Determination Of Selenium In Serum Research Articles

Determination of selenium in serum in the presence of gadolinium with ICP-QQQ-MS.

Gadolinium (Gd)-based magnetic resonance imaging (MRI) contrasting agents interfere with the determination of selenium (Se) when analysed by single quadrupole inductively coupled plasma-mass spectrometry (ICP-MS). This paper demonstrates that an ICP-triple quadrupole-MS (ICP-QQQ-MS) with oxygen mass shift overcomes Gd(++) interference on Se(+) and mitigates typically encountered matrix and spectral based interferences. Normal human serum was diluted in a solution containing isopropanol, EDTA, NH4OH and Triton X-100. Samples were unspiked (control) serum; serum spiked with 0.127 μmol L(-1) Se or 127 μmol L(-1) Gd; and serum spiked with both 0.127 μmol L(-1) Se and 127 μmol L(-1) Gd. Consideration of collision/reaction gases and conditions for interference mitigation included helium (He); a 'low' and 'high' hydrogen (H2) flow, and oxygen (O2). The instrument tune for O2 was optimised for effective elimination of interferences via a mass shift reaction of Se(+) to SeO(+). The ICP-QQQ-MS was capable of detecting trace (>9.34 nmol L(-1)) levels of Se in serum in the presence of Gd in our simulated post-MRI serum sample. The multi-tune capabilities of the ICP-QQQ-MS may be adapted to eliminate other specific isobaric interferences that cause false positive results in other analyses where the analyte is confounded by doubly charged and/or polyatomic species.

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.

Evaluation of a tunable bandpass reaction cell inductively coupled plasma mass spectrometer for the determination of selenium in serum and urine

A Dynamic Reaction Cell™ inductively coupled plasma mass spectrometer (DRC-ICP-MS) was evaluated for the determination of selenium in serum and urine. Reaction cell conditions were evaluated for the suppression of Ar 2 + dimer at m/ z 78 and 80 using methane as the reaction gas. A diluent containing 10% ethanol, 1% nitric acid, 0.5% Triton X-100 with gallium and yttrium internal standards was used to dilute urine and serum samples. Instrument response calibration was achieved by using aqueous acidic standards spiked into a urine matrix. Slopes for aqueous inorganic selenium, seleno- dl-cystine, seleno- dl-methionine and trimethylselenonium iodide spiked into urine and serum matrices were nearly identical. In general, reagent blank readings and detection limits were significantly lower in the DRC mode (reaction cell pressurized) than the standard mode (cell vented). Average results for the analysis of National Institute of Standards and Technology Standard Reference Material (NIST SRM) 1598 bovine serum (attained over 13 days) are: 43.8±3.6 μg Se/l. Reference concentration is 43.6±3.6 μg Se/l. For NIST SRM 2670 Normal Urine the DRC-ICP-MS results are 30.7±4.6 μg Se/l with a certified concentration of 30±8 μg Se/l. For NIST SRM 2670 Elevated Urine the DRC-ICP-MS results are 463±35 μg Se/l with a certified concentration of 460±30 μg Se/l. The DRC-ICP-MS results for selenium determinations in urine and serum survey samples from the Institut National de Sante Publique du Quebec were compared with the reference concentrations and results produced by conventional ICP-MS. While conventional ICP-MS gave acceptable results for survey samples, DRC-ICP-MS gave excellent results for both urine and sera. Closer correlation was observed for DRC-ICP-MS results with target concentrations than with conventional ICP-MS.

Study and comparison of several chemical modifiers for selenium determination in human serum by Zeeman electrothermal atomic absorption spectrometry

The conditions for the determination of selenium in human serum samples using a Zeeman graphite furnace with integrated platform graphite tubes are established. Performance characteristics including background signal, analytical signal and the effects on the platform of several chemical modifier solutions of varying concentrations were studied and compared. Ashing and atomising curves were obtained for each chemical modifier solution. The optimal measuring conditions were established for each modifier. The most appropriate modifier was then chosen on the basis of the sensitivity and detection limits for the determination of selenium in serum. The method was validated by analysing a Seronorm™ Trace Element (Oslo, Norway) quality control serum (78 μg l −1) and a ‘Second-Generation’ freeze-dried human serum, from the University of Ghent (1.05 μg g −1 dry-weight). The values obtained were 81.5 ± 1.8 μg Se l −1 and 1.08 ± 0.02 μg Se g −1, respectively. These results are consistent with the certified values of both reference materials.

