Letter: Hair-metal binding.

reduce the MMT partial pressure to an even smaller value. It is obvious from the above that the po£-sibility of hazardous exposure of customers has to be much lower even than would be the case for TEL. When this is considered in light of the studies of Kehoe et al. in the 1960s on lead alkyls and service station attendants (who would have more exposure than self-service customers) in which it is concluded that no hazard existed, it would be extremely difficult to visualize the possibility of any hazard from use of MMT. Dear Sir: We noted in a recent publication by Hin-ners et al. (1) that they had taken care to evaluate potential interferences in their atomic absorption spectrophotometric analyses of hair for sodium, magnesium, potassium , calcium, manganese, iron, nickel, copper, zinc, cadmium and lead. We were initially pleased to note that full recoveries indicated no interferences since we had earlier reported that there were no interferences when atomic absorption was used to determine cadmium, copper, lead and zinc (2). However, we did find the use of the expression full recoveries unusual since the percent recovery for each metal is usually reported and should have been included in this publication. On reading further we were disappointed to find a poor sense of logic in their discussion of interferences. These authors had suggested that: since additions of standards to portions of both their extracts and digests gave full recoveries indicating no interferences, calibration by the method of standard additions was not necessary. What is confusing here is that additions of standards to portions of the extracts and digests is calibration by the method of standard additions. This error in logic is compounded by their statement tMaT: the use of the method of standard additions seems redundant after demonstrating that interference was absence, since they had apparently used the method of standard additions to obtain the results which indicated a lack of interferences. We presume that the end of their above statement should have been more correctly written as: interferences were absent. We also wish to point out that additions of standards to digests can not be used to claim total recovery since this technique does not evaluate losses, if any, in the process of digestion. It would have been better to have added the standards to the hair samples prior to digestion. It does seem redundant that these authors …