Sample collection method

Analysts should discuss sample-collection methods with those responsible. Frequently, the methods result in biased data due to venting, failure to blow down the sample lines, and contamination. These are limitations that must either be corrected or accepted and understood. Sampling must be conducted within the safety procedures established for the unit. Since samples may be hot, toxic, or reactive in the presence of oxygen, the sample gatherers must be aware of and implement the safety procedures of the unit. 

Sampling artifacts. The use of in situ pumps to collect water samples for " Th analysis permits simultaneous collection (and separation) of different particle fractions as well as dissolved Th. As pumping systems have been modified to permit determination of POC on the pump filters, it became possible to compare POC determined from the pump samples with conventional POC determinations made on small volume samples (0.5 - 2 L) taken from hydrocasts. The JGOFS data from multiple studies show large discrepancies between these two sample collection methods, with pump POC values 3 to 100 times lower than bottle POC values. Possible artifacts with each approach have been identified. For example Moran et al. (1999) have suggested that DOC is adsorbed onto... 

Demonstrating sample collections methods for chemical and biological analysis... 

A critical examination of the analytical procedures used prior to 1977 showed these to be inadequate for the determination of organic compounds in combustion effluents of special concern were the short-comings in sample collection methods. These short-comings are delineated in a review published recently (2). Because of these sampling uncertainties, the continuous development and validation of new procedures and sampling systems was an essential element of this study. 

The Guardian Explosives Detection Security Portal (Fig. 6) is manufactured and marketed by Syagen Technology, Inc., of Tustin, CA [48], This portal was the result of two research and development efforts that included collaboration between Syagen and Sandia National Laboratories, funded by TSL, and a project at Sandia, funded by DOE [33,49], The detector utilized in the portal is a quadrupole ion trap, time-of-flight (QitTof ) mass analyzer [50,51], The mass analyzer identifies explosives by time-of-flight and mass-to-charge (m/z) ratio, which increases the accuracy of the identification of the explosive. The foundation of the sample collection method in this portal is an air shower [52],... 

Thomas, K.W., L.S. Sheldon, E.D. Pellizzari, R.W. Handy, J.M. Roherds, and M.R. Berry. 1997. Testing dupUcate diet sample collection methods for measuring personal dietary exposures to chemical contaminants. J. Expo. Anal. Environ. Epidemiol. 7(l) 17-36. 

All of the sample collection methods suffer from inlet losses, as the reactive organic peracids and peroxides tend to decompose on unconditioned surfaces. Aerosols deposited in samphng hnes can also react with the peroxides, with subsequent loss of sample. For this reason, sample lines must be kept clean and as short as possible. A surfaceless intake scmbber has been designed to avoid surface loss. This system minimizes surface contact of the sample by eliminating all surfaces at the intake. 

The serum is aliquoted 20 pL per tube, stored at -70 °C and used only once after thawing. Several articles have discussed the importance of standardization of preanalytical factors such as patient preparation and sample collection methods for MS-based proteomics profiling (17,18,19,20). 

The sample collection method used depends on the sample type and amount. In practice, sample collection is done by someone other than the analyst. For example, blood samples are usually taken by hospital nurses and environmental samples by municipal authorities. In order to be sure that (i) the results of determinations bear comparison with other laboratories, (ii) solid conclusions can be drawn from the results, and (iii) the sample taken is representative, special attention must be paid to sampling, and, if possible, for various sample types confirmed sample collection instructions must be used. 

Historically, pnibhshed values of the h/h concentration of both tissue and body fluids from healthy subjects have varied greatly. These great differences were attributed to numerous variables, such as age, sex, dietary habits, physiological conditions, environmental factors and numerous other X-factors. Given the delicate nature and the instability of biological samples, it has been concluded that improper sample collection methods and manipulation drastically affects the iodine content of biological matrices. 

What type of sample collection method are you planning on using, i.e. distillation, direct purge-and-cryofixation ... 

In the calibration of thermal desorption tubes, the same conditions should predominate as in sample collection. Methods such as the liquid application of a calibration solution to the adsorption materials or the comparison with direct injections have been shown to be unsatisfactory. Alternatively, Certified Reference Standards (CRSs) are available (e.g. Markes Int., UK). CRS tubes are recommended in many key standard methods (e.g. US EPA Method TO-17) for auditing purposes and as a means of establishing analytical quality control. CRS tubes are often certified traceable to primary standards, have a minimum shelf life of typically 6 months. They are available ready for use with concentrations... 

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