The determination of selenium in serum and urine by inductively coupled plasma mass spectrometry: comparison with Zeeman graphite furnace atomic absorption spectrometry

An inductively Coupled Plasma Mass Spectrometric (ICPMS) method for the determination of selenium in both serum and urine is described. 78Se is used analytically in spite of 38Ar40Ar isobaric interference at mass 78. Initially 82Se was monitored but, limited isotope abundance and therefore limited detection capability for urine selenium precluded continued use. An ethanol–Triton X-100-nitric acid diluent was used to dilute serum and urine and enhance selenium ionization so that both serum and urine can be analyzed with the same calibration curve. Results derived by the ICPMS method were compared with Zeeman Graphite Furnace Atomic Absorption Spectrometry (ZGFAAS) using nickel as the matrix modifier. Detection limits for ZGFAAS and ICPMS using mass 78 are 2.9 and 0.25 μg/l, respectively. ICPMS and ZGFAAS instrument responses were recorded for additions of inorganic selenium, trimethylselenonium iodide, seleno-dl-methionine, and seleno-dl-cystine to urine and serum. ICPMS slopes for all compounds added to urine and serum were found to be nearly identical. ZGFAAS response for each compound was more variable than ICPMS. ZGFAAS response for trimethylselenonium iodide was approximately 3-fold lower than for the other compounds. ZGFAAS regression slopes and correlation coefficients were 0.72 and 0.8139 for reference urine samples. ICPMS regression slope and correlation coefficient vs. the reference target values were 0.95 and 0.9700 for the same urines. Regressions slopes and correlation coefficients for reference sera were 1.01 and 0.9912 for ICPMS and 1.12 and 0.9648 for ZGFAAS. We conclude that ICPMS produced more accurate results than ZGFAAS for selenium in serum and urine.

The use of ETV-ICP-MS for the determination of selenium in serum

The development of a novel procedure for the accurate determination of selenium in serum using electrothermal vaporisation inductively coupled plasma mass spectrometry (ETV-ICP-MS) is described. The proposed method eliminates the need for a lengthy sample digestion procedure (a requirement with many methods for the analysis of biological samples), utilising a simple 1+19 dilution of the serum with 1% nitric acid. Many of the interferences normally associated with the determination of selenium by ICP-MS are successfully eliminated with careful optimisation of the ETV temperature program and modifier system. Analytical characteristics for 74 Se, 77 Se, 78 Se and 82 Se are reported, including detection limits (3σ blank) of approximately 0.1 ng g –1 for 77 Se and 82 Se. Short- and long-term reproducibility data between 4.7 and 4.9% and 3.2 and 3.8% (RSD) for 77 Se and 82 Se, respectively, are shown. The accuracy of the method, which included Te as an internal standard, was demonstrated with the analysis of three internal quality control samples and the certified reference material NIST SRM 1598 (bovine serum). Results within 10% of the target value were achieved for three of the four isotopes studied, with slightly worse results for 78 Se owing to the large interference from argon adduct ions on this isotope. Preliminary work involving the addition of nitrogen to the argon aerosol carrier gas was successful in reducing the ArAr interference at m/z 78.

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 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.

Simple Method for the Accurate Determination of Selenium in Serum by Using Inductively Coupled Plasma Mass Spectrometry

A simple 1+15 dilution of 200 µl volumes of serum with a diluent containing 1.0% v/v butan-l-ol; 0.66% Triton X-100; 0.01 mol l -1 NH 3 , 0.0002 mol l -1 (NH 4 ) 2 H 2 EDTA and 0.002 mol l -1 NH 4 H 2 PO 4 enables ICP-MS to provide accurate and precise measurements of total selenium concentrations. Interferences from argon-adduct ions on selenium isotopes 77 Se, 78 Se are eliminated and are considerably reduced at 82 Se by the presence in the diluent of butan-l-ol. The other reagents prevent blockage of the torch injector tube during prolonged, ≥6 h, analytical runs. The detection limit (3 s blank) is 0.02 µmol l -1 (1.5 µg l -1 ) and within-run RSDs range from 3.4 to 7.5% at 0.3 µmol l -1 , to 1.5 to 2.0% at 2.1 µmol l -1 . Analyses of 12 sera from an external quality assessment program, of a commercially available reference serum material (Nycomed) and of in-house internal quality control sera gave excellent agreements with median/target concentrations over the range 0.3 to 3.3 µmol l -1 . The ICP-MS data showed small, but acceptable, negative biasses at 1.0 µmol l -1 of: -3.8% and -5.0% at 77 Se and 78 Se, respectively.

