Techniques of sampling

Air-free filling is necessary when taking certain water samples, e.g. for determining oxygen (see Instructions). The same applies to further special determining processes. 

In general, the bottles should be prerinsed at least five times with the water to be sampled and then filled so that a gas bubble of approximately bean size remains in the bottle. Only in few exceptional circumstances is it necessary to fill the bottle completely, e.g. for determining radioactivity. In such cases, care should be taken to protect water in glass bottles from heat or, for example, to ensure that the water is able to expand via the stopper and a water-filled rubber tube, as otherwise the 

When producing composite samples care should be taken to measure the water and to ensure that secondary contamination, and influences from increases in temperature or from atmospheric oxygen, are as far as possible excluded or taken into consideration in evaluation. 

If water samples contain settleable substances, it may be appropriate 

A basic distinction can be made between batch sampling (individual samples) and continuous sampling (time-proportional or flow-proportional). 

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The procedure of determination of metals in the thin layer without elimination of the non-volatile organic components for different paints containing inorganic pigments was developed. Several techniques of sampling from paint-and-lacquer materials for X-ray fluorescence analysis were proposed. For the study of nonhomogenity of metal distribution in the thin layer we used additionally the local method of X-ray fluorescence analysis. 

The complex of the following destmctive and nondestmctive analytical methods was used for studying the composition of sponges inductively coupled plasma mass-spectrometry (ICP-MS), X-ray fluorescence (XRF), electron probe microanalysis (EPMA), and atomic absorption spectrometry (AAS). Techniques of sample preparation were developed for each method and their metrological characteristics were defined. Relative standard deviations for all the elements did not exceed 0.25 within detection limit. The accuracy of techniques elaborated was checked with the method of additions and control methods of analysis. 

The main reason for pursuing on-line LC-GC is that FIPLC provides far better resolution than conventional techniques of sample preparation (e.g. involving... 

Dark-field electron microscopy (in which the image is formed from the scattered beam), when combined with improved techniques of sample handling and preparation and minimal radiation exposure, can lead to images of sufficiently undamaged DNA at a resolution of 10 A (116). Figure 45 shows such an image in which the two-dimensional projection of the helix is clearly visible on the undamaged part of the molecule. 

Due to the high magnification power of the electron microscope, the microstructure of liquid crystals can be visualized. However, aqueous samples do not survive the high vacuum of an electron microscope without loss of water and thus change of the microstructure. Therefore, special techniques of sample preparation are necessary prior to the electron microscopy. Freeze fractme has proved to be successful (Fig. 8),... 

We believe that we have developed a technique of sample preparation which practically eliminates this problem. Below is a description of our technique and some of the data which we have obtained on a-methyl-styrene. Our results on styrene have appeared elsewhere (21, 22) and are mentioned here only by way of comparison. 

To maintain perspective, we must consider artificial radioactivity in comparison with the natural radioactivity with which man has learned to live, and some with which he hasn t (such as the radon and thoron daughters of uranium). To provide good information efficiently we who are working on various aspects of this problem need to trade ideas and criticisms and techniques of sampling, analysis, data reduction, and interpretation. 

Automatic headspace samplers are available from manufacturers of gas chromatographs. These devices are based on the technique of sampling an amount of vapor above the sample itself. Samples are sealed, neat or in a suitable solvent, in containers, and hold at a preset temperature in a thermostatted liquid bath. The headspace vapor results as a partition equilibrium is established between the liquid or solid and the gaseous phase of the volatiles. As each sample is presented to the analyzer, the vessel is punctured and a portion of the headspace gas is withdrawn by a pneumatic injection technique and forced into the column. The main application for those samplers is in the routine analysis of low-boiling fractions in samples containing nonvolatile solids or high-boiling components. Some of the more popular applications today are ... 

R. E. Lee and S. L. Walter, Techniques of Sampling and Analysing Hot Flowing Sodium—Potassium Alloy TR-4, MSA Research Corp., Evans City, Pa.,... 

The techniques of sample preparation, extraction (isolation), and/or preconcentration of analytes are usually applied in the analysis of trace components of gaseous, liquid, and solid samples. During this operation, transport of analytes from primary matrices (donors) to the secondary matrix (the acceptor) takes place. It should be remembered, however, that the extraction and preconcentration steps could be a source of environmental pollution. The techniques of sample preparation introduced in this chapter have the following advantages253 ... 

Many attempts have been made to locate K-casein in the casein micelle by electron microscopic methods, but the chief problems have been a lack of sensitivity in some of the methods used and doubts about the reliability of the techniques of sample preparation in not altering micellar structure. 

The selection of appropriate sample preparation technique is very important for accurate analysis. Techniques of sample preparation for raw rubber identifications are as follows ... 

