Spectrochemical buffer

The detection limits for most elements are of the order of 5-100 ng/mL. For elements with very sensitive atomic lines such as As, B and P, the detection limits are slightly lower than in ICP-AES [371]. The high level of detection is also certainly related to the high resolution of the Echelle spectrometer used. Different concentrations of alkali elements, however, cause higher matrix effects than in ICP-AES and may even necessitate the use of spectrochemical buffers. The analytical precision achievable is high and RSDs below 1% can be reached. The system can cope with high salt contents (>100 g/L) and has found considerable use e.g. for water analysis [372], and especially for the analysis of seawater, brines and even oils. 

Describe the considerations involved in selecting (a) an internal-standard element and spectral line (b) a spectrochemical buffer (c) a matrix diluent. 

Spectrochemical buffer. A substance which is part of the sample or which is added to the sample, and which reduces interference effects. 

Chemical interference occurs, and to suppress such interferences a spectrochemical buffer solution equivalent in amount to 10% of the total sample solution volume is added. Such a buffer contains 1500 pg of lanthanum and 100 pg of cesium in a 1 ml volume. 

A membrane filter which can be dissolved in acetone, or a spectrochemically pure graphite filter which can be examined directly with a powder DC-arc technique, can provide passable results. After air has been drawn through a previously weighed filter, the membrane filter is dissolved in acetone, then centrifuged. The particulates are collected, dried, and weighed then a spectroscopic buffer is added composed of 1 part NaF and 1 part graphite powder, with 100 ppm indium oxide and 20,000 ppm tantalum oxide as internal standards. About 35 mg of the final mixture is placed in a graphite electrode and arced at 15 A for 60 sec in a controlled (90% At-10% O2) atmosphere. 

Harvey s original work (1947), in which he published k values for 42 elements in 36 different matrices, illustrated the significance of matrix effects on spectrochemical analytical data. If all samples could be reduced to a common matrix, semiquantitative and quantitative spectrochemical analysis could be simplified. A method to accomplish this, in part, involves the addition of another substance to the sample. The added substance is frequently referred to as a spectroscopic buffer and is added in sufficient quantity to become a major constituent of the sample mixture. 

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