Blood alcohol measurements determined by headspace gas chromatography have been challenged on the grounds that the presence of the preservative sodium fluoride in blood samples artificially increases headspace alcohol concentrations due to a salting out effect. Blood samples containing varying amounts of ethanol and sodium fluoride (NaF) were tested using semi-automated headspace gas chromatography with n-propyl alcohol as the internal standard to assess the validity of this challenge. Miller et al found, in fact, that under these test conditions the measured alcohol levels are systematically depressed as the amount of sodium fluoride in the blood sample increases.
Blood was drawn from each of six subjects near the time of estimated peak blood alcohol concentration. Each subject had three blood samples taken to which 0, 5, and 10mg/mL of NaF were added. The blood alcohol concentration for each tube was determined twice for each tube
data(salting1.df)A data frame containing four variables
| [,1] | subject | numeric factor | subject identifier 1-6 |
| [,2] | tube | numeric factor | tube 1,2,3 for each subject |
| [,3] | rep | numeric factor | levels 1,2 indicating replicate measurement |
| [,4] | NaF | numeric factor | the level of sodium fluoride added in mg/mL |
| [,5] | conc | numeric | alcohol concentration in g/100mL |
Note that the blocking and treatment factors in this data frame are
numeric. Therefore, to use them as such will require the use of factor
or ordered.
B.A. Miller, S.M. Day, T.E. Vasquez, F.M. Evans, Absence of salting out effects in forensic blood alcohol determination at various concentrations of sodium fluoride using semi-automated headspace gas chromatography, Science & Justice, Volume 44, Issue 2, April 2004, Pages 73-76.