Accreditation and Quality Assurance (v.14, #12)

Trace amount of substance fractions of air pollutants in zero air are measured applying sensitive analytical methods in combination with the infrastructure to operate zero air generators under simulated field conditions at place. The uncertainties of the amount of substance fractions of a diluted standard gas mixture and the dilution offsets are calculated under conditions that consider the effect of trace amounts of analyte in the zero gas with increasing dilution of a gravimetric gas standard. The analytical methods and their calibration, the test procedure and results for various zero air generators are described. The results are compared with the specifications, the Swiss regulatory requirements and the European norms for monitoring ambient air pollutants. By knowing the residual amount of substance of the analyte in a zero gas, the instrument offsets by dilution can be eliminated and the uncertainties for the measurement values of the diluted standard gas mixtures be calculated.
Keywords: Dilution; Gas standard; Generator; Ion-molecule reaction mass spectrometry; Testing; Offset; Performance; Trace analysis; Zero air; Zero gas

FTIR and GC as complementary tools for analysis of corrosive gases by James Tshilongo; Angelique Botha; Mellisa Janse van Rensburg; Nompumelelo Leshabane; Napo Godwill Ntsasa (655-663).
The gas metrology laboratory of the National Metrology Institute of South Africa has developed methodology for the gravimetric preparation of corrosive gas mixtures such as nitric oxide (NO) in nitrogen, as well as sulphur dioxide (SO2) in nitrogen or synthetic air. Fourier transform infrared (FTIR) spectroscopy has been used to analyse for trace and ultra trace levels of infrared active gaseous species, such as NO, nitrogen dioxide and SO2 that are difficult to analyse by other means. These corrosive gas mixtures are also analysed using gas chromatography with pulsed helium ionisation detection to complement the work done using FTIR with infrared active impurities. A comparison between the techniques of FTIR, gas chromatography and non-dispersive infrared spectroscopy for corrosive gas analysis is also presented.
Keywords: FTIR; MALT; Quantitative analysis; GC

Towards the simultaneous detection of the low nmol/mol range of CO, CH4 and CO2 in nitrogen using GC-FID by Mellisa Janse van Rensburg; Angelique Botha; Napo G. Ntsasa; James Tshilongo; Nompumelelo Leshabane (665-670).
The trace detection of carbon monoxide (CO), methane (CH4) and carbon dioxide (CO2) by gas chromatography with flame ionisation detection (GC-FID) can be enhanced by paying attention to several practical aspects of the measurement process. Choosing the appropriate column material, column conditioning, sample loop size, methaniser temperature, detector temperature, flow rate, back-pressure regulation and peak integration method can all affect the repeatability of peak areas of very small peaks. The relative effect of each of these variables is discussed in the context of achieving simultaneous detection of CO, CH4 and CO2 in nitrogen in the low nmol/mol range.
Keywords: Trace; Gas chromatography; Carbon monoxide; Carbon dioxide; Methane; Optimisation

pH and electrolytic conductivity as parameters to characterize bioethanol by Petra Spitzer; Paola Fisicaro; Steffen Seitz; Rachel Champion (671-676).
To guarantee the quality of bioethanol and avoid damage to the fuel system in a car, the determination of acidity, water content, as well as chloride, sulfate, alkali metal and alkaline earth metal content are important. Electrochemical quantities like pH and electrolytic conductivity are frequently used in biofuel analysis as sum parameters mainly to indicate the risk of corrosion. Many standards and measurement methods used today in the analysis of biofuel are adopted from specifications and test methods originally developed for fossil-based fuels and commercial alcohol. This results from the rapid expansion of the biofuel production. There are efforts to solve remaining metrological and regulatory issues on a regional and international basis on a short term. In the following an overview on the fundamentals for the measurement of pH in bioethanol blends is given. It will be discussed if the electrolytic conductivity of the bioethanol could be a reliable measure of corrosion causing ionic contaminations in biofuel. State of the art, limitations and future tasks for metrology will be discussed.
Keywords: Bioethanol; pH; Electrolytic conductivity

Metrological issues in energy measurement on biogas by Manfred Hoppe; Peter Schley; Martin Uhrig (677-683).
The use of biogas as regenerative energy can be achieved more efficiently by injecting the treated biogas into natural gas grids since the localisation of the biogas CHP (combined heat and power) plant is made independent from the site of the biogas production. Thus, the utilisation of the heat generated in the CHP plant may be optimised. For that reason, the National and European regulations support injection into the natural gas grid. This paper deals with the general metrological issues concerning injection from the specific aspects of measurement technology. The issues discussed include the adjustment of biogas to the characteristics of natural gas (treatment to produce biomethane) and the measurement of biomethane calorific value. Measuring the calorific value of natural gas today is almost always based on the use of process gas chromatographs specifically designed for the analysis of typical natural gases. Natural gas chromatographs are only suitable under minted conditions for use with biomethane due to differences in the composition of natural gas and biomethane. This paper explains the specific issues and solutions for the measurement of the calorific value of biomethane and their implementation in current plants equipped with injection facilities.
Keywords: Biogas; Metrology; Calorific value; Gas chromatography; Sensor systems

Biofuels today and tomorrow: effects of fuel composition on exhaust gas emissions by Matthias Ußner; Franziska Müller-Langer (685-691).
Due to current and future policy targets, and rapid technical developments, biofuel options are already available and in use in commercial applications. However, there is still doubt about which of the more promising alternatives will be widely accepted in future within the transportation sector. This includes aspects of biofuel properties and their effects on exhaust gas emissions and engine technology. This article addresses the status of current technology, reviews the progress of commercialisation of biofuel production, and gives an outline of its future development. Moreover, it provides an insight into the influence of biofuel composition on the internal combustion process and exhaust gas emissions. To assess biofuel sustainability, all aspects such as fuel production, fuel chemical composition, combustion behaviour, engine technology, and exhaust gas emissions have to be taken into account. Potential application fields and emerging challenges for measurement technology are identified in all these areas.
Keywords: Biofuels; HCCI; Exhaust gas emission; Combustion process; Combustion analysis

A recent paper of Meinrath (Accred Qual Assur 13:179–192, 2008) addresses matters of statistical analysis when the data are thought to have been drawn from a normal distribution with unknown mean and variance. In this comment we clarify, correct and enlarge upon points made there.
Keywords: Confidence interval; Data analysis; Estimator; Goodness of fit; Normal distribution; Outlier