Gas Chromatography Used to Conduct Blood Tests in DWI or DUI Cases in Louisiana
Updated: Feb 5
1. When Can a Law Enforcement Officer Request a Chemical Test of a Motorist’s Blood,
Breath, Urine or Other Bodily Substance?
2. What is Gas Chromatography?
3. Can the Motorist Request a Blood Test of His Own After the Arrest?
4. Who Pays for the Additional Chemical Test of the Motorist’s Blood, Breath, or Urine?
5. Are the Results of the Chemical Tests Admissible in Evidence?
6. What is the Statutory Presumption of Intoxication?
7. What if the motorist BAC was less than 0.08?
When Can a Law Enforcement Officer Request a Chemical Test of a Motorist’s Blood, Breath, Urine or Other Bodily Substance?
When a motorist is arrested for a DWI related offense in Louisiana, the law enforcement officer has a right to request that the motorist submit to a chemical test to examine his blood, breath, urine, or other bodily substance for the purpose of determining the alcoholic content of his blood, and the presence of any abused substance or controlled dangerous substance in his blood. ((1. La. R.S. 32:661.)) One of the most common chemical tests is the blood test where a technician uses a gas chromatograph to determine the percent of alcohol in the motorist’s blood. The person or laboratory conducting the chemical analysis of the motorist’s blood has a duty to conduct the
analysis under the rules and regulations approved and promulgated by the Louisiana Department of Public Safety and Corrections (DPSC) and the person or laboratory must possess a valid permit issued by said department for the purposes of conducting the blood test. ((2. La. R.S. 32:661.)) If the blood test is not conducted pursuant to the DPSC rules and regulations, the results of the blood test will not be admissible in a criminal prosecution for DWI, DUI, or other criminal case against the motorist where the State relies on the statutory presumption of intoxication .((3. State v. Rowell, 517 So.2d 799 (La. 1988).))
What is Gas Chromatography?
Gas chromatography is the method used to analyze the amount of alcohol in a person’s blood. In Louisiana, the Louisiana Department of Public Safety and Corrections (DPSC) has approved two methods for alcohol analysis of blood. The methods approved for alcohol analysis of blood are:
(1) gas chromatography—headspace sampling with internal standard; and (2) gas
chromatography—direct injection with internal standard. ((4. State v. Rowell, 517 So.2d 799 (La. 1988); La. Admin Code. tit. 55, pt. I, § 555, Certified Techniques of Analyst, State of Louisiana, Division of Administration, Office of State Register, Louisiana, LAC,
Gas chromatography is based on the different rates at which components of a mixture pass through a stationary medium. It functions to separate and measure the different components of a mixture. In a blood alcohol analysis, the substances which are separated and measured are the ethyl alcohol present in the blood sample drawn from an individual and a known amount of another species of alcohol (the internal standard) which has been added to the blood sample. The gas chromatograph consists of a heated column through which a stream of gas is passed at a steady rate. When a mixture is injected into the heated column, it evaporates immediately and its different components are carried through the column by the gas. Because different components of a mixture pass through the column at different rates, they are separated. As each component exits the column, it is detected and measured.
The first step in the process is to calibrate the gas chromatograph by injecting an alcohol sample with a known concentration. Next, a blank sample containing only the internal standard is injected into the gas chromatograph to insure that it contains no ethyl alcohol. This demonstrates that the individual's blood sample is not being contaminated by adding the internal standard. A calibration check is then run with known concentrations of alcohol. Finally, the internal standard is added to the blood sample and this mixture is injected into the gas chromatograph. The alcohol in the individual's blood sample and the internal standard are separated and exit the column individually. A detector attached to the end of the column senses the different substances as they
exit. This detection is recorded in the form of peaks on a graph. The individual's blood alcohol concentration is determined by comparing the peak representing the alcohol in his blood to the peak representing the known amount of alcohol (the internal standard). ((5. State v. Rowell, 517 So.2d 799, 801-802 (La. 1988).))
Can the Motorist Request a Blood Test of His Own After the Arrest?
Yes. After the motorist submits to the chemical test requested by the law enforcement officer, the motorist can request a blood test of his own. He may have a physician, physician assistant, chemist, registered nurse, licensed practical nurse, emergency medical technician, nurse practitioner, or other qualified technician of his own choosing to administer a chemical test or tests in addition to any administered at the direction of a law enforcement officer. ((6. La. R.S. 32:665.))
Who Pays for the Additional Chemical Test of the Motorist’s Blood, Breath, or Urine?
The cost of the additional test must be paid for by the motorist. Moreover, if the motorist does not obtain an additional test of his blood, breath, or urine, that does not mean that the test requested by the law enforcement officer is not admissible at a trial. ((7. La. R.S. 32:665.))
Are the Results of the Chemical Tests Admissible in Evidence?
The admissibility of the results of the chemical tests of a motorist’s blood depends on whether the law enforcement officials and the technicians who tested the blood complied with the DPSC regulations. If the law enforcement officials and technicians complied with the DPSC regulations, the results may be admissible depending on whether the evidence complies with the Louisiana Code of Evidence and other rules governing the admissibility of evidence. If the law enforcement officials and the technicians did not comply with the DPSC regulations, then the results will not be admissible in evidence if the prosecution relies on the statutory presumption of
intoxication provided by LSA-R.S. 32:662 that resulted as a consequence of the blood test. ((8. State v. Rowell, 517 So.2d 799, 801-802 (La. 1988).))
What is the Statutory Presumption of Intoxication?
The results of a blood alcohol can lead to certain legal presumptions in a DUI or DWI trial regarding a motorist’s intoxication while he was operating a motor vehicle. These presumptions can be used by the district attorney to prove that the motorist was driving while intoxicated. Under La. R.S. 14:98(A)(1)(b), the prosecution can obtain a conviction for DWI if it proves that the defendant was operating a motor vehicle when his blood alcohol concentration (BAC) is 0.08 or more by weight based on grams of alcohol per one hundred cubic centimeters of blood.
When the State proves that a motorist’s BAC level was 0.08% or more, the State has met its burden of proving that the operator of a motor vehicle was intoxicated.
What if the motorist BAC was less than 0.08?
If the motorist’s blood alcohol concentration (BAC) at that time of the arrest as determined by a chemical test was 0.05 percent or less by weight, it is presumed that the motorist was not under the influence of alcoholic beverages. If the motorist’s BAC at that time of the arrest was in excess of 0.05 percent but less 0.08 percent by weight, this fact does not give rise to any presumption that the motorist was or was not under the influence of alcoholic beverages.
However, this fact may be considered with other competent evidence in determining whether the person was under the influence of alcoholic beverages. ((9. La. R.S. 32:662)).