Determination of selenium and tellurium compounds in biological samples by ion chromatography dynamic reaction cell inductively coupled plasma mass spectrometry

An ion chromatography-inductively coupled plasma mass spectrometric (IC-ICP-MS) method for the speciation of selenium and tellurium compounds namely selenite [Se(IV)], selenate [Se(VI)], Se-methylselenocysteine (MeSeCys), selenomethione (SeMet), tellurite [Te(IV)] and tellurate [Te(VI)] is described. Chromatographic separation is performed in gradient elution mode using 0.5 mmol L(-1) ammonium citrate in 2% methanol (pH 3.7) and 20 mmol L(-1) ammonium citrate in 2% methanol (pH 8.0). The analyses are carried out using dynamic reaction cell (DRC) ICP-MS. The DRC conditions have also been optimized to obtain interference free measurements of (78)Se(+) and (80)Se(+) which are otherwise interfered by (38)Ar(40)Ar(+) and (40)Ar(40)Ar(+), respectively. The detection limits of the procedure are in the range 0.01-0.03 ng Se mL(-1) and 0.01-0.08 ng Te mL(-1), respectively. The accuracy of the method has been verified by comparing the sum of the concentrations of individual species obtained by the present procedure with the total concentration of the elements in two NIST SRMs Whole Milk Powder RM 8435 and Rice Flour SRM 1568a. The selenium and tellurium species are extracted from milk powder and rice flour samples by using Protease XIV at 70 degrees C on a water bath for 30 min.     

Determination of iodine and bromine in plasma and urine by inductively coupled plasma mass spectrometry

The simultaneous determination of iodine and bromine in plasma and urine by inductively coupled plasma mass spectrometry, using a Nermag prototype instrument, is described. The sample preparation involves only a 10-fold dilution with a diluent containing europium as an internal standard followed by direct nebulisation in the plasma. The iodine, bromine and europium ions are measured at m/z = 127, 79, and 153, respectively. The sensitivity of the method, with detection limits of 1.6 and 52 micrograms l-1 for iodine and bromine, respectively, is satisfactory for clinical applications. The calibration graphs were linear over the ranges 0-400 micrograms l-1 and 0-40 mg l-1 for iodine and bromine, respectively, which are wide enough for most assays. The recoveries were close to 100% with coefficients of variation of less than 3%. The within-day and between-day reproducibility was about 5%. The concentrations of iodine and bromine in the plasma of 26 healthy individuals were 58 +/- 12 micrograms l-1 and 4.1 +/- 0.9 mg l-1, respectively. The amounts of iodine and bromine eliminated in urine were 94 +/- 97 micrograms per 24 h (range 27-403 micrograms per 24 h) and 3.6 +/- 1.7 mg per 24 h, respectively. These results are in agreement with reported values.     

Determination of iodine in seafood by inductively coupled plasma/mass spectrometry.

A method was developed for determination of total iodine content in different standard reference materials (SRMs) and seafood products by inductively coupled plasma/mass spectrometry (ICP/MS). If iodine is present as iodide and nitric acid is used in the wet digestion system, the observed signal is not stable when iodine is measured by ICP/MS at m/z 127. To stabilize the iodine signal, 3% ammonia solution (1 + 1, v/v) was added to the digest. The limit of quantitation of the method, defined as 6 times the standard deviation in the blank solution (n = 20) was estimated to be 15 mg/kg (using 0.2 g dry mass and a dilution factor of 50). The precision, expressed as repeatability of the iodine concentration, varied between 3.2 and 12% in SRMs, with concentrations of 4.70-0.17 mg/kg dry matter. The described method was compared with a method using tetramethylammonium hydroxide extraction. Both methods showed good precision and trueness by analyses of SRMs. The 2 methods were used to determine iodine in seafood from the Barents Sea, the Norwegian Sea, and the North Sea. The results showed great variation between different fish species as well as between individuals within a species. The lowest values of iodine were recorded in muscle of ling (Molva molva) with a mean of 0.07 mg/kg fresh weight and a variation between 0.03 and 0.11 mg/kg fresh weight. The highest values were found in cod (Gadus morhua) from the Barents Sea, with a mean of 2.5 mg/kg and a variation between 0.7 and 12.7 mg/kg fresh weight.     

