By Deandra Grant, J.D., M.S. (Pharmaceutical Science), ACS-CHAL Forensic Lawyer-Scientist, Certified Intoxilyzer Operator and Maintenance Technician
If you submitted to a breath test during a DWI arrest in Texas, the instrument that generated your result was the Intoxilyzer 9000, manufactured by CMI, Inc. of Owensboro, Kentucky. Texas adopted the Intoxilyzer 9000 around 2015, replacing the older Intoxilyzer 5000 EN. It is the sole approved evidential breath testing instrument for the Texas Breath Alcohol Testing Program, administered by the Texas Department of Public Safety (DPS) Office of the Scientific Director.
Prosecutors present the Intoxilyzer 9000 result as a definitive measurement of your blood alcohol concentration. The reality is more complicated. The Intoxilyzer 9000 is a sophisticated infrared spectrometer, but it has documented limitations, features that Texas has chosen not to use, and maintenance gaps that raise serious questions about the reliability of any given result.
I am a trained operator and maintenance technician on breath testing instruments, and I teach forensic chromatography and drug analysis at Axion Analytical Labs. What follows is a technical but accessible explanation of how the Intoxilyzer 9000 works and where it can be challenged.
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How the Intoxilyzer 9000 Works
The Principle: Infrared Spectrometry
The Intoxilyzer 9000 operates on the principle of infrared (IR) spectrometry. Ethanol molecules absorb infrared light at specific wavelengths. By measuring how much infrared light a breath sample absorbs, the instrument calculates the amount of ethanol present.
The process follows the Lambert-Beer Law: the amount of infrared energy absorbed by a substance is proportional to the number of absorbing molecules in the sample path. More ethanol molecules in the breath sample mean more infrared absorption, which translates to a higher reported BAC.
The Optical Bench
Inside the Intoxilyzer 9000 is an optical bench containing a heated sample chamber, a pulsed infrared light source at one end, and a pyroelectric detector at the other end. When a subject blows into the instrument, breath passes through the heated sample chamber. The infrared light source emits IR energy at multiple wavelengths through the chamber. The detector at the other end measures how much energy arrives, i.e. the difference between what was emitted and what was received represents the energy absorbed by ethanol (and potentially other substances) in the sample.
The instrument uses multiple wavelengths of infrared energy to improve specificity. Ethanol has a characteristic absorption pattern across several wavelengths that is distinct from most other compounds. By comparing absorption at multiple wavelengths, the instrument’s microprocessor attempts to distinguish ethanol from interferents like acetone.
The Testing Sequence
A standard Intoxilyzer 9000 test in Texas follows this sequence:
- The operator confirms a 15-minute observation period was completed (to prevent mouth alcohol contamination)
- The instrument performs an air blank to confirm the sample chamber is clean (result must be 0.000)
- The instrument analyzes a reference standard (a known ethanol solution) to verify calibration (result must be between 0.070 and 0.090 g/210L)
- Another air blank (must be 0.000)
- The subject provides Breath Sample 1 by blowing steadily into the mouthpiece
- Another air blank
- The subject provides Breath Sample 2
- Final air blank
- The two subject results must not differ by more than 0.020 g/210L
The instrument reports results in grams of alcohol per 210 liters of breath, as required by Texas Penal Code §49.01(1)(a).
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The Problems with the Intoxilyzer 9000
1. The Partition Ratio Assumption
The Intoxilyzer 9000 measures alcohol in breath, not in blood. To convert a breath measurement to a blood alcohol equivalent, the instrument assumes a blood-to-breath partition ratio of 2100:1, meaning that the concentration of alcohol in 2100 milliliters of exhaled breath equals the concentration in 1 milliliter of blood.
This ratio is a population average. Individual partition ratios vary significantly. There is a range documented in the scientific literature from approximately 1300:1 to 3100:1. A person with a lower-than-average partition ratio (e.g., 1500:1) will produce a breath test result that overestimates their actual blood alcohol concentration. The Intoxilyzer 9000 has no mechanism to determine or adjust for an individual’s partition ratio.
For a person with a true BAC of 0.07, a partition ratio of 1500:1 instead of the assumed 2100:1 could produce a reported result above 0.08 — a false positive for the legal limit based entirely on normal physiological variation.
2. Mouth Alcohol and Slope Detection
Residual alcohol in the oral cavity — from a recent drink, a burp, gastroesophageal reflux disease (GERD), or acid reflux — can produce a dramatically inflated breath result because the sensor encounters highly concentrated alcohol from the mouth before it encounters the lower-concentration deep lung air the instrument is supposed to measure.
The Intoxilyzer 9000 includes a slope detection algorithm designed to identify mouth alcohol by monitoring the shape of the breath alcohol curve as the subject blows. Mouth alcohol typically produces a rapidly declining curve rather than the plateau expected from deep lung air. In the 9000, this is accomplished by pulsing the infrared source at 10 cycles per second, generating a breath sample reading every 100 milliseconds across each of its four filtered points. Whether this approach is adequate is an open question. At least one independent hands-on evaluation found that Michigan’s outgoing DataMaster DMT actually outperformed the 9000 on slope detection. Patrick T. Barone and Michael J. Boyle, writing in the Michigan State Appellate Defender Office’s Criminal Defense Newsletter, noted that testing showed “the DMT performed better than the 9000 regarding slope detection; or Residual Alcohol Detection System (RADS).” (Introducing the Intoxilyzer 9000 — Michigan’s New Breath Test Instrument, SADO Criminal Defense Newsletter, April 2023, citing Semenoff, An Independent Review of the Intoxilyzer 9000, Pt. 2, Counterpoint: The Journal of Science and the Law, Vol. 2, Issue 2, Article 4 (2017).)
