A simple and sensitive continuous hydride generation system for the determination of arsenic and selenium by atomic absorption and atomic fluorescence spectrometry

The development and optimization of a continuous hydride generation system for atomic absorption spectrometry (a.a.s.) and atomic fluorescence spectrometry (a.f.s.) is described. Sodium tetrahydroborate(III) solution and sample solution are delivered by two small peristaltic pumps to a gas/liquid separator. The evolved hydrides are swept to a miniature argon/hydrogen diffusion flame burning on a borosilicate glass tube. Detection limits (2σ) obtained for arsenic are 0.8 ng ml^-1 by a.a.s. and 0.34 ng ml^-1 by a.f.s., and for selenium 0.5 ng ml^-1 by a.a.s. and 0.13 ng ml^-1 by a.f.s. Linear working ranges are typically 1–100 ng ml^-1 with a typical measurement time of 1 min per sample or standard.     

Determination of arsenic in steel and cast iron by hydride-generation atomic absorption spectrometry

A procedure is described for the determination of arsenic in steel and cast iron by atomic absorption spectrometry after hydride generation with sodium tetrahydroborate. The samples are decomposed with a nitric/perchloric acid mixture. The data are evaluated directly against acidic standard solutions of arsenic(V). The limit of detection is about 1 μg g^?1 and the precision is better than 4% for concentrations exceeding 10 μg g^?1.     

Comparison of ten digestion procedures for the determination of arsenic in soils by hydride-generation atomic absorption spectrometry

Ten different digestion methods were investigated for the determination of arsenic in soils by hydride-generation atomic absorption spectrometry. These methods included a dry ashing/digestion, several acid-leaching procedures, and digestions in a pressure decomposition vessel or a Kjeldahl apparatus. A certified reference sample was analysed and the results obtained for five other soil samples were compared with the data obtained by spectrophotometry. A nitric/sulphuric acid digestion was the most suitable. A brief interference study is reported.     

The determination of selenium by atom-trapping atomic absorption spectrometry

The application of atom-trapping atomic absorption spectrometry to the determination of selenium has been studied in detail. The optimum experimental parameters were established and the interference of major elements on the determination of selenium was studied using collection on a cold silica tube. The atom-trapping atomic absorption technique gives a detection limit of 0.03 ppm after 2-min collection on silica in an air—acetylene flame. This compares with ca. 1 ppm by the conventional absorption technique at the same 196.1-nm line. Methods to minimize interferences were examined, including the use of a double tube arrangement, an aluminium oxide-coated silica tube and ion-exchange separation. A combination of combustion in an oxygen flask and collection from an air—acetylene flame on the aluminium oxide-coated silica tube yielded satisfactory results in the analysis of four plant tissue samples.     

Simultaneous determination of arsenic, selenium, tin and mercury by non-dispersive atomic fluorescence spectrometry

A procedure is described for simultaneous determination of arsenic, selenium, tin and mercury in aqueous solution by non-dispersive atomic-fluorescence spectrometry. Radiofrequency-excited EDLs, 100% modulated in the kHz region, were used for atom excitation. Sodium tetrahydroborate was used as reductant and a hydrogen-argon miniflame as atomizer. In the optimized procedure, which uses 1 ml of sample, the limits of detection (three times the standard deviation of the blank) were 0.04, 0.08, 0.1 and 0.1 ng ml for arsenic, selenium, tin and mercury respectively. The linear dynamic range was greater than three decades for all analytes and the precision was better than 7% (typically 3%) for concentrations 1 ng ml . Results for mutual interference effects are reported. Copper, nickel, lead and cobalt interfered only with selenium (5 ng ml ), when present in at least 200-fold weight ratio to it. Using 5 ml of sample improved the limits of detection for selenium and arsenic (0.01 and 0.02 ng ml respectively), but at the expense of greater interference. Recovery from spiked natural water samples was better than 95% at the ng ml level, except for selenium in sea-water, when the recovery was only 85%. Determination of the four elements, including standard-addition and background measurements, requires about 10 min.     

