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Liquid Phase Extraction

المؤلف:  Max M. Houck، Jay A. Siegel

المصدر:  Fundamentals of Forensic Science

الجزء والصفحة:  p361-362

2026-08-11

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Liquid Phase Extraction

In order to accomplish an efficient separation, the pH range of the drug must be known. Most drugs are either acidic or basic in aqueous solutions. A few drugs, such as caffeine are neutral. An acidic drug is one whose pH is between 1 and 7, and a basic drug has a pH between 7 and 14. The pH dictates the method of extraction. As an example, consider a urine sample containing cocaine. Urine is very acidic and cocaine is a basic drug. In an acidic medium, then, cocaine would exist in what is known as the salt (ionic) form. The cocaine has an H+ attached to it and there would be an anion such as Cl− present. This form of cocaine is very soluble in urine. If the solution is made basic, the cocaine reverts to its free base form as plain cocaine. This form is not soluble in urine or other aqueous solutions and the cocaine would precipitate out. An organic solvent is then added in which the cocaine is very soluble. This solvent doesn’t mix with the urine and thus the cocaine can be efficiently separated from the urine this way. Acidic drugs such as the barbiturates can be extracted from urine using an acid extraction rather than a basic extraction. Liquid phase extraction is not a suitable technique where two or more acidic or basic drugs are known to be present. This is because all of the acidic or basic drugs will be extracted together and they cannot be separated by this method.