Negative Thermionen-Massenspektrometrie von Selen

Summary Selenite and selenate were determined in ground waters with isotope dilution mass spectrometry (IDMS). This species analysis was possible by the use of an⁸²Se enriched selenite and selenate spike and a Chromatographic separation of both species after the isotope dilution step. In a column filled with the DEAE cellulose anion exchanger selenite could be separated with 1 mol/l formic acid, whereas selenate was eluted with 0.1 mol/1 nitric acid. The mass spectrometric isotope ratio measurement was carried out in a thermal ionization instrument using the formation of negative Se^– thermal ions for detection. Selenite, selenate and total selenium in ground water samples were determined in the concentration range of 0.2–20 n/g with relative standard deviations of 0.5%–5%. The selenate concentration was approximately ten to eighty times higher than the corresponding selenite concentration. There was always a difference of about 8% between the sum of the selenite and selenate concentrations and the total selenium concentration which can possibly be attributed to water-soluble selenides and elementary selenium, respectively.

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Herrn Prof. Dr. R. Neeb zum 60. Geburtstag gewidmet     

DRC™ ICP-MS coupled with automated flow injection system with anion exchange minicolumns for determination of selenium compounds in water samples

A flow injection system with anion exchange resin minicolumns was coupled with dynamic reaction cell (DRC™) ICP-MS for the determination and speciation of selenite and selenate at sub μg L⁻¹ levels. The charged selenate and uncharged selenite were separated on the first resin column in which only selenate was retained. The unretained selenite was then deprotonated with alkaline solution, and the resulting anionic selenite species was collected on the second column serially connected downstream. By setting a sample loop, total selenium can be determined together with selenite and selenate. The selenium species was eluted by nitric acid and carried to DRC™ ICP-MS for their detection. Using ammonia as reaction gas, the detection of ⁷⁸Se was improved. The enrichment factor was 20 for 10 mL of sample. The standard deviations (n = 5) of peak heights were 4.9%, 4.1%, and 7.0% for a 5.0 × 10⁻² μg L⁻¹ selenite and selenate, and total Se, respectively. The calibration graphs were linear from 2.0 × 10⁻² to 1.0 μg L⁻¹ selenite and selenate. And, the linearity for total selenium was good in the range of 10.0 × 10⁻² to 1.0 μg L⁻¹. The proposed method has been demonstrated for the application to natural and bottled drinking water samples.     

Determination of selenite and selenate in drinking water: a fully automatic on-line separation/pre-concentration system coupled to electrothermal atomic spectrometry with permanent chemical modifiers

A time-based flow injection (FI) separation pre-concentration system coupled to an electrothermal atomic absorption spectrometer (graphite furnace) has been developed for the direct ultra-trace determination of selenite and selenate in drinking water. The pre-concentration of both forms of selenium is carried out onto a micro-column packed with an anionic resin (Dowex 1X8) that is placed in the robotic arm of the autosampling device. Selenite and selenate are sequentially eluted with HCl 0.1 M and HCl 4 M, respectively. The interference of large quantities of chloride during selenium atomisation is prevented by using iridium as a “permanent” chemical modifier. The features of the pre-concentration separation system for both species are: 53% efficiency of retention and an enhancement factor of 82 for a pre-concentration time of 180 s (sample flow rate=3 ml min⁻¹) with HCl elution volumes of 100 μl. The detection limit (3 s) is 10 ng l⁻¹ for the two species and the relative standard deviation (n=10) at the 200 ng l⁻¹ level is 3.5% for selenite and 5.6% for selenate. The addition of selenite and selenate stock standard solutions to tap water samples yields a 97-103% recovery of both species.     

