Attacking and Defending Drunk Driving Tests by ImObersteg Anne D. & McMurray Mary Catherine & Bartell Donald J

Author:ImObersteg, Anne D. & McMurray, Mary Catherine & Bartell, Donald J. [ImObersteg, Anne D.]
Language: eng
Format: epub
Publisher: James Publishing
Published: 2018-03-28T16:00:00+00:00

§11:121 Simulators, Simulator Solutions and Standard Gases

“Calibration” of a machine generally refers to the actual manipulation of the inner workings of the machine, such that the machine result matches a pre-determined vapor/solution/gas or known alcohol concentration.

“Accuracy Checks” or “Calibration Checks” generally refer to the comparison of the alcohol concentration read by the machine with the actual concentration of the ethanol in the device employed, without changes made in the breath machine. Accuracy checks are often performed periodically to ensure that the machine’s internal calibration is still valid. If the accuracy of the machine is unsatisfactory, the machine is then re-calibrated. A little more than half the states run an accuracy check as part of each breath test to assure some level of accuracy at the time of testing.

Whether an Accuracy Check or a Calibration is to be performed, the procedure is implemented with an external standard—either a liquid simulator, or dry gas standard. (Accuracy checks can also be performed using an internal standard in the machine, generally a quartz crystal or the filters for the frequency selections. However, calibration is never performed using an internal standard.) The simulator is a jar, partially filled with a liquid of known alcohol concentration. The liquid is heated to 34° C +/− 0.2, and the vapor in the headspace in the sealed jar is pumped into the machine and analyzed. The reading in the machine must match the vapor concentration of the solution, as determined by Henry’s Law. The dry gas is (usually) a NIST-traceable cylinder under pressure, which when opened, will deliver ethanol gas at a pre-determined concentration.

The purpose of these devices is to “simulate” a breath specimen. However, these devices do not actually mimic human breath nor do they match the actual delivery of the subject’s breath into the machine. Simulators are unlike human breath: they contain pure ethanol and water (or pure gas), the vapor/gas is pumped in the machine at a constant pressure, and often not through the actual breath tube, but via a side port. Thus, one would expect many of the human physiological variables that are present in the delivery of an actual test would not affect the accuracy or calibration procedure.

Studies have been performed to determine the stability and reliability of simulators and their respective vapors/gas/solution. A stability study was performed on alcohol simulator solution, stored in sealed polyethylene bottles at 4° C and at room temperature. Twenty tests were performed on an Intoxilyzer 5000 Evidential Breath-Alcohol Analyzers using a Guth ® Breath Test Simulators at 34° C. No significant changes occurred during the one-year study period in the concentration of the aqueous simulator alcohol solution, at a 90% or higher confidence level. [Dubowski KM, Good-son EE, Sample M Jr., Storage Stability of Simulator Ethanol Solutions for Vapor-Alcohol Control Tests in Breath-Alcohol Analysis, J Anal Toxicol. 2002 Oct;26(7):406-410.]

Internal standards are not true calibration (accuracy) checks, but rather, they are checks of the IR signal. Fuel cells do not use an internal standard. Internal standards are beam attenuators, meaning they block some transmittance of light to the detector.

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