Direct determination of selenium in human blood serum and plasma by electrothermal atomic absorption spectrometry.

A method is described for the direct determination of selenium in serum or plasma by electrothermal atomic absorption spectrometry with deuterium-arc background correction. Samples are diluted (1 + 2) with a modifier containing palladium nitrate and Triton X-100. Samples are atomised from a L'vov platform in a pyrolytically-coated electrographite tube and peak area signals are measured. Direct determination is possible by using selenium standards matched to the physiological concentrations of sodium chloride, calcium and phosphate. The detection limit is 6 micrograms/L in the original sample. Precision at a selenium concentration of 97 micrograms/L was 2.2% RSD within batch and 3.0% RSD between batch. Accuracy is shown by (i) analysis of a Seronorm reference serum (value obtained 97 +/- 3 micrograms/L; recommended value 96 micrograms/L); (ii) recovery of added selenium (93.3 +/- 6.7% and 98.2 +/- 3.3% at additions of 30 and 60 micrograms/L, respectively) and (iii) comparison of results with mean of all laboratories in an external quality assessment scheme.

Determination of aluminium in serum, dialysate fluid and water by inductively coupled plasma optical emission spectrometry.

Methods for the determination of aluminium in serum, dialysate fluid and water by inductively coupled plasma optical emission spectrometry are described and validated. Aluminium was measured at 167 nm using an argon purged monochromator. Matrix effects in serum and dialysate fluid were overcome by using an yttrium internal standard. Serum was found to have a complicated background in the region of 167 nm: careful selection of the wavelength used for background correction is therefore a pre-requisite for accurate analysis. The method for serum was validated by comparison with electrothermal atomization atomic spectrometry and the limit of agreement determined to be +/- 0.3 mumol/L. Routine performance in a quality assessment scheme has been highly satisfactory for a period of 1 year. The method is ideal for fast and accurate monitoring of patients potentially at risk from aluminium toxicity.

Rapid partial digestion of biological tissues with nitric acid for the determination of trace elements by atomic spectrometry.

Determination of Cu, Fe, Mn and Zn in fresh bovine liver and BCR bovine liver and pig kidney reference materials, after digestion at 105 degrees C with nitric acid for various times, showed that the trace elements were completely released after heating for only 20 min. Centrifugation of the samples after digestion improved the separation from undigested fat. This partial-digestion method, based on heating about 0.2 g of sample with 2 ml of nitric acid for 20 min, was tested on a range of biological reference materials and on fresh bovine liver for the four elements. Comparison was made with results obtained after digestion by a recommended hydrogen peroxide--sulfuric acid digestion procedure. Results obtained by inductively coupled plasma atomic emission spectrometry or by flame and graphite-furnace atomic absorption spectrometry showed good agreement between the two digestion procedures, and results for the reference materials agreed well with the certified values. Between-batch precision was better than 4% for Cu, Fe and Zn at levels of 30 to 190, 210 to 320 and 100 to 140 micrograms g-1, respectively. For Mn, the precision varied between 7 and 14% for measured concentrations of 8 to 12 micrograms g-1. The partial-digestion procedure offers simplicity, speed, low cost and the ability to handle a large number of samples at the same time.

Ranitidine suppresses aluminium absorption in man.

1. Intragastric pH monitoring was performed before and after the single-blind administration of ranitidine or placebo (saline) in eight healthy subjects and four patients with end-stage renal disease who were on regular haemodialysis. 2. The subjects were studied on two occasions and were given aluminum hydroxide (1185 mg) orally 90 min after the administration of ranitidine or saline. 3. Plasma aluminum concentrations and, in normal men, urinary excretion of aluminum were monitored before and after the oral aluminum load. 4. Intragastric pH increased significantly with ranitidine but not with placebo (P less than 0.001). Urinary aluminum excretion increased significantly after the administration of aluminum hydroxide during the placebo phase (P less than 0.001) but not during the ranitidine phase. Plasma aluminium concentrations were higher in the patients with renal failure than in the normal subjects (P less than 0.05), but were unchanged in both groups after the oral aluminium load. 5. This study shows that gastric pH is an important factor in the modulation of aluminum absorption in man, and indicates that reducing gastric acid secretion with ranitidine may reduce the toxicity of orally administered aluminium compounds.

Aluminium content of water for injection used with recombinant human erythropoietin.

Human recombinant erythropoietin is of proven value in the treatment of the anaemia of renal failure. The aluminium content of 36 ampoules of water for injection supplied for use with recombinant erythropoietin has been measured and ranged from 24 to 450 micrograms/l, with a median of 251 micrograms/l. In three samples, which may have been contaminated on opening, the range was from 1770 to 6160 micrograms/l. In Water for Injection BP, values ranged from 66 to 140 micrograms/l with a median of 99 micrograms/l. Reconstituted erythropoietin did not contain any more aluminium than could be accounted for by the water. Ampoules of a second brand of erythropoietin, supplied already in solution, contained from 506 to 837 micrograms/l aluminium (median 682 micrograms/l). In view of the lifelong duration of erythropoietin therapy clinicians and pharmaceutical companies should be aware of this potential problem. Although the amount of aluminium delivered with each injection is usually less than 4 micrograms, it is suggested that active steps are taken to establish a British Pharmacopoeia limit on the aluminium content of injections.

