Design, fabrication and performance evaluation of a 22-channel direct reading atomic emission spectrometer using inductively coupled plasma as a source of excitation

The indigenous design, fabrication and performance evaluation of a polychro mator, using inductively coupled plasma (ICP) as a source of excitation, ar e described. A concave holographic grating is used as the dispersing elemen t and a Paschen-Runge mount is chosen to focus the spectra over a wide rang e along the Rowland circle. Twenty-two exit slits, mounted along the circle , precisely correspond to the wavelengths used for determination of up to t wenty elements present in the plasma. Radiations emerging from the exit sli ts are detected by photomultiplier tubes placed behind them. The photomulti plier signal is recorded by an electronic system consisting of an integrato r and a PC-based data acquisition system. The performance of the spectromet er has been evaluated with an ICP excitation source. Synthetic standards in deionized water containing a mixture of twenty impurities have been analys ed. Typical determination limits observed for elements range from sub-ppm t o ppm levels. All the elements present as impurities can be detected simult aneously. It is also observed that each element has a different emitting re gion in the ICP flame for which the maximum signal to the background is obt ained. The determination limits obtained corresponding to these zones are t he lowest. A study of the sensitive emitting zones for several elements has been carried out and the results are demonstrated by photographs of the IC P flame. The study will help in achieving the minimum value of determinatio n limit for an impurity element.