Efficient and clean pre-concentration of ultra-trace calcium channel blockers from biological matrices via a hyphenated procedure of two sequential dispersive solid/liquid phase microextractions.

In the present work, we propose a safe, simple, and relatively rapid procedure for the efficient clean-up and pre-concentration of ultra-trace calcium channel blockers (CCBs) from the human plasma and urine samples followed by high performance liquid chromatography-ultraviolet detection. The proposed sample preparation method is a combination of two microextraction methods termed as ultrasound-assisted dispersive micro solid-phase extraction coupled with air-agitated liquid-liquid microextraction based on solidification of a floating organic droplet (UA-dμSPE-AA-LLME-SFO). A superior clean-up and a higher pre-concentration factor are two valuable outcomes of the mentioned procedure, leading to an accurate measurement of the therapeutically low concentrations in the biological samples. The basis of the first dispersive micro solid-phase extraction is an effective nano-adsorbent named the PANI-DBSNa/TiO2 nano-composite. It was easily synthesized sonochemically by the in situ chemical oxidative polymerization method as core-sell structures, and subsequently, characterized by different techniques including FESEM, XRD, and TGA. The optimum conditions enriched via the response surface methodology (RSM) consisted of pH 12.1, 23 mg of the PANI-DBSNa/TiO2 nano-composite, a sonication time of 4.3 min, 225 μL of methanol, and 78 μL of 1-undecanol. Under the optimum experimental conditions, the good linear ranges of 4.0-4000, 8.0-10000, and 7.0-8000 ng mL-1 were obtainable for diltiazem, amlodipine, and verapamil, respectively, with the correlation of determinations (R2s) higher than 0.99 and the low limits of detection (LODs) of 1.5-3.0 ng mL-1. The relative standard deviations (%RSDs) were in the span of 5.5-6.5% (n = 3); implying on the satisfactory repeatability (or reproducibility). The enrichment factor (EF) and extraction recovery percentage (%ER) values were found to be 68 and 65% for diltiazem, 80 and 75% for amlodipine, and 46 and 45% for verapamil, respectively.