The method is based on catalysed ignition of a sample portion in a flow of oxygen, capture of mercury by an amalgamator and measurement of the mercury vapour's absorbance after thermic release from the amalgamator. Three powdered food samples, a certified reference material (CRM) human hair and a reference material (RM) urine (liquid) were measured in the first range of the instrument (the possible contents determined according to our measurement procedure were 0.0003-0.5 ppm). The calibration function used was a line passing through the origin. The combined standard uncertainties of the mercury determinations were computed from uncertainty components of five quantities: absorbance of the sample, absorbance of the sample blank, slope of the calibration line, correction factor of the abscissa axis, and mass or volume of the sample. The most important uncertainty component is the uncertainty of the sample absorbance measurement which amounts to 52% of the determination uncertainty at the minimum (RM urine) and about 90% at the maximum (in our laboratory homogenized powdered food samples; analysis of variance showed their homogeneity to be insufficient). The results of the CRM and RM analyses do not indicate a significant systematic error for this determination. The relative expanded uncertainty (coefficient was 2) of the determination increases from 9 to 13% for the insufficiently homogenized samples with decreasing mercury content (range of 0.004-0.03 ppm); higher homogeneity of samples results in a decrease of the expanded uncertainty, e.g. 4.6% for the liquid sample (RM urine).

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A method is reported for the determination of gallium in a-alumina powder (corundum) by electrothermal atomisation of the sample introduced in the form of a suspension (slurry) into a graphite atomiser, either on the wall or a platform [ l o pI of 0.25% mlv suspension in ethanolwater (9 + I)]. The measurements were carried out at 294.4 nm with deuterium background correction. For calibration, standard oxides were prepared either with gallium occluded within the alumina matrix or adsorbed on alumina present in the a-or y-modification. It was found that alumina decreases markedly the volatility of gallium and increases the sensitivity of the determination in comparison with aqueous nitrate solutions containing no aluminium (ca. 8-fold when atomised from the wall for gallium occluded within a-alumina). The mini-platform effect of alumina on the atomiser wall is considered to be the main reason for the increase in peak size. When atomising from the platform, the peak of gallium occluded within a-alumina exhibits a time delay of about 500 ms compared with y-alumina. Based on the ascertained dependences of the atomisation signal on several variables (including the mode of combining gallium with alumina, i.e., occlusion or adsorption), suitable procedures for correct Cali bration are suggested.

Mg(OH)2 was precipitated from MgCl2 and NaOH solutions in a continuous agitated reactor and the effects of the solutions concentration, residence time of suspension in the reactor and stoichiometric ratio of the reacting components on the properties of Mg(OH)2 were studied. The properties of the resulting suspension were evaluated on the basis of its filtration resistance α as determined by a filtration test. The value of α is inversely proportional to mean residence time of the suspension in the reactor and it depends, at the same time, on the ratio of concentration of the precipitated solutions γ = [MgCl2]/[NaOH]. A critical value of γ can be assessed for a continuous reactor and when this value is exceeded a comparatively well filtering suspension with α ≦ 1012 m · kg−1 is always obtained. The relationship between α and the parameters of the precipitation process was expressed quantitatively within the framework of the exiting theories.