Preparation of samples for analysis

Samples collected for spectral analysis, can typically be classified into three categories (1) solids, (2) liquids, and (3) gases. This chapter deals strictly with the collection and preparation of solid and Uquid samples as other chapters describe the collection and sample preparation of gases. 

Liquid samples generally fall into one of three different categories  

In addition to simply obtaining a representative sample of the original liquid, storage is also an important consideration. Depending upon the particular type of analysis that is going to be performed on the sample, various types of sample containers are recommended. In the case of the analysis of organic solutions, it 

With the advent of faster and more sensitive detectors and analysis systems, the possibility of real-time analyses being performed on samples has dramatically improved. To obtain representative samples for such analyses, short bypasses are often introduced into flow lines. These can divert a small amount of the total liquid into the particular instrument being used for analysis (e. g. spectrophotometers, etc.). When such bypasses are inserted into the overall flow of the reaction process, it is important to ensure that they do not change the flow of the original system, possibly skewing the sample that is being analyzed. 

Once a representative sample has been obtained from the object of interest, the next step is to prepare the sample for analysis. Since sample preparation depends upon both the analyte (e. g. iron in water, polycyclic aromatic compounds in benzene, etc.) and the instrumentation used to perform the spectroscopic measurement (e. g. UV—VIS or IR absorption, luminescence, Raman, HPLC-fluorescence, and GC-MS, etc.), details of the preparation process will vary from analysis to analysis. Many general procedures have been developed over the years for the preparation of various types of samples prior to analysis. Most of these procedures can be classified based upon the types of samples that are to be analyzed, either sohds or liquids. Within each of these categories exist several subcategories based upon the type of analyte to be measured. 

From air-dried soil samples, coarser pieces of the skeleton and possible residual plant materials are removed. The sample is then ground, to disintegrate agglomerated clods but not skeleton particles. The disintegrated earth is screened through a sieve (usually with a mesh size of about 2 mm). The sample prepared in this way is poured to form a conical pile. The pile is then quartered with the help of a suitable tool. The two opposite portions are taken as a sample. The quartering procedure is repeated to reach the sample amount required for the chemical analysis. 

The soil analysis is then frequently performed without further sample treatment. In certain cases, however, it is necessary to obtain a solution from the sample, i.e. to make an extract. 

Usually only a small portion of the sample is water-soluble (chlorides, nitrates, nitrites, sulphates, alkali metals — when unbound in silicates, glycides, fatty acids, humic substances). The extract for the determination of nutrients (nitrogen, phosphorus, potassium, trace elements) is prepared with the use of leaching solutions 1% citric acid, 1% potassium sulphate, 1% hydrochloric acid, calcium lactate, etc. 

Sample decomposition is frequently necessary, depending on the purpose of the analysis and character of the component to be determined. The most frequently adopted procedures are as foUows  

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It should be mentioned that, because the microstructure and properties of this ionomer are known to be quite sensitive to history and the details of preparation of samples for analysis, an effort has been made in this article, where possible, to delineate these important parameters in each described study so that the results of different investigations can be meaningfully compared. 

All the steps from preparation of sampling equipment, sampling, transport, storage, preparation of samples for analysis and the analysis itself are subject to artifact problems. Artifact problems can mean too little or too much of the analyte of interest. It can also mean the presence of a compound that in fact does not exist in the measured object, or the complete absence of a compound that in fact exists in the measured object Artifact problems for the different steps will be discussed in the individual paragraphs. 

Chapter 19 Preparation of Samples for Analysis The Key to Analytical Success. 431... 

NMR spectrometers are expensive instruments, representing one of the largest financial investments a chemical laboratory is likely to make, and to get the best results from these they must be operated and maintained in the appropriate manner. This chapter explores some of the fundamental experimental aspects of relevance to high-resolution, solution-state NMR spectroscopy, from instrumental procedures through to the preparation of samples for analysis. Later sections also deal with the basics of calibrating a spectrometer and assessing its performance. 

Norrish, K. Hutton, J.T. (1964) Preparation of samples for analysis by X-ray fluorescence spectrography. 1. Lusion in borate glass. 2. Powder samples. CSIRO Div. of Soils Div. Rep. No.3. 

In the preparation of samples for analysis they are hydrolyzed for several hours in tubes designed to prevent loss of chloride (as HCl) in the fumes frequently formed on reaction with water. 

Preparation of samples for analysis resembles that used to prepare samples for electron microscopy. In general, preparation consists of polishing small specimens and mounting them on a planchet. A common planchet consists of a cylinder of vitreous carbon with polished ends. The planchet must provide a conductive pathway to drain the charge imparted by the impact of the primary ion beam. Without some means to dissipate the charge, the sample will become charged, which can deflect the primary ion beam and can interfere with the extraction of secondary ions. 

Much of the laboratory time (perhaps 70-80%) will be taken up with routine samples taken from the processing line, and examination of these samples is designed to detect any problem. The preparation of samples for analysis takes a long time, therefore routine samples should be taken on days when analysis may be started and finished conveniently. Details of bottlenecks and problems are given. The remainder of the time will be spent examining any samples involved in the outbreak of a foodborne disease and dealing with consumer complaints. 

Preparation of Samples for Analysis. The cotton gauze pads, both garment and respirator, were prepared for analysis by halving the pads diagonally resulting In a 51.61 cm and a 19.35 cm sample, respectively. The urine samples were thawed and duplicate aliquots of 5 or 10 ml were removed for analysis. 

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