The 15-minute observation period is supposed to address mouth alcohol, but officers must continuously observe the subject during this entire window. If the subject burps, has GERD, or has any oral exposure to alcohol during the observation period and the officer does not notice and restart the clock, the mouth alcohol safeguard fails entirely. GERD is a particularly difficult problem in this context — it can introduce alcohol into the oral cavity silently, with no observable sign for the officer to detect and no audible belch to trigger a reset.
3. Interfering Substances
The Intoxilyzer 9000’s use of multiple IR wavelengths is designed to identify interferents. When the instrument detects an absorption pattern inconsistent with pure ethanol, it is supposed to flag the test. However:
- Acetone: Produced naturally by people with diabetes, people on ketogenic diets, and people who are fasting. While the instrument is designed to detect and subtract acetone interference, the effectiveness of this subtraction depends on the specific concentration and the presence of other variables.
- Other volatile organic compounds: Isopropanol, methanol, toluene, and other substances that absorb infrared energy at overlapping wavelengths may not be fully compensated for by the instrument’s interferent detection algorithms.
- Radio frequency interference (RFI): Cell phones and police radios emit electromagnetic radiation that can potentially affect electronic instrumentation. The Intoxilyzer 9000 includes RFI detection, but its effectiveness in all real-world conditions has been questioned.
4. Features Texas Has Chosen Not to Use
This is one of the most significant issues with the Texas implementation. The Intoxilyzer 9000 is capable of producing histograms which are graphical representations of the subject’s breath flow, volume, and duration during each blow. A histogram would allow the operator, the laboratory, and the defense to verify that the subject provided a proper deep lung sample and to detect anomalies like mouth alcohol spikes.
Texas DPS has chosen not to activate the histogram function. This means that critical data about the quality of the breath sample is generated by the instrument but not made available to anyone — not the operator, not the prosecutor, not the defense, not the jury. The instrument has the capability to provide this transparency, and the state has deliberately chosen not to use it.
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5. Maintenance and Calibration Gaps
Prior to 2020, DPS required monthly on-site inspections of every Intoxilyzer 9000 in Texas by a Technical Supervisor. During COVID-19, these inspections were suspended. This means that instruments that were previously checked monthly for calibration accuracy, reference system integrity, and environmental conditions have gone extended periods without independent verification.
Additionally, the Intoxilyzer 9000 is not warranted by the manufacturer to be accurate or reliable for human testing. The manufacturer’s warranty covers the instrument’s ability to analyze a reference sample solution but not its accuracy when measuring a human breath sample under real-world conditions. This distinction is rarely disclosed to juries.
6. The 0.020 Agreement Requirement
Texas requires that the two breath samples agree within 0.020 g/210L. This tolerance is designed to ensure consistency, but consider what it actually allows: if your first result is 0.08 (at the legal limit) and your second result is 0.06 (below the legal limit), both results “pass” the agreement requirement. One puts you over the limit and one puts you under but the test is deemed valid. A 0.020 range on a 0.08 threshold represents a 25% margin, which is substantial for an instrument whose results can determine whether a person goes to jail.
Other Breath Testing Instruments
While the Intoxilyzer 9000 is the approved instrument in Texas, other states use different devices. The DataMaster DMT, used in several states, operates on a similar infrared spectrometry principle but with different hardware and software implementations. The Dräger Alcotest, widely used in New Jersey and other jurisdictions, combines infrared spectrometry with electrochemical fuel cell technology for dual-detection. Understanding the differences between instruments is relevant for defense attorneys handling cases that cross state lines or involve federal DWI on military installations or federal property.
How to Challenge Intoxilyzer 9000 Results
- Demand maintenance and calibration records for the specific instrument used in your case, including all records since the last in-person Technical Supervisor inspection
- Request the operator’s certification and training records to verify they were qualified to administer the test
- Obtain the complete test record including all air blanks, reference standard results, and both subject samples
- Ask why the histogram function was not activated — the instrument can produce this data, and the state’s refusal to use it deprives the defense of information about sample quality
- Review video of the testing to verify the 15-minute observation period was properly conducted and documented
- Investigate medical conditions including GERD, diabetes, ketogenic diet, and any condition producing acetone or other volatile organic compounds
- Challenge the partition ratio assumption through expert testimony on individual variability
- Challenge the manufacturer’s warranty — the instrument is not warranted for human breath testing accuracy
At Deandra Grant Law, Deandra Grant is a trained operator and maintenance technician on breath testing instruments. She teaches the science of forensic analytical instruments at Axion Analytical Labs and understands the Intoxilyzer 9000 at the component level. When we challenge your breath test result, we are not guessing at what might have gone wrong. We know the instrument, its capabilities, its limitations, and the specific ways the Texas implementation falls short of what the science requires. Call (214) 225-7117 or visit texasdwisite.com.
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