Towards non-invasive optical blood alcohol measurement: Multi-variate analysis of in vitro NIR spectra

The long-term aim of our research is to develop near infra-red spectroscopy for non-invasive measurement of blood alcohol concentrations. The absorption spectrum of ethyl-alcohol could possibly provide the means for such an approach, but the absorption bands of other molecules, such as glucose and acetaldehyde, together with the very low in vivo ethyl-alcohol concentrations (EAC), represent significant analytical challenges. Here we present results of our in vitro investigation of ethyl-alcohol absorption spectra, and the use of multiple linear regression analysis to predict EAC in the presence of glucose and acetaldehyde. We used ethyl-alcohol and mixed solutions of ethyl-alcohol, glucose, and acetaldehyde. The latter were divided into three experimental systems as ethyl-alcohol/glucose, ethyl-alcohol/acetaldehyde, and ethyl-alcohol/glucose/acetaldehyde solutions. The range of EAC used was the same as that found in blood. The results showed good correlation between the actual EAC and the predicted EAC (control; R = 0.99, mean absolute error (MAE) = 0.12 mg/ml: glucose system; R = 0.97, MAE = 0.18 mg/ml: acetaldehyde system; R = 0.99, MAE = 0.23 mg/ml: glucose & acetaldehyde system; R = 0.98, MAE = 0.19 mg/ml). We conclude that the change of glucose and acetaldehyde concentration does not measurably affect the absorption bands of ethyl-alcohol.