John M. Ottaway

Atom-formation processes in carbon-furnace atomizers used in atomic-absorption spectrometry.

A mechanism for the production of atoms during carbon-furnace atomization is presented, based on the reaction MO(s) + C(s) --> CO(g) + M(g) The lowest temperature at which this reaction is thermodynamically feasible has been calculated for 27 elements and is shown to be consistent, for the majority of elements, with the lowest temperatures at which a substantial population of the atoms appears in the carbon-furnace atomizer. The theory has been developed further to explain qualitatively the losses of elements that occur during heating cycles before the atomization.

Evaluation of a slurry technique for the determination of lead in spinach by electrothermal atomic-absorption spectrometry

A simple method for the determination of lead in spinach involving minimum sample preparation is described. The powdered spinach is suspended in a thixotropic thickening agent, Viscalex HV30, and the slurry is injected directly into the electrothermal atomiser. Oxygen is introduced during the ashing stage to allow the use of higher ash temperatures and to avoid the build up of carbonaceous residue in the tube. Concentrations of powdered spinach up to 10%m/V can be tolerated in the suspension. Good agreement was achieved between results obtained by a standard additions procedure and by direct calibration with aqueous standards, and also by an alternative wet digestion procedure.

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).

The application of gel filtration and electrothermal atomic absorption spectrometry to the speciation of protein-bound zinc and copper in human blood serum

Abstract Gel filtration with Sephadex G-100 is used to partition zinc- and copper-containing proteins in samples of human sera. The zinc and copper content in the fractions collected are determined by electrothermal (carbon furnace) atomic absorption spectrometry without sample pretreatment. Proteins associated with both metals are measured by immunonephelometry. The results confirm the known association of zinc with α 2 -macro-globulin and albumin, but association with other proteins was also found. This combination of techniques provides a method of estimating copper bound to caeruloplasmin and non-caeruloplasmin. Essential clean-up procedures are described.

A microcomputer-controlled background correction system for atomic spectrometry

A novel instrument system has been designed for use in atomic spectrometry. An Apple microcomputer is used to control data acquisition and perform data processing in a single-channel spectrometer system, which may be applied to continuum-source atomic-absorption or atomic-emission measurement. Wavelength modulation, a rapid, repetitive scanning procedure, is employed to perform automatic background correction under computer control. The microcomputer programs are written in BASIC with incorporated assembly language subroutines. The system may be used in a steady-state atomisation mode (e.g., flames) or in a transient atomisation mode (e.g., electrothermal atomisers) for either absorption or emission measurement. The microcomputer program provides peak-height and peak-area data simultaneously and a procedure is available that allows the extension of the linear calibration range. Detection limits obtained using the system are comparable to previously reported values. The software organisation and operating procedures are described and illustrated using typical output signals measured by the system.

Determination of ionic surfactants by flow injection pseudotitration.

Two flow-through surfactant-selective electrodes have been developed which are selective for anionic and cationic surfactant ions. They employ PVC membranes containing appropriate ion-exchanging salts, coated on the internal wall of a graphite tube. The performance of the electrodes as sensors in a flow injection pseudotitration has been evaluated. By relating peak width to the logarithm of the concentration of a series of standard surfactants, a linear calibration graph may be produced. This permits the determination of unknowns by extrapolation. The system is of particular value when applied to the control analysis of known standards.

Determination of gold in blood fractions by atomic-absorption spectrometry using carbon rod and carbon furnace atomisation

A comparison of procedures that involve the use of either carbon rod or carbon furnace atomisation in order to determine, by atomic-absorption spectrometry, the level of gold in whole blood, plasma and serum from patients undergoing gold treatment for rheumatoid arthritis is described. A procedure using carbon furnace atomisation is preferred because of its simplicity and sensitivity. The detection limits for gold, obtained by using the preferred procedure, in serum, plasma and whole blood are 0.002, 0.002 and 0.004 5 µg ml–1, respectively. The relative standard deviations are 1.9% for 0.063 µg ml–1 in serum, 2% for 0.061 µg ml–1 in plasma and 7.3% for 0.030 µg ml–1 in whole blood. The method is used to confirm that most gold is carried in the serum fraction of blood, to determine the gold level in white cells and to demonstrate that the gold level in the ultra-filtrate is low.

Determination of chromium in steel by atomic-absorption spectrometry with an air-acetylene flame.

A new atomic-absorption procedure is described for the determination of chromium, at levels up to 1%, in steel. The method involves the use of the air-acetylene flame and incorporates 8-hydroxyquinoline as a releasing agent to suppress metallic interferences. Chemical operations have been reduced to a minimum in order to provide a simple, rapid and accurate procedure.

Simultaneous multi-element analysis by carbon furnace atomic emission spectrometry

The application of carbon furnace atomic-emission spectrometry (CFAES) to simultaneous multi-element analysis has been investigated using a direct-reading spectrometer system. A computer-controlled wavelength modulation system employing a quartz refractor plate is used to provide automatic background correction in both the single and multi-element modes. Detection limits obtained using a three-step square-wave modulation waveform with this system are comparable to those previously obtained using the rotating sector method of modulation. The linear range of calibration graphs has been extended to 4–5 orders of magnitude by measurement of emission intensities off the centre of the line profile. The potential of CFAES as a technique for simultaneous multi-element analysis is demonstrated by the determination of trace elements in NBS standard reference materials and orange and pine-apple juice samples.

Simultaneous multi-element analysis by continuum source atomic-absorption spectrometry with graphite probe electrothermal atomisation

An automatic graphite probe atomiser has been used in conjunction with a continuum source atomic-absorption spectrometer system (SIMAAC) for the simultaneous determination of up to 15 elements. The influence of the atomisation stage temperature on the magnitude and precision of peak-height and peak-area signals has been investigated for a range of elements. A compromise atomisation temperature of 2700 °C was found to give efficient atomisation and good peak-height sensitivity for all the elements studied. In comparison with tube-wall and platform atomisation, probe-SIMAAC detection limits (0.01–7.0 µg l–1) are equivalent or superior, except for the less volatile elements (e.g., V, Mo). Analysis of NBS Standard Reference Materials (bovine liver, rice flour and wheat flour) indicated that the probe procedure was more accurate than tube-wall atomisation methods, but less precise than platform atomisation methods.