Standard operating procedures method errors

Your list should have included at least some of the items mentioned above, but you may well have identified other sources of uncertainty. Remember that uncertainty is not about mistakes. The uncertainty estimate is intended to reflect the likely variation in results when a method is carried out correctly and operating under statistical control. Your list of sources of uncertainty should not therefore include any gross errors such as contamination of samples, mistakes in calculations or the analyst failing to follow the standard operating procedure correctly. 

In summary, when using the indirect" technique for optical trace analysis, all of the points mentioned above have to be considered and have to be validated when setting up a standard operation procedure" (SOP), in order to conform to good laboratory practice (GLP) analysis methods. This means an extra work load compared with validation of the direct optical trace analysis procedure. Sometimes there is no way of getting round this so-called less elegant , more cumbersome and more error prone indirect technique. However, if it is performed correctly and judged critically, it is still a good method and should easily allow optical trace analysis down to 0.1% and lower. 

In many industries frequency and method of checking, together with accepted limits, will be determined by the standard operating procedure (SOP) adopted and may well be done on a daily basis. Regular performance checks are common sense. If a system is only checked once every 6 months and then found to be in error, 6 months work is suspect. 

Method of Operation. The experimental procedure is standardized to avoid gross errors due to variations in surface condition of the evaporator test section. Each tube (of commercially available drawn copper) is degreased overnight by... 

The analytical uncertainty should be reduced to one-third or less of sampling uncertainty (16). Poor results obtained because of reagent contamination, operator errors ia procedure or data handling, biased methods, and so on, can be controlled by proper use of blanks, standards, and reference samples. 

The ICP-OES-FIA technique allows a rapid and routine method of analysis for both major and trace levels of metals in aqueous and non-aqueous solutions in most samples provided that the sample is in solution form. The flow injection method can be used to correct for baseline drift that may originate from uncontrollable thermal and electronic noise during analysis. However, these errors can be corrected if the peak obtained is measured over at least three points, i.e. immediately before the peak, at the peak and immediately after the peak and the height or area is integrated over these points. The elaborate time consuming correction procedures required for batch operations are not required for FIA methods and the baseline is defined by the emission obtained from the carrier liquid and is reproduced between each sample injection. A typical FIA analysis of signals for standards and samples is shown in Figure 7.11 for triplicate injections of variable concentrations of boron. 

If methods are used in which the overall recovery is 70% or above, and if the possibility of accidental but undetected very large losses is reduced by using a minimum of steps and transfer operations, or by automation, it is questionable whether in practice the precision will be greatly increased by current techniques of using internal radioactive standards. In the case of many urinaiy steroids, conjugated internal standards would be required for full control of the procedure and are not yet generally available. Finally the technique itself is not error-free, even in the absence of isotope effects, and the usual techniques employed so far often involve very small volumes of volatile solvents in which transfer errors can be large unless very superior manual technique is used. 

Also COSMO and lEF are affected by both discretization and tail errors. The entity of the errors are however lower, at least by an order of magnitude, than those found in standard PCM. The reason is due to the use of operators related to the electric potential instead of the electric field, as standeird electrostatics would require. So, when N2 or N3 axe sufficient, COSMO-PCM and lEF-PCM can be used without corrections. Moreover, for more difficult cases, where a N3 procedure was found to be necessary in the standard PCM, a by far simpler N2 correction is sufficient for COSMO and lEF. This lowering in the level of the correction can even reverse the trend in the computational times in favor of the lEF method, if compared to the standard PCM. This is particularly true in computing hyperpolarizabilites [38], for the reason we shall explain later. We have no COSMO hyperpolarizabilities calculations to compare. 

---