Reproducibility of measurements

The main purposes of the System of accreditation is to ensure reproducibility of measurements, harmonisation of rules and procedures of the National system of accreditation with guidelines of international organizations and national systems of different countries, creation of conditions for mutual recognition of the results of testing, calibration, attestation. 

The use of peroxyacids, including PMSA, makes it possible to improve photometric method of nickel determination - to increase selectivity, accuracy and reproducibility of measurements. Peroxyacids as oxidants ai e used for nickel determination in aluminium and copper alloys, natural waters, stomatological products. 

Fig. 13.22 (a) MNF/microsphere tool for surface sensing, (b) Transmission power dependence on the position of the microsphere at the diffraction grating surface. Comparison of two measure ments of the same grating region shows the reproducibility of measurements. Reprinted from Ref. 42 with permission. 2008 Optical Society of America... 

The observed range of natural variations of 5 Ca is about 4 to 5%o in terrestrial materials and up to 50%o in high temperature condensate minerals in carbonaceous chondrites. The typical reproducibility of measurements is about +0.15%o. Broader application of Ca isotope measurements in geochemistry may be possible, particularly if the reproducibility can be improved to 0.05%o to 0.03%o. There is hope that this can be achieved either with inductively coupled plasma source mass spectrometry (Halicz et al. 1999) or with a new generation of multi-collector thermal ionization mass spectrometers (Heuser et al. 2002). 

Molecular spectroscopic techniques have been widely used in pharmaceutical analysis for both qualitative (identification of chemical species) and quantitative purposes (determination of concentration of species in pharmaceutical preparations). In many cases, they constitute effective alternatives to chromatographic techniques as they provide results of comparable quality in a more simple and expeditious manner. The differential sensitivity and selectivity of spectroscopic techniques have so far dictated their specihc uses. While UV-vis spectroscopy has typically been used for quantitative analysis by virtue of its high sensitivity, infrared (IR) spectrometry has been employed mainly for the identihcation of chemical compounds on account of its high selectivity. The development and consolidation of spectroscopic techniques have been strongly influenced by additional factors such as the ease of sample preparation and the reproducibility of measurements, which have often dictated their use in quality control analyses of both raw materials and finished products. 

The accuracy of results (the interlaboratory reproducibility of measurements) was poor or even dramatically low. The scatter in M and values obtained for identical samples in the different participating laboratories reached several hundred of percent (2000% for poly(acrylic acid). 

The popular weak solvents, which promote polymer adsorption are cyclohexane, dichloro methane, dichloroethane and toluene. Unfortunately, any standardization of the eluent purity/content of admixtures does not exist. This might be one of reasons why it is sometimes difficult to maintain long-term repeatability and interlaboratory reproducibility of measurements in polymer HPLC. 

For grain size not bigger than 0.6 mm, the Bohme s disc ensures reproducibility of measurement in the limit of 1.5%, clearly distinguishing materials even of the same type but different origin. 

To improve reproducibility of measurements, internal standardization is required to correct possible instrument drift or changes in the ablation efficiency. The isotope 65Cu was selected as an internal standard because it is present in every sample at relatively high concentrations allowing for accurate measurement. Figure 1 shows signals after normalization. 

Often of general interest is the reproducibility of measurements when operator, equipment or environment is not the same. One must commonly distinguish clearly between uncertainties applicable to measurements at different times (called repeatability [9]) and those made in different places (called reproducibility). A statistical analysis of homogeneity may be needed whenever a measurement is made on a representative sample from the object to be evaluated. 

The method parameters to include in system suitability are based on the analytical technique itself and on the particular requirements of the individual method. Most quantitative analytical techniques will have a reproducibility of measurement requirement for system suitability. Quantitative impurity analyses should have a limit of detection (LOD) or LOQ measurement. This is necessary because response may be instrument-dependent or may change from day to day. Table 7 lists suggested system suitability requirements for chromatographic methods from November 1994 Center for Drug Evaluation and Research (CDER) reviewer guidance [2],... 

After extensive baseline studies, FTIR-RTM was used for measuring the level of cure. The primary reasons for this decision was the high reproducibility of measuring cure by following isocyanate... 

Reproducibility of measurements of major dissolved ions can, in theory, be better than 1%. However, in real life poorer reproducibilities are common. In Table 5.5 the reproducibility values of +4.7% for the sodium data and + 4.5% for the chlorine data are on the limit of acceptance. However, 10% for calcium and 12% for HC03 are shaky, and the value of 70% for S04 is totally unacceptable. 

Further work should be done to test the quality of the method (by studying a reference sample of well-known density) and the reproducibility of measurements on germanium samples prepared in different ways. 

Rothwell PM, Gibson RJ, Villagra RC et al. (1998). The effect of angiographic technique and image quality on the reproducibility of measurement of carotid stenosis and assessment of plaque surface morphology. Clinical Radiology 53 439-443... 

The chaotic behaviour of box C shows that questions of measurement theory and the concept of predictabifity are not just at the foundations of quantum mechanics, but enter in an equally profound way already on the classical level. This was recently emphasized by Sommerer and Ott in an article by Naeye (1994). They argue that in addition to the problem of predictability the problem of reproducability of measurements in classically chaotic systems has to be discussed. The results of Fig. 1.9 indicate that the logistic map displays similar complexity. In fact, regions which act sensitively to initial conditions, intertwined with regions where prediction is possible, are generic in classical particle dynamics. 

Increasingly severe demands for improved sensitivity, accuracy and reproducibility of measurement have perhaps been the main considerations involved in the tendency toward instrumental miniaturization. 

Precision describes the reproducibility of measurements—in other words, the closeness of results that have been obtained in exactly the same way. Generally, the... 

Reproducibility of measurements of the dielectric characteristics of ice samples may be related to factors such as aging, impurities, inclusion of gas, and the presence of crystal imperfections. Inclusion of gas is one of the most important factors preventing realization of reproducible measurements. Using ice samples grown from well-degassed water, Auty and Cole were able to measure ice samples reproducibly. 

In addition, the cumulative size distribution obtained for pure micron-ized and supercritically produced powders, combined with computation of the aerodynamic diameter according to Eqs. (2) and (3), shows that FPF of supercritically produced particles is about 50%, twice as much as FPF for micronized powder and close to the dispersion efficiency found with lactose (76). The correct values for the total emitted dose of drug particles also were confirmed. In all cases, the state of dispersion for the different formulations was correctly predicted and the results obtained showed good agreement with the cascade impactor measurements made on the same samples. Therefore laser diffraction has distinct advantages over impactor techniques with respect to the speed and reproducibility of measurements and can be used as a complementary method for analysis of aerosol behaviour of different formulations. 

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