Current Calibration Practices for Flame Atomic Absorption Spectrometry - 1. Initial Results from a Survey

Information about 309 different routine analyses by flame atomic absorption spectrometryhas been obtained from a questionnaire survey. The information is analysed according to themethods of overcoming interferences, the methods of curve fitting and the reasons forchoosing a particular calibration method. The results indicate that most methods suffer frominterference effects and that the addition of matrix modifiers or the matching of standards isthe most popular approach to overcoming these effects. Manual curve fitting procedures arestill widely used and 5-point calibrations are the most used. No clear cut reasons for choice ofcalibration strategy emerge from this preliminary analysis of the returns to date

Flow Manifold for Automated On-Line Dilution of Standards for Flame Atomic Absorption Spectrometry and Its Use in a Null Measurement Method

A flow manifold that automatically dilutes solutions presented to a flame atomic absorption spectrometer while maintaining a constant flow to the nebuliser is described. The manifold is based on a fixed-speed pump, together with a computer-controlled stream switching valve and pump. The computer is also used for data acquisition and handling. In addition to the production of solutions for a conventional calibration procedure, the system is also used for a novel calibration procedure whereby the stock standard solution is automatically diluted by a known factor until its absorbance matches that of the sample. This null measurement method avoids the need to fit a curve to a set of calibration points. The performance of both methods compares favourably with the conventional procedure with errors ranging from 0.0 to 4% and no significant bias at the 99% confidence level. Problems with pulsations in the flow caused by peristaltic pump rollers were encountered with the consequent difficulties of accurate flow-rate measurement. Attempts to improve the speed of the method by the use of flow injection introduction were not successful owing to these pulsations in the flow

A Comparison of Curve Fitting Algorithms for Flame Atomic Absorption Spectrometry

A comparison of six commercially available curve fitting algorithms for calibration in flame atomic absorption spectrometry (FAAS) has been made. Programs using the algorithms were written in BAsrc for a microcomputer and, where possible, tested against the commercial version. Calibration curves for magnesium, chromium and nickel produced by the algorithms were compared, on the basis of the sum of squares of the percentage deviations and its root mean square, with each other and with linear interpolation and manual fitting. The standard deviations of the goodness of fit parameters were calculated to indicate significant differences between the fits obtained. With the exception of the simple parabola, linear interpolation and manual methods, which were significantly poorer, the algorithms performed similarly. In general the errors in curve fitting were well below 5% for the commercial algorithms

Supercritical carbon dioxide as a carrier for sample introduction in atomic absorption spectrometry

The use of a supercritical carbon dioxide carrier to transport organic solutions of metal complexes to a heated restrictor is demonstrated as a means of aerosol or vapour generation for sample introduction in flame atomic absorption spectrometry. Calibrations obtained using conventional pneumatic nebulisation of continuously aspirated solutions or using flow injection into a water carrier are compared with those obtained using the carbon dioxide carrier. Injection of solutions of copper pyrrolidinedithiocarbamate in 4-methyl pentan-2-one into a carbon dioxide carrier at 1000 p.s.i. was shown to be 1.2 times more sensitive than injection of the same solutions into a water carrier with conventional nebulisation. The sensitivity of continuous nebulisation of the solutions, however, was not achieved. Dissolution of solid copper acetyl acetonate in supercritical carbon dioxide is demonstrated and subsequent vaporisation followed by atomisation in a heated quartz furnace is shown to occur

Study of the Possible Benefits of Flow Injection Sample Introduction for Flame Atomic Absorption Spectrometry

Flow injection techniques for use with atomic spectrometry are briefly reviewed, from which it is apparentthat there has been a considerable increase in interest recently in on-line pre-concentration and matrixisolation methods. In addition to the use of immobilised reagents and solvent extraction, methods based onprecipitation and collection of the precipitate in the manifold have been reported. The possible benefits ofrunning the nebuliser under starvation conditions both with and without air compensation are examinedtogether with the benefits of peak-area as opposed to peak-height measurements, claimed in some previousstudies to lead to improved detection limits. It is shown that with a Baird Atomic A3400 nebuliser thedepressive effect of phosphate on calcium may be removed at low flow-rates and that with a Philips SP9nebuliser the best detection limits are obtained when strategies for maximising the peak height are adopted.Preliminary results for the generation of a volatile metal chelate (copper trifluoroacetylacetonate) as the basisfor matrix isolation show a considerable improvement in peak-area sensitivity over conventionalnebulisation, although the peak-heig ht sensitivity is similar

Design and operation of an autosampler controlled flow-injection preconcentration system for lead determination by flame atomic absorption spectrometry

Flow-injection manifolds are described which allow the preconcentration of lead for flame atomic absorption determinations, using columns contained within the sample loop of an injection valve. An interface was designed which allowed the valves and pump in the system to be controlled by an autosampler which enabled precise timing of preconcentration and elution steps. The effects of sample flow rate, buffer pH and buffer type for preconcentration and eluent concentration and flow rate were investigated in order to obtain optimum performance of the system. A 50-times improvement in detection limits over conventional sample introduction was obtained for a sample volume of approximately 12 ml, preconcentrated for 150 s. The injection of eluent, as opposed to the use of a continuously flowing eluent stream, enabled this reagent to be conserved