Sample Selection and Preparation

Amino acid contents have been studied in a variety of biological samples. Of these, plasma, urine, cerebrospinal fluid (CSF), and brain tissues, which are accessible and clinically significant, have received most attention. Other samples investigated include am-niotic fluid, blood cells, feces, sweat, saliva, hair, fingernails, and fingerprints. 

Isolation of Amino Acids from Bioiogicai Samples 

In most cases, biological samples are deproteimzed and an aliquot of the supernatant is brought to dryness. The residue can subsequently be denvatized and analyzed without any isolation procedure. Alternatively, the amino acids in an aliquot of the deproteimzed sample can be isolated on an lon-exchange resin column. Dowex 50W-X8 (100-200 mesh) resin is most commonly used for this purpose (Desgres et al., 1979 Chauhan and Darbre, 1982 Gabrys and Konecki, 1983). 

A typical procedure involves a glass column (5 cm x 3 mm, id) with a glass-wool plug at the bottom, packed with the resin (H ) in water up to a height of 1 cm. An aliquot of the biological sample (e.g., 100-500 xL of unne) that has been adjusted to pH 1-2 with HCl, is layered on top of the resin. All the noncationic impurities will be washed through the resin with 2 mL of deionized water. The amino acids are eluted with 2 mL of 4M ammonium hydroxide at a flow rate of one drop every 5-10 s. The eluate is then dried, derivatized, and analyzed 

The low volatility of amino acids caused by the presence of —NH2, —OH, —SH, and —COOH groups in the molecules renders the GC analysis of free amino acids virtually impossible The difficulties in selecting a suitable derivative are caused largely by the wide variation in structures and chemical properties of the side chain in ammo acids. Problems are encountered particularly 

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Careful sample selection and preparation are the prerequisites for a successful analysis (Boguski and McIntosh, 2003). Postmortem brain samples for our studies were obtained from the M RC London Brain Bank for Neruodegenerative Diseases, Institute of Psychiatry. The AD patients fulfilled the National Institute of Neurological and Communicative Disorders and Stroke and Alzheimer s Disease and Related Disorders Association (NINCDS/ADRDA) criteria for probable AD (Mirra et al., 1991). A definite diagnosis of AD was performed by historical analysis of the brain samples, which was consistent with the CERAD criteria (Tierney et al., 1988). The brain regions temporal, frontal, occipital, parietal cortex, and cerebellum of patients with AD (72.3 7.6 years old) and controls (72.6 9.6 years old) (Seidl et al., 1997) were used for the studies at the protein level. The... 

Sample Selection and Preparation. Samples were selected from two high-volatile bituminous coals, namely, Illinois No. 6 bright coal and an eastern Kentucky splint coal from Perry County. The choice of these coals was based on the desire to contrast the fine structure of coals of equal rank but of different lithotypes. For both coals the samples were obtained from limited regions of their respective coal seams. Detailed coal petrography was performed on these samples, and TEM specimens were subsequently selected from representative polished blocks. 

Crushing versus melting. Those non-cosmogenic components which cannot be avoided by careful sample selection and preparation must be corrected for. Usually the... 

Odor testing may be performed by a selected group of panelist to either determine the effect of various additives on the odor or taste of a medium or to determine the odor or taste sensitivity of a particular group of people. For this purpose, a series of samples is prepared in concentration scale which increases in geometric increments. At each concentration step two samples containing the medium alone are given to a panelist. The panehst should determine which sample is different firom the other two samples. The panelist should begin wifli the lowest concentration selected to be two or three concentration steps below estimated threshold. The method description contains information on sample selection and preparation, result, and precision determination. 

Define work areas within each process area Select and prepare sampling sites Define employee job classifications... 

The selection and preparation of the samples very often is the most crucial item in an interlaboratory test. All characteristics that could affect the integrity of the test have to be considered. This includes homogeneity and stability, which are dealt with in detail later. The PT provider has to look for possible changes in and the effect of ambient conditions on the samples. 

As far as is practically possible, the selection and preparation of samples must take into account all possible variations in the matrix of the material to be analysed. The applicability of the method should be studied using various samples ranging from pure standards to mixtures with complex matrices as these may contain substances that interfere to a greater or lesser extent with the quantitative determination of an analyte or the accurate measurement of a parameter. Matrix effects can both reduce and enhance analytical signals and may also act as a barrier to recovery of the analyte from a sample. 

