The supercritical fluid extraction (SFE) behavior of cocaine and its major metabolite benzoylecgonine (BZE) was investigated and found to be highly dependent upon the chemical nature of the matrix and the manner in which the target drug analytes are incorporated into or on the matrix. The recovery of cocaine from Teflon wool, filter paper, drug-fortified hair, and drug user hair was studied using a variety of CO2/modifier mixtures. Incorporation of a triethylamine (TEA)/water modifier mixture provided dramatic improvements in the recovery of cocaine from interactive matrixes. The results suggest that the SF extractability of cocaine is not limited by analyte solubility; rather, desorption of cocaine from hair binding sites is a rate-limiting step in the SFE process. A displacement SFE mechanism is hypothesized in which TEA (as the triethylammonium cation) competes with cocaine for negatively charged hair binding sites. The dependence of extractability on hair/drug binding interactions allows the differentiation of cocaine present at different discrete sites in hair based on differences in SFE behavior. These findings suggest the potential for distinguishing exogenous (i.e., environmental) from endogenous (i.e., physiological) sources of drugs in hair. In contrast to the results observed for cocaine, SFE recoveries of BZE were poor from all matrixes and under all conditions studied. Its increased polarity, the presence of an additional binding site, and the possibility of multiple charged states suggest that poor BZE recoveries may be due to both poor analyte solubility and failure to desorb the analyte from hair binding sites under the conditions employed.
Supercritical fluid extraction‐radioimmunoassay (SFE‐RIA) was evaluated as a rapid screening tool for the detection of cocaine residues in human hair. SFE was performed using carbon dioxide modified with triethylamine (TEA) and water, with off‐line collection of extracted cocaine in methanol. Extracts were analyzed for the presence of cocaine using a commercially available solid‐phase RIA kit. In order to develop a suitable RIA calibration method for reliable measurement of cocaine in SF extracts, calibration data was compared for methanolic standards both with and without the presence of the SF modifier. Methanol had only a minor impact on immunoassay performance, producing an 11% decrease in maximum binding counts. In contrast, the presence of TEA/H2O profoundly degraded assay performance, producing a 60% suppression in assay counts. To preserve RIA sensitivity, SF extracts were evaporated under nitrogen to remove the modifier and reconstituted in methanol for RIA analysis. Incorporation of the evaporation step permitted the use of modifier‐free cocaine calibrators in methanol. Calibration data was ät to a four‐parameter logistic model. SFE‐RIA analysis of a series of drug‐free hair samples established an RIA cut‐off value for distinguishing between a negative and presumptive positive cocaine sample at an SF extract concentration of 1.2 ng/mL, or a hair concentration of 0.07 ng/mg. The robustness of the SFE‐RIA method was demonstrated by the analysis of a variety of hair samples from both drug users and non‐users. The quantitative SFE‐RIA findings correlated well with the values obtained by an acid incubation/GC‐MS method. © 1996 John Wiley & Sons, Inc.
Abstract. Supercritical fluid extraction-radioimmunoassay (SFE-RIA) was evaluated as a rapid screening tool for the detection of cocaine residues in human hair. SFE was performed using carbon dioxide modified with triethylamine (TEA) and water, with off-line collection of extracted cocaine in methanol. Extracts were analyzed for the presence of cocaine using a commercially available solid-phase RIA kit. In order to develop a suitable RIA calibration method for reliable measurement of cocaine in SF extracts, calibration data was compared for methanolic standards both with and without the presence of the SF modifier. Methanol had only a minor impact on immunoassay performance, producing an 11% decrease in maximum binding counts. In contrast, the presence of TEA/H,O profoundly degraded assay performance, producing a 60% suppression in assay counts. To preserve RIA sensitivity, SF extracts were evaporated under nitrogen to remove the modifier and reconstituted in methanol for RIA analysis. Incorporation of the evaporation step permitted the use of modifier-free cocaine calibrators in methanol. Calibration data was fit to a four-parameter logistic model. SFE-RIA analysis of a series of drug-free hair samples established an RIA cut-off value for distinguishing between a negative and presumptive positive cocaine sample at an SF extract concentration of 1.2 ng/mL, or a hair concentration of 0.07 ng/mg. The robustness of the SFE-RIA method was demonstrated by the analysis of a variety of hair samples from both drug users and non-users. The quantitative SFE-RIA findings correlated well with the values obtained by an acid incubation/GC-MS method. 0 1996 John Wiley & Sons, Inc.
Chemical solubility and equilibria are paramount for understanding everyday systems. Recent events have led to more interest by the general public in chemical equilibria that occur in drinking water systems. This presents a great opportunity to increase student interest and engagement in the more complicated aspects of chemical equilibria. Shiny Apps allow exploration of complex equilibria without requiring that students (or instructors) get buried in the minutia. The application presented here, https:// bazilio.shinyapps.io/LeadSolubilityCaseStudy/, can be used for instruction in chemistry or environmental science and only uses an internet browser such as Safari or Chrome; it is compatible with mobile browsers. Students are assigned a case study on the Flint, Michigan Water Crisis which guides them through lead sulfate, chloride, phosphate, and hydroxide equilibria, using the app to explore their intuitions about this complex chemical system.
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