Cobalt as internal standard for arsenic and selenium determination in urine by simultaneous atomic absorption spectrometry

The effectiveness of internal standardization for simultaneous atomic absorption spectrometry (SIMAAS) was investigated for As and Se determination in urine. Co and Sn were selected as internal standard (IS) candidates based on the evaluation of some physico-chemical parameters related to the atomization. Correlation graphs, plotted from the normalized absorbance signals (n = 20) of internal standard (axis y) versus analyte (axis x), precision, and accuracy of the analytical results were the supportive parameters to choose Co as the most appropriate IS. The urine samples were diluted 1 + 2 to 1.0% (v/v) HNO₃ + 80 μg L⁻¹ Co²⁺. The mixture 20 μg Pd + 3 μg Mg was used as chemical modifier and the optimized temperatures for pyrolysis and atomization steps were 1400 and 2300 °C, respectively. The characteristic masses for As (47 ± 1 pg) and Se (72 ± 2 pg) were estimated from the analytical curves. The detection limits (n = 20, 3δ) were 1.8 ± 0.1 and 2.6 ± 0.1 μg L⁻¹ for As and Se, respectively. The reliability of the entire procedure was checked with the analysis of certified reference material from Sero AS(Seronorm™ Trace Elements in Urine). The obtained results showed the matrix interference disallowed the instrument calibration with aqueous standards. The best analytical condition was achieved when matrix-matched standards were used in combination with Co as IS, which improved the recoveries obtained for As. Under this experimental condition, eight urine samples were analysed and spiked with 10 and 25 μg L⁻¹ As and Se. The mean recoveries were 96 ± 6% (10 μg L⁻¹ As), 95 ± 6% (25 μg L⁻¹ As), 101 ± 7% (10 μg L⁻¹ Se), and 97 ± 4% (25 μg L⁻¹ Se).     

Reduction of effects of structured non-specific absorption in the determination of arsenic and selenium by electrothermal atomic absorption spectrometry

The presence of iron and phosphates in biological matrices causes deuterium arc background-correction systems to overcompensate at several arsenic and selenium resonance lines. The addition of platinum as matrix modifier has a significant effect on both the absorbance/time profile of iron and the formation of gaseous phosphate decomposition products. A nickel/platinum matrix modifier is shown effectively to control the problems in the determination of selenium arising both from thermal instability and spectral interferences. The same combination eliminates the spectral interferences found at the arsenic resonance lines. Remaining problems are the thermal stabilization of organometallic arsenic compounds present in biological samples. When radioactived-labelled ⁷⁴As compounds prepared in vivo were applied, none of the tested matrix modifiers (Ni, Cu, Ag, Pd, Zr, Ce, Ce + magnesium nitrate) showed a significant influence on the volatility of arsenic in whole blood and urine from rats.     

Iron(III) as releasing agent for copper interference in the determination of selenium by hydride-generation atomic absorption spectrometry

Iron(III0 has a very effective releasing effect on the depressive interference from copper(II) on the determination of selenium by hydride-generation atomic absorption spectrometry. In solutionwith 100 mg 1^?1 Cu(II), 10 μg 1^?1 Se(IV) and 2.0 mol l^?1 HCl, the absorbance obtained was much higher when 8 g 1^?1 Fe(III) was added than for any earlier releasing agent.     

Determination of total inorganic arsenic in water using on-line pre-concentration and hydride-generation atomic absorption spectrometry

A rapid and sensitive method for the on-line separation and pre-concentration of inorganic arsenic in water samples is described. The analyte in the pentavalent oxidation state is reduced to its trivalent form with l-cysteine and the total inorganic arsenic is sorbed onto activated alumina in the acid form in a mini-column coupled to a FI-HG AAS system. Afterwards, it is eluted with 3 mol l⁻¹ HCl. An enrichment factor of 7 was obtained, allowing an analytical flow rate of about 28 determinations per hour. The limits of detection (3σ) and of quantification (10σ) were calculated as LOD = 0.15 μg l⁻¹ of As and LOQ = 0.5 μg l⁻¹ of As, respectively. Relative standard deviations (n = 10) less than 8% were obtained for different arsenic concentrations and the accuracy was verified by analysing certified reference materials. Different kinds of samples, such as mineral water, drinking water, river water and natural spring water were analyzed and good agreement was obtained with the values from spiked experiments.     

Determination of selenium in human body fluids by hydride-generation atomic absorption spectrometry : Optimization of sample decomposition

The accuracy of the determination of selenium in human body fluids by hydride-generation a.a.s. depends critically upon the sample decomposition-method used. Digestion with HNO₃ alone gave low selenium recoveries, but with nitric, sulfuric and perchloric acids at a final temperature of 310°C gave results that agreed with those obtained by other techniques. The recovery of selenomethionine added to whole blood and of trimethylselenonium iodide added to urine was 97–104%. The average selenium values found for 6 healthy individuals were 88 μg l^?1 in whole blood, 75 μg l^?1 in blood plasma and 307 μg (kg Hb)^?1 in erythrocytes. A detection limit of 5 μg l^?1 Se in body fluids was found under routine conditions.     

