Reagents Used in Sample Preparation

Solvent/Reagent Blank. A solvent blank checks solvents and reagents that are used during sample preparation and analysis. Sometimes, a blank correction or zero setting is done based on the reagent measurement. For example, in atomic or molecular spectroscopy, the solvents and reagents used in sample preparation are used to provide the zero setting. 

Table 3.3 List of common fusion reagents used in sample preparation...

Errors in External-Standard Calibration When external standards are used, it is assumed that the same responses will be obtained when the same analyte concentration is present in the sample and in the standard. Thus, the calibration functional relationship between the response and the analyte concentration must apply to the. sample as well. Usually, in a determination, the raw response from the instrument is not used. Instead. the raw analytical response is corrected by measuring a blank. An ideal blank is identical to the sample but without the analyte. In practice, with complex samples, it is too time-consuming or impossible to prepare an ideal blank and a compromise must be made. Most often a real blank is either a solvent blank, containing the same solvent in which the sample is dissolved, or a reagent blank, containing the solvent plus all the reagents used in sample preparation. 

Nondrug-related impurities can be extracted from various components employed in the sample preparation of a low-dose drug product. Classic sources of this type of contamination are glassware,20 filters, centrifugation tubes, HPLC vials and caps and transfer pipettes.20 Chemicals from the pH electrode can also be extracted into the sample diluent while adjusting the pH of the solution. In addition, impurities in reagents used in sample preparation1 can pose issues. 

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]. 

Some detection procedures involve the loss of the sample for example, in the flame ionization detectors used in gas chromatography the sample is burnt, while in liquid chromatography the addition of a colour reagent will also result in the loss of the sample. For such methods to be used in a preparative... 

Blanks account for interference by other species in the sample and for traces of analyte found in reagents used for sample preservation, preparation, and analysis. Frequent measurements of blanks detect whether analyte from previous samples is carried into subsequent analyses by adhering to vessels or instruments. 

In a further method, sample digests are prepared according to method 1(c) of the Analytical Methods Committee [ 100] using precautions described subsequently [101]. The resulting 100 ml of digest, which is in normally 5% v/v sulfuric acid, should not be colourless and should contain any suspended solids. At the same time, prepare two reagent blanks from the volume of acid used in sample oxidation. 

Materials that come in contact with the blank and the samples may also be the source of contamination. Laboratory equipment for sample preparation, storage, and analysis must be made of non-reactive materials compatible with the chemical reagents equipment used in sample digestion must be thermally stable. Quartz glass, PTFE, and polyethylene are common non-contaminating materials used in elemental analysis procedures. 

The calibration blank in trace element analysis is prepared by acidifying reagent water with the same concentrations of the acids used in the preparation of standards and samples. It serves as a calibration point in the initial calibration. As part of an analytical batch, the calibration blank is analyzed frequently to flush the analytical system between standards and samples in order to eradicate memory effects. Calibration blanks are also used in inorganic compound analysis, where they are prepared with the chemicals specified by the method. 

The instrument blank is the reagent used in the final preparation of the samples, which is injected into the analytical system after high level standards and samples have been analyzed. Analysis of instrument blanks removes memory effects from the analytical system. A calibration blank used for flushing the system in trace element analysis is an example of an instrument blank. 

QC) samples may be prepared. By way of example, a blind sample containing only the solvents/reagents used in preparation of each type of sample is always prepared. 

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