Determination of selenium compounds in urine by high-performance liquid chromatography--inductively coupled plasma mass spectrometry

Selenium species, selenite, selenate, selenomethionine (Semet), seneloethionine (Seet) and trimethylselenonium ion (TmSe) were separated in aqueous solution using a gel-permeation (polyvinyl alcohol-based resin) GS-220 column by eluting with 25 mM tetramethylammonium hydroxide and 25 mM malonic acid at pH 7.9. The GS-220 column coupled with inductively coupled plasma mass spectrometry was used for the separation, identification, and quantification of selenium compounds present in certified reference material (CRM) No. 18 human urine from the National Institute for Environmental Studies in Japan (NIES). Spiking of the authentic standard to the urine and use of a silica-based LC-SCX cation-exchange column validated the peak of selenium compounds. High concentrations of chloride and bromide in the urine eluted from the GS-220 column formed molecular ions 40Ar37Cl+ and 81Br1H+ in the plasma, and these molecular ions created additional peaks in the chromatograms when 77Se and 82Se isotopes were monitored respectively. Thus, both the isotopes were selected concurrently for signal monitoring to eliminate the interfering signals. On the LC-SCX column, chloride and bromide were eluted with selenate and complicated its determination, but the peak of TmSe was baseline separated from rest of the Se compounds. Two unknown Se compounds were detected in both the columns. An additional Se compound having the same retention time as that of Semet was detected on the LC-SCX column. Peaks of selenite, selenate, TmSe and unknown selenium compounds in the urine were baseline separated on the GS-220 column, and were free from interferences. Therefore, the GS-220 column was used for the determination of selenium compounds in NIES CRM No. 18. Unknown Se compounds were the predominant selenium species followed by selenite, TmSe and selenate. The estimated value of TmSe as Se, by the standard additions method using the GS-220 column, was 3.42 +/- 0.17 microg l(-1) and was in good agreement with the LC-SCX value [3.38 +/- 0.21 (n=5) microg l(-1)].     

Preconcentration and determination of trace elements with 2,6-diacetylpyridine functionalized Amberlite XAD-4 by flow injection and atomic spectroscopy

An on-line flow injection method for the direct determination of trace elements in environmental samples is described. A mini-column packed with 2,6-diacetylpyridine functionalized Amberlite XAD-4 was used to preconcentrate and separate 8 trace metals (Cd, Co, Cu, Mn, Ni, Pb, U and Zn) from water and extracts from solid samples. The metals were eluted with 0.1 M HNO(3) directly to the detection system (either inductively coupled plasma-mass spectrometry (ICP-MS) or flame atomic absorption spectrometry (FAAS)). As well as demonstrating that the resin could be used to preconcentrate ultra-trace analytes from natural waters, it was also shown to work well at a pH of 5.5. Therefore, after treatment of sample digests with sodium fluoride, samples that contain extremely large concentrations of iron may be analysed for trace analytes without the excess iron overloading the capacity of the resin. To this end, the analytes Cd, Co, Cu and Ni were preconcentrated from acid extracts of certified soil/sediment samples and then eluted with nitric acid to be determined on-line. Limits of detection (3sigma) of Cd = 0.33 microg l(-1), Co = 0.094 microg l(-1), Cu = 0.34 microg l(-1), Mn = 0.32 microg l(-1), Ni = 0.30 microg l(-1), Pb = 0.43 microg l(-1), U = 0.067 microg l(-1) and Zn = 0.20 microg l(-1) for the FI-ICP-MS system and Cd = 22 microg l(-1), Co = 60 microg l(-1), Cu = 10 microg l(-1) and Ni = 4.8 microg l(-1) for the FI-FAAS system were obtained. Analysis of certified reference materials showed good agreement with the certified values using the two methods.     

