Uncertainty budget for final assay of a pharmaceutical product based on RP–HPLC

Compliance with specified limits for the content of active substance in a pharmaceutical drug requires knowledge of the uncertainty of the final assay. The uncertainty of measurement is based on the ISO recommendation as expressed in the Guide to the Expression of Uncertainty in Measurement (GUM). The reported example illustrates the estimation of uncertainty for the final determination of a protein concentration by HPLC using UV detection, using the approach described by EURACHEM/CITAC. The combined standard uncertainty for a protein concentration of 2400 µmol/L was estimated to be 14 µmol/L.. All known and potential uncertainty components are presented in Ishikawa diagrams and were carefully evaluated using Type A or Type B estimates. Special efforts were made to avoid duplication or omission of significant contributions to the combined uncertainty. Hence, before accepting the uncertainty budget, the estimated combined standard uncertainty was verified using the variation observed in a number of quality control samples.     

Synthesis of precision for the certification of phosphorus in biological materials by INAA

The -emitter³²P was used to determine total phosphorus by INAA in Skim Milk Powder RM 63, a material now certified by the EEC Bureau of Reference (BCR). Samples and comparator were irradiated in the Danish reactor DR 3. One month later the samples were dissolved in water and aliquots counted with a GM end-window counter using absorber thicknesses of zero to 400 mg/cm². The Synthesis of Precision was introduced to find the absorber best suited for discriminating against other -emitting isotopes and at the same time giving maximum precision.     

The quality of consensus values

The definition of a metrological term “quality” is discussed in relation to a series of consensus values pertaining to a set of measurement results from an actual PT exercise. It was concluded that the definition used by ISO in quality management systems could be readily interpreted in the metrological sphere.     

A TEM and XRD study of the SbNbSe3 misfit layer structures

Two new misfit layer structures have been synthesized within the Sb-Nb-Se system. Powder X-ray diffraction and electron microscopy techniques (electron diffraction, HREM, XEDS) have been used to determine the nature of their structure. According to TEM and XEDS data (for more than 15 crystals studied) both phases are monolayer type, i.e. (SbSe)1+delta (NbSe2). Electron microscopy reveals a composite modulated structure that consists of the periodical intergrowth of a pseudotetragonal SbSe layer, denominated as Q, and a pseudohexagonal layer NbSe2, denominated as H. Both layers fit along b, stack along c and do not fit along a (misfit) giving rise to an incommensurate modulation along this direction. The two phases differ in the symmetry of the Q layers being in one case orthorhombic (for delta = 0.17) and monoclinic in the other (for delta = 0.19). After the characterization of the sample by electron microscopy the unit cells of the basic layers could be refined for both phases by powder X-ray diffraction: aQ = 5.824(2) A, bQ = 5.962(5) A, cQ = 23.927(6) A, alpha = 90 degrees, beta = 90 degrees and gamma = 90 degrees and aH = 3.415(5) A, bH = 5.962(6) A,, cH = 11.962(1) A, alpha = 90 degrees, beta = 90 degrees and gamma = 90 degrees for the orthorhombic phase; aQ = 5.844(2) A, bQ = 5.981(1) A, cQ = 23.919(5) A, alpha = 90 degrees, beta = 90 degrees and gamma = 96.00(3)degrees and aH = 3.439(1) A, bH = 5.994(2) A, cH = 11.956(3) A, alpha = 90 degrees, beta = 90 degrees and gamma = 90 degrees for the monoclinic phase. The phase with the monoclinic Q-sublattice often appears as twinned crystals. The more abundant crystals are disordered intergrowths of both monolayer phases.     

Fast transportation system evaluation at the Danish Mach 1 irradiation facility

The sensitivity of short-lived indicator isotopes in neutron activation analysis depends on the rapidity with which the sample is moved out of the irradiation position. The precision and accuracy of the analytical result, however, are determined by the random and systematic errors in the duration of the irradiation and decay prior to the measurement. Transportation systems differ considerably with respect to the influence of factors such as pressure, temperature, sample weight, and interaction between irradiation and decay times. The Mach 1 transportation system for the Danish Reactor DR 3 has been investigated experimentally, and a determination of its performance characteristics makes it possible to estimate thea priori precision of analytical methods based on indicators with half-lives down to 20–25 ms.     

Validation of methods for the determination of aluminium in fish gills by INAA and ICP-MS

In a European study of fish death in mixing zones of rivers with different acidities a reliable determination of Al and other elements in gills from freshwater fish was required, and both INAA and ICP-MS were studied as candidate reference methods. INAA requires minimum sample handling with a correspondingly small risk of contamination and no blank value; however, a careful study was needed of both nuclear interference from P and the increased detection limit caused by other major elements in the sample, before reliable results for Al could be ascertained. ICP-MS requires dissolution of the sample with a resulting risk of contamination and a significant reagent blank; while sensitivity was good, the interference from N created problems for sample decomposition in the microwave oven. Our experience with actual samples indicates that both methods suffer from considerable contamination problems, requiring that samples be handled in a clean bench with superpure reagents. Nuclear interference was determined experimentally by irradiating stoichiometric P-compounds with and without a Cd-shield; the observed interference of 1 g Al from 50 mg of P was found to require no correction in almost all cases. The accuracy of results was ascertained by analyzing SRM 1577 Bovine Liver.     

Validation of a loss-free counting system for neutron activation analysis with short-lived indicators

The use of loss-free counting systems makes possible the exact correction for pile-up and dead-time losses during counting of a mixture of short-lived radionuclides even at very high count rates. However, counting statistics cannot be calculated by taking into account only the Poisson distribution of the incoming -quanta, such as is done in existing computer programs for -spectrometry. At moderate count rates Müller statistic was found to account for the observed variability between duplicate countings; however, at higher count rates the variability of weighing factors was found to be significant in comparison with the Müller statistic. While counting statistics could not be correctly estimated for short-lived species, experiments showed excellent accuracy for initial dead times up to 90%.     

Verification testing of commercially available computer programs for photopeak area evaluation

Computer programs available from three major manufacturers of systems for -ray spectrometry were tested by measuring the same¹⁵²Eu source under nearly identical conditions. Results for the evaluation of peaks with full widths at half maximum ranging from less than 3 and up to 15 channels were compared with those obtained by a reference program based on peak integration using optimum peak boundary selection. Two out of three commercial programs produced results without significant influence of peak width, but none of them could maintain the same level of statistical control throughout the range of interest that the reference program does.