Determination of vanadium by reaction cell inductively coupled plasma mass spectrometry

Recent advances in inductively coupled plasma mass spectrometry (ICP-MS) have included the addition of interference reduction technologies, such as collision and reaction cells, to improve its detection capability for certain elements that suffer from polyatomic interferences. The principle behind reaction cell (RC)-ICP-MS is to remove a particular polyatomic interference by dissociation or formation of a different polyatomic species that no longer interferes with the analyte of interest. However, some interferences cannot be removed by commonly reported reaction gases, such as hydrogen, oxygen, or methane, necessitating using more reactive and hazardous gases, such as ammonia. The current study investigates oxygen as a reaction gas in RC-ICP-MS to specifically react with vanadium analyte ions, rather than the interferents, to produce a polyatomic analyte species and thereby provide a way to analyze for vanadium in complex environmental matrices. The technique has been tested on a series of river water, tap water, and synthetic laboratory samples, and shown to be successful in vanadium analyses in high chloride and sulfate matrices. The zinc isobaric interference on the new vanadium oxide analyte at m/z 67 is also investigated, and can be corrected by using a standard mathematical correction equation. The results of this study further increase the utility of RC-ICP-MS analytical techniques for complex environmental matrices.     

Determination of arsenic species by inductively coupled plasma mass spectrometry with ion chromatography

Five arsenic species, trimethylarsine oxide, dimethylarsenic acid, monomethylarsonic acid, arsenobetaine and sodium arsenite, in urine were analysed by inductively coupled plasma mass spectrometry with ion chromatography (IC ICP MS). Since the toxicities of different arsenic compounds are different, speciation of arsenic compounds is very important in the investigation of metabolisms. In this paper, we applied ion chromatography (IC) as a separation device and inductively coupled plasma mass spectrometry (ICP MS) as a detection device. For separation of the five arsenic compounds, an anion-exchange column and, as mobile phase, tartaric acid were used. The eluent from the IC column was introduced directly into the nebulizer of the ICP MS and analysed at 75 amu. Detection limits were from 4 to 9 pg as arsenic.     

Determination of sulfur-containing amino acids by capillary electrophoresis dynamic reaction cell inductively coupled plasma mass spectrometry

Capillary electrophoresis dynamic reaction cell™ inductively coupled plasma mass spectrometry (CE-DRC-ICP-MS) for the determination of sulfur-containing amino acids is described. The sulfur-containing amino acids studied include l-cysteine, l-cystine, dl-homocystine and l-methionine. The species studied were well separated using a 70 cm length×75 μm i.d. fused silica capillary while the applied voltage was set at +22 kV and a 10 mmol l⁻¹ disodium tetraborate buffer (pH 9.8) containing 0.1 mmol l⁻¹ EDTA and 0.5 mmol l⁻¹ Triton X-100 was used as the electrophoretic buffer. The sulfur-selective electropherogram was determined at m/z 48 as by using its reaction with O₂ in the reaction cell. The method avoided the effect of polyatomic isobaric interferences at m/z 32 caused by and on by detecting as the oxide ion at m/z 48, which is less interfered. The detection limit of various species studied was in the range of 0.047-0.058 μg S ml⁻¹, which corresponded to the absolute detection limit of 1.3-1.6 pg S based on the injection volume of 27 nl. We determined the concentrations of selected sulfur-containing amino acids in urine and nutritive complement samples. The recovery was in the range of 92-128% for various species.     

Uranium analysis in urine by inductively coupled plasma dynamic reaction cell mass spectrometry

Urine uranium concentrations are the best biological indicator for identifying exposure to depleted uranium (DU). Internal exposure to DU causes an increased amount of urine uranium and a decreased ratio of ²³⁵U/²³⁸U in urine samples, resulting in measurements that vary between 0.00725 and 0.002 (i.e., natural and depleted uraniums ²³⁵U/²³⁸U ratios, respectively). A method based on inductively coupled plasma dynamic reaction cell mass spectrometry (ICP-DRC-MS) was utilized to identify DU in urine by measuring the quantity of total U and the ²³⁵U/²³⁸U ratio. The quantitative analysis was achieved using ²³³U as an internal standard. The analysis was performed both with and without the reaction gas oxygen. The reaction gas converted ionized ²³⁵U⁺ and ²³⁸U⁺ into ²³⁵UO₂⁺ (m/z=267) and ²³⁸UO₂⁺ (m/z=270). This conversion was determined to be over 90% efficient. A polyatomic interference at m/z 234.8 was successfully removed from the ²³⁵U signal under either DRC operating conditions (with or without oxygen as a reaction gas). The method was validated with 15 urine samples of known uranium compositions. The method detection limit for quantification was determined to be 0.1 pg U mL^–1 urine and an average coefficient of variation (CV) of 1–2% within the sample measurements. The method detection limit for determining ²³⁵U/²³⁸U ratio was 3.0 pg U mL^–1 urine. An additional 21 patient samples were analyzed with no information about medical history. The measured ²³⁵U/²³⁸U ratio within the urine samples correctly identified the presence or absence of internal DU exposure in all 21 patients.The opinions and assertions expressed herein are those of the authors and are not to be construed as official or as representing the views of the Armed Forces Institute of Pathology, the Department of the Army, or the Department of Defense     

