Gas chromatographic method for the determination of selenite and total selenium in sea water

A method is described for the determination of dissolved selenite and total selenium in natural waters. The detection limit is approximately 10 pmol l^-1 and the reproducibility ±2.4% (1σ) at 394 pmol l^-1. A 100-ml sample containing selenite is reacted with 4-nitro-o-phenylenediamine to form 5-nitropiazselenol which is extracted into toluene and then determined by gas chromatography with an electron-capture detector. Other forms of selenium can be determined after photo-oxidizing samples under controlled pH conditions. This leads to a reproducible proportionation of species between selenite and selenate. The method has been used successfully to analyze samples both at sea and in the laboratory.     

Evaluation of laboratory performance in IMEP water interlaboratory comparisons

The aim of International Evaluation Programme (IMEP) is to present objectively the quality of chemical measurements. Participants in IMEP compare their reported measurement results with independent external certified reference values with demonstrated traceability and uncertainty, as evaluated according to international guidelines. Three major interlaboratory comparisons (ILCs), IMEP-6, IMEP-9 and IMEP-12, on trace elements in water were carried out from 1994 to 2000. Participants' results for Cd, Fe and Pb concentrations from these three different IMEP water ILCs were compared by means of suitable performance indicators. The performance evaluation criteria were set according to the requirements stated in the Council Directive 98/83/EC of 3 November 1998 on the quality of water intended for human consumption. Two different performance indicators were selected for evaluation of the individual participants' results: the commonly used z-score and the not so well-known E _n number. The group performance indicator is based on the variation of z-scores. To assess the individual measurement performance, not only the deviation of the reported measurement values from the certified reference value, but also criteria for maximum and minimum acceptable uncertainties were taken into account. The participants' performance is also reviewed by means of using a simple graphical tool, called “Naji-plots”.     

Catalytic polarographic determination of total selenium in tea leaves

The catalytic polarographic determination of selenium(IV) by use of the SeSO(2-)(3) -KIO(3) system is sensitive, accurate, rapid and requires only small quantities of sample. The detection limit for selenium(IV) is 0.04 ng/ml in the final solution. The working range of the calibration is 0.04-2.5 ng/ml. Se(VI) present can be reduced with hot hydrochloric acid to Se(IV), allowing determination of the total selenium.     

WEFTA interlaboratory comparison on total lipid determination in fishery products using the Smedes method

Lipid determination by the Smedes method was tested in an interlaboratory trial performed by nine laboratories from seven countries belonging to the West European Fish Technologists Association Analytical Methods Working Group. Five samples of fish and fishery products with different lipid contents, including two blind duplicates, were distributed among the participants. All laboratories applied a slightly modified Smedes method, which included extraction of lipids by cyclohexane and isopropanol, transfer of lipids to the cyclohexane phase by addition of water, phase separation by centrifugation, and gravimetric lipid determination. The results indicate that the RSD for reproducibility (RSD(R)) was between 4.11 and 6.31% for samples with moderate (7%) and high (14%) lipid content, depending on the sample. Larger SDs among the laboratories were obtained for a cod sample with low lipid content of 0.5%. The method is judged to be suitable as a routine method for lipid determination in fish and fishery products.     

The determination of selenium in water samples from the environment

A method for the determination of selenium by preconcentration and thermal neutron activation is presented. Selenium is adsorbed on active charcoal after reduction to the elemental state. By varying the conditions of the reduction, it is possible to measure the total selenium content and tetravalent selenium separately. The contribution of hexavalent selenium is obtained by substraction. The lower limit of determination is 5 ng°1⁻¹. About 40 samples per day can be handled by one analyst. The preconcentration can be performed at the sampling site resulting in samples, which can be stored easily for later analyses by neutron activation.     

Nafion-based optical sensor for the determination of selenium in water samples

An optical chemical sensor responsive to selenium (SeO₃²⁻) in water samples was developed. Its matrix was nafion membrane suffused with an organic ligand p-amino-p’-methoxydiphenylamine or variamine blue (VB). The method of analysis was flow injection (FI) where in the membrane was fixed in a flow-through demountable measuring cell and connected to a computer-controlled simple spectrophotometer.

Variamine blue was previously established to determine amounts of selenium in water and other media by means of a spectrophotometer. The method involved reacting selenite with potassium iodide to generate iodine gas, which reacts with variamine blue to form a colored species.

Experimental results showed the optrode to be an effective tool in analyzing the selenium content of water samples particularly for remote or in situ applications. Interference studies proved that the method is free of intervention from tested ions.     

Kinetic-spectrophotometric determination of selenium in natural water after preconcentration of elemental selenium on activated carbon

A simple, accurate, sensitive and selective method is described for rapid determination of ultra-trace quantities of selenium. Selenium (IV) was collected on activated carbon after reduction to elemental Se by l-ascorbic acid. The collected selenium was then determined based on its accelerating effect on the oxidation reaction of methyl orange with bromate in acidic media. Total amount of Se(IV) and Se(VI) were collected on AC after their reduction by hydrazine. Se(IV), Se(VI) and total selenium could be determined by the method. Selenium in the range 10-10 000 ng could be determined by the method. The method was used to the determination of Se(IV), Se(VI) and total selenium in natural water with satisfactory results.     

