David J. Halls

Determination of aluminium in blood plasma or serum by electrothermal atomic absorption spectrometry

Abstract A carbon-furnace atomic absorption method is used to determine aluminium in blood serum or plasma, diluted (1 + 2) with purified water prior to injection (20 μl) into the furnace. Procedures are described to reduce contamination during sample collection, storage and preparation of samples. A study of the interferences of inorganic ions shows that the temperature programme developed minimises these, allowing the use of aqueous standards for calibration. Ashing at 1400°C, prior to atomisation, also removes non-specific background effects, and optical correction is not required. A sample throughput of 50 duplicate analyses per day is possible and the precision (between batch) at 24 μg Al l-1 was 11.2% (n = 10) and at 340 μg Al l-1 was 6.3% (n = 18). Down to 4 μg Al l-1 can be determined. Reference values for a healthy population were 4.1–20 μg Al l-1 (mean 10.2).

Analytical minimalism applied to the determination of trace elements by atomic spectrometry. Invited lecture

In analytical minimalism, each stage of the analysis is evaluated to minimize the time, cost, sample requirement, reagent consumption, energy requirements and production of waste products. These parameters are often inter-related. If the objective of digestion of biological tissues, foodstuffs and environmental samples is taken as the complete dissolution of the trace elements, then the time of digestion by conventional heating can be reduced considerably to times comparable with pressure digestion using microwave heating. The development of rapid and simple partial digestion techniques is reviewed. In electrothermal atomic absorption spectrometry, by assessing the function and time of each stage in the programme, it has been possible to reduce the programme time to about 30 s for a number of determinations. Recent developments in fast furnace technology are reviewed, particularly on omission of the ashing stage and drying with hot injection or high temperatures. With reduction in furnace programme time, the time taken by the autosampler (30–35 s) becomes dominant. Developments to reduce this time by 10–20 s are discussed. In the evaluation of results, minimal time and effort by the analyst is ensured by customized computer programmes. The programmes, variants of one or two basic programmes, are adapted for each determination to retain the value of standards, to correct for blanks and to allow conversion from g l–1 to mol l–1.

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.

Determination of aluminium in dialysate fluids by atomic-absorption spectrometry with electrothermal atomisation

Matrix effects in the determination of aluminium in dialysate fluids by electrothermal atomic-absorption spectrometry are overcome by the addition of nitric acid (to give a final concentration of 2%V/V) to the fluid. Analyses may be made by a rapid two-step heating programme giving a total time per injection of 59 s; in the first step, drying and ashing are combined. A detection limit of 1 µg l–1 is achieved and reproducibility is better than 2% in the range 30–120 µg l–1. Concentrations of aluminium of <1–11 µg l–1 were determined in various batches of commercially supplied peritoneal dialysis fluid. Haemodialysate fluid concentrations varied from <1 to 31 µg l–1 with 62% of the samples examined having concentrations less than 5 µg l–1.

Factors influencing lead concentrations in shed deciduous teeth

Data collected for the Edinburgh Lead Study have been used to investigate lead concentrations in childrens 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.

Direct determination of cadmium in urine by electrothermal atomisation atomic absorption spectrometry

Omission of the ashing stage in the determination of chromium in urine by electrothermal atomisation atomic absorption spectrometry (ETA-AAS) led to an increase in the background absorbance, but the values found were still within a range which a deuterium-arc background correction system is capable of correcting. Rapid three-stage furnace programmes omitting the ashing stage were developed for two systems: one for an instrument with deuterium-arc background correction using an uncoated tube and the other for a Zeeman-effect system using a pyrolytically coated tube. Cycle times of 53 and 70 s, respectively, were achieved for these methods which were developed for monitoring occupational exposure. Small matrix effects were overcome by adding a surfactant, Triton X-100, to the diluent. Samples and standards were diluted 1 + 1 with 1%V/V HNO3 and 0.25%V/V Triton X-100. Results obtained by the two methods agreed well (r= 0.997) and also with those obtained by a slower method using an ashing stage (r= 1.000). It was concluded that Zeeman-effect background correction was unnecessary for this determination and that faster and more precise results could be obtained with the simpler system using deuterium-arc background correction.

Determination of lead in teeth by atomic absorption spectrometry with electrothermal atomisation

After dissolution of whole teeth in nitric acid, the digests are evaporated to dryness and re-dissolved in 5%V/V nitric acid. Lead is determined by atomic absorption spectrometry with electrothermal atomisation directly against standards in 5%V/V nitric acid. Interference from the tooth matrix is shown to be minimal. Accuracy is demonstrated by satisfactory recovery of added lead, by analysis of the IAEA reference material H-5 animal bone, and by inter-laboratory comparison. Determination of lead in the two halves of 61 split teeth showed a high correlation (r= 0.987) with a mean difference of 0.8 µg g–1.

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.

The problem of background correction in the determination of chromium in urine by atomic absorption spectrometry with electrothermal atomisation

A previously described positive interference in the determination of chromium in urine was ascribed to the failure of the deuterium arc background correction system to correct fully for background absorption. In this work, it is shown that the interference is dependent on the gain setting of the photomultiplier and on the atomisation temperature. At temperatures below 2400 °C the interference is absent, but on increasing the atomisation temperature from 2400 to 2700 °C the interference increases in severity. The interference is thought to be emission caused by chromium together with potassium and sodium in the matrix. Lowering the atomisation temperature to 2400 °C allows the determination of chromium in urine without significant interference using conventional deuterium arc background correction.

Omission of the ashing stage in the determination of aluminium and lead in waters by graphite furnace atomic absorption spectrometry

Omission of the ashing stage in the determination of aluminium and lead in waters by graphite furnace atomic absorption spectrometry on uncoated tubes initially led to lower sensitivity and poor accuracy. Sensitivity could be restored by increasing the drying time to about 40 s or by increasing the drying temperature. The original effect is thought to be due to interference from water vapour; the time was insufficient to remove water vapour before atomisation occurred. Higher drying temperatures (180–260 °C), leading to rapid expulsion of the water vapour, gave results with no loss in precision. A temperature of 250 °C held for 12 s was chosen for drying. With these revised programmes having no ashing stage, satisfactory recovery was demonstrated for aluminium (98 ± 6%, n= 10) and lead (101 ± 2%, n= 8) in domestic water samples. Cycle times were 54 and 55 s for aluminium and lead, respectively. The method for lead involved the use of a mixture of lanthanum and nitric acid as a modifier, but omission of the ashing stage did not affect the accuracy. In a separate experiment, it was shown that the suppression of sulphate interference by the lanthanum modifier was the same with and without an ashing stage.