Application of ion-exchange separations to determination of trace elements in natural waters-IX: simultaneous isolation and determination of uranium and thorium

A method is described for the determination of uranium and thorium in samples of natural waters. After acidification with citric acid the water sample is filtered and sodium citrate and ascorbic acid are added. The resulting solution of pH 3 is passed through a 4-g column of Dowex 1 x 8 (citrate form) on which both uranium and thorium are adsorbed as anionic citrate complexes. Thorium is eluted with 8M hydrochloric acid and separated from co-eluted substances by anion-exchange in 8M nitric acid medium on a separate 2-g column of the same resin in the nitrate form. After complete removal of iron by washing with a mixture consisting of IBMK, acetone and 1M hydrochloric acid (1:8:1 v v ) and treatment of the resin with 6M hydrochloric acid, the uranium is eluted from the 4-g column with 1M hydrochloric acid. In the eluate thorium is determined spectrophotometrically (arsenazo III method) while fluorimetry is employed for the assay of uranium. The procedure was used for the determination of uranium and thorium in numerous water samples collected in Austria, including samples of mineral-waters. The results indicate that a simple relationship exists between the uranium and thorium contents of waters which makes it possible to calculate the approximate thorium content of a sample on the basis of its uranium concentration and vice versa.     

Synthesis of cross-linked chitosan modified with the glycine moiety for the collection/concentration of bismuth in aquatic samples for ICP-MS determination.

A chelating resin, cross-linked chitosan modified with the glycine moiety (glycine-type chitosan resin), was developed for the collection and concentration of bismuth in aquatic samples for ICP-MS measurements. The adsorption behavior of bismuth and 55 elements on glycine-type chitosan resin was systematically examined by passing a sample solution containing 56 elements through a mini-column packed with the resin (wet volume; 1 ml). After eluting the elements adsorbed on the resin with nitric acid, the eluates were measured by ICP-MS. The glycine-type chitosan resin could adsorb several cations by a chelating mechanism and several oxoanions by an anion-exchange mechanism. Especially, the resin could adsorb almost 100% Bi(III) over a wide pH region from pH 2 to 6. Bismuth could be strongly adsorbed at pH 3, and eluted quantitatively with 10 ml of 3 M nitric acid. A column pretreatment method with the glycine-type chitosan resin was used prior to removal of high concentrations of matrices in a seawater sample and the preconcentration of trace bismuth in river water samples for ICP-MS measurements. The column pretreatment method was also applied to the determination of bismuth in real samples by ICP-MS. The LOD of bismuth was 0.1 pg ml(-1) by 10-fold column preconcentration for ICP-MS measurements. The analytical results for bismuth in sea and river water samples by ICP-MS were 22.9 +/- 0.5 pg ml(-1) (RSD, 2.2%) and 2.08 +/- 0.05 pg ml(-1) (RSD, 2.4%), respectively.     

Separation and preconcentration of iron(II) and iron(III) from natural water on a melamine-formaldehyde resin

A combined method for the preconcentration and selective spectrophotometric determination of both valencies of iron, i.e., Fe(II) and Fe(III), down to 0.4 mug l(-1) has been developed. Iron(III) from synthetic and natural water samples has been concentrated on a melamine-formaldehyde resin at pH 5; iron(II) was not retained under identical conditions. The oxidized iron was concentrated on a second resin column. The iron in both columns was eluted with 1 M HCl solution and separately analyzed by the 1,10-phenanthroline-citrate spectrophotometric method. The effect of pH, adsorption and elution rates, and interferences on the developed procedure were investigated. Metal ions that can be retained by the resin at moderate concentrations, e.g., Al(3+), do not cause interference in more dilute solutions encountered in natural water samples. At least 160-fold volume enrichment can be easily obtained using an adsorption flowrate of 50 ml min(-1). A hydrothermal water sample was analyzed by the recommended procedure and by a literature method, and the results were statistically compared by t- and F-tests.     

The efficiency of cellix-p for the preconcentration of lead and other trace metals from waters

The cheating ion-exchanger Cellex-P, a cellulose phosphate ester, is shown to be effective for the preconcentration of Cu, Ni, Mn, Cd, Zn and Pb from water. The pH of the sample is not critical within the approximate range 5–8. The collected ions can be eluted efficiently in 10–25 ml of 1 M nitric acid from 2–16.5-cm columns of resin. Common salts present in natural waters do not interfere. Cellex-P is used for the preconcentration and determination of the metal ions in potable water by graphite-furnace atomic absorption spectrometry.     

