The properties of chromogenic reagents used for the absorptiometric determination of aluminium in water are compared, and an experimental comparison of catechol violet, Eriochrome cyanine R and stilbazo has been made. Catechol violet is considered to be the most suitable and a method involving the use of this reagent has been developed. When using this method, the standard deviation of the analytical results varied from 0.004 to 0.008 mg 1-1 of aluminium for concentrations of 0.05 and 0-3 mg 1-1 of aluminium, respectively. With the exception of fluoride, substances normally present in treated waters did not cause important interference. The effect of fluoride (1 mg 1-1 or less) is tolerable for most purposes, but appreciably greater concentrations require preliminary removal of fluoride or correction for its effect. Satisfactory results have been obtained with the method in six other laboratories. The method is simple and rapid ; ten samples can be analysed in approximately l & hours, The method has advantages over other commonly used methods, and is recommended for use in water analysis laboratories.THE concentration of aluminium in potable water is often an important factor in assessing both the quality of the water and also the performance of the associated treatment plant. Concentrations of less than 0.1 mg 1-1 of aluminium are the common aim, and we required an analytical method capable of the following performance : Concentration range . . . . 0 to 0.3 nig 1-1 of aluminium Standard deviation >0.005 mg 1-1 of aluminium or 5 per cent. of the aluminium Bias .. .. .. . . > O -O l mg 1-1 of aluminium or 10 per cent. of the aluminium . . . . concentration (whichever is the greater) concentration (whichever is the greater)Several analytical techniques have been used for determining such aluminium concentrations, but we restricted our attention to absorptiometric methods (measuring in the visible region) because the necessary instrumentation is usually available in laboratories concerned with the analysis of potable water.When this work was started, aluminon was the most commonly used chromogenic reagent in this country. A number of standard methods using this reagent1-3 are based largely on the work of Packham,* who showed that aluminon has the following disadvantages:(i) the coloured product is a lake, and thus requires very careful control of all experimental conditions as well as the addition of a colloid stabiliser [gum arabic or poly( vinyl alcohol)] ;(ii) in order to achieve proper colour development, the sample must be heated, which is inconvenient and increases the analytical time;(iii) the calibration graph is not linear;(iv) close control of the temperature of the processed sample is desirable, the optical (v) fluoride causes very large negative errors; for example, 1.0 mg 1-1 of fluoride causes (vi) different batches of aluminon may give markedly different calibration graphs. density changing by approximately 0.6 per cent. "C-l at 20 "C; an error of -0.07 mg 1-1 of aluminium when 0-1 mg 1-1 of aluminium...
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