breath analyzer

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BREATH ANALYZERS LABORATORY

A breath analyzer measures how much alcohol is in the air you breathe out. The device uses that measurement to estimate how much alcohol is in your blood. That number is known as your BAC, or blood alcohol content. The quantitative determination of ethanol in exhaled air (BrAC – Breath Alcohol Content) is done, in general, by two different analytical methods, using an electrochemical cell, or by infrared absorption.

The basic principle that supports the use of breath analyzers is that there is a physiological relationship between the concentration of alcohol in the exhaled alveolar air (BrAC) and the concentration present in the blood (BAC). Thus, the concentration of alcohol in the exhaled air is directly proportional to its concentration in the blood when it passes through the lungs. This relationship is a function of the average physical constitution of the population and is not identical in all countries. In Portugal, the conversion of breath alcohol content (BrAC) into blood alcohol content (BAC) is based on the principle that 1 mg of alcohol per liter of exhaled air is equivalent to 2.3 g of alcohol per liter of blood: 1mg / L (BrAC) = 2.3 g / L (BAC).

Although breath analyzers are mostly used to control the consume of alcohol by drivers on the road, there is a growing number of companies that use them to ensure that their workers are not under the influence of alcohol when carrying out their professional activities.

FIELDS OF ACTIVITY

The Breath Analyzers Laboratory activity is essentially focused on the:

- screening breath analyzers calibration

The breath analyzers in the scope of calibration are used by police, hospital and industrial entities. This type of breath tester allows quick and practical use and it is not subject to metrological control. However, it should be calibrated periodically. Calibration is done using the comparison method and the measurements are carried out in the range of 0 g / L to 3 g / L BAC, with 1 to 5 concentrations, depending on the application instrument and customer choice. In this procedure we use certified reference materials (CRM) of gas mixtures of ethanol in nitrogen. These mixtures have traceability to primary standards produced in IPQ. The molar fractions of these reference mixtures in mol/mol units are processed in g/L using an equation that uses the molar mass of ethanol, the molar mass of nitrogen, the density of nitrogen, and a conversion factor specific for each type of breath analyzer.

- evidential breath analyzer’s metrological control

In Portugal, the metrological control of evidential breath analyzers is regulated according to the recommendation OIML R126, which contains a regulatory framework that defines the maximum permissible errors (EMA) for the metrological checks. The Ordinance No. 1556/2007, December 10, approved the new rules of metrological control of breath analyzers.

The verification procedure is based on the comparison method by which the instrument reading is compared with the conventionally true value of the reference gas that had been subjected to analysis in the respective breath analyzer, thereby simulating the exhaled air. The reference gas, known as Certified Reference Material (CRM) consists of binary mixtures of ethanol in nitrogen and comes in five different concentrations, covering the measuring range of breath analyzers in check. For each concentration level repeatability tests are carried out, with determination of the standard deviation, error and associated uncertainty.

TRACEABILITY

The mole, symbol mol is the SI unit of amount of substance. One mole contains exactly 6,022 140 76 × 10²³ elementary entities. This number is the fixed numerical value of the Avogadro constant, N_A when expressed in the unit mol^-1 and is called the Avogadro number.

The amount of substance, symbol n of a system is a measure of the number of specified elementary entities. An elementary entity may be an atom, a molecule, an ion, an electron, any other particle or specified group of particles.

External document:

Mise en pratique for the definition of the mole in the SI

The measurements traceability is to national and international standards, guaranteed by traceable equipment to the SI units and by the adoption of preparation and certification of gas mixtures methods in agreement with the applicable international standards.

The accuracy of the measurements made is proven through the participation in projects and in international comparisons, and it is demonstrated by the acceptance and inclusion in the Capacities of

Measurement and Calibration (CMC) BIPM database for IPQ gas mixtures.