Once samples are acquired, voucher specimens must be maintained according to standard accepted methods and the collected specimens must be extracted or otherwise processed to prepare samples for biological evaluation. The goal of sample handling and preparation is to select for positives (remove nuisance compounds), prepare the samples to be compatible with existing (and future) bioassays, and store both the collected unprocessed material and the processed samples in a manner that is easily retrievable and maximizes stability. 

The choice of sample preparation method is crucial in chemical analysis because it is often the most critical and time-consuming step of an analytical process.35 There is a wide choice of methods for sample pretreatment and preparation for further analysis. Unfortunately, however, there are no universal methods of sample treatment because analytical samples come in a huge variety of forms. Ideally, the sample preparation methodology should be solvent-free, simple, inexpensive, efficient, selective, and compatible with final analytical methods. 

In conducting the tumbler test for friability, great care must be taken in selecting and preparing the sample. Since the procedure for friability determinations requires the use of 1.5- to 1.05-in. coal, it is necessary that samples be selected from this size range. It is also necessary that each lump be free from cracks or any indications of faults which might bias the results. The lumps selected are carefully screened through a 1.5-in. screen and those sizes retained on the 1.05-in. screen to the amount of 1000 g are placed in the pebble mill and turned as described above. 

Srinivasa Rao Y, Shukla RN, Maheshwari S, Kulkarni AY, Jivendra Y (1983) Determination of permanganate and kappa number of pulp with high ash content. IPPTA 20(3) 55-56 Stewart CM, Foster OH, Cohen WE, Leslie RT, Watson AJ (1951) The selection and preparation of a reporducible wood sample for chemical studies. Appita 5 267- 311 Swan B (1965) Isolation of acid-soluble lignin from the Klason lignin determination. Sven Papperstidn 68 791-795... 

Sample collection and preparation are crucial issues for any bioanalytical application in order to address the complexity of samples originating from biological tissues and fluids. It is necessary to cope with the lack in concentration sensitivity typical for capillary separation techniques, to avoid interference from matrix components as well as to ensure analyte stability. In peptide analysis, a strong focus exists on handling small-volume samples and on selective concentration of the analyte in order to overcome limitations with respect to loadability. In addition, loss of analyte frequently occurs due to degradation by proteases and due to adsorption to surfaces, which accordingly needs to be minimized. 

We will address sampling concerns and selected sampling procedures and preparation for air, water, and solids below. But first, let s look at some generic sampling techniques. 

A broad range of technical requirements is important in a laboratory quality system. These include aspects such as the selection of appropriately qualified and experienced personnel sampling, sample handling and preparation laboratory accommodation and environmental conditions equipment and reagents calibration reference standards and reference materials traceability (of standards and of samples) the selection or development, validation, and control of methods estimation of the uncertainty of measurements reporting of results and quality control and proficiency testing. 

The spectra measured by any method of optical spectroscopy may be subject to qualitative (what is it ) or quantitative (how much is it ) evaluation. We assume here that the basic rules described in other chapters for the overall analytical process are obeyed, in particular for sample selection and sample preparation. Errors during sample preparation or simply due to an incorrect positioning of the specimen in the optical beam can never be corrected for in the measured spectra. Restricted quality in the experimental spectra will lead to errors either in qualitative evaluation (e.g. iU-defined results in spectral search) or in quantitative evaluation (e.g. erroneous determination of concentration). 

When designing an electrochemical experiment, there are several factors that need to be decided. It is common that the design of the experiment and the preparation of samples comprise the hardest and most time-consuming part of electrochemical experimentation. Decisions need to be made regarding sample selection, surface preparation, masking to expose a certain area, specifics of the experimental... 

The granular raw material was previously divided into quarters and dried, following ASTM E 877-03 determinations to select and prepare iron ore samples and related materials. In file table 1 is shown the chemical compositions of iron ore used m experiments, in the table 11 is presented... 

Selected analytical methods, adopted by the American Oil Chemists Society (AOCS) for characterizing composition, structure, physical properties, and stability of fats and oils, are summarized below. Prescribed equipment must be used and conditions followed. Some of these techniques are limited to specific oil species, but adaptations are available for other species. Procedures for sample drawing and preparation also are specified. 

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