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Drunk Driving: Is A Blood Test Really a Blood Test. Gas Chromatography 101

Sep 2nd, 2016 Blood Testing

When you are arrested for drunk driving an officer has a right to request that you submit to a chemical test[1], including a breath, blood, or urine.  The most common request is for a subject to submit to a breath test on a DataMaster (often referred to as a breathalyzer), which is typically because it is an easier option for the officer.  However, in other cases whether by obtaining a warrant or voluntary consent a blood draw is requested.  It is often considered that a blood test is more reliable, but it is absolutely necessary that your attorney understand how a blood test works and how it is analyzed in order to fully represent the interests and rights of someone charged with drunk driving.  The following is a summary of that process:

First, it is important to understand that it truly is not “blood” that is analyzed but rather a comparison of known and unknown volatiles.  Further, it is important to understand that the State “expert” does rather little in the analysis of a sample, and understanding and ultimately cross-examining the witness is grounded in understanding Headspace Gas Chromatography and the Chromatograms.

The Michigan State Police (MSP) Forensic Lab will receive a specimen of a subject’s blood contained in 2 separate 10 ml gray stoppered tubes, which will be contained within a sealed kit[2] that should have been mailed via first class mail by the officer who participated in the blood-draw.  The kit is received by MSP, documented by a lab tech, and stored in their temperature controlled storage room.  The tubes are also presumed to contain a known amount of preservative and anti-coagulant[3] both in an effort to maintain the integrity of the sample.  Therefore, even at this stage, the State does not have your blood but a mixture.

A Lab Analyst will obtain this mixture when they are prepped to run it through a Head Space Gas Chromatograph, and again alter the mixture to something new.  First, the Lab Analyst will take some of the mixture and pour it into a new vessel or tube.  Then the Lab Analyst will use a pipettor (like a syringe) that will withdraw an amount of that mixture and put it into a new vessel while also introducing another new volatile, which in Michigan will be n-propanol and t-butanol[4], which are both types of alcohol but will be introduced in separate vessels or tubes.  The reason for two separate tubes is because the sample will be run through two identical yet separate machines.  Now there will be two tubes, each including the mixture plus a new volatile, which will act as an internal standard.

The next step is to heat this mixture.  The mixture of the blood, the two chemicals from the original tube, the volatile internal standard, are heated in order to reach a partition or equilibrium wherein it is theorized that the amount of analyte in the gas above the liquid represents a known correlation of the analyte in the mixture.  The purpose of this exercise is for the chromatograph to analyze and more specifically separate the gas as it travels throughout the machine.

In Michigan, the process is automated, which means that a pipettor automatically withdraws or siphons an amount of the head space, or gas, from the heated mixture and will inject it into the gas chromatograph through the injection port[5].  Once injected a carrier gas is needed in order to move the volatile gas through the machine.  In Michigan, Helium is utilized to force the gas through, which must be done at constant pressure and flow rate.  This gas, or two gases, will pass through what is called a column[6], which is used to separate in order to measure the volatile.  The column is located in the oven of the machine, which will be heated to a constant temperature[7].  The column is to slow down certain analytes wherein there will be an expected time the analyte will exit the column.  At the end of the column, the volatile is introduced to an FID or a Flame Ionization Detector, wherein the FID passes the sample and carrier gas (and whatever is coming through the column) through a hydrogen air flame.  The FID burns the organic compounds that pass through which create increased ions.  A polarizing voltage attracts these ions to a collecter located near the flame.  The current produced is proportional to the amount of the sample being burned.  This current is sensed by an electrometer, converted to digital form, and sent to an output devise, which ultimately creates the chromatograms that defense counsel have an opportunity to review.

The chromatograms, specifically the subject sample, will indicate the two peaks that have been created.  One peak will be the known volatile, the internal standard, wherein there is an expected time it will pass through the machine and also a known amount that will be measured by determining the area contained under the peak.  The other peak will be the believed ethonal alcohol, wherein the level will be determined by measuring the area under the peak.  Again, this is a comparative analysis.  The calculation that is ultimately made is based upon the software attached to the machine, which is unknown, even to the State, but will result in a measurement of ethanol alcohol in units of grams alcohol per 100 milliliters of blood.

Therefore, this process is assuming the blood was drawn properly, transported and stored properly, that it is mixed properly with an internal standard, that the volatile sample is heated properly, the correct amount of gas was siphoned and then injected, that the carrier gas is at a constant flow, and the oven is held at a constant temperature, and column is the correct length and width and separates the analytes passing through, the FID burns properly, and the detection system detects the correct charges and charts is properly.

This is merely a summary of the events that transpire in analyzing a sample of your blood believed to contain ethanol alcohol, and clearly, to simply accept the result without an educated and experienced attorneys review of the process is mistake that may result in a life changing event.  Therefore, if you have a case that involves the analysis stemming from a blood draw you must be confident that your counsel is confident in understanding this complex process.


[1] MCL 257.625a

[2] Tri Tech Forensics: company contracted with Michigan State Police to provide kits for blood specimen collection.

[3] According to Kit components, each tube contains 100 mg of sodium fluoride and 20 mg of potassium oxalate.

[4] These are internal standards for the gas chromatograph.

[5] Note that the septum is typically replaced once per week and will be recorded in the maintenance records, and may need replacement from cracking, seal issues, and leaks.

[6] Michigan uses Resteck column 30m x .53mm ID

[7] Michigan oven temperature is to 45 degrees C.