Cyclodextrin-Modified Micellar UPLC for Direct, Sensitive and Selective Determination of Water Soluble Vitamins in Milk

Abstract

Cyclodextrin-modified micellar ultra pressure liquid chromatography (CD-MUPLC) was firstly developed and directly applied to the simultaneous determination of water-soluble vitamins thiamine hydrochloride (VB1), pyridoxine hydrochloride (VB6) and ascorbic acid (VC) in milk samples. A hybrid isocratic mobile phase consisting of β-cyclodextrin (β-CD, 5.0 mmol L−1) and cetyltrimethylammonium bromide (CTAB, 0.1 mol L−1) in the presence of acetic acid (0.1 mol L−1) at pH 2.9 on a RP-C18 column at 25.0°C was successfully used. The separation of vitamins was achieved in less than 10 min at a 0.2 mL min−1 flow rate showing adequate linearity at 245 nm in the ranges of 5.0–500.0 μg L−1 for VB1, 5.0–1000.0 μg L−1 for VB6 and 5.0–10000.0 μg L−1 for VC with coefficients of variation (r2) of 0.9999, 0.9987 and 0.9971, respectively. In addition, limits of detection obtained were 0.885, 1.352 and 1.358 μg L−1 and limits of quantification were 2.681, 4.096 and 4.115 μg L−1 for VB1, VB6 and VC, respectively. The high sensitivity of the proposed CD-MUPLC-UV method permitted its applications to the determination of water-soluble vitamins VB1 (32–488 μg L−1), VB6 (82–95 μg L−1) and VC (790–45000 μg L−1) in breast and bovine milk samples. The relative standard deviations and recoveries ranged between 0.07 and 2.14% and between 85.27 and 114.8%, respectively, indicating the accurate and precise measurements without any negative impact of matrix. The current analytical method illustrated several advantages including direct, sensitive, selective and non-consuming organic solvents over the hitherto published methods. These features could be attributed to the four-point competitive interactions among analytes, pseudostationary phases and modified C18 stationary phases.

A Simple and Reliable Liquid Chromatographic Method for Simultaneous Determination of Five Benzodiazepine Drugs in Human Plasma

“…Figure 3 shows that working at buffer pH 7.0 led to an increase in the column efficiency (ranged from 16,000 to 26,000 N/m) and asymmetry factor (AS) (bromazepam = 1.00, clonazepam = 1.05, diazepam = 1.20, lorazepam = 1.14, and nordiazepam = 1.00), which is probably due to its effect on the sharpness of the peaks. On the other hand, it is well known for the most robust retention conditions, the mobile phase pH should be beyond 1.5 units from the compound's pKa, where ionization is entirely suppressed [19,20]. Therefore, buffer pH 7.0 was chosen as the optimum pH for the simultaneous separation of selected BZD drugs.…”