Supercritical fluid extraction of chloramphenicol from milk and human serum using an analog modifier

Supercritical fluids have solvation power similar to liquids, but also possess higher diffusion coefficients and lower viscosities at the same temperature. Supercritical fluids have the potential to extract analytes at a more rapid extraction rate than possible with liquid extraction. Generally, supercritical fluid extraction (SFE), can provide extraction efficiencies comparable to Soxhlet methods, but only take 30-45 minutes, a fraction of the time needed for Soxhlet extraction, which can take up to 16 hours.;Most SFE extractions are done with non-polar carbon dioxide. Adding a polar liquid such as methanol to the carbon dioxide will increase its polarity. Only limited amount of methanol can be added, since increasing the percentage of methanol as a modifier may lead to phase separation and loss of extraction efficiency.;Antibiotics and drugs are both high in polarity and molecular weight. Chloramphenicol (CAP), an antibiotic has a molecular weight of 323.14 dalton and polar groups (aromatic nitro group, one primary and one secondary alcohol groups, secondary amino group, and keto group).;Chloramphenicol from milk and human serum can be trapped on silica gel. Modifiers that compete with chloramphenicol for silica gel active sites dramatically increase extraction yield. The effectiveness of these modifiers in increasing the extraction of chloramphenicol is determined by their structure and functional groups present.;Methanol modified supercritical carbon dioxide has been used to extract trapped CAP from silica gel. A second modifier, which is called, the analog modifier, may be added along with methanol. The choice of the second modifier depends on the chemical structure of the analyte of interest. The second modifier should possess some structural similarities to the analyte molecule so it can displace the adsorbed analyte from the matrix.;The effects of temperature, pressure, extraction time, percent water, and modifier present on the extraction efficiency have been investigated.;The role of nitromethane, the analog modifier used to extract chloramphenicol from silica gel, was also investigated. The effect of nitromethane alone was demonstrated especially with pure silica gel. The extraction efficiency did not change when methanol was used as a second modifier.;The effect of nitromethane and methanol together as modifiers, on the extraction efficiency of CAP from human serum and milk was also investigated. To obtain maximum extraction efficiency two modifiers were necessary. It was found that 42% of the added CAP could be extracted from milk and that CAP could be quantitatively extracted from human serum consistently. It has been found that each modifier may play a different role in the extraction. Nitromethane displaces the polar chloramphenicol molecules from the active silanol groups on the silica gel and protein molecules. Nitromethane may also saturate the remaining free silanol groups on the silica gel and prevents re-adsorption of CAP molecules on the silica gel.;Methanol acts to dissociate the drug-protein complex, and keeps CAP molecules soluble in the supercritical fluid during extraction. Methanol may also prevent re-adsorption of CAP molecules on silica gel by shifting the mass transfer constant to favor the supercritical fluid rather than the silica gel. The extracted chloramphenicol was analyzed by HPLC.