Thermochemical reagent

Solid substances such as AgCl and also PTFE powder can be used as thermochemical reagents (see e.g. Ref. [191] for an ICP application). In the case of Ti in the presence of C and PTFE the following reactions have to be considered ... 

The use of solid thermochemical reagents is well known from early dc arc work and has been continuously refined in spectrochemical analysis. More recently they have also been shown to be very effective for analyte volatilization from refractory ceramic powders introduced as slurries into the graphite furnace in the work of Krivan et al. (see e.g. Ref. [194]). Thermochemical modifiers have also been shown to be efficient when using ETV for sample volatilization only and introduction of the vapor into an ICP (see e.g. [195]). 

In-situ thermal destruction of the matrix or selective volatilization can be applied. The latter has proved useful in geological samples [123]. Selective volatilization of volatile elements from refractory matrices is useful spectral interference from matrices with complex spectra can be avoided. The approach can also be used for the volatilization of refractory oxide- or carbide-forming elements, which form volatile halogenides (e.g., Ti). Here, substances such as AgCl or polytetra-fluoroethylene (PTFE) powder can be used as thermochemical reagents [121]. In the case of Ti in the presence of C and PTFE, the following reactions have to be considered ... 

Thermochemistry is especially important reliable matrix destruction and removal of matrix elements without analyte loss. Thermochemical reagents such as quarternary ammonium salts (RjN Cr) mineralize organic samples at temperatures below 400 °C, and prevent losses of elements which are volatile or form volatile, perhaps organic, compounds. This may be helpful for Cd and Zn, which form volatile compounds in a number of organic matrices. Removal of NaCl, present in most biological samples, may be helpful to prevent matrix interference this must be done at low temperature to prevent analyte loss, and can be achieved by the addition of NH4NO3 ... 

Direct sample insertion allows the direct analysis of used oils [222] and of microamounts of sediments [226] as well as the determination of volatile elements in refractory matrices [224]. Difficulties lie in the calibration and in the signal acquisition. The latter necessitates a simultaneous and time-resolved measurement of the transient signals for the line and background intensities to be made in trace analysis. This may become easier when applying CCD detection with the appropriate software. Also in the case of direct sample insertion the use of thermochemical reagents has been found to be usefiil [469]. An extremely sensitive technique lies... 

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