The mouth alcohol defense to DUI breath tests remains viable no matter what breath test machine was used in your DUI case.
The Breathalyzer Models 900, 900A, and 1000, which are no longer in production, require the operator to determine when a deep lung breath sample has been provided. Unlike most modern devices, the Breathalyzer Models 900, 900A, and 1000 do not have an automated slope detection system. Many devices, such as the Draeger Alcotest 9510 and Alcotest 7110 MKIII-C, and the Intoxilyzer Models 5000 and 8000, employ an infrared slope detection system in the effort to detect mouth alcohol. In those devices that use infrared slope detection, the breath testing device is programmed so that it has a “picture” of what an acceptable breath sample should look like. If the sample does not fall within the acceptable parameters of what the device believes that a breath sample should look like, the machine should produce an error message. These devices presume that the alcohol concentration will rise sharply until it plateaus (or flattens out). It is estimated that first 2/3 of the breath sample introduced into the device is discarded in the effort to obtain a test comprised of end-expiratory air.
If the subject's breath test is performed upon a Breathalyzer Model 900, 900A, or 1000, failure of the officer to comply with 20-minute pre-test observation requirements will be very difficult. In DUI cases involving breath tests performed upon a Breathalyzer Model 900, 900A, or 1000, the officer performing the test is responsible for ensuring that alveolar air is tested. In contrast, if the test is performed upon a device equipped with an infrared slope detector, such as the Draeger Alcotest 9510 or Alcotest 7110 MKIII-C, the practitioner must be prepared to demonstrate the inadequacies of the slope detector. The discussion below of the inadequacies of slope detectors may serve as a good starting point.
Don't forget to investigate your state's own internal tests of various breath test devices and their respective ability to detect to mouth/residual alcohol. Below is an example of what you may find:
Harding and Zettl, supra note 1, at § 7.6.
See id. at § 7.2 for a succinct description of almost every breath testing device employed in the United States.