Nondestructive analytical techniques extraction

Although composed of weak and overlapping spectral features, near-infrared spectra can be used to extract analytical information from complex sample matrices. Chemical sensing with in-line near-infrared spectroscopy is a general technique that can be used to quantify multiple analytes in complex matrices, often without reagents or sample pretreatment.7-9 Applications are widespread in the food sciences, agricultural industry, petroleum refining, and process analytical chemistry.10-13 These activities demonstrate that near-infrared spectroscopy can provide selective and accurate quantitative measurements both rapidly and nondestructively. 

Reproducibility is defined as "the closeness of agreement between independent test results obtained under stipulated conditions."238 Reproducibility is indicated by the standard deviation a small value of standard deviation assures the best reproducibility. The reproducibility of sampling directly affects the reproducibility of the analytical information. It is essential to secure homogeneity of the sample for both destructive and nondestructive analysis (surface analysis). The sampling process for destructive analysis must be reproducible. There are two important steps concentration and separation. Usually, the techniques used are extraction and chromatography. Assurance of the best operational parameters guarantees that reproducibility will have the maximum value. 

As shown in the lower pathway in f-igure 32-8. a destructive method requires that the analyte be separated from the other components of the sample prior to counting. If a chemical separation method is used, this technique is called radiochemical neutron activation. In this case a known amount of the irradiated sample is dissolved and the analyte separated by precipitation, extraction, ion exchange, or chromatography. The isolated material or a known fraction thereof is then counted for its gamma — or beta — activity. As in the nondestructive method, standards may be irradiated simultaneously and treated in an identical way. Equation. 32-21 is then used to calculate the results of the analysis. 

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