Determination of selenium in serum by hydride generation atomic absorption spectrometry for calculation of daily dietary intake

Hydride generation atomic absorption spectrometry was used to determine the selenium concentrations in 130 samples of human serum from a control group of inhabitants in the southern part of the province of Granada (Spain). The mean selenium concentration in serum was 74.9 μg/l. This concentration did not vary significantly (P > 0.05) in relation to the sex of the subject, with concentrations of 80.6 μg/l in men and 70.7 μg/l in women. These mean values correspond to a mean daily dietary selenium intake of 50.4 μg per day in men and 44.6 μg per day in women. A considerable number of the individuals in the study area therefore have a daily selenium intake lower than the recommended dietary allowance of 70 μg per day for men and 55 μg per day for women. Likewise, the measured selenium concentrations in the basic health zones of the area were not statistically different (P > 0.05). The differences in selenium concentration between subjects in coastal zones and mountainous zones are therefore not significant.

Direct Determination of Selenium in Human Blood Serum and Plasma by Electrothermal Atomic Absorption Spectrometry

A method is described for the direct determination of selenium in serum or plasma by electrothermal atomic absorption spectrometry with deuterium-arc background correction. Samples are diluted (1 + 2) with a modifier containing palladium nitrate and Triton X-100. Samples are atomised from a L'vov platform in a pyrolytically-coated electrographite tube and peak area signals are measured. Direct determination is possible by using selenium standards matched to the physiological concentrations of sodium chloride, calcium and phosphate. The detection limit is 6 micrograms/L in the original sample. Precision at a selenium concentration of 97 micrograms/L was 2.2% RSD within batch and 3.0% RSD between batch. Accuracy is shown by (i) analysis of a Seronorm reference serum (value obtained 97 +/- 3 micrograms/L; recommended value 96 micrograms/L); (ii) recovery of added selenium (93.3 +/- 6.7% and 98.2 +/- 3.3% at additions of 30 and 60 micrograms/L, respectively) and (iii) comparison of results with mean of all laboratories in an external quality assessment scheme.

Concanavalin A-bound selenoprotein in human serum analyzed by graphite furnace atomic absorption spectrometry

We developed an assay for the direct determination of selenium in serum with a Perkin-Elmer Model 4100ZL Zeeman atomic absorption spectrometer and Ag-Cu-Mg modifier. We used this assay to analyze concanavalin A-bound selenoprotein (CABSP) in human serum after concanavalin A (ConA) affinity chromatography. The CABSP was identified as a single-chain glycoprotein of 57.3 kDa. Carbohydrate units were N- and O-linked to the protein. The selenium moiety was selenocysteine. Total selenium, glutathione peroxidase (GPX; EC 1.11.1.9), ConA-bound selenium (CABS), and alpha 1-acid glycoprotein (AAG) were determined in normal subjects and patients with various pathological conditions. CABS accounted for 44.1% +/- 6.3% of total selenium in sera from normal subjects and 46.5% +/- 3.9% to 55.1% +/- 8.1% in sera from patients with a variety of diseases. Total selenium in serum was well correlated with serum CABS (r = 0.860), but not with serum GPX activity (r = 0.117), for all patients studied. Serum CABS increased in normal subjects after selenium supplementation. Serum CABSP did not behave as an acute-phase reactant, compared with AAG.

Comparison of chemical modifiers for simultaneous determination of different selenium compounds in serum and urine by Zeeman-effect electrothermal atomic absorption spectrometry

The thermal stability of selenite, selenate, selenomethionine and trimethylselenonium was studied using different chemical modifiers in various amounts. The normally recommended amounts of nickel nitrate, magnesium nitrate, copper nitrate, copper nitrate mixed with magnesium nitrate, palladium nitrate and palladium nitrate in combination with magnesium nitrate were investigated. None of the studied modifiers stabilized the four species to the same extent. In aqueous solutions, addition of 2.7 µg of Pd or 7.5 µg of Pd + 5 µg of Mg(NO3)2 stabilized selenite, selenate and selenomethionine equally, while the sensitivity of trimethylselenonium was only 55% using palladium and 85% using palladium and magnesium nitrate. These chemical modifiers were used for the determination of selenium in serum. In aqueous solution, addition of 11 µg of Pd + 1128 µg of Mg(NO3)2 resulted in an equal stabilization of selenite, selenate and trimethylselenonium, while the sensitivity of selenomethionine was 15% higher. This chemical modifier was not applicable to serum and urine, as a white layer accumulated in the graphite tube during the experiments. Using the modifier containing 7.5 µg of Pd + 5 µg of Mg(NO3)2 for analysis of National Institute of Standards and Technology (NIST) Standard Reference Material (SRM) Freeze-dried Urine the selenium concentration was 27.2 ± 1.3 µg l–1(certified value, 30 ± 8 µg l–1). The result of the analysis of the serum reference material. Seronorm, was 96.6 ± 1.8 µg l–1 of Se (recommended value 96 µg l–1). This chemical modifier is proposed as the best choice among the examined modifiers for determination of selenium in serum and urine.

