Error sample, handling

For assays of stable materials with wide ranges of tolerable error, sample handling is of little concern. For assays of labile materials, especially assays for purity or for minor components, controlled sample handling procedures need to be established. There are three potential ways in which a sample may become contaminated, namely by the sampling tools, sample containers, and degradation on storage. 

The inherent lability of alkene- and hydroxyalkanesulfonates, variations in isomer composition, and the presence of the disulfonates are features which complicate AOS analyses. Improper sample handling, such as exposure to high temperatures, can also alter active matter composition. Consequently, analytical procedures have been developed that minimize potential sources of error. 

The use of internal standards is somewhat controversial.115 There is agreement that an internal standard may be used as a correction for injection volume or to correct for pipetting errors. If an internal standard is included before sample hydrolysis or derivatization, it must be verified that the recovery of the internal standard peak is highly predictable. Ideally, the internal standard is unaffected by sample handling. Using an internal standard to correct for adsorptive or chemical losses is not generally approved, since the concentration of the standard may be altered by the conditions of sample preparation. An example of internal vs. external standards is given in Chapter 4. 

Patterson CC, Settle M (1976) The reduction of orders of magnitude errors in lead analysis. In LaFleur PD (ed) Accuracy in trace analysis sampling, sample handling, analysis. NBS Special Publication 422, p. 321... 

The elimination of mannal sample handling with the inherent gain in safety and, to some extent, the elimination of operator error (and being able to maintain sample integrity). 

Internal Standard. The use of internal standard is critical in bioanalytical methods to improve precision and accuracy. The role of internal standard is to mimic the analyte of interest. It should be added before sample preparation/extraction to account for losses and errors introduced during the process. The more sample handling steps there are, the greater the error becomes, because errors are additive. In this case, the use of internal standard minimizes errors significantly. 

Moreover, because of sample handling and densitometric quantification, a high error was observed for double determination of gel electrophoresis... 

The chemist interprets the results of trip and equipment blank analyses to identify sample management errors during sampling, sample handling, and decontamination procedures and to determine whether these errors may have affected the collected sample representativeness. The chemist qualifies the data according to the severity of the identified variances from the SAP specifications and may even reject some data points as unusable. Example 5.8 shows a logical approach to the interpretation of the trip and equipment blank data. 

The analytical process consists of a series of steps sampling, sample handling, laboratory sample preparation, separation and quantitation, and statistical evaluation. Each one of these steps is important if accurate results are to be obtained, but the key component of the analytical process is sample preparation. It is important to bear in mind that these analytical steps are consecutive the next step cannot begin until the preceding one has been completed. If any one of these steps is not carried out properly, the overall performance of the procedure will be poor, errors will be introduced, and inconsistency in the results can be expected. 

Sample handling high flexibility regarding sample concentration, solvent, and column temperature optimal reproducibility of absolute retention times demand for analyses requiring high accuracy high risk of systematic errors. 

In addition to sampling procedures, sampling bias and sampling errors are introduced, leading to some guidance on sample handling, shipping, and chain-of-custody procedures. 

While these methods both share the distinct advantage of looking directly at the active ingredient of the formulation they also share a number of disadvantages. Because of the small quantities released, sample preparation techniques, can frequently be elaborate and therefore very time consuming. Since each step in the preparation of a sample is a potential source of error, this increased complexity can also decrease the accuracy of the method. Considerations of this type led this laboratory to the use of labeled pheromones to decrease sample handling and to increase the quantitative accuracy, however, liquid scintillation counting does not provide qualitative information about the labeled species. 

Experimental procedures for quantitative mass spectrometric analysis usually involve several steps. The final error results from the accumulation of the errors in each step, some steps in the procedure being higher error sources than others. A separation can be made between the errors ascribable to the spectrometer and its data treatment on the one hand and the errors resulting from the sample handling on the other. 

Normally, the sample handling errors are higher than those due to the mass spectrometer and thus make up the greater part of the final error. Handling errors can be numerous, such as the error in measuring a sample volume and the error in the introduction into the spectrometer. 

A proteomic analysis of a sample usually consists of four steps. These are extraction of the proteins from the sample, their separation, detection, and finally identification/analysis of the individual separated proteins. Major attention must be paid to the sample processing, sample handling, and the sample clean-up since any error or sample loss during this stage influences the final result. 

Table III lists the material balances for the preparative separations. These are the percent weight recoveries for either asphaltene or maltene defined, using the sulfur balance for an example, as the sum of the amount of sulfur in each cut times the cut weight percent divided by the total sulfur. In general, the balances are in the 80-120% range, which is reasonable considering the amount of sample handling involved. The recoveries are out of line only in a few cases, most notably the Prudhoe Bay maltene nickel balance. In addition, a comparison of the calculated elemental values for the total residua differ somewhat from the raw total values for several residua. These discrepancies are probably attributable to the small samples, multiple sample manipulations, and compounding of individual errors when the asphaltene and maltene data are summed. The data-fitting routine described in the next section was used to obtain a set of best fit data, which were used in the subsequent size calculations.

Mass spectrometer precision was determined by making repeated measurements on a gas sample prepared by combustion of carbon isotope reference material NBS-22. The standard deviation of the mean derived from 10 consecutive measurements of this gas was 0.02 %o The error associated with the combustion and purification procedure was measured by replicate combustions of the NBS-22 reference material, which resulted in a standard deviation of 0 12 %o for five samples ITius, the overall precision associated with the mass spectrometric measurement of vs PDB was 0.12 %o, or in absolute terms, 1.3 ppm. Most of the error clearly was associated with the combustion and sample handling process. Since sealed-tube combustions have been shown to produce theoretical recoveries of carbon (33). these small errors most likely arise from handling the CO2 after it is released from the sample tube ... 

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