An empirical method for predicting detonation pressure of CHNOFCl explosives

This paper describes a new method for prediction of the Chapman-Jouguet detonation pressures of CHNOFCl explosives using the heat of detonation, Q_det, the number of moles of gaseous products of detonation per gram of explosive, α, and the average molecular weight of gaseous products, M. The equation has the form: P_CJ=15.88α(MQ_det)^1/2ρ₀²−11.17, where P_CJ is the Chapman-Jouguet detonation pressure and ρ₀ the loading density. Calculated P_CJ by this procedure show good result with respect to measured detonation pressure for any pure or mixture of ideal and some of less ideal CHNOFCl explosives at ρ₀>0.8 g/cm³.     

The effect of (natural) polyols on the initial colour of heavy metal- and zinc-free poly(vinyl chloride)

The propensity of (natural) polyols dispersed in heavy metal- and zinc-free PVC sheets to improve the initial colour, e.g. the colour during the first minutes of exposure to high processing temperatures (short-term stability), has been investigated. It is shown using W(Lab) values that the initial colour improves upon addition of polyols containing primary hydroxyl groups. The polyols act as HCl scavengers, presumably via an acid-catalysed S_N2 substitution of the primary hydroxyl groups by chloride ions. In contrast, polyols with only secondary or tertiary hydroxyl groups accelerate the thermal degradation of PVC. Notwithstanding, the efficacy of the (natural) polyols containing primary hydroxyl groups will be reduced if the polyol is susceptible to competitive acid-catalysed intramolecular cyclodehydration reactions under the processing conditions. This is substantiated by a comparison of the behaviour of mannitol and 3,4-di-O-methyl-d-mannitol. The methylated derivative, which is less prone to undergo intramolecular cyclodehydration, improves the initial colour of heavy metal- and zinc-free PVC sheets more significantly than mannitol itself.     

A novel approach of initial vectors construction in iterative target transformation factor analysis

The construction of the favorable initial iterative vectors is the key to iterative target transformation factor analysis (ITTFA). A tentative approach to construct the better initial vectors, which is based on the chromatographic information provided by evolving factor analysis (EFA), is proposed. A region, which contains the peak position at maximum height, is determined. Several elements in the region of each initial vector, instead of one element, are initialized as 1. The elements out of the region are initialized as 0. So it is not necessary to determine the exact peak position at maximum height for the resolution of partly overlapping chromatographic profiles, which may avoid the divergence brought by determination of the peak position at maximum height. In addition, it may give acceptable resolution for the embedded peaks. It is applied to resolve 2D-simulated data and experimental liquor GC/MS data, the resolutions are reasonable and improved.     

The determination of an accepted reference value from proficiency data with stated uncertainties

Proficiency data with stated uncertainties represent a unique opportunity for testing that the reported uncertainties are consistent with the Guide to the expression of uncertainty in measurement (GUM). In most proficiency tests, however, this opportunity is forfeited, because proficiency data are processed without regard to their uncertainties. In this paper we present alternative approaches for determining a reference value as the weighted mean of all mutually consistent results and their stated uncertainties. Using an accepted reference value each reported uncertainty estimate can be expressed as an E _n number, but a value of confirms its validity only if the uncertainty of the reference value is negligible in comparison.Reference values calculated for results from an International Measurement Evaluation Programme (IMEP-9) by “bottom up” as well as “top down” methods were practically identical, although the first strategy yielded the lowest uncertainty. A plot of individual coefficients of variation (CV) versus E _n numbers helps interpretation of the proficiency data, which could be used to validate relative uncertainties down to <1%.     

Isotope dilution GC-MS routine method for the determination of butyltin compounds in water

A standard GC-MS instrument with electron impact ionisation has been used to develop a fast, simple and reliable method for the simultaneous determination of monobutyltin (MBT), dibutyltin (DBT) and tributyltin (TBT) in water samples. Isotope dilution analysis (IDA) is used for the determination of species, taking advantage of a commercially available spike solution containing a mixture of MBT, DBT and TBT enriched in ¹¹⁹Sn. Method detection limits for 100-mL samples were between 0.18 and 0.25 ng L⁻¹ for the three butyltin compounds with typical RSD between 2 and 4% at levels between 100 and 10 ng L⁻¹, respectively. Recovery of tin species in spiked samples (natural water, wastewater and seawater) was quantitative. The stability of butyltin compounds in collected seawater samples was also studied. The addition of a 1% (v/v) glacial acetic acid preserved tin species in the samples for at least 5 days at room temperature. The IDA method was finally implemented in a routine testing laboratory and it was subsequently accredited by the Spanish National Accreditation Body according to the requirements of UNE-EN ISO/IEC 17025.     