Since the discovery of this phenomenon with isoniazid over 40 years ago, nearly a dozen related drugs and chemicals have been found to be similarly influenced by genetic variation in this acetylase enzyme. Therefore, the likelihood of a slow acetylator encountering such a chemical/drug has increased. DNA amplification assay techniques of samples obtained from leukocytes, single hair roots, buccal epithelia, or other tissue have been developed that can be used to predict the acetylation phenotype of an individual. The availability of such information could, theoretically, be used to assess workers at high risk for toxicity (e.g., chemical workers exposed to arylamines normally inactivated by acetylation). 

The selection of the proper technique of sampling is one of judgment and experience the test of the selected technique lies in its reliability for estimating a given attribute for the universe under consideration. Thus, the attribute measured from the sample should approximate the... 

The precision and accuracy of the analytical methods depends strongly on the desorption efficiency which is the percent removal of contaminent from the collection media. An Electron Capture detector will definitely increase the accuracy of chlorinated species. Precision is increased by using the solvent flush technique of sample injection. 

Other researchers have evaluated the crystallinity index by using IR spectrophotometry. This method requires the KBr pellet technique of sampling. The X-ray diffraction method was investigated for its potential as a nondestructive technique for recording changes in cellulose as it ages. 

If tiie sample is a potential oxidising agent, other techniques of sample prep ation should also be used in order to check the reliability of the spectra obtained from the [Pg.245]

The techniques of sample preparation and sample drying influence the pore size distribution, the total pore volume, the median and the bulk density as well as the uncertainty of the determined characteristics. 

In the United States most of the analytical and test methods are described by the AOCS. These well-established test procedures have afforded an adequate quality assessment of raw materials or end products or both. Selected anal5d ical methods adopted by AOCS for identification of the type, determination of the composition, detection of additives, physical properties, and stability of fats and oils, are summarized below. These methods are subject to the use of prescribed equipment and techniques of sampling and testing as specified by the AOCS [6]. 

Fox, B.W., Techniques of Sample Preparation for Liquid Scintillation Counting. North Holland, Amsterdam, 1976. 

The most commonly used technique of sample introduction is aspiration of the solution into the argon plasma flame. Because of the high temperatures in the flame, many of the problems associated with atomic absorption are eliminated. However, matrix effects such as significant differences in viscosity between sample and standard solutions can still have an effect. When needed, most of the techniques of sample introduction used in atomic absorption spectrophotometry can also be used for sample introduction in emission spectrophotometry [see the review articles " listed in the references]. 

In linear development of a chromatogram, unidirectional or bidirectional developments of the chromatogram are possible. Similarly, as in liquid column chromatography, there are possible, in this case, either on-line or off-line techniques of sample application, separation, and detection, as well as various modifications (e.g., partly off-line method). Bidirectional development can also be vertical. Using vertical bidimensional development, applying different eluents, components of complex, difficult mixtures can be separated. The separation of such mixtures is also possible by means of this technique using multiple automatic development of chromatogram. 

There are far more experiments presented here than you are expected to do. Your instructor will select or suggest those that are best suited to the needs of the class or your particular area of interest. They involve commercial products or natural samples for the most part. A wide variety of samples are involved because the techniques of sample preparation are very important for satisfactory results. While most of the experiments can be completed in one laboratory period, several cannot. In those experiments, you can either spend extra time, your instructor can suggest portions to omit, or some portions can be done for you. These are real world samples. They sometimes smell, they do not always dissolve as you would like them to, and most contain interfering substances. Therefore, the author believes it is important that you learn how to handle various samples and recommends that do as much as you can in the time allotted. 

In this method, the sample is injected directly onto the column. Here, the sample is not contained in the glass insert. Columns with a small inside diameter are unsuitable for this technique of sample itroduction. As on-column injection is a splitless method, only low-concentration samples can be injected. This method is suitable for polar and thermally unstable components. 

These applications of FT-IR in fuel science are reviewed in the following pages The paper describes techniques of sample preparation) quantitative analysis of spectra for solids liquids and gases and applications to hydrocarbon analysis and conversion ... 

The techniques of sample preparation of pharmaceuticals are essentially those discussed more generally earlier in this book, such as the preparation of films, mulls, pellets, and solutions, and the use of ATR. Carol (1957) referred to most of these methods for the preparation of pharmaceutical compounds. Warren et al. (1967) have discussed pharmaceutical applications of the internal refiection technique. They have given examples of the suitability of the method for the analyses of less... 

GLC is not a good method for occasional use the equipment is costly, should be run frequently and needs a fair amount of skill. For regular use it is far more satisfactory and some of the newer techniques of sample injection are going a long way towards improving its effective sensitivity. 

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