Atomic-absorption spectrophotometric determination of ultramicro amounts of selenium(IV) and total selenium in sulphuric acid

Summary Ultramicro amounts of selenium in sulphuric acid are determined by a new atomic absorption spectrophotometric method. Selenium(IV) is directly determined ater extraction into toluene with an aromatic o-diamine and addition of nickel(II) prior to atomization; the determination of total selenium (0, IV and VI) needs a treatment of the sample with selected oxidizing and reducing agents.In the studied samples, total selenium (0.003–0.022 g of Se in 1 ml sulphuric acid) is present only in the tetravalent state. The detection limit of the method is 0.003 g of selenium.

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Atomabsorptions-spektralphotometrische Bestimmung von Ultramikromengen Selen(IV) und Gesamtselen in Schwefelsäure

Zusammenfassung Selen(IV) kann direkt bestimmt werden nach Toluolextraktion der mit einem aromatischen o-Diamin behandelten Lösung und Zusatz von Nickel(II). Die Bestimmung von Gesamtselen (0, IV, VI) erfordert eine Vorbehandlung mit Perchlor- bzw. Salpetersäure und Wasserstoffperoxid. Die Nachweisgrenze des Verfahrens beträgt 0,003 g Se. In den untersuchten Proben war das Gesamtselen (0,003–0,022 g/ml) nur als Se(IV) vorhanden.

     

Cofactors in Biota: results of a German interlaboratory exercise on the determination of total lipids in fish tissue

 The content of total lipids is a common cofactor necessary for a normalisation of organic contaminant concentrations in biological materials. Lipids are routinely determined gravimetrically after extraction of the material with chlorinated solvents. A new method substituting chlorinated solvents for a cyclohexane/isopropanol mixture was to be evaluated by an intercomparison exercise. The participating laboratories were requested to determine total lipid content in three different samples of fish tissue following their own procedures as well as the new method described in a standard protocol. No significant differences in the overall means of total lipid content were found for the investigated samples regardless of the determination method. Using the harmonised protocol of the new method, between laboratory reproducibilities below 10% were obtained in the exercise. The results indicate the applicability of the harmonised method for the determination of total lipids as a cofactor in the analyses of contaminant concentrations in marine biota samples. Received: 27 June 2000 / Accepted: 20 September 2000     

Automatic determination of total carbohydrates in sea water

Summary The recommended method is based on the l-tryptophane/sulphuric acid reaction and has been adapted for a continuous flow system with the Technicon AutoAnalyzer. A supplementary run (cold run) is required with more than 10mol/l of nitrate. The presence of acetone or formaldehyde must be avoided. Total carbohydrates can be determined by this method within the range of 0.02–5mg/l. The relative coefficient of variation at the 1 mg/l level is 0.25 % (glucose).

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Automatische Bestimmung von Gesamt-Kohlenhydrat in Meerwasser

Zusammenfassung Die empfohlene Methode basiert auf der l-Tryptophan-Schwefelsäure-Reaktion und wurde dem Durchflußsystem des Technicon AutoAnalyzers angepaßt. Bei einem Nitratgehalt von mehr als 10mol/l ist zur Feststellung einer Korrektur ein zusätzlicher »kalter« Durchlauf notwendig. Aceton oder Formaldehyd dürfen nicht anwesend sein. Die Bestimmung kann im Bereich von 0.02–5 mg/l erfolgen und weist einen relativen Variationskoeffizienten von 0.25 % bei 1 mg/l auf (Glucose).

     

A semi-automated method for the determination of total arsenic and selenium in soils and sediments

Acid digestion with nitric, perchloric and hydrofluoric acids under oxidizing conditions with addition of permanganate and persulfate is utilized to extract inorganic and organic forms of arsenic and selenium from all phases of sediments including the silicate lattice. After sample dissolution a completely automated system is used to reduce arsenic and selenium to their corresponding hydrides and determine them by quartz-tube atomic absorption spectrometry. The method is directly applicable to batch routine analysis of large numbers of environmental samples.     

Rapid determination of total trihalomethanes index in drinking water

A method for the rapid determination of total trihalomethanes (THMs) index in drinking water has been developed by using a headspace-mass spectrometry (HS-MS) system and partial least squares (PLS) multivariate regression approach. Due to the presence of residual amounts of chlorine and organic matter in the drinking water, the use of a quenching reagent in order to avoid THM generation during the sample manipulation is necessary. The optimization experiments revealed that ascorbic acid was the best quenching reagent compared with sodium thiosulfate and ammonium sulfate. The use of a classification chemometric technique as soft independent modeling of class analogy before the PLS regression improved the results obtained in the prediction of the total THMs index, lowering the relative standard error of prediction (RSEP) from 11.4% to lower than 6.0%. The results obtained by the proposed HS-MS method were compared with those provided by a conventional chromatographic method after analyzing 20 real drinking water samples. A good agreement in the results was observed and no systematic differences were found, which corroborates the good performance of the proposed method.     

