The precision of an activation analysis method prescribes the estimation of the precision of a single analytical result. The
adequacy of these estimates to account for the observed variation between duplicate results from the analysis of different
samples and materials, is tested by the statistic T, which is shown to be approximated by a chi-squared distribution. Application
of this test to the results of determinations of manganese in human serum by a method of established precision, led to the
detection of airborne pollution of the serum during the sampling process. The subsequent improvement in sampling conditions
was shown to give not only increased precision, but also improved accuracy of the results.
The errors of analysis due to the different parameters involved in 14 MeV neutron activation analysis method are studied. Formulae to calculate these erros have been developed when possible. Otherwise they have been evaluated for special experimental situations. Special cases where some parameters become critical, as far as precision is concerned, have been mentioned.
The IAEA conducted the IAEA-CU-2006-06 Proficiency Test (PT) on “The determination of major, minor and trace elements in ancient
Chinese ceramic” in 2006. The results of this PT showed that of the 21 analytes reported by our laboratory 9 failed the precision
criteria. Therefore the results reported by our laboratory along with the results of other laboratories which carried out
analysis using neutron activation analysis (NAA) were studied. It was found that the major factor contributing towards data
falling in the “Warning” category, failing the precision criteria was the high uncertainties cited in the certificates of
the reference materials (RMs) used for quantification of data. In this regard, it is recommended that synthetic standards
should be prepared and used on a routine basis especially for the measurement of the elements K, Eu, Lu, Ta, Tb and Yb.
Four different approaches to PIXE data obtained in repeated measurements on thick standards have been evaluated in terms of precision and accuracy. Both were found to be the best when determinations relative to an external standard were normalized to a composition assumed to be 100% oxides.
Authors:M. Antony, J. Bueb, W. Herrmann, and V. Ndocko Ndongué
The half-life of38Cl obtained by thermal neutron capture was measured to be 37.236±0.009 min. Values of the energy levels of38Ar from
– decay of38Cl were determined with a better precision than those available in the literature.
The widespread introduction of rapid pneumatic sample transfer systems has enabled instrumental neutron activation analysis to be based on an increasing number of very short-lived activities. Furthermore, these transfer systems have been interfaced to computer-based MCA's so that the experimenter has complete control over irradiation, decay and counting times, as well as being able to arrange the automatic transfer of numbers of samples between the various stations. Thus the analyst now has a series of options available to him to make the best use of time and facilities. Based on the requirements of detection limits and precisions, he will choose between various irradiation and counting régimes (a) single i.e. conventional (b) cyclic and (c) repeated; or he may choose to replicate the sample a number of times. This paper examines how detection limits and precisions are affected by the above options. By considering a specific isotope, being detected in backgrounds of different half-lives, it is possible to calculate signal-to-noise ratios in each of these cases, and hence compare these régimes from this aspect. Based on calculations for the isotope77mSe (17.5 s), which is now being widely accepted as the basis for selenium analysis, it is shown that, if a low detection limit is the prime consideration, then replicating samples is the procedure of choice; however, if commercial considerations of sample throughput are important then a pseudocyclic régime would provide the best compromise.
Authors:W. Görner, D. Alber, A. Berger, O. Haase, G. Monse, and Chr. Segebade
In activation analysis of traces in small samples, the non-equivalence of the activating radiation doses of sample and calibration material gives rise to sometimes tolerable systematic errors. Conversely, analysis of major components usually demands high trueness and precision. To meet this, beam geometry activation analysis (BEAMGAA) procedures have been developed for instrumental photon (IPAA) and neutron activation analysis (INAA) in which the activating neutron/photon beam exhibits broad, flat-topped characteristics. This results in a very low lateral activating flux gradient compared to known radiation facilities, however, at significantly lower flux density. The axial flux gradient can be accounted for by a monitor-sample-monitor assembly. As a first approach, major components were determined in high purity substances as well as selenium in a cattle fodder additive.
Authors:Mirko Prosek, Alenka Golc-Wondra, Irena Vovk, and Janko Zmitek
A wide spread of measurements is typical in quantitative TLC. Improved reproducibility and speed can be achieved by automatic and controlled sample application, chromatographic development, and data acquisition and processing. Secondary chromatography is the main reason for poor precision in TLC. With
up to 10% this is by far the largest source of uncertainty. During the drying process mobile phase evaporates from the upper surface of the plate, and molecules of separated components inside the layer move up or down. Our experimental results show the strong dependence of the intensity of reflected diffuse light on the position of the spots inside the layer. Experimental results gave us an idea how to construct a device for drying and derivatization of TLC plates and a device which reduces uncontrolled propagation and non-homogeneous vertical in-depth distribution of spots during drying and derivatization was constructed. In addition the device designed is safer to use than a hair dryer. A laminar flow of air or inert gas constantly removes solvent vapor from the upper layer of the adsorbent and accelerates drying. Temperature is controlled and varies in a predetermined manner at predetermined intervals. Temperature gradient, which cannot be avoided in flow systems is controlled and is oriented in the direction of chromatographic development. The construction of the device results in identical drying conditions for substances with the same
. Diffusion of the analyte is controlled and standardized and inhomogeneous in-depth distribution of compounds inside the adsorbent is minimized. Heating grade, heating intervals, pulses, switching, and other conditions are preset or programmable. The TLC dryer constructed reduces uncontrolled propagation and non-homogeneous vertical in-depth distribution of spots during drying and derivatization, which results in significantly improved reproducibility and precision. This is very important because in quantitative TLC most measurements are performed in reflectance mode.
We investigated the plutonium assay method that uses the plutonyl trinitrate tetrapropyl-ammonium ion-pair solvent extraction with spectrophotometry of the extract as a candidate method capable of providing robustness and precision. To identify and assess the effect of factors on the precision, we looked at sampling techniques, silver oxide oxidation conditions extraction time, extract stability, and temperature dependence of the extract analytical peak height and position. We obtained a precision of 0.12%.
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.