The role of proficiency testing in the detection and resolution of calibration bias in the LeadCare® blood lead analyzer; limitations of peer-group assessment

Following implementation of the CLIA ‘88 laboratory regulations, the primary role of proficiency testing (external quality assessment, PT) in the U.S. has been widely viewed as one of assuring regulatory compliance. PT can also be an effective tool for detecting widespread analytical problems, subject to limitations based on the method of PT assigned value determination. A recent case study describes the role of two PT programs in detecting and resolving a calibration bias in the LeadCare blood lead analyzer, and illustrates the limitations of peer-group target determination in fulfilling that PT role.     

Testing equivalence between two laboratories or two methods using paired-sample analysis and interval hypothesis testing

A modified interval hypothesis testing procedure based on paired-sample analysis is described, as well as its application in testing equivalence between two bioanalytical laboratories or two methods. This testing procedure has the advantage of reducing the risk of wrongly concluding equivalence when in fact two laboratories or two methods are not equivalent. The advantage of using paired-sample analysis is that the test is less confounded by the intersample variability than unpaired-sample analysis when incurred biological samples with a wide range of concentrations are included in the experiments. Practical aspects including experimental design, sample size calculation and power estimation are also discussed through examples.     

Assessing contaminated hydrogen peroxide for safe storage and transportation using the FTAI

Hydrogen peroxide is a very versatile oxidizing agent, and it is also environmentally compatible considering that the products of its exothermic decomposition are oxygen and water.When kept in a clean temperature-controlled environment, the self-reaction (decomposition) rate is extremely low. However, it is well known that even a small amount of contamination will dramatically increase the reaction rate. This paper describes the use of the fast thermal activity interpreter (FTAI) instrument to examine the chemical reactivity of commercially available 50% hydrogen peroxide at two different temperatures (30 and 40°C) both with and without contamination. The results show that at 30°C a small amount of rust (330 ppm) increases the reaction rate of 50% hydrogen peroxide by a factor of 50. When the temperature is increased to 40°C, the reaction rate is further increased by almost a factor of four. The implication for reactivity management is that at this contamination level most practical vessel sizes would require emergency venting capability. An evaluation was then performed to determine the emergency venting requirement for the safe transportation or storage of the contaminated hydrogen peroxide. It was determined that for quantities of the material less than 5 gallons, conventional breather vents would be sufficient to accommodate the gas evolved. However, for larger quantities, a safety relief device would be needed. For example, for a 400-gallon tote bin at 40°C the required minimum vent area is estimated to be 4.3 in², corresponding to a minimum vent diameter of 2.3 inches.     

Do proficiency tests always verify laboratories’ performance? The case of FAPAS PT 0270

In this paper, the case of FAPAS PT 0270 “Doramectin and Oxfendazole in Sheep Liver” is discussed. During evaluation of the data received from participants (determination of total, oxidised oxfendazole residue and calculation of the sum of oxfendazole and oxfendazole sulfone residues), significant differences were observed between the results obtained by use of two analytical approaches. This phenomenon can be explained by the route of oxfendazole metabolism, which results in the presence of fenbendazole in the sample. This was not predicted by the provider; consequently, not all the necessary tests on the material were conducted. Due to the high uncertainty of the z-scores in this test, the results of the PT cannot be used for purposes of evaluation, and the benefits of participation in PT 0270 are questionable.     

A new approach in assessing microbiological results in water analysis proficiency testing

Due to the relatively large spread in the results of microbiological proficiency tests, the z-scores are often not able to detect zero or low results as being ‘bad’ results. This paper describes an adapted z-score based on the average or the standard deviation of the 50% ‘highest’ results. The combination of the adapted z-scores of four samples enables a better judgement of the performance of each laboratory. Papers published in this section do not necessarily reflect the opinion of the Editors, the Editorial Board or the Publisher.