Sample handling procedures, field

The field investigator s residue sample handling procedures and equipment are always inspected. It is policy that samples be held at the field locations for only short periods however, accurate records are kept on the storage and handling conditions from the time a sample is collected until it is shipped to the laboratory. The elapsed time from collection until a sample is placed in a freezer must be recorded as well as the location of the freezer and the temperature of the freezer during the storage. The sample storage freezer and the records kept on it are always inspected. 

One alternative method for preparing field fortifications solutions/suspensions is to prepare each fortification sample of each matrix in a separate mini-vial in the analytical laboratory and ship the vials to the field for use. This procedure precludes the use of pipets in the field and may be useful when Field Scientists not experienced in the use of pipets are involved in the field fortification process. One disadvantage of this procedure is that the mini-vials, if not designed correctly, will be hard to handle in the field, and surface tension of the suspension or fortification solution will tend to leave unacceptable amounts of the solution/suspension in the vial or at the lip of the vial and not on the matrix in question. This procedure may lead to cross-contamination of samples as the field fortification liquid is forced from the top... 

The handling of solid sorbents, often used in pre-packed tubes, is more convenient than the use of organic solvents to trap VOCs from the air, especially for sampling in the field. The typical laboratory safety procedures required for the handling of organic solvents are not required for solid sorbent samples. 

Frequent use should be made of field and laboratory blanks these are essential for discovering the weak links in the sampling, handling, and analytical procedures. The blank results should also be used to correct measurements when necessary. The detection limits for the methods need to be quantified as 3 times the standard deviations of the blanks. The chemicals used may themselves be a source of contamination for some elements and have to be checked. 

This chapter aims to provide a step-by-step guide for practitioners involved in the collection of contaminated samples by reviewing current groundwater sampling techniques and procedures and highlighting the major sources of uncertainty associated with sample collection. On-site water-quality measurements, quality assurance procedures and sample handling techniques designed to maintain the representativeness of the sample from field to laboratory are also discussed. 

The techniques developed cover various fields, including textural characterisation, elementary and structural analysis and the analysis of composition and surface sites. The book describes the major phases of the technique s development and industrial application, presents its basic concepts and provides a general deKription of industrial equipment, all in a manner that is fully accessible to the non specialist. There is a particular focus on measurement (sample handling, test duration, calibration procedures, etc.) and performance (precision, application limits, possible errors and artefacts), illustrated by concrete examples of catalyst analysis. 

To ensure consistency and efficiency, sample handling (filtration, decantation, centrifugation, sample splitting, etc.), preservation, storage, and transportation procedures must be properly and accurately documented, and adhered to by field personnel. 

A sample subdivided in the field and preserved separately should be used whenever possible, to assess the variability of sample handling, preservation, and storage along with the variability of the analysis process. If the nature of the matrix, the sample acquisition procedure, or the analytical technique prevents the assessment of the entire measurement system, the replicate samples used to assess precision should be selected to incorporate as much of the measurement system as possible. 

Sample preparation is the most general application of both workstations and robotic stations as the tasks involved in this step of the analytical process are the most time-consuming, error prone, and difficult to develop by unskilled operators in addition, safety restrictions apply when toxic materials are to be handled. The use of a specific approach depends on the number of steps involved and their complexity. Table 1 summarizes the features of selected general and specific sample pretreatment procedures used in the environmental and clinical fields. Whereas most environmental samples subjected to a robotic treatment are solid, those dealt with by clinical... 

As field desorption (FD) refers to an experimental procedure in which a solution of the sample is deposited on the emitter wire situated at the tip of the FD insertion probe, it is suited for handling lubricants as well as polymer/additive dissolutions (without precipitation of the polymer or separation of the additive components). Field desorption is especially appropriate for analysis of thermally labile and high-MW samples. Considering that FD has a reputation of being difficult to operate and time consuming, and in view of recent competition with laser desorption methods, this is probably the reason that FD applications of polymer/additive dissolutions are not frequently being considered by experimentalists. 

A study of mercury in Lake Michigan found levels near 1.6 pM (1.6 X 10 12 M), which is two orders of magnitude below concentrations observed in many earlier studies.5 Previous investigators apparently unknowingly contaminated their samples. A study of handling techniques for the analysis of lead in rivers investigated variations in sample collection, sample containers, protection during transportation from the field to the lab, filtration techniques, chemical preservatives, and preconcentration procedures.6 Each individual step that deviated from best practice doubled the apparent concentration of lead in stream water. Clean rooms with filtered air supplies are essential in trace analysis. Even with the best precautions, the precision of trace analysis becomes poorer as the concentration of analyte decreases (Box 5-2). 

Proper sample preservation and handling in the field and at the laboratory the correct application of subsampling techniques during analysis the use of proper preparation and analysis procedures—all of these are important in maintaining the collected sample representativeness. 

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