Permanent chemical modifiers have been shown to prolong graphite tube lifetime while reducing the furnace cycle time, thus improving cost-effectiveness. In this work, iridium is used as a permanent chemical modifier for the first time in the determination of selenium by tungsten-coil atomic absorption spectrometry ŽW-Coil AAS.. The iridium modifier is thermally coated onto the tungsten coil. After coating, the coil can be used for 300-400 firings without further application of the modifier. Thermal treatment with iridium permits operating with higher pyrolysis temperature and coil lifetime is extended up to 1600 firings. The sensitivity and linearity of the method is improved, and the analytical procedure allows the use of analyte solutions containing up to 8% nitric acid. The short-term stability of the absorbance measurements is demonstrated by the reproducibility in the measurements of a Se amount 6ng. 30 times higher than the limit of detection Ž0.2 ng.. A 7% relative standard deviation ŽR.S.D.. was observed for 10 consecutive measurements of 6 ng Se. The long-term stability is almost as good: less than 9% R.S.D. over a 3-week period and 1500 firings. The surface of the tungsten-coil treated with iridium is examined before and after intensive use by scanning electron microscopy. Finally, the thermal treatment of the tungsten-coil with iridium appears to delay the appearance of selenium atoms by approximately 0.2 s although the integrated absorbance measurements are unaffected. The magnitude of delay decreases with coilage.

The techniques of field analytical chemistry _FAC. have the potential to reduce both analysis time and cost byproviding analytical data on site while eliminating the need for sample collection and transport. These methods couldbe of considerable interest in the fields of environmental monitoring and industrial process control. Much of FAC isaccomplished through the use of portable analytical instruments. The emphasis of this review was on field-portableatomic spectrometry, with particular focus upon two techniques: laser-induced breakdown spectroscopy _LIBS. andtungsten coil atomic absorption spectrometry _W Coil AAS.. LIBS and W Coil AAS have been described in detail,with special attention to instrumentation, analytical performance, applications and examples of portable devices. Thetwo techniques were compared and found to be complimentary. Competing technology, not necessarily based uponatomic spectrometry, was also briefly discussed in order to provide a glimpse of the overall picture of FAC techniquesused for the determination of metals. These rival techniques include X-ray fluorescence spectrometry _XRF.,immunoassay, capillary electrophoresis _CE., and electrochemical sensors.

A pulsed (10 Hz) optical parametric oscillator (OPO) lasersystem based on