Adsorption onto hybrid hectorite-hydroxyethyl cellulose composite as a pre-concentration method for the spectrophotometric quantification of a cationic organic molecule, irinotecan

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This study develops a pre-concentration methodology for pharmaceutical irinotecan, as a model cationic organic molecule. The methodology is based on the adsorption and quasi-desorption of irinotecan onto a hybrid hectorite clay-hydroxyethyl cellulose composite (Bentone LT). Upon incubation of the loaded composite with mixtures of acetone:water or acetonitrile:water, at a specific range of relative volumes, fast and massive composite expansion was observed macroscopically. Ιrinotecan could be assayed in the supernatant, most likely still bound onto delaminated clay (i.e. quasi-released), at concentrations up to about 90% of the loaded compound. Constant quasi-release efficiency was verified, independent of irinotecan concentration in the loading medium. The effect of salt concentration in loading and release medium and of adsorbate-to-adsorbent ratio on irinotecan quasi-release was investigated.Bentone LT adsorption/quasi-release-based methodology was validated as a pre-concentration step for photometric quantification of irinotecan in dilute aqueous solutions. Standard curves were linear over the concentration range of 31 to at least 700 ng/mL. A pre-concentration factor of 76.8-fold was achieved. Pearson's coefficient of determination for calibration curves prepared on different days was ≥0.980 for all 7 replicate irinotecan quantifications in aqueous solutions of 42 mL. Percent Coefficient of Variation (CV%) on all quality control levels was ≤13.03% for repeatability and ≤ 12.83% for intermediate precision. Bias was ≤ ±9.9% on all quality control levels. The Limit of Detection (LOD) and Limit of Quantitation (LOQ) were determined to be 10.38 and 31.44 ng/mL, respectively. This is around 30 times lower than in the hyphenated-assay non-complemented by a pre-concentration step. These results indicate that the proposed pre-concentration method allows quantitative determination of the studied cationic organic with acceptable analytical characteristics, in dilute aqueous solutions.