Volume 17, Issue 2 (April 1972)

    Sulfuric Acid Concentration in the Catalyzed Breathalyzer Ampules

    (Received 27 September 1971; accepted 24 November 1971)

    Published Online: April

    CODEN: JFSOAD

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    Abstract

    During the last fifteen years the Breathalyzer has been the most widely used instrument in North America for determining blood alcohol concentrations by means of breath analysis [1,2]. Of the parameters which may affect the alcohol readings, those related to the composition of the ampule reagent are among the most important. At present the manufacturing specifications used by Scientific Services are, by volume, 50 percent aqueous sulfuric acid, 0.025 percent weight per volume, potassium dichromate, and 0.025 percent weight per volume, silver nitrate [3]. The total volume of this solution in the ampules may be 3.00 to 3.07 ml. The inclusion of the silver nitrate as a catalyst is a modification of the original formulation which involved only the potassium dichromate in the aqueous sulfuric acid solution [4]. It has been shown that the potassium dichromate concentration may vary between 0.015 percent and 0.035 percent weight per volume, and the sulfuric acid concentration may vary between 16 and 20 normal without loss in accuracy [5]. Under these conditions ethanol samples introduced into the ampules at approximately 65 C were oxidized stoichiometrically to acetic acid within 90 s [1]. The ethanol is first oxidized to acetaldehyde, a short-lived intermediate, rapidly oxidized to acetic acid. Stronger oxidizing conditions than exist in the ampule are needed to take the oxidation beyond the acetic acid stage [2,6,7]. The equations representing the stoichiometry of this progressive oxidation of ethanol are as follows: 1) 2K2Cr2O7 + 8H2SO4 → 2Cr2(SO4)3 + 2K2SO4 + 8H2O + 6O2) CH3CH2OH + O → CH3CHO + H2O 3) CH3CHO + O → CH3COOH 4) CH3COOH + 4O → 2CO2 + 2H2O


    Author Information:

    Bergh, AK
    Scientific Services, “L” Directorate, Royal Canadian Mounted Police, Ottawa,

    Rodgers, PG
    Scientific Services, “L” Directorate, Royal Canadian Mounted Police, Ottawa,


    Stock #: JFS10865J

    ISSN: 0022-1198

    DOI: 10.1520/JFS10865J

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    Author
    Title Sulfuric Acid Concentration in the Catalyzed Breathalyzer Ampules
    Symposium , 0000-00-00
    Committee E30