Chemical analysis of manganese nodules : Part II. Determination of uranium and thorium after anion-exchange separation

A method is described for the determination of uranium and thorium in manganese nodules. After dissolution of the sample in a mixture of perchloric and hydrofluoric acids, uranium is adsorbed on the strongly basic anion-exchange resin Dowex 1 (chloride form) from 6 M hydrochloric acid. The effluent is evaporated and the residue is taken up in 7 M nitric acid—0.25 M oxalic acid; thorium is then isolated quantitatively by anion-exchange on Dowex 1 (nitrate form). Thorium is eluted with 6 M hydrochloric acid and determined spectrophotometrically by the arsenazo III method. Uranium is eluted from the resin in the chloride form with 1 M hydrochloric acid and then separated from iron, molybdenum and other co-eluted elements on a column of Dowex 1 (chloride form); the medium consists of 50% (v/v) tetrahydrofuran, 40% (v/v) methyl glycol and 10% (vv) 6 M hydrochloric acid. After removal of iron and molybdenum by washing the resin with a mixture of the same composition and with pure aqueous 1 M hydrochloric acid, the adsorbed uranium is eluted with 1 M hydrochloric acid and determined by fluorimetry. The method was used successfully for the determination of ppm-quantities of uranium and thorium in 60 samples of manganese nodules from the Pacific Ocean.     

Methode d'elution selective pour l'extraction des metaux lourds de l'eau de mer sur resine chelatante: A selective method of elution for the extraction of heavy metals from sea waters on a chelating resin

A selective method of elution for the extraction of heavy metals from sea waters on a chelating resin.The extraction of heavy metals in sea water with Chelex 100 prior to their determination by atomic absorption spectrometry (a.a.s.) with electrothermal atomization is discussed. Maximum retention of heavy metals is not obtained with the resin in the H⁺ form, because it is gradually transformed in contact with sea water by the fixation of alkali and alkaline-earth cations which are eluted simultaneously with the heavy metals and interfere during a.a.s. The separation of heavy metals is quantitative on Chelex 100 in the Ca²⁺ form; treatment with dilute acetic acid (1 + 99) eliminates the alkali and alkaline-earth metals fixed on the resin before elution or the heavy metals. Elution with 1 M nitric acid gives simultaneous and quantitative recovery of Cu, Pb, Ni, Zn, Cd and Co; intermediate elution with 0.01 M nitric acid isolates Zn, Cd and Co from Cu and Pb, which are subsequently eluted with 1 M nitric acid.     

Preconcentration and atomic absorption determination of iron by sequential injection analysis

A sequential injection analysis (SIA) assembly for the atomic absorption determination of Fe(III) in natural waters is proposed. Iron is preconcentrated on a microcolumn packed with a chelating resin (Chelex 100) that is inserted in the manifold. The sample is passed through the column and the iron retained by the resin is subsequently eluted with 2 M HNO(3). The proposed SIA system affords automatic preconcentration, elution, detection of Fe(III), data acquisition and treatment. When 9 ml of iron solution containing 0.4 or 1 mg l(-1) was passed through the resin, the retention efficiency was 93.1 +/- 0.6 and 7.4 +/- 3.0% respectively, and when 27 ml of iron solution of 0.2 mg l(-1) was preconcentrated, the retention was 8.4 +/- 2.9%. The detection limits thus achieved is 12 mug l(-1) when 9 ml of sample are preconcentrated and 6 mug l(-1) for 27 ml.     

