Standard Deviation Of Analytical Results Research Articles

Trace analysis of zinc and bismuth in high purity tin by polarized zeeman atomic absorption spectrometry with direct atomization of solid samples

Traces of zinc and bismuth in small amounts of high purity tin (0.5 ∼ 25 mg) were determined by polarized Zeeman AAS with direct atomization of a solid sample in a electrothermal graphite-cup cuvette. Standard solutions of zinc and bismuth were employed for the calibration curve. Absorption intensities (peak areas of the absorption signals) for zinc and bismuth were not influenced by the residual tin in a graphite-cup cuvette, up to 25 mg for zinc and up to 10 mg for bismuth. The relative standard deviations of analytical results were 9 ∼ 43% for 0.002 ∼ 0.05 ppm of zinc and 5 ∼ 10 % for 0.06 ∼ 1.3 ppm of bismuth. Detection limits were 0.012 ng for zinc and 0.03ng for bismuth. These values correspond to 0.0005 ppm of zinc in 25 mg of tin and 0.03 ppm of bismuth in 10 mg of tin. Time (incl. weighing the sample) required for analyzing one sample was about 5 min.

A new fluorometric method of analysis of selenium in sea water

A new method of determination of selenium and separation of Se(IV) and Se(VI) in sea water is described. The selenium is determined by fluorometric method using Se-DAN complex in cyclohexane media. Prior to the fluorometric determination, Se(IV) is separated from sea water by means of Se(IV)-DDTC complex which is adsorbed on the macroreticular resin. As to the separation of the total selenium from sea water sample, the reduction and coprecipitation method is used. Se(VI) is determined with the same method as used for the total selenium after the separation of Se(IV). The average recoveries are 92.5±1.3% for Se(IV) and 97.4±0.9% for ∑Se. The standard deviation of analytical results is below 10%.

The manual determination of ammonia in fresh waters using an ammonia-sensitive membrane-electrode

The use of a commercially-available ammonia-sensitive membrane-electrode for the manual determination of ammonia in discrete samples of fresh water has been investigated and the analytical procedure is described. The electrode is simple and convenient to use, and a sample can be analyzed in a few minutes. For normal routine analysis, the lower limit of determination is approximately 0·1 mg N 1 −1 though smaller concentrations can be measured. The relative standard deviation of analytical results varied from approximately 10 to 3 per cent as ammonia concentration increased from 0·1 to 4 mg N 1 −1. Results for samples of river water agreed well with those obtained by absorptiometric methods of analysis; the electrode responds to amines but otherwise appears to be essentially specific for ammonia. Use of the electrode will be advantageous in a number of applications, and it also has good potential for the on-line analysis of fresh waters.

The determination of ammonia in boiler feed-water with an ammonium-selective glass electrode

An investigation has been made into the accuracy of ammonium-selective (ammonium-responsive) glass electrodes for determining ammonia (10 to 1000 µg 1–1) in boiler feed-water and similar high-purity water samples from power stations. The electrode potential follows the Nernst equation in samples containing up to 10 000 mg 1–1 of ammonia, the pH of which is controlled between 8·0 and 8·4 by the addition of triethanolamine-hydrochloric acid buffer solution. However, interfering species in the buffer solution cause a detectable deviation from Nernstian response at low ammonia concentrations (less than 1000 µg 1–1). By use of a calomel-0·1 N hydrochloric acid reference electrode, reproducible results have been obtained in static buffered solutions containing 10 to 1000 µg 1–1 of ammonia. Of the other impurities likely to be present in power-station waters only sodium caused a serious effect (100 µg 1–1 of sodium is equivalent to 25 µg 1–1 of ammonia). The within-batch standard deviations of analytical results were 2, 7, 17 and 33 µg 1–1 at concentrations of 10, 100, 500 and 1000 µg 1–1 of ammonia, respectively. Details of a recommended analytical procedure for discrete samples are given, and the application of the ammonium-selective electrode to continuous on-stream analysis is briefly discussed.

The performance-characteristics of analytical methods—II

Statements on the errors of analytical results are an important aspect of characterizing the performance of analytical methods. The general nature of random and systematic errors is briefly discussed, and methods of numerically defining the former are considered. It is suggested that the standard deviation of analytical results be used exclusively as the quantitative measure of precision within the context of performance-characteristics. Techniques for, and precautions to be observed in, estimating standard deviation are critically discussed. On this basis, general principles are proposed that should be observed whenever possible in experimental tests to estimate standard deviation.

The absorptiometric determination of silicon in water. Part VII. Improved method for determining the total silicon content of high-purity water

A method is described for determining the total silicon content of high-purity waters; this method allows more precise results to be obtained than the method given in Part III of this series. Silicon in the water is initially concentrated on a mixture of finely ground cation and anion-exchange resins, which are then ignited and fused with sodium carbonate. The resulting melt is dissolved in water and silicate is determined absorptiometrically as the reduced β-molybdosilicic acid. The standard deviation of analytical results for 1-litre samples containing between 0 and 100 µg of silica was about 3 µg of silica. Ten analyses and the necessary blank determinations can be carried out in 8 hours.

Colorimetric determination of organic iodine using flask combustion

A simple colorimetric method for determining organic iodine involving the flask combustion and the successive dilution of liberated iodine in a definite volume of hydrocarbon solvent has been investigated.An organic sample containing about 2mg of iodine was burnt in a dry oxygen flask and 3ml of toluene or xylene was pipetted to the flaring lip at the top of flask. The solvent was drawn into the flask by loosening the stopper because of a reduced pressure produced in the flask after combustion, and the flask was stood for 5 minutes for complete absorption of iodine in the solvent. Twenty milliliters of the same solvent was further pipetted to the flask and the absorbance of the solution was measured at 505mμ for toluene or at 500mμ for xylene.A statistic comparison showed that the substitution of above solvents by benzene gave higher standard deviation of analytical results (Table VI) probably due to its higher volatility.A presence of chlorine above 4% in the sample gave lower analytical results due to formation of ICI. Sulfur in the sample gave sulfuric mist in the flask which made the solution turbid. This interference was avoided by standing the flask for 1 hour after the combustion until the sulfuric mist sank to the bottom of the flask.

The determination of sodium in high purity water with sodium-responsive glass electrodes

A detailed investigation has been made of the accuracy of sodium-responsive glass electrodes for determining sodium (1 to 50 µg per litre) in high purity waters (e.g., condensed steam and boiler feed-water) from power stations. The electrode potential can be made to follow the Nernst equation down to a sodium concentration of about 1 µg per litre by controlling the pH of the sample and by using a continuous flow of the sample past the electrode. Octadecylamine seriously affected the response of the electrodes, but other impurities likely to be present in power-station waters caused no significant effects. The standard deviation of analytical results varied from 0·4 to 1·2 µg per litre at concentrations of 2 and 26 µg of sodium per litre. Details of a recommended analytical procedure for discrete samples are given.

The absorptiometric determination of silicon in water. Part VI. Determination of polymeric silicic acid

A method is described for determining polymeric silicic acid in water. The sample is first digested with sodium hydroxide to convert the polymer into “reactive” silicon, which is then determined absorptiometrically. The extent to which certain other forms of “non-reactive” silicon are determined has also been established. In conjunction with methods for “reactive” and total silicon, the method is useful in helping to distinguish between the different forms of “non-reactive” silicon that may occur in samples. At concentrations of about 0·02 p.p.m. of silica, the standard deviation of analytical results was about 0·001 p.p.m. of silica. Ten samples can be analysed in about 3 hours.