Sample and standard preparation

The extent to which a sample has to be prepared for analysis will be dependent on the nature of the sample that is presented for analysis. For example, a single bag of white powder will require minimal preparation and can be sampled, diluted in an appropriate solvent, mixed, filtered, and dispensed into an HPLC vial ready for analysis. However, not all forensic samples are quite so simple and, even when they might appear simple, some sample pretreatment will be required in order to ensure homogeneity. In most forensic laboratories, a diverse range of samples will require HPLC analysis some examples are given in Table 3.6. 

Reference standards, on the other hand, require a more simple preparation regime. The standard of interest is usually prepared by direct immersion in a suitable solvent. It should be noted, however, that it is recommended that at least one reference standard solution be subjected to the same extraction processes that are applied to the sample. This standard solution will act as a quality control (QC) sample in order to check the extraction processes. 

Toxicology Blood Urine Stomach contents Liver 

The extraction process will be discussed in greater detail later in this section under each of the extraction techniques. 

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The precision of a test method is the variability between test results obtained on the same material using a specific test method (ASTM, 2004 Patnaik, 2004). The precision of a test is usually unrelated to its accuracy. The results may be precise, but not necessarily accurate. In fact, the precision of an analytical method is the amount of scatter in the results obtained from multiple analyses of a homogeneous sample. To be meaningful, the precision study must be performed using the exact sample and standard preparation procedures that will be used in the final method. Precision is expressed as repeatability and reproducibility. 

FIGURE 5 Typical chromatogram ofswab blank, swab sample, and standard preparation. 

Sample and Standards Preparation. Shellfish samples were extracted by the standard bioassay procedure (1). Prior to injection into the HPLC, protein was precipitated with 1.5% TCA at I C (60ul) 50% TCA to 2 ml extract). The samples were then centrifuged, an aliquot diluted 1 3 with water and filtered (. 5 urn). 

Dilution during Sample and Standard Preparation. Minimize the number of dilutions required to give the final dilutions of the sample and standard solutions. Each dilution step will have the potential to introduce error in the procedure. 

Benzalkonium chloride ( ) is used as an antimicrobial preservative in Nasonex. It is quantifiable using a HPLC method with a column that has a cyano group chemically bonded to porous silica particles. The HPLC was equipped with a UV-Vis detector, a 150 mm x 4.6 mm, 3- jm Spherisorb S3 CN column. The mobile phase consisted of 45% acetonitrile in 0.05 M phosphate buffer (pH 6.0). The flow rate was set at 1 mL/min. The following procedure was used for sample and standard preparations. About 2.5 g of Nasonex was transferred into a 25-mL volumetric flask. This was diluted to volume with acetonitrile and... 

Using a loop injector, inject 20 yl of Sample and Standard Preparation. 

The validation report should contain reference to the analytical methods (specific code number used as identifier within the pharmaceutical organization) and the corresponding drug substance or product name. Note that for early-phase method validation reports the results maybe filled in a predefined table and compared against the acceptance criteria. However, for late-phase validation, more explicit reports are generated explaining each and every experiment, with detailed steps of sample and standard preparation. 

The irradiation container is unloaded and the samples and standards prepared for radionuclide assay. After irradiation no care whatever need be taken to avoid contamination of the sample by non-radioactive impurities. Time performs the same function as a skilled chemist if the radionuclide to be measured has a longer half-life than the interferences. For example, trace Cr is easily measured in the presence of Ti even though the neutron-capture products of both elements emit gamma rays of exactly the same energy. Gram for gram, Tl emits 1000 times more photons per second than does Cr immediately after a 1-minute irradiation, but Cr is 2000 times more radioactive than Tl two hours later. 

Experimental design - describes the procedure that will be followed including the number of batches, replicates, analysts, instruments, and any additional detail that may not be covered in the method but is critical to the transfer such as sample and standard preparation, number of injections for each as well as how many samples can be injected between standards, dissolution de-aeration procedure, time frame for completing all testing once the samples are received, such as 30 days. 

In the ICH guidelines analytical validation relates to test procedures. A test procedure is a more precise and comprehensive term than analytical method as it includes the technique, the sample and standard preparation, the use of apparatus, the formulae for calculation, etc. (cfr. Table 8.1). Validation... 

Miiltiple samples and standards prepared for routine titiimetiic, chromatographic, spectrometric and other types of instrumental analysis can be loaded into autosamplers that transfer them one at a time to the instrument for analysis in a pre-determined sequence. 

The repeatability of the sample and standard preparation can be assessed by preparing ten samples and standards from the sample source and examining the coefficient of variation of the response. 

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