Good laboratory practice sample preparation

Dew-point measurement is a primary method based on fundamental thermodynamics principles and as such does not require calibration. However, the instrument performance needs to be verified using salt standards and distilled water before sampling (see Support Protocol). To obtain accurate and reproducible water activity results with a dew-point instrument, temperature, sensor cleanliness, and sample preparation must be considered. Equipment should be used and maintained in accordance with the manufacturer s instruction manual and with good laboratory practice. If there are any concerns, the manufacturer of the instrument should be consulted. Guidelines common to dew-point instruments for proper water activity determinations are described in this protocol. The manufacturer s instructions should be referred to for specifics. 

Closely related to preventive action is the process audit. Such an audit is performed as part of a laboratory assessment for each test on the proposed scope of accreditation. Performance of a test procedure is observed relative not only to the requirements of the ISO 17025 standard (or ISO Guide 25) but also with respect to performing the ASTM or ISO test method properly. As a minimum, the laboratory must have properly calibrated equipment, the current test method, and trained testing personnel. In addition, a representative number of test demonstrations will reveal whether good laboratory practices are observed in sample preparation, using the correct test parameters and calculating the results. When operators and technicians accept responsibility through such demonstrations, they tend to commit to the quality process. Real improvement occurs with involvement at all levels. 

Good laboratory practice in initial sample preparation... 

In this section we provide some practical considerations to chemists not familiar with the use of immunoassays for food contaminants. We focus primarily on the use of 96-well microtiter ELISA. Regardless of the type of sample and analysis, good laboratory practices (GLPs) and international standards organization (ISO) standards, where they apply, need to be followed to ensure the quality of results and the minimization of variability. Like any other analytical protocol, the analysis of contaminants by immunoassay is a combination of three sequential steps sample collection and preparation, sample analysis, and data processing followed by the interpretation of results. 

The practical execution of viscosity measurements requires the use of good laboratory practice even if the experiments are relatively easy to do. Besides the basic safety regulations for the use of chemicals and liquids, a tidy sample preparation and a precise execution of the experiment is the prerequisite for the determination of the exact viscosimetry parameters of a polymer solution. 

For the determination of trace metals in biological materials, in addition to Good Laboratory Practice further particularities have to be respected because the metal concentration in the matrix is extremely low. The most important disturbances are caused by contamination. The falsification of the results can be so enormous that these become nonsensical. Sources of contamination include the utensils used in sample preparation, all equipment having contact with the samples in the analytical procedure, water, reagents, and components in the environment. Because of the low metal content in the samples, instability of the solutions and matrix effects play an important role. Therefore standards and reference materials as well as the analytical procedure have to meet extremely high requirements [35,36]. 

Work performed in a laboratory must be traceable. This is achieved when all relevant information from sample preparation to experiments and reporting of data are recorded on paper or stored in a computer. In practice, this requires a quality management system of the laboratory. Continued effort toward good quality practice in the laboratory and, if possible, national accreditation of the laboratory (testing methods) is recommended. 

Samples gathered and solutions prepared by laboratory personnel must be properly labeled at the time of sampling or preparation. In addition, a complete record of the sampling or preparation should be maintained. Sound quality assurance practices include a notebook record where one can find the source and concentration of the material used, the identity and concentration of the standard being prepared, the name of the analyst who prepared it, the specific procedure used, the date it was sampled or prepared, and the expiration date for any stored solutions. The reagent label should have a clear connection to the notebook record. A good label includes an ID number that matches the notebook record, the name of the material and its concentration, the date, the name of the analyst, and the expiration date. See Workplace Scene 2.5. 

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