TOLERANCE
Tolerance is defined as the diminution of the effectiveness of a drug after a period of prolonged or heavy use of that drug or a related drug (cross-tolerance).
Two types of tolerance are relevant with alcohol. 1) Metabolic Tolerance occurs when the body oxidizes, or metabolizes, ethanol at a higher than standard rate. In some instances, chronic alcoholics can metabolize ethyl alcohol 72% faster than a normal adult. Severe alcoholic can actually achieve peak blood alcohol concentrations with a lesser amount of alcohol.
2) Functional Tolerance occurs when the bodily organ actually becomes desensitized. In some instances, documented by studies, abusers of alcohol can tolerate as much as two times the amount of alcohol with the same level of affect. It is difficult to determine the level of functional impairment, as each individual develops a different level of tolerance.
GENDER & AGE DIFFERENCES
As stated previously, the amount of water each person possesses will affect the concentration or Molar (M) strength of ethanol within the bloodstream. Certain body types possess greater and lesser relative percentages of water.
A sweeping generalization is to state women tend to have a lower percentage of water weight and a higher percentage of fat.
As such, a woman would be more greatly affected by the same amount of alcohol as a man due to the greater ethanol concentration. Women with a lower body fat percentage, such as a professional athlete, would similarly have a greater water weight than a rotund male.
The amount of water the body possesses as we age becomes lower. Even without an increase of weight, elder adults slowly "dry out." With a lesser amount of overall water within the system, a smaller amount of alcohol is increasingly potent. The following table is a good reference point for determining the differences between gender and age.
Average Total Body Water
Age Male Female
18 to 40 61% 52%
over 60 51% 46%
Another interesting disparity among the sexes is the apparent ability of women to more efficiently eliminate from the body. Frankly, the reasons for such are unknown. No scientific study has conclusively proven whether women metabolize alcohol more easily through the liver, excrete it through the skin or exhale it through respiration. Some studies have shown woman can rid their bodies of alcohol at a rate of 10% faster than men.
THE ALCOSENSOR: HOW IT WORKS
The AlcoSensor uses an electrochemical fuel cell. Most experts believe the fuel cell converts ethanol to acetic acid through a chemical reaction. If you recall, that is what the liver does in the human body during metabolism. Again, acetic acid is the chief component of vinegar.
During the testing, the conversion produces two free electrons per molecule of alcohol. The upper surface of the fuel cell is where the transfer of electrons takes place. Hydrogen ions, which carry a positive charge (H+) are released in the process. That positive charge is transferred to the lower surface of the fuel cell.
Due to the reaction process, the upper surface of the plate becomes inundated with excess electrons. The lower surface ends up with too few electrons. Once the two surfaces are connected, a current of electricity flows to equalize the respective surface charges. This current is a direct indication of the amount of alcohol consumed by the fuel cell. Measuring the electrical current created, testing devices establish a numerical value. With increasing levels of ethanol the current strength is increased.
Because of the expense of Infra Red (IR) technology (which is incidentally used on the Intoxilzyer 5000), companies that produced breath sampling machinery began to perfect less sophisticated, yet reasonably reliable machines.
An English scientist is credited with discovering the fuel cell in the early 1800's. Into a bath of acid, sulfuric to be exact, he placed two platinum bars or electrodes. He then supplied hydrogen to one electrode and oxygen to the other electrode. A current of electricity was created, which is now known as a fuel cell.
In the 1960s, researchers at the University of Vienna demonstrated a fuel cell that reacted only to ethanol. This evolved into the present-day cell used in all fuel cell based breath alcohol measurement instruments.
The fuel cell within the Alcosensor utilizes platinum electrode, known as "platinum black." Impregnated within the electrode, there is a layer of an acidic solution. The diagram supra is drawn indicating a "porous layer with electrolyte."
A porous surface is one in which substances can generally pass through easily. At the electron size, it works roughly like a screen on the front porch door. The porous surface is mixed with an electrolyte. Electrolytes are a general category of chemicals that allow for the efficient transfer of energy. Essentially, they allow electrons to pass between substances without stealing or adding electrons during the transfer.
The key to alcosensor testing is to utilize chemical compounds that create an electrical current only when exposed to C2H5OH. That unique chemical reaction transfers some of the positive electrons from the ethanol, to the top platinum plate, through the porous electrolyte zone, down to the bottom platinum plate. The difference in charges between the platinum plates is then measured.
Electrochemical devices have become increasingly more reliable since the 1970's. Many of the initial problems with the technology did not necessarily involve the science of the fuel cell itself. Instead, the method of obtaining the requisite sample and allowing its release were problematic.
Some fuel cells were "tricked" or indicated false-positive results because previously sampled ethanol was allowed to leak back into the testing chamber. Other machines were plagued by the inability to measure the electron variance between the plates. In some instances, the method of measuring the electrical current used too much energy.