The determination of selenium in sea water,silicates and marine organisms

Spectrophotometric procedures are described for the determination of selenium in sea water, silicates (especially marine sediments) and marine organisms. Coprecipitation with iron(III) hydroxide at pH 4–6 is used to concentrate selenium and to separate it from many of the commoner elements. Separation from iron and other cations is achieved by ion exchange. Selenium is determined photometrically with diaminobenzidine. Isotope dilution with selenium-75 is used to correct results for the small losses occurring during the analysis. Silicates can be decomposed without loss of selenium by means of a mixture of hydrofluoric and nitric acids. The method of Cummins et al., with sulphuric and perchloric acids in presence of molybdate ion, is highly satisfactory for the decomposition of bio-materials. For sea water, which contains ca. 0.4–0.5 <mg Se/l, a standard deviation of 0.03 μg/l was obtained. A silicate sediment and a sea weed containing ca. 1.5 μg Se/g and 0.8 μg Se/g respectively gave coefficients of variation of 8.0% and 4.7%. The U.S. Geological Survey standard granite G1 was found to contain 2.5 ± 0.1 μg Se/g.     

Organic-free water for total organic carbon determination

Commercially available “organic-free” water is compared with water cleaned by ultraviolet (u.v.) radiation for applicability to total organic carbon determinations. The u.v.-treated water contains an organic carbon concentration less than the detection limit of the method used (0.056 mg C l^-1). The commercially processed water lacks the consistently low blank level required for use in TOC determinations.     

Cooperative interlaboratory surveys of the determination of cadmium in whole blood

Summary The Subcommittee on Cadmium of the IUPAC Clinical Chemistry Division's Commission of Toxicology performed two cooperative interlaboratory surveys from 1979 to 1981 for the determination of cadmium in whole blood. The goal was to study the suitability of a possible standardized method. This paper presents the results of two pilot studies and the two surveys for cadmium in blood. The first survey (1979 to 1980) involved 21 participants from 10 countries; the second (1981) 30 participants from 14 countries. Significant improvements in the ability to analyze endogenous concentrations of cadmium in blood occurred in the 14 laboratories which participated in both surveys. However, most participants experienced difficulty in analyzing concentrations higher than 15 g/l. It was concluded the suggested standardized method gives a better precision and fewer outliers if compared with other methods.     

The gas chromatographic determination of selenium(IV) and total selenium in natural waters with 1,2-diamino-3,5-dibromobenzene

The total selenium and selenium(IV) contents in sea water and river water can be determined directly by a gas chromatographic method with l,2-diamino-3,5-dibromobenzene without preconcentration. The reagent reacts only with selenium(IV) to form a 4,6-dibromopiazselenol; other oxidation states of selenium must therefore be converted to the tetravalent state for total selenium determinations. The piazselenol formed can be extracted quantitatively into 1 ml of toluene from 500 ml of sample water. A method is proposed for the determination of selenium(IV) and total selenium in natural waters at levels as low as 2 ng l^-1. Coastal sea water and river water in Japan contain 8–30 ng of Se(IV) and 20–50 ng of total Se per liter.     

Bead-injection determination of total mercury in river water samples.

A bead-injection system is proposed for total mercury determination in river-water samples. The procedure is based on the introduction of a defined quantity of a resin suspension in the flow system. The selected beads are packed inside of a flow cell and the formed resin mini-column constitutes the optical path. The sample volume is then selected, and its passage by the mini-column allows retention of the mercury ions on the surfaces of the beads. The introduction of a spectrophotometric reagent in the flow system leads to the formation of a colored Hg-dithizone complex on the surface of the bead, which is spectrophotometricaly monitored. The spent beads are directed to waste, allowing the system to become ready to process another sample. The proposed system handles about 20 measurements per hour, consuming 1000 microl of the sample, 1 mg of Chelex 100 resin and 1.25 microg of Dithizone per determination. When 1000 microl of the sample is injected, a linear analytical curve is obtained (A = 0.0052[Hg] + 0.1028, from 0 up to 30 microg l(-1), R2 = 0.995); the detection limit is estimated to be 0.9 microg l(-1). The results are precise, r.s.d. < 9%; spiked sample recoveries within 91.2 and 109% are found.     

锅炉水总碱度测量不确定度的评估

对锅炉水中总碱度测量不确定度的来源进行分析,评定了总碱度测定过程中测量重复性、天平、标准物质纯度、滴定管和移液管等因素对总碱度测量不确定度的影响,计算得到炉水水样总碱度为26．00mmol／L时,扩展不确定度为0．12mmol／L。在总碱度的测量过程中,滴定管和移液管的准确度是影响总碱度测量不确定度的主要因素。