Evaluation of Echelle-spectrometer/charge-injection-device combination for simultaneous multielement determinations in graphite-furnace atomic-absorption spectroscopy

Chunming Hsiech, Purdue University

Abstract

A charge-injection device has been coupled to an echelle grating spectrometer for simultaneous multielement determinations by continuum-source, graphite-furnace, atomic absorption spectroscopy. The multielement determinations of transient signals from graphite furnace were achieved as a result of the combination of high spectral resolution (0.004 nm at 400 nm), large spectral range (about 40 nm), and signal-integrating capability of the charge-injection device. Novel data processing procedures were developed to obtain atomic absorption spectral information either from a continuous spectral range of about 40 nm or from selected absorption lines. With wavelength-prediction, the scanning routine can identify an unknown absorption line and can select lines for qualitative determinations. The relative standard deviation in the measurements of signals at 100% T was less than 3% for most of absorption lines investigated between 300 and 430 nm. The relative error in the measurement of absorbances with this detection system was less than 5% with absorbance between 0.2 and 0.6. The characteristic concentrations (1% absorption) were 1.6, 2.6, 2.9, and 3.8 ng mL$\sp{-1}$, respectively for Cu, Mn, and two Cr lines. These values are similar to those (1.3, 2.2, 1.2 and 3.6 ng mL$\sp{-1}$, respectively) obtained for single-element detection with an image-dissector system. A kinetic, predictive method was also developed for the multielement determinations. In this predictive method, a first-order kinetic model was fitted to integrated data for the time-dependent absorbance with a modified Levenberg-Marquardt method. The relative error of the predicted initial concentration was less than 3% with a fitting range of at least 2 half-lives, ratio of rate constants of 4, and data density of 2.5 points per half-life. At the atomization temperature of 2400$\sp\circ$C, the relative error coefficients in the determination of Cr, Mn, K, Yb and Fe with the predictive method were found 2 to 10-fold and 2 to 27-fold less than those with conventional peak-area and peak-height methods, respectively.

Degree

Ph.D.

Advisors

Pardue, Purdue University.

Subject Area

Analytical chemistry

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