H2SO4/HNO3/H2O2 was found to be effective for destruction of human milk samples. In conjunction with a sensitive hydride generation atomic fluorescence spectrometry detection system, it is suitable for determination of selenium in those samples where the available mass of breast milk and the low selenium concentration are limiting factors. Only 1 g of milk sample is needed. The procedure is simple, rapid and of low contamination potential since it is performed in the same Teflon tube from weighing to measurement. The digestion of 20 samples is completed in three hours. The detection limit is 0.25±0.04 ng g−1 of a measured solution of sample or 2.5 ng g−1 of milk. The relative uncertainty is 10% (coverage factor of 2.3, 95% probability). Because of these advantages the method is particularly suitable for epidemiological studies. The mean concentration of selenium in 62 samples of human milk from lactating women residing in the North East of Italy was 12±3 ng g−1, which is in the range of reference data.

AAS method for determination of selenium in therapeutical nutritions

An AAS method with graphite furnance and hydride system was developed and validated for determination of selenium in pharmaceutical dosage forms used as therapeutical nutritions. The method was applied for determination of selenium in three therapeutical nutritions after microwave digestion. Acid samples with Pd/Mg nitrate as a modifier were used for graphite furnace and acid samples with sodium borhydride alkaline solution for hydride system. Validation of applied method was carried out by determination of linearity (in concentration range from 15 to 75 µg/l for graphite furnace technique and from 5 to 25 µg/l for hydride system) as well as accuracy, precision, detection and quantification limit. The results obtained have shown that the proposed AAS method with graphite furnace and hydride system for determination of selenium in therapeutical preparations are sensitive, accurate and reproducible.

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.

Determination of trace selenium in human plasma and hair with ternary inclusion compound-fluorescent spectrophotometry.

A method for determination of selenium in plasma and hair with ternary inclusion compound-fluorescent spectrophotometry has been developed. The determination of selenium in plasma and hair can be performed directly in aqueous solution. Blood and hair samples were destroyed by oxygen flask combustion. The linear range was 10-500 ng mL-1 for plasma and 10-100 ng mL-1 for hair. Within-day and day-to-day precisions for plasma ranged from 5.4% to 9.3% (n = 7) and from 3.5% to 14.5% (n = 7), respectively. Within-day precisions for hair ranged from 0.6% to 6.2% (n = 7). Recoveries ranged from 91.0% to 97.8% for plasma and from 95.0% to 102.0% for hair. The blood samples from 15 Hans and 20 Uygurs in Xinjiang Uygur automatic region and 23 Hans in Liaoning province were collected and determined. It was indicated that no statistically significant difference in plasma selenium concentration of the Hans between Xinjiang and Liaoning was found (F = 1.36, P > 0.05). However, there were statistically significant differences between the Hans and the Uygurs in Xinjiang (F = 1.01, P < 0.01) and between males and females in the two areas (P < 0.01). There was a low correlation between plasma selenium concentration and hair selenium concentration. The ratio of hair selenium concentration to plasma selenium concentration was 2.17, with a range of 1.63-2.88.

Flow injection spectrophotometric determination of trace amounts of selenium

A simple, rapid and sensitive flow injection spectrophotometric method for determination of selenium (0.005–1.5 μg ml −1) is described. The method is based on the catalytic effect of Se(IV) on the reduction reaction of thionine (TN) with sulphide ion, monitored spectrophotometrically at 598 nm. The detection limit is 5 ng ml −1 the relative standard deviation for eight replicate measurements is 1.1% for 1 μg ml −1 of selenium. The sampling rate is 25–30 samples h −1. The procedure was applied successfully to the determination of selenium in real samples.

Comparison of mineralization methods for fluorimetric determination of selenium in milks

Methods for the mineralization of milk samples (whole milk, casein and the total protein fraction) were studied. The dry ashing method was eliminated because low recoveries (<10%) of Se were obtained. Acid-induced digestion was assayed using several mixtures of acids: HNO3–HClO4, HNO3–HClO4– H2SO4, HNO3–HClO4–TCA (where TCA is trichoroacetic acid). The proportions and total amounts of the acids were also varied and the effect of this investigated. Mixtures HNO3–HClO4 and HNO3–HClO4–H2SO4 were not adequate to induce complete mineralization of the milk samples. The mixture HNO3–HClO4–TCA (3:1:2) was able to digest skimmed milk. Two successive digestions with this mixture (HNO3–HClO4–TCA (3:1:2)] were necessary to induce the complete digestion of casein and the total protein fractions and, in the latter case, a recovery of 94.5±5.2% (100 μg Se/l) was achieved.

Application of the Slurry Technique to the Determination of Selenium in Fish Samples by Electrothermal Atomic Absorption Spectrometry

A slurry technique was applied in the development of a sensitive and precise method for selenium determination in fish samples without sample pre-treatment. Several pyrolysis curves were investigated and different chemical modifiers were tested. Ammonium oxalate was used to improve the selectivity. Calibration within the range 2.5–25.0 µg l -1 Se was performed with aqueous standards. The detection limit was calculated as 0.33 µg l -1 and the RSD of the measurements was 5.9% for repeatability and 9.2% for reproducibility. The reliability of the entire procedure was confirmed by analysis of a standard reference material and by comparison with a microwave digestion procedure.

High-Performance Liquid Chromatographic–Fluorescence Determination of Traces of Selenium in Biological Materials

An improved method for the determination of selenium in biological materials has been developed. This work both extends and validates the procedure of Vézina and Bleau (J. Chromatog.426, 385–391, 1988) which is based on high-performance liquid chromatographic determination of the fluorophore formed by reaction of Se(IV) with 2,3-diaminonaphthalene. The mass detection limit is 48 pg selenium (3σ) and the concentration detection limits are 48 parts per trillion in biological fluids and 120 to 480 parts per trillion in dried biological materials. The linear dynamic range of the method has been extended up to approximately 800 ng. Relative standard deviations of 9.4 to 2.7% were observed in repeated analyses of standards in the range of 0.5 to 500 ng. The proposed method was validated with respect to 23 biological reference materials spanning an 1800-fold range of selenium concentrations and was found to be free of significant constant or proportional biases despite greatly different matrix compositions. This method offers an unsurpassed combination of sensitivity, accuracy, linear dynamic range, and freedom from matrix interferences and may be considered a reference method for the reliable determination of selenium in biological materials.