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

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

Determination of organometallic compounds by capillar gas chromatography – inductively coupled plasma mass spectrometry

The separation and detection of volatile organometallic compounds containing tin, iron, and nickel has been achieved using capillary GC–inductively coupled plasma–mass spectrometry (capillary GC-ICP-MS). Detection limits range from 3.0 to 7.0 pg/s. The presence of volatile organotin compounds in a harbor sediment has been confirmed. The retention range of the organometallic compounds analyzed by capillary GC-ICP-MS has been extended considerably beyond that possible in earlier studies (retention indices up to 3400).     

Determination of the ratio of calcium to phosphorus in foodstuffs by dynamic reaction cell inductively coupled plasma mass spectrometry

An inductively coupled plasma mass spectrometer (ICP–MS) equipped with a dynamic reaction cell (DRC) was used for the determination of Ca and P in foodstuffs. In this study, two different reaction gases, CH₄ and O₂, were introduced successively through the different channels to alleviate different interferences in the same analysis run. The effect of the operating conditions of the DRC system was studied to get the best signal-to-noise ratio for each element. The interfering ⁴⁰Ar⁺ at m/z 40 was reduced in intensity by up to five orders of magnitude by using 1.0 mL min^–1 CH₄ as reaction cell gas in the DRC. On the other hand, by using O₂ as the reaction gas, ³¹P⁺ was converted to ³¹P¹⁶O⁺ that could be detected at m/z 47 where there was less interference. The limits of detection for Ca and P were 0.2 ng mL^–1 and 0.3 ng mL^–1, respectively. This method was used to determine the concentrations of Ca and P and the ratio of Ca to P in NIST SRM 1549 non-fat milk powder and NIST RM 8345 whole milk powder reference materials and an infant milk powder and an infant cereal-rice sample purchased locally. The results for the reference samples agreed satisfactorily with the reference values. The accuracy of the determination was better than 4.1 and 0.9% for Ca and P, respectively. The results for infant milk powder and infant cereal were also found to be in good agreement with the value on the bottle label. Precision (RSD) between sample replicates was better than 4.8% for all the determinations.     

Speciation of arsenic by ion chromatography inductively coupled plasma mass spectrometry using ammonium eluents

A method based on ion chromatography (IC) and inductively coupled plasma MS (ICP-MS) was developed for the speciation of arsenic in water and soil extracts. An anion-exchange column (G3154A/101) was used to separate As(III), As(V), dimethylarsinic acid (DMA), and monomethylarsonic acid (MMA) with excellent resolution. Various ammonium salts, including NH4H2PO4, (NH4)2HPO4, (NH4)2CO3, and NH4HCO3, were examined as eluents to reduce matrix interference from chloride and to solve clogging problems. The best arsenic speciation was obtained within 9 min with excellent resolution and without interference from high chloride concentrations using an eluent containing 7.5 mM (NH4)2HPO4 at pH 7.9. The detection limits for the target arsenic species ranged from 0.1 to 0.4 microg/L with direct injection of sample without matrix elimination. The proposed method was effectively demonstrated by determining arsenic species in contaminated waters and soils of Bangladesh.     

