Uncertainty of Blood Alcohol Concentration (BAC) Results as Related to Instrumental Conditions: Optimization and Robustness of BAC Analysis Headspace Parameters

Abstract

Analysis of blood alcohol concentration is a routine analysis performed in many forensic laboratories. This analysis commonly utilizes static headspace sampling, followed by gas chromatography combined with flame ionization detection (GC-FID). Studies have shown several "optimal" methods for instrumental operating conditions, which are intended to yield accurate and precise data. Given that different instruments, sampling methods, application specific columns and parameters are often utilized, it is much less common to find information on the robustness of these reported conditions. A major problem can arise when these "optimal" conditions may not also be robust, thus producing data with higher than desired uncertainty or potentially inaccurate results. The goal of this research was to incorporate the principles of quality by design (QBD) in the adjustment and determination of BAC (blood alcohol concentration) instrumental headspace parameters, thereby ensuring that minor instrumental variations, which occur as a matter of normal work, do not appreciably affect the final results of this analysis. This study discusses both the QBD principles as well as the results of the experiments, which allow for determination of more favorable instrumental headspace conditions. Additionally, method detection limits will also be reported in order to determine a reporting threshold and the degree of uncertainty at the common threshold value of 0.08 g/dL. Furthermore, the comparison of two internal standards, n-propanol and t-butanol, will be investigated. The study showed that an altered parameter of 85 °C headspace oven temperature and 15 psi headspace vial pressurization produces the lowest percent relative standard deviation of 1.3% when t-butanol is OPEN ACCESS Chromatography 2015, 2 692 implemented as an internal standard, at least for one very common platform. The study also showed that an altered parameter of 100 °C headspace oven temperature and 15-psi headspace vial pressurization produces the lowest MDL of 0.00002 g/dL when n-propanol is implemented as an internal standard. These altered headspace parameters have the potential to produce more precise and accurate BAC determination.

Comparative Study of Sample Carriers for the Identification of Volatile Compounds in Biological Fluids Using Raman Spectroscopy

“…The GC methods, also, can achieve very low limits of detection (LoDs) of alcohol in blood reaching as low as 10 μg/mL or 12.5 nL/mL [ 10 ] while using rather low quantity (100–500 μL) of the biological sample [ 10 , 11 , 12 ]. Although the GC methods are the most reliable in measuring the alcohol levels in human body fluids, they often suffer from sample preparation issues [ 13 ]. Moreover, GC is a destructive technique for the sample, while experienced personnel are required for the preparation of the samples and their analysis.…”

Quantification Bias in Blood Alcohol Determination by Headspace Gas Chromatography

“…The majority of these materials are aqueous solutions produced according to ISO Guide 34 and satisfy the regulatory needs posed by ISO 17025. However, the opportunity to use aqueous calibrators to quantify BRIEF REPORT blood samples should be carefully evaluated, even if an internal standard is used to correct for the differences among samples and calibrators 5,6 . The actual efficacy of the internal standard needs to be experimentally verified.…”

“…A "good" internal standard is chemically similar to ethanol without any chromatographic overlap with the target substance or other volatiles that could be present in the samples (e.g., acetone, methanol or acetaldehyde). n-propanol is commonly considered the best suited substance for this purpose, even if t-butanol is also used 5,6 . The samples can also be diluted with water up to practically correct for the matrix mismatch (usually a 1:10 dilution is sufficient) 7 .…”

Comments on: Uncertainty of Blood Alcohol Concentration (BAC) Results as Related to Instrumental Conditions: Optimization and Robustness of BAC Analysis Headspace Parameters. Chromatography 2015, 2, 691–708

“…

The 2015 publication of original research by Boswell and Dorman [1], Uncertainty of Blood Alcohol Concentration (BAC) Results as Related to Instrumental Conditions: Optimization and Robustness of BAC Analysis Headspace Parameters described an evaluation of the effect of modifying headspace parameters on ethanol analysis by gas chromatography with dual flame ionization detection (GC-FID). The data reported may be useful when developing a new method for ethanol analysis, however there are several suggestions and considerations that should be made regarding implementing the protocol, as described in the paper.

1.

…”