Other devices could accurately detect high levels of ethanol, but were completely inaccurate with lower percentages of alcohol. Given the nature of the driving while impaired laws, minimal differences could have monumental effects. Fuel cell response now covers a complete range of alcohol concentration expected in breath. This range is from 5 to 900 parts per million (PPM) of ethanol in the sample.
When a precise volume of breath sample is passed across a fuel cell, the amount of electricity from the cell rises from zero to a peak number. As all the electrons are used up or transferred, the electrical charge then decays back to zero.
The Intoximeters, Inc., AlcoSensor III uses what is called a "peak measurement technique." Of the different methods available, it is likely the most accurate. Its major flaw, if it may be considered such, is the amount of time it takes to convert the electrical current. Added time is the result of increased accuracy.
For all breath alcohol measurement devices, it is critical to obtain a deep lung sample. In the past, most instruments using fuel cells introduced a sample across the fuel cell by drawing this sample through a small port connected to a pump mechanism. That process caused problems and frequently unreliable test results.
Intoximeters, Inc., came up with a unique mechanism for drawing deep lung breath samples in its AlcoSensor III, AlcoSensor IV and AlcoMonitors. It works similarly to a piston within an engine. The down-stroke draws in the air, which amounts of approximately 1cc. All alcohol drawn in by the sampling stroke is continuously exposed to the fuel cell surface.
There are only two stroke operating positions. With such simplicity, the sampling is very fast and relatively consistent. The alcosensor, after having confirmed no residual alcohol remains in the sampling chamber, is "cocked" for the test. Simultaneously the port, or opening through which the sample is drawn is sealed off with suction, thereby creating somewhat of a vacuum over the top platinum surface.
COMPARITIVE ANALYSIS & INCORRECT RESULTS
Alcohol specificity in testing remains an issue in fuel cell technology. In the early 1990's, investigators at the University of Tennessee at Memphis measured the response of fuel cells to substances other than ethyl alcohol. The list was created based upon those chemicals scientists anticipated might be present at the time of testing.
The instruments used in the study were the AlcoSensor III and AlcoSensor IV, as created by Intoximeters, Inc. During testing, different chemicals were introduced to the fuel cell electrode surfaces. The tests were broken down into two, separate phases. In Phases I and II, the investigators used an AlcoSensor III and an AlcoSensor IV connected in series.
Phase II used alcohol concentrations of 0.1 gm/dl to test the response of both instruments separately to ethanol, methanol, and isopropanol. Essentially, they tested the machines both to the know concentration of substances introduced and compared the repetitive machinery to one-another. The tables below show an abbreviated listing of the investigation's results.
Realistically, the alcohol specificity of the fuel cell is quite efficient. As the test results indicate, the electrochemical response is extremely accurate and not easily subject to misidentification. That is not to say the machine is infallible. There are instances when the machine will indicate positive tests results, even when the subject has not consumed an alcohol beverage. The two most common
Phase I / Test Results Substance Vapor Concentration AlcoSensor III Response AlcoSensor IV Response
(mg/l) (gm/dl) (gm/dl)
Acetaldehyde 0.1 0.002 0.002
Acetone 0.1 0.0 0.0
Acetonitrile 0.1 0.0 0.0
Benzene 0.05 0.0 0.0
2-Butanol 0.1 0.001 0.002
Carbon Monoxide 0.05 0.0 0.0
Contact Cement 0.06 0.0 0.0
Cyclohexane 0.1 0.0 0.0
Diethylether 0.1 0.0 0.0
Ethylacetate 0.06 0.0 0.0
Gasoline 0.1 0.0 0.002
Isoprene 0.1 0.002 0.002
Isopropanol 0.06 0.006 0.005
Lacquer Thinner* 0.1 0.002 0.002
Methane 0.1 0.0 0.0
Methanol 0.04 0.009 0.008
MEK 0.06 0.0 0.0
n-Pentane 0.1 0.0 0.0
n-Hexane 0.1 0.0 0.0
n-Heptane 0.1 0.0 0.0
n-Octane 0.1 0.0 0.0
Mineral Spirits 0.1 0.0 0.0
Tetrachloroethylene 0.05 0.0 0.0
Toluene 0.05 0.0 0.0
111-Trichlorethane 0.1 0.0 0.0
Trichlorethylene 0.1 0.0 0.0
Xylene 0.1 0.0 0.0
*contained alcohol Phase II / Test Results Substance Equivalent BAC
AlcoSensor III Response AlcoSensor IV Response
Ethanol 0.1 0.100 0.100
Methanol 0.1 0.043 0.047
Isopropanol 0.1 0.042 0.042