Synthesis of novel chitosan resin derivatized with serine moiety for the column collection/concentration of uranium and the determination of uranium by ICP-MS

A chitosan resin derivatized with serine moiety (serine-type chitosan) was newly developed by using the cross-linked chitosan as a base material. The adsorption behavior of trace amounts of metal ions on the serine-type chitosan resin was systematically examined by packing it in a mini-column, passing a metal solution through it and measuring metal ions in the effluent by ICP-MS. The resin could adsorb a number of metal cations at pH from neutral to alkaline region, and several oxoanionic metals at acidic pH region by an anion exchange mechanism. Uranium and Cu could be adsorbed selectively at pH from acidic to alkaline region by a chelating mechanism; U could be adsorbed quantitatively even at pH 3–4. Uranium adsorbed on the resin was easily eluted with 1 M nitric acid: the preconcentration (5-, 10-, 50- and 100-fold) of U was possible. The column treatment method was used prior to the ICP-MS measurement of U in natural river, sea and tap waters; R.S.D. were 2.63, 1.13 and 1.37%, respectively. Uranium in tap water could be determined by 10-fold preconcentration: analytical result was 1.46±0.02 ppt. The resin also was applied to the recovery of U in sea water: the recovery tests for artificial and natural sea water were 97.1 and 93.0%, respectively.     

Ion-exchanger colorimetry-VI Microdetermination of nickel in natural water

Ion-exchanger colorimetry with 1-(2-pyridylazo)2-naphthol (PAN) has been developed for the determination of nickel at the mug/l. level in natural water. With 1 litre of sample the detection limits are 1.3 x 10(-9)Mi.e., 0.077 mug/l. for fresh water and 5.8 x 10(-9)Mi.e., 0.34 mug/l. for sea-water. The distribution ratio is 5 x 10(4). Copper and zinc, which form coloured species with PAN in the resin phase, can be completely eluted with a masking solution composed of EDTA and thioglycollic acid (pH 7.8). Cobalt can be determined simultaneously by measurement at 628 nm.     

Liquid-liquid extraction separation and sequential determination of plutonium and americium in environmental samples by alpha-spectrometry

A procedure is described by which plutonium and americium can be determined in environmental samples. The sample is leached with nitric acid and hydrogen peroxide, and the two elements are co-precipitated with ferric hydroxide and calcium oxalate. The calcium oxalate is incinerated at 450 degrees and the ash is dissolved in nitric acid. Plutonium is extracted with tri-n-octylamine solution in xylene from 4M nitric acid and stripped with ammonium iodide/hydrochloric acid. Americium is extracted with thenoyltrifluoroacetone solution in xylene at pH 4 together with rare-earth elements and stripped with 1M nitric acid. Americium and the rare-earth elements thus separated are sorbed on Dowex 1 x 4 resin from 1M nitric acid in 93% methanol, the rare-earth elements are eluted with 0.1M hydrochloric acid/0.5M ammonium thiocyanate/80% methanol and the americium is finally eluted with 1.5M hydrochloric acid in 86% methanol. Plutonium and americium in each fraction are electro-deposited and determined by alpha-spectrometry. Overall average recoveries are 81% for plutonium and 59% for americium.     

Separation of arsenic(III) and arsenic(V) in ground waters by ion-exchange

The predominant species of arsenic in ground water are probably arsenite and arsenate. These can be separated with a strong anion-exchange resin (Dowex 1 x 8; 100-200 mesh, acetate form) in a 10 cm x 7 mm column. Samples are filtered and acidified with concentrated hydrochloric acid (1 ml per 100 ml of sample) at the sample site. Five ml of the acidified sample are used for the separation. At this acidity, As(III) passes through the acetate-form resin, and As(V) is retained. As(V) is eluted by passage of 0.12M hydrochloric acid through the column (resulting in conversion of the resin back into the chloride form). Samples are collected in 5-ml portions up to a total of 20 ml. The arsenic concentration in each portion is determined by graphite-furnace atomic-absorption spectrophotometry. The first two fractions give the As(III) concentration and the last two the As(V) concentration. The detection limit for the concentration of each species is 1 mug l .     

