Investigating the properties of subcritical water extraction with pharmaceutical tablets

Abstract

The properties of subcritical water extraction (SWE) in the sample preparation of pharmaceutical tablets were investigated. Tablets comprised of microcrystalline cellulose excipients broke apart up to 80 times faster in subcritical water than they did in room temperature water, while those containing starch readily broke apart in either. Tablets containing starch were also observed to gelatinize or “paste” over several SWE conditions, impeding subsequent filtration and analysis. This effect was avoidable, however, since it was demonstrated to disappear with increases in extraction time and temperature or decreases in sample size. Using SWE, two common over-the-counter pharmaceuticals were extracted under optimized conditions from tablets comprised of either microcrystalline cellulose or starch excipients. Analyte recoveries of 95% or more were obtained at 150 °C for vitamin C (ascorbic acid) tablets in as little as 8 min for the extraction of a whole intact tablet, 6 min for two half tablets, and 5 min for a ground tablet. By comparison, this occurred at 250 °C in just 2 min for an intact slice of an acetaminophen tablet. Reproducibility was generally quite good with these trials producing RSD values of less than 2%. The results indicate that SWE can be a potentially viable and efficient method for the sample preparation of whole, sliced, or ground pharmaceutical tablets, and further exploration of this approach is promising.