High-performance liquid chromatography/inductively coupled plasma mass spectrometry and tandem mass spectrometry for the detection of carbon-containing compounds

High-performance liquid chromatography (HPLC) combined with inductively coupled plasma mass spectrometry (ICPMS) has been studied as a means for the detection of carbon to provide a 'universal' method for detecting organic compounds in chromatographic eluents. Carbon is particularly difficult to ionise and the amount of carbon present in normal chromatographic systems leads to high backgrounds, making detection a challenge. Novel separation approaches were therefore employed, using either entirely aqueous eluents (at temperatures of 60 and 160 degrees C, dependent on the column used) to eliminate the organic modifier completely, or isotopically enriched solvents. For the aqueous eluents, detection limits for sulphanilamide were found to be 2.26 microg, corresponding to 1.13 micromol (0.47 micromol of carbon), injected on a conventional 4.6 mm i.d. column. The use of a narrow bore column with highly isotopically enriched 12C-methanol (99.95 atom%) as organic modifier for the mobile phase enabled the detection of 86 micromol for 13C-triple-labelled caffeine and 79 micromol for 13C-double-labelled phenacetin. The sensitive detection of 12C-compounds with 13C-enriched methanol as organic modifier proved impractical due to a lower level of isotopic enrichment (99 atom%) of this solvent, with the residual 12C-methanol resulting in significant interference.     

离子色谱(IC)-电感耦合等离子体质谱(ICP-MS)法测定食品接触涂层制品中可迁移六价铬

此研究旨在建立食品接触涂层制品中低含量可迁移六价铬的一种快速、准确的测定方法。试样经过水和4%乙酸迁移试验后,以75 mmol/L硝酸铵溶液（调节pH=7.0）为洗脱液,经过NP5阴离子柱分离,选择碰撞（KED）监测模式,用离子色谱（IC）-电感耦合等离子体质谱（ICP-MS）法测定样品中六价铬的迁移量。实验发现,以水和4%乙酸作模拟物进行迁移试验,六价铬迁移量在0～5.0 μg/L 范围内线性关系良好,相关系数均大于0.999,检出限低至0.05 μg/kg。三种浓度水平的加标回收率试验结果为81.5%～94.7%,精密度结果为3.1%～7.2%。与紫外可见分光光度（UV-Vis）法相比,检出限更低,抗基质干扰性更好。对购于商超和电商平台的多种食品接触涂层制品进行测试,结果显示,该方法快速、准确,适用于食品接触涂层制品中低迁移量的六价铬的快速测定。     

Speciation of arsenic compounds by coupling high-performance liquid chromatography with inductively coupled plasma mass spectrometry

There is considerable evidence that toxicity and physiological behavior of arsenic depends on its chemical forms. Arsenic speciation became therefore the subject of increasing interest in recent years. A sensitive method for the determination of arsenic species has been developed. The proposed procedure involves the use of high-performance liquid chromatography and inductively coupled plasma mass spectrometry (HPLC-ICP-MS). Six arsenic compounds were separated by anion-exchange chromatography with isocratic elution using tartaric acid as mobile phase with an elution order: arsenocholine, arsenobetaine, dimethylarsinic acid, methylarsonic acid, arsenous acid and arsenic acid. The chromatographic parameters affecting the separation of the arsenic species were optimized. Analytical characterization of the method has been realized with standard solutions. The detection limits for six arsenic compounds were from 0.04 to 0.6 g/L as As element. The repeatability (expressed by R.S.D) was better than 7% for all investigated compounds. The HPLC-ICP-MS system was successfully applied to the determination of arsenic compounds in environmental and biological samples in g/L level.     

Determination of iodine and bromine compounds in foodstuffs by CE-inductively coupled plasma MS

A CE-inductively coupled plasma mass spectrometric (CE-ICP-MS) method for iodine and bromine speciation analysis is described. Samples containing ionic iodine (I(-) and IO(3)(-)) and bromine (Br(-) and BrO(3)(-)) species are subjected to electrophoretic separation before injection into the microconcentric nebulizer (CEI-100). The separation has been achieved in a 50 cm length x 75 microm id fused-silica capillary. The electrophoretic buffer used is 10 mmol/L Tris (pH 8.0), while the applied voltage is set at -8 kV. Detection limits are 1 and 20-50 ng/mL for various I and Br compounds, respectively, based on peak height. The RSD of the peak areas for seven injections of 0.1 microg/mL I(-), IO(3)(-) and 1 microg/mL Br(-), BrO(3)(-) mixture is in the range of 3-5%. This method has been applied to determine various iodine and bromine species in NIST SRM 1573a Tomato Leaves reference material and a salt and seaweed samples obtained locally. A microwave-assisted extraction method is used for the extraction of these compounds. Over 87% of the total iodine and 83% of the total bromine are extracted using a 10% m/v tetramethylammonium hydroxide (TMAH) solution in a focused microwave field within a period of 10 min. The spike recoveries are in the range of 94-105% for all the determinations. The major species of iodine and bromine in tomato leaves, salt, and seaweed are Br(-), IO(3)(-), I(-), and Br(-), respectively.     