Hot-injection procedures for the rapid analysis of biological samples by electrothermal atomic-absorption spectrometry.

The combination of palladium/hydrogen matrix-modification and injection of samples into a graphite tube at 120 degrees has allowed the accurate determination of copper, iron, lead and nickel in biological reference materials (urine, milk powder and bovine liver). Palladium modification allowed the use of a standard ashing temperature of 1000 degrees for all four elements. Direct aqueous calibration was applied without the need for standard additions. The total heating cycle, from the start of sample injection, took 45 sec.

Determination of nine inorganic elements in human autopsy tissue.

A survey of nine elements of accepted clinical relevance has been performed on tissue sets comprising of kidney, liver, heart and muscle taken at autopsy from healthy individuals killed as the result of an accident. The concentrations are reported using tissue wet weight, dry weight and nitrogen content as frames of reference. This has allowed direct comparisons to be made with other studies without resort to the use of conversions, using average factors, between one frame of reference and another. Such conversions are shown to be unreliable and may generate spurious differences. The results obtained are largely consistent with those reported from studies in other parts of the world.

Factors influencing lead concentrations in shed deciduous teeth.

Data collected for the Edinburgh Lead Study have been used to investigate lead concentrations in children's naturally shed deciduous teeth. A within-child multiple-regression analysis has shown that the upper jaw has a higher concentration of lead than the lower, and that there is a gradient of decreasing concentration from the front to the back of the mouth. Even after the effects of jaw and tooth type have been allowed for, the concentration is still found to be negatively correlated with the weight of the tooth and with the age at which the tooth was shed. No statistically significant effects could be attributed to caries, fillings, or the incomplete resorption of roots. A single-valued index of tooth lead has been derived for each child, taking into account the fact that children gave different types of teeth.

Essential trace element provision to patients receiving home intravenous nutrition in the United Kingdom.

The methods of provision of essential trace elements to patients receiving long-term home intravenous nutrition in the U.K. have been reviewed and their trace element status has been assessed. Over a 2 year period, 57 patients based on 15 hospitals throughout the country were studied. Although biochemical abnormalities of trace element status were frequent, related clinical complications were apparently rare. Zinc provision from commercial preparations generally required further supplementation. Copper requirements were variable. Manganese provision from trace element mixtures and chromium provision from contaminants of other parenteral nutrient solutions were excessive in many cases. Aluminium contamination is not significant in the nutrient solutions currently used in the U.K. The most common depletion state is for selenium which should probably be provided on a routine basis. The clinical consequences of long-term under- or over-provision of trace elements by the intravenous route requires further study.

Selenium depletion and its correction in a child with homocystinuria.

A child of 10 months with proven homocystinuria was found to be selenium depleted and we report the serial monitoring of replacement therapy. Selenium, as an enriched yeast preparation, equivalent to 50 mug on alternate days was required for maintenance. Indices of selenium status returned to normal in varying times. The child initially demonstrated an abnormality of an in vitro challenge by hydrogen peroxide to her erythrocytes, that returned to within normal limits with selenium therapy alone, the serum vitamin E concentration being normal.

Aluminium hydroxide versus sucralfate as a phosphate binder in uraemia.

In an attempt to discover a phosphate binding agent for use in uraemia that would not lead to appreciable systemic absorption of aluminium the effect of sucralfate was evaluated after three weeks and compared with that of the existing standard agent aluminium hydroxide. Sucralfate caused a decrease in serum phosphate concentration comparable with that obtained with aluminium hydroxide, but similar absorption of aluminium resulted. Sucralfate may be the phosphate binder of choice in patients with uraemia and peptic ulceration; care should be taken in using large doses of the drug in patients with normal renal function.

The effect of oral aluminium therapy on plasma aluminium levels in patients with chronic renal failure in an area with low water aluminium.

In a low water aluminium area ( less than or equal to 0.4 micromoles/1) plasma aluminium levels were normal in 31 non-dialyzed and 7 peritoneally-dialyzed patients unless oral aluminium hydroxide was prescribed. Plasma aluminium levels were above normal in 26 patients on maintenance hemodialysis, but when aluminium hydroxide intake stopped there was a decrease in pre-dialysis plasma aluminium. Poor compliers (indicated by plasma phosphate levels) showed no change. Oral aluminium hydroxide can make a major contribution to plasma aluminium levels in patients with renal failure and should be treated with the same caution as high dialyzate aluminium. Post-dialysis plasma aluminium levels were always higher than pre-dialysis levels both on and off aluminium therapy despite the low dialyzate aluminium concentration. This rise may be due to tissue redistribution.