The determination of mercury by non-flame atomic absorption and fluorescence spectrometry.

An isotopic dilution method has been developed for the determination of ²²⁶Ra and ²²⁸Ra in sea water and sediments with ²²³Ra as a yield tracer. An alternative procedure which obviates the need for ²²³Ra is demonstrated for sediments by the assay of ²²⁴Ra and ²²⁸Th which occur naturally in sediments. In addition, a direct method for β-counting ²²⁸Ra–²²⁸Ac is proposed. Radium, polonium, thorium and uranium isotopes and ²¹⁰Pb are coprecipitated from sea water with aluminum phosphate carrier. The radium and lead-210 are coprecipitated with lead nitrate in sediment leachings. All radium procedures utilize identical chemical isolation and the cathodic electrodeposition of radium. Subsequently, the α-radiation emitted by ²²⁶Ra, ²²³Ra and ²²⁴Ra is determined by pulse-height analysis: the ²²⁸Ra-²²⁸Ac and ²¹⁰Pb-²¹⁰Bi are measured by low background anticoincidence β-counting techniques. This method was used for samples containing 10^-11–0.5 · 10^-12 g of ²²⁶Ra and 10^-13–10^-15 g of ²²⁸Ra and gave a precision of 3–6% and 5–10% respectively, even though radium levels an order of magnitude less can be measured. The ²²⁶Ra method is applicable to all environmental samples, whereas ²²⁸Ra determinations are limited to applications where the ${}^{228}\text{Ra}{}^{226}\text{Ra}$ activity ratio is greater than 0.1. This method is especially attractive for studies of parent-daughter disequilibria.     

The atomic absorption spectrometric determination of arsenic and selenium in mineral waters by electrothermal atomization

A procedure for the determination of arsenic and selenium in mineral waters based on electrothermal atomic absorption spectrometry is described. Because of matrix effects and the inadequate detection limits for direct determinations, both elements are separated from the macrocomponents by co-precipitation in hydrated iron(III) oxide. The precipitate is dissolved in 0.2 M sulphuric acid for injection. The detection limits are 0.2 and 0.5 μg l^?1 for arsenic and selenium, respectively.     

Investigations on atomization mechanisms in hydride-generation atomic absorption spectrometry

Summary Experiments are carried out where hydrides are collected in a cold trap, revolatilized, and conducted into a heated quartz tube with a controlled stream of pure or mixed gases. In the presence of hydrogen, atomization proceeds via hydrogen radicals formed in the quartz tube in a rather restricted area. Lifetime of the analyte atoms is at least three orders of magnitude longer than that of the H radicals. In the absence of hydrogen the hydrides are thermally decomposed but only in part atomized. The species formed during the thermal decomposition, probably an oxide and/or the element, are retained in the heated quartz tube to essentially 100%. The deposited species can be re-volatilized and atomized in part when hydrogen enters the heated quartz tube at a later time.

---

Untersuchungen über Atomisierungsmechanismen in der Hydrid-Atomabsorptionsspektrometrie

Zusammenfassung Es wurden Versuche durchgeführt, bei denen die Hydride in einer Kühlfalle gesammelt, wieder verflüchtigt und mit einer kontrollierten Strömung reiner oder gemischter Gase in ein beheiztes Quarzrohr geleitet werden. In Gegenwart von Wasserstoff erfolgt die Atomisierung über H-Radikale, die sich in einer begrenzten Zone in dem Quarzrohr bilden. Die Lebensdauer der Analytatome ist mindestens drei Größenordnungen länger als die der H-Radikale. In Abwesenheit von Wasserstoff werden die Hydride thermisch zersetzt, aber nur teilweise atomisiert. Die bei der thermischen Zersetzung gebildete Substanz, wahrscheinlich ein Oxid oder das Element, verbleibt praktisch zu 100% in dem beheizten Quarzrohr. Die abgelagerte Substanz kann teilweise wieder verflüchtigt und atomisiert werden, sobald Wasserstoff in das beheizte Quarzrohr gelangt

     

The deterioration of closed silica tubes in hydride-generation atomic absorption spectrometry

Under the conditions normally encountered in hydride evolution for atomic absorption spectrometry, devitrification of quartz to β-cristobalite occurs. For selenium, this devitrification is detrimental to the analytical characteristics of the method. Analytical performance and the life-span of the atomizer can be dramatically improved by the use of sulfuric acid instead of hydrochloric acid in the generation medium. An attempt is made to explain the deterioration and its possible influence on the atomization of hydrogen selenide.     