Pre-concentration and separation of vanadium on Amberlite IRA-904 resin functionalized with porphyrin ligands

Among several methods, enrichment techniques based on sorption onto chelating resins seem convenient, rapid and capable to achieve a high concentration factor. Amberlite IRA-904 resin modified with tetrakis (p-carboxyphenyl) porphyrin (TCPP) was used to pre-concentrate vanadium species. Several parameters, such as sorption capacity of the chelating resin, pH for retention of V(IV) and V(V), volume of sample and eluent, were evaluated. Both vanadium species sorbed on TCPP-modified resin were eluted by use of 2 M nitric acid and determined by atomic absorption spectrometry. The recovery values were >94% and pre-concentration factor of 110 was obtained. For speciation studies, CDTA was added to the sample for complexing vanadium(IV), which was not retained on the microcolumn. The proposed method was examined for reference standard material (TM-25.2) and river water sample.     

Development of rapid plutonium analysis for environmental samples by isotope dilution/inductively coupled plasma mass spectrometry with on-line column.

This paper describes our development of a rapid on-line column/ID-ICP-MS technique for the analysis of plutonium (Pu) in environmental samples using an UTEVA extraction chromatograph resin (UTEVA resin) column. It took only 40 min to separate and measure Pu in the sample solution, including the time for conditioning the resin column for the next analysis. In our method, Pu in a 3 M nitric acid solution was fed to the UTEVA resin, and then eluted from the resin by reducing Pu to Pu(III) with 3 M nitric acid mixed with 0.01 M ascorbic acid after washing the resin. The outflow from the resin column was directly introduced to an ICP-MS system. The low concentration of ascorbic acid and the small volume of the eluting solution (0.6 mL) made successive stable analysis possible without any skimmer cone clogging. The chemical recovery of Pu during column operation was 70%, and typical lower detection limits for 239Pu, 240Pu and 242Pu were 9.2, 4.3 and 7.5 fg (21, 36 and 1.1 microBq), respectively. We analyzed five international standard materials for Pu, and obtained good results.     

Atomic-absorption determination of beryllium in liquid environmental samples

A method is described for the atomic-absorption determination of beryllium in liquid environmental samples after separation by solvent extraction and cation-exchange. The beryllium is first isolated from natural waters and beverages by chloroform extraction of its acetylacetonate from a solution at pH 7 and containing EDTA. The chloroform extract is then mixed in the ratio of 3:6:1 with tetrahydrofuran and methanol containing nitric acid, and passed through a column of Dowex 50 x 8 (H(+)-form). After removal of acetylacetone, chloroform and tetrahydrofuran by washing the resin bed with methanol-HNO(3), beryllium is eluted with 6M hydrochloric acid and determined by atomic-absorption spectroscopy. The method was successfully applied to determine beryllium in tap-, river- and sea-water samples, mineral waters and wines. Beryllium contents in the range from < 0.01 to 2.3 microg/l were found in these materials.     

Sensitivity Enhancement in ICP Emission Spectrometry with Microcolumn Preconcentration and Ultrasonic Nebulisation

To improve the measurement capability of ICP emission spectrometry, microcolumn preconcentration using an iminodiacetate chelating resin (Muromac A-1) has been combined with ultrasonic nebulisation for determination of ultratrace elements (V, Mn, Fe, Co, Ni, Cu, Zn, Cd, Pb and U) in natural waters including seawaters. Trace element deposition was achieved at pH 5 and elution was effected by injection of nitric acid (250 µl, 2.0 M). Sensitivity enhancement factors between 26 and 44 were achieved with on-line preconcentration (sample volume of 10 ml) and detection limits were improved by up to two orders of magnitude relative to conventional pneumatic nebulisation of original water samples. The method was successfully applied to mineral, rain and sea water samples.