Calibration in quantitative analysis Part 1. General considerations

Mathematical procedures for calibration require assumptions to be made, e.g. the homogeneity of variances and the mathematical relationship between the analyte content x and the signal y. Little is known about the magnitude of errors arising from incorrect assumptions. The variation of the standard deviation of the analytical procedure with the content of the analyte, the selection of the type of mathematical relationship between x and y, and the types of errors made in testing hypotheses are discussed. In certain practical situations, the standard deviation (s.d.) is nearly independent ofx if x 50p. If the s.d. is constant, calibration relations of the typey = a + bx are frequently to be preferred; with a constant r.s.d.. relations of the type log y = a + b logx have advantages

Calibration in quantitative analysis Part 1. General considerations

Mathematical procedures for calibration require assumptions to be made, e.g. the homogeneity of variances and the mathematical relationship between the analyte content x and the signal y. Little is known about the magnitude of errors arising from incorrect assumptions. The variation of the standard deviation of the analytical procedure with the content of the analyte, the selection of the type of mathematical relationship between x and y, and the types of errors made in testing hypotheses are discussed. In certain practical situations, the standard deviation (s.d.) is nearly independent ofx if x 50p. If the s.d. is constant, calibration relations of the typey = a + bx are frequently to be preferred; with a constant r.s.d.. relations of the type log y = a + b logx have advantages

Determination of and differentiation between cassimerite and silicate-bound tin in silicate rocks containing traces of tin

A simple, sensitive and reproducible method is described for the determination of tin in silicate rocks at the ppm level. By applying a selective decomposition it seems possible to differentiate between tin present in the silicate lattice, in readily-accessible cassiterite (SnO2) and in cassiterite enclosed in the silicate. The final determination is made by extraction and photometry with phenylfluorone. Results for total tin agree well with those obtained by X-ray fluorescence

Extractive spectrophotometric determination of micro and sub-micro amounts of fluoride

A simple and sensitive extractive spectrophotometric determination of fluoride with the cerium(III)-alizarin complexan chelate has been investigated. The fluoro chelate formed is extracted into n-pentanol containing triethylamine. It is possible to achieve under selected conditions a selective extraction of the cerium(III)alizarin complexan-fluoride chelate. The stability of the chelate, the effect of temperature and the low absorbance of the blank are discussed. It is found that it is necessary to add a pH 9 buffer before the extraction. Procedures are given for the determination of 0.1–1 μg of fluoride in a 4-ml sample and 5–25 μg of fluoride in a 90-ml sample

Theoretical considerations on the indirect determination of anions : Determination of sulphate with barium chloranilate

Some anions (sulphate) may be determined by their reaction with a slightly dissociated or slightly soluble compound (barium chloranilate), another anion (chloranilate ion) being liberated and its extinction measured. An equation is given in this paper for the relationship between the concentration of sulphate and the extinction. For low concentrations the equation is non-linear. A calibration curve, prepared under standardised conditions, agrees well with theory. It shows a precision of about 5 % at 20 μg of sulphate. At higher levels the precision is slightly better. It is proved that many interferences of foreign ions may be explained quantitatively by consideration of the activity coefficients. The scope of this method is discussed

Rapid iodometric determination of copper in some copper-base alloys

Copper-base alloys, especially those containing tin, are readily dissolved in a mixture of hydrofluoric and nitric acids. In the resulting solution copper can be titrated iodometrically in the conventional manner