Simple and sensitive determination of arsenic by volatile arsenic trichloride generation atomic fluorescence spectrometry

A simple, sensitive and interference-free method was proposed for the determination of arsenic, based on the generation of volatile arsenic trichloride coupled with atomic fluorescence spectrometry. Thiourea, together with l-ascorbic acid, was used to reduce As(V) to As(III), and the chloride generation was based on the reaction between As(III) and hydrochloric acid. Under the optimized experimental conditions, the present procedure allows for the quantification of arsenic in the concentration range of 0.01–4.0 mg L⁻¹, with a limit of detection (3σ) of 6.0 μg L⁻¹. The relative standard deviation (R.S.D.) is 4.0% for 0.1 mg L⁻¹ arsenic (n = 7). Finally, the proposed method was successfully applied to the determination of arsenic in several certified reference samples (stainless steel, alloy steel, copper alloy and water sample) and real samples (brass material and spiked cobalt material), with analytical results well-agreed with those by ICP-MS.     

Atom cell for use in hydride-generation atomic fluorescence spectrometry

An electrically-heated silica tube atom cell is described for the determination of selenium in blood serum. The detection limit was 1.4 ng in 10 ml of aqueous solution. The r.s.d. at 10, 50 and 200 ng of selenium was 6.8% (n = 5), 4.3% (n = 6) and 4.7% (n = 10) respectively. Calibration was linear up to 600 ng.     

AB-DTPA浸提-原子荧光法测定土壤中有效砷和有效硒

硒和砷是土壤中重要元素,目前关于提取测定有效硒和有效砷的报道还比较缺乏。本文采用原子荧光光谱法,以AB-DTPA为浸提剂,建立了一种准确测定本地区土壤中有效硒和有效砷的分析方法。通过考察浸提剂加入量,即土液比（m/v）;浸提时的振荡时间和振荡频率的影响,确立了适用于本地区土壤有效硒和有效砷提取分析的有效方法,结果表明：随着浸提剂的不断加入,所测土壤中有效硒和有效砷含量逐渐增大,当土壤称样量和浸提剂使用体积比为1:5时,所测土壤有效硒和有效砷含量最高,继续加入浸提剂后形成稀释效应导致测量结果偏低,故将土液比（m/v）定位1:5;当振荡时间不断增大时,所测所测土壤中有效硒和有效砷含量逐渐增大,振荡时间在30min时,浸提效果最佳,继续增加振荡时间到50min时对浸提效果影响不大,故将30min确立为最佳振荡时间;随着振荡频率的增大,有效硒和有效砷提取量逐渐增加,振荡频率在90-130r/min之间时,浸提效果最好,继续增大振荡频率,所测土壤中有效硒和有效砷含量变化不大。通过上述条件探索,选取五种土壤标准物质（GBW07441,GBW07442,GBW07443,GBW07444,GBW07445）进行验证,结果表明五种不同的土壤标准物质中有效硒和有效砷含量测定值准确,测定误差在-2.84~1.03mg/Kg,相对标准偏差为5.32%~8.85%,精密度和准确度均满足国家相关标准要求。     

The determination of selenium by atomic absorption spectrophotometry

The problems involved in the determination of selenium by atomic absorption spectrophotometry are discussed. A practical method is described for which the sensitivity is approximately 1 p.p.m. Such concentrations can be determined in organic samples, but with mineral samples the preliminary treatment renders the procedure unsuitable for concentrations lower than 50 p.p.m. in a sulphide ore.     

Study of some interfering processes in the arsenic, antimony and selenium determination by hydride generation atomic absorption spectrometry

Summary A detailed study of interfering processes in the determination of As, Sb and Se using a twin-channel hydride generation flow-system is presented. The influence of As, Sb, Se and Sn on all three studied elements has a similar character and occurs in the gas phase only. In the presence of bismuth and tellurium interferences occur also in the liquid phase. It was found that arsenic and antimony may influence the analytical signals of elements with analytical lines in the range from 190 to 235 nm by non-specific absorption due to molecular band spectra.Dedicated to Professor Dr. Wilhelm Fresenius on the occasion of his 80th birthday