IMPROVEMENT OF SELECTIVITY WITH NUMERICAL DERIVATIVE TECHNIQUES IN INDUCTIVELY COUPLED PLASMA ATOMIC EMISSION-SPECTROMETRY

One of the most attractive features of derivative spectrometry is its higher resolving power. In the present power, numerical derivative techniques are evaluated from the viewpoint of increase in selectivity, the latter being expressed in terms of the interferent equivalent concentration (IEC). Typical spectral interferences are covered, including flat background, sloped background, simple curved background and various types of line overlap with different overlapping degrees, which were defined as the ratio of the net interfering signal at the analysis wavelength to the peak signal of the interfering line. the IECs in the derivative spectra are decreased by one to two order of magnitudes compared to those in the original spectra, and in the most cases, assume values below the conventional detection limits. The overlapping degree is the dominant factor that determines whether an analysis line can be resolved from an interfering line with the derivative techniques. Generally, the second derivative technique is effective only for line overlap with an overlapping degree of less than 0.8. The effects of other factors such as line shape, data smoothing, step size and the intensity ratio of analyte to interferent on the performance of the derivative techniques are also discussed. All results are illustrated with practical examples.

ADVANCED ELECTROANALYTICAL CHEMISTRY IN CHINA .1. GENERAL ASPECT AND SOME METHODOLOGIES

The Research on Electroanalytical chemistry in China started mainly from the beginning of new China in 1949. It has already good basis and development nowadays. A review with references to the end of seventies has been published in "Reviews in Analytical Chemistry" 1) and in a book titled "Fifty years of Chinese Chemistry" edited by the Chinese Chemical Society in 1985 2). Since then more than thousand papers have been published, and it is impossible and also not necessary to describe all of them. This review only deals with the main progress of electroanalytical chemistry in China in recent years. Some new developed methodologies will be reviewed by S. Dong in the next article.

Study of the carbonaceous deposits formed on a Mo/HZSM-5 catalyst in methane dehydro-aromatization by using TG and temperature-programmed techniques

Carbonaceous deposits formed during the temperature-programmed surface reaction (TPSR) of methane dehydro-aromatization (MDA) over Mo/HZSM-5 catalysts have been investigated by TPH, TPCO2 and TPO, in combination with thermal gravimetric analysis (TG). The TPO profiles of the coked catalyst after TPSR of MDA show two temperature peaks: one is at about 776 K and the other at about 865 K. The succeeding TPH experiments only resulted in the diminishing of the area of the high-temperature peak, and had no effect on the area of the low-temperature peak. On the other hand, the TPO profiles of the coked catalyst after succeeding TPCO2 experiments exhibited obvious reduction in the areas of both the high-and low-temperature peaks, particularly in the area of the low-temperature peak. On the basis of TPSR, TPR and TPCO2 experiments and the corresponding TG analysis, quantitative analysis of the coke and the kinetics of its burning-off process have been studied. (C) 2001 Elsevier Science B.V. All rights reserved.