Nondestructive analytical procedures

The objective ia any analytical procedure is to determine the composition of the sample (speciation) and the amounts of different species present (quantification). Spectroscopic techniques can both identify and quantify ia a single measurement. A wide range of compounds can be detected with high specificity, even ia multicomponent mixtures. Many spectroscopic methods are noninvasive, involving no sample collection, pretreatment, or contamination (see Nondestructive evaluation). Because only optical access to the sample is needed, instmments can be remotely situated for environmental and process monitoring (see Analytical METHODS Process control). Spectroscopy provides rapid real-time results, and is easily adaptable to continuous long-term monitoring. Spectra also carry information on sample conditions such as temperature and pressure. 

Variety of biochemical composition and physical features of milk, as well as compound forms of mineral components foreordain necessity to develop the analytical procedures, in which initial sample state suffers minimum change. Absence of dried milk reference standai ds (RSMs) is an obstacle to use nondestructive XRF for solving the given analytical task. In this communication results of nondestmctive x-ray fluorescence determination of Na, Mg, Al, Si, P, S, Cl, K, Ca, Cr, Mn, Fe, Ni, Cu, Zn, Rb, Sr, Zr in dried milk powders of limited mass (less than 2 g), obtained with using plant RSMs to calibrate, ai e discussed. 

Characterization of the objects based on the holistic approach is often combined with point analysis, in which the material composition of a minute portion of the object is determined by classical analytical procedures or instrumental methods. Since the samples under examination are unique and irreplaceable, the specimens should be submitted to nondestructive or at least microdestructive analysis. Nevertheless, a number of instrumental techniques require the total or partial destruction of the... 

Because of the nature of the samples involved in this study, special, preferably nondestructive analytical procedures must be used. In addition most museums will not permit, or at least find it difficult to arrange for, the transfer of a coin or art object to an outside laboratory. Further, the types of data to be acquired will generally be significant only if a statistically large number of samples is analyzed. These problems are all quite different from those normally encountered in analytical chemistry and thus restrict in some cases the accuracy and precision of the data. 

As discussed in the previous chapter a preparation procedure leads to several sets of samples, often produced in batches. It is necessary to assess that no difference exists within each of the sets, between sets and between batches. Consequently, homogeneity testing will try to measure differences between sub-samples within or between vials of materials. As it is not possible to measure all samples produced (unless a nondestructive technique is available) a strategy for the selection of representative samples is necessary. To demonstrate the absence or the existence of differences between samples, it is necessary that the analytical procedure is fully reproducible. If differences between measurements are too large due to the measurement method, inhomogeneity cannot be detected. In order to reveal presence of spot contamination, the measurement must be done on the substance of interest or any other substance known to present exactly the same properties and showing the same behaviour or distribution pattern (tracer). 

Interesting features of potentiometric transducers are simplicity of instrumentation (only a potentiometer is needed), low cost, selectivity, and the nondestructive nature of the analytical procedure. 

The methods used for analytical characterization of UFg can be divided into two main groups analytical procedures that are used to assess the quality of the materials and its compliance with specifications and nondestructive analysis (NDA) methods for assay of closed cylinders containing UFg or online monitoring. 

Analytical procedures may be either destructive or non-destructive. Indirect or destructive methods require a significant alteration to the sample so that the additives can be removed from the plastic material for subsequent detection. Direct or nondestructive methods involve minimal sample preparation which greatly speeds up the analytical procedure. Quantitative analytical procedures are either continuous or discontinuous. In non-continuous routine analytical procedures a smaU amount of substance is analysed which is considered to be representative of the whole sample. Errors are introduced by the sampling procedures and no measure of continuous changes in the composition of the material is obtained. Continuous monitoring needs more resources but can give a better and more extensive measure of the composition of the material and variations in time (c/r Chp. 7). 

When using a multitechnique approach to problem solving, care must be taken that the application of one technique to a specimen does not Jeopardize the validity of subsequent analyses by other techniques. Under this criterion if that validity is unaffected, then the technique first applied can be said to be nondestructive. The criterion puts obvious constraints on the sequence in which techniques should be used, beginning with the least destructive and ending with the most. A corollary of this criterion is that in cases where there are continuing ex situ or in situ specimen treatments requiring periodic analysis, then the analytical procedure should not itself affect the course of the treatment(s). 

SERS sensitive detection, identification and quantification of trace amounts of drugs and their uptake in the human body have importance in medical, forensic and criminal investigations. SERS analysis is fast, nondestructive and can be done in situ using a portable Raman spectrometer which is a big advantage when compared with separation and chemical analytical procedures. 

Nondestructive radiation techniques can be used, whereby the sample is probed as it is being produced or delivered. However, the sample material is not always the appropriate shape or size, and therefore has to be cut, melted, pressed or milled. These handling procedures introduce similar problems to those mentioned before, including that of sample homogeneity. This problem arises from the fact that, in practice, only small portions of the material can be irradiated. Typical nondestructive analytical techniques are XRF, NAA and PIXE microdestructive methods are arc and spark source techniques, glow discharge and various laser ablation/desorption-based methods. On the other hand, direct solid sampling techniques are also not without problems. Most suffer from matrix effects. There are several methods in use to correct for or overcome matrix effects ... 

The analytical technique used strongly influences the type of sampling procedure. Sampling methods fall into two categories destructive or nondestructive, depending on the effect of the sampling procedure on individual FDR particles, acids tending the break down the particles. 

Bond Inspection. After the adhesive or sealant is cured, the joint area can be inspected to detect gross flaws or defects. This inspection procedure can be either destructive or nondestructive. The nondestructive type of tests can be visual or use advanced analytical tests. These types of bond inspections are described below. 

Figure 32-8 is a block diagram showing the flow of sample and standards in the two most common types of activation methods, destructive and nondestructive. In both procedures the sample and one or more standards are irradiated simultaneously with neutrons (or other types of radiation). The samples may be solids, liquids, or gases, although the first two are more common. The standards should physically and chemically approximate the sample as closely as possible. Generally, the samples and standards are contained in small polyethylene vials heat-scaled quartz vials are also used on occasion. Care must be taken to ensure that the samples and standards are exposed to the same neutron flux. The time of irradiation depends on a variety of factors and often is determined empirically. Frequently, an exposure time of roughly three to five times the half-life of the analyte product is used (see Figure 32-7). Irradiation times generally vary from a few minutes to several hours.

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