Analysis of phosphorus herbicides by ion-pairing reversed-phase liquid chromatography coupled to inductively coupled plasma mass spectrometry with octapole reaction cell

A reversed phase ion-pairing high performance liquid chromatographic (RPIP-HPLC) method is developed for the separation of two phosphorus herbicides, Glufosinate and Glyphosate as well as Aminomethylphosphonic acid (AMPA), the major metabolite of Glyphosate. Tetrabutylammonium hydroxide is used as the ion-pairing reagent in conjunction with an ammonium acetate/acetic acid buffering system at pH 4.7. An inductively coupled plasma mass spectrometer (ICP-MS) is coupled to the chromatographic system to detect the herbicides at m/z = 31P. Historically, phosphorus has been recognized as one of the elements difficult to analyze in argon plasma. This is due to its relatively high ionization potential (10.5 eV) as well as the inherent presence of the polyatomic interferences 14N16O1H+ and 15N16O+ overlapping its only isotope at m/z = 31. An octapole reaction cell is utilized to minimize the isobaric polyatomic interferences and to obtain the highest signal-to-background ratio. Detection limits were found to be in the low ppt range (25-32 ng/l). The developed method is successfully applied to the analysis of water samples collected from the Ohio River and spiked with a standard compounds at a level of 20 microg/l.     

Determination of selenium in sediment by isotope-dilution inductively coupled plasma mass spectrometry with an octapole reaction cell

A method is described for determination of selenium in sediment by isotope-dilution inductively coupled plasma mass spectrometry with an octapole reaction cell (ID–ICP–ORCMS). Sediment samples were digested with HNO₃, HClO₄, and HF, and the digestion included an elaborate evaporation process to remove bromine from the digested solution. Simple strong cation-exchange disk filtration was used to remove rare earth elements (REE) from the digested solution, because REE²⁺ seriously interfere with Se isotopes (i.e. ¹⁵⁶Gd²⁺ with ⁷⁸Se⁺, ¹⁶⁰Gd²⁺ with ⁸⁰Se⁺). Addition of acetic acid to the filtrate was examined to improve the sensitivity of ICP–ORCMS measurement of Se⁺ by means of a carbon-enhancement effect. The interfering for selenium isotopes were almost eliminated by use of H₂ as reaction gas. Interference from BrH⁺ formed in the reaction cell was negligible because the Br was removed in the evaporation process. Approximately 99.5% of REE were removed by cation-exchange disk filtration yet more than 99% of Se remained in the filtrate solution. The intensity for Se⁺ was enhanced approximately fourfold by addition of 5% (v/v) of acetic acid whereas that for was barely enhanced. Measured ⁸⁰Se/⁷⁸Se ratios in unspiked digested solutions of the sample were in good agreement with that for an Se standard solution. The analytical results for Se in the certified reference materials MESS-3 and PACS-1 were in good agreement with their certified values, with small uncertainties.      

Determination of B,Si, P and S in steels by inductively coupled plasma quadrupole mass spectrometry with dynamic reaction cell

An inductively coupled plasma quadrupole mass spectrometer equipped with a dynamic reaction cell™ (DRC) was successfully used for the accurate determination of B, Si, P and S in steel samples, using the reaction of Si⁺, P⁺ and S⁺ ions with O₂ in the cell. The method obviated the effect of polyatomic isobaric interferences at m/z 28, 31 and 32 by detecting ²⁸Si⁺, ³¹P⁺ and ³²S⁺ as the oxide ion ²⁸Si¹⁶OH, ³¹P¹⁶O and ³²S¹⁶O at m/z 45, 47 and 48, respectively, which is less interfered. The effects of the operating conditions of DRC system were optimized to get the best signal to noise ratio for ²⁸Si¹⁶OH, ³¹P¹⁶O and ³²S¹⁶O. As there is no spectroscopic interference, boron was determined under the standard mode. Validation of the method was carried out by the determination of B, Si, P and S in steel standard reference materials (NIST SRM 361, 362 and 364). Since the sensitivities of Si, P and S in digested sample solutions and standard solutions were found to be quite different, standard addition method was used for the determination of B, Si, P and S in this study. Good agreement was obtained between the certified values and the experimental results. The precision between sample replicates was better than 6.3% for all the determinations.