Determination of selenium in human serum using a direct hollow-cathode discharge atomic emission spectrographic technique

Samples of serum and a series of aqueous standards of SeO2 were dried on to the wall of an aluminium cathode cup at a temperature of 293 K, thus ensuring a sample preparation procedure without loss of analyte. Using the Se II 444.62-nm and Se II 444.95-nm spectral lines, the detection limit for the proposed method was established as being 1 ng ml–1. The selenium content of the samples varied between 80 and 120 ng ml–1, which is two orders of magnitude higher than the detection limit of the proposed method. The sodium content of the serum did not interfere in the determination, as the amount of sodium present (140 mmol 1–1) was less than the concentration which can cause a decrease in the spectral line intensity. The relative error of the concentration values is less than 5%. The determination of selenium in serum was performed using direct hollow-cathode discharge atomic emission spectrographic analysis. Optimum conditions for the determination were established. It was found that sputtering of selenium could be achieved, with a satisfactory detection limit and acceptable accuracy, at a power of 240 W. Water cooling was at a flow-rate of 8 I min–1, which provided equal temperatures of the neutral gas and cathode of 430 ± 50 K, which is lower than the melting-points of Se and SeO2.

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.

Improved determination of selenium in serum by Zeeman atomic absorption spectrometry.

We have improved Zeeman atomic absorption spectrometric determination of selenium in serum by using an acidic solution of Ag + Cu + Mg as a matrix modifier and performing the charring step in flowing O2. Under these conditions, we could calibrate serum results with selenium standards in bovine albumin solutions. Mean analytical recovery was 98%, and the CV was 1.8% within runs, 2.9% between runs. Analysis of Reference Materials from the U.S. National Bureau of Standards (SRM 909 and RM 8419) yielded the values of 106 (SD 2.4) and 15 (SD 1.6) microgram/L, respectively, in good agreement with the expected values (106 and 16, respectively). The method--being reliable and relatively simple and rapid--is suitable for use in epidemiological screenings. Mean selenium concentrations in serum sampled from 274 adults in central Italy were 90 (SD 15) microgram/L. For 11-year-old children, these values were lower and showed a tendency to sex-related difference: 82 (SD 9.9) microgram/L for 97 boys, 78 (SD 9.3) microgram/L for 90 girls.

Elimination of chloride interference on the determination of selenium in serum by inductively coupled plasma mass spectrometry

The presence of chloride ions in sample solutions may cause interferences in the determination of certain elements (particularly V, Cr and As) by inductively coupled plasma mass spectrometry (ICP-MS). This may be problematic in clinical samples such as tissue, protein and urine where the measurement of elements, present at physiologically active levels, can be impaired by these spectral interferences. A procedure is described whereby a chromatographic separation is employed to de-salt serum samples, rendering a sample solution free of chloride. Using this procedure, ICP-MS can be used to measure the Se content of serum solution accurately without interference.

A methodological comparison of hydride and carbon furnace atomic absorption spectroscopy for the determination of selenium in serum

Two methods based on different chemical and physical principles for the determination of selenium in serum are elaborated, evaluated and compared — the hydride atomic absorption (AAS) technique and the carbon furnace technique. For the hydride AAS technique a wet destruction method is described. The sensitivity of the method is 10 μg Se/1. The carbon furnace technique makes use of the fact that selenium forms refractory selenides when nickel compounds are added. The sensitivity of the carbon furnace technique is 11 μg, Se/1. The determination of selenium in serum by the hydride AAS and carbon furnace technique correlates satisfactorily (correlation coefficient 0.94; mean value for the hydride AAS 69.1 μg Se/1; mean value for the carbon furnace 67.4 μg Se/1) indicating that with the carbon furnace technique total selenium (inorganic and organic) is determined. A reference range was established with 99 persons (42 men and 57 women) which show an average selenium content in serum of 80.55 (SD 13.78) μg Se/1 [1.02 (0.17) μmol Se/1].

Determination of serum selenium by means of solvent extraction combined with activation analysis.

Abstract A method for the determination of selenium in serum was developed employing a combination of solvent extraction and neutron activation analysis. The loss of selenium by volatilization during digestion was minimized by use of a single-oxidant at low temperature. Comparative analysis was performed to illustrate the efficacy of the method.