Problems in Commercial Kits of 25-Hydroxy Vitamin D and the Development of Simple, Robust and Faster HPLC Method.

Vitamin D is a lipid-soluble compound that plays a key role in bone mineral metabolism. The commercial current kits and several published assay methods (High-performance liquid chromatography (HPLC) and Immunoassay) are complicated due to the use of multiple reagents, larger sample volume, high backpressure, longer extraction time, evaporation under nitrogen after extraction, significant interference and antibody cross-reactivity. Here we report a new HPLC method for the determination of 25-hydroxyvitamin D2 (25-OHD2) and 25-hydroxyvitamin D3 (25-OHD3) that is simple (no evaporation), rapid (10-minute run time) and robust. Serum sample (300 µl) is mixed with 300 µl acetonitrile containing lauraphenone as internal standard. After vortexing and centrifugation, the supernatant was loaded into C18 extraction cartridges, washed with 70% methanol and then eluted with 200 µl of a mixture of 70% ethanol and 30% isopropyl alcohol (IPA). The eluent was mixed with 50 µl of water and injected into the HPLC-UV system for analysis. The method proved to be linear in the range of 10-750 nmol/L of 25-OHD2 and 25-OHD3. The intra- and inter-assay precision was less than 10 for both compounds at four different concentrations. The method was compared with (LC-MS/MS) and the correlation coefficients (R2) were 0.9454 and 0.9673 for 25-OHD2 and 25-OHD3 respectively. The proposed HPLC method is simple, rapid, robust and free from the most common problems encountered with commercial kits. It can be used in a high-volume laboratory that uses the HPLC method for the simultaneous determination of 25-OHD2 and 25-OHD3 in serum samples.

Accurate determination of Biotinidase activity in serum by HPLC and its utilization as second tier test for the confirmation of initial positive newborn screening results.

Diagnosis of Biotinidase deficiency (BTD) is extremely important to avoid several neurodevelopmental problems in early childhood. Colorimetric and fluorometric methods lack specificity and selectivity due to several interferences resulting in a high number of false positive results. We developed an HPLC method for BTD activity in serum with fluorescent detection. In colorimetric assays, biotinidase attacks the amide linkage of the artificial substrate biotinidyl-4-aminobenzoic acid (B-PABA) and releases p-aminobenzoic acid (PABA), which is converted to a purple dye by diazotization reaction. The newly developed method injects the reaction mixture directly into the HPLC column and quantifies using a six-point calibration curve without coupling and diazotization reaction. The method is linear over the 5-1000 µmol/L range. The detection and quantitation limits were 2.5 µmol/L and 5.0 µmol/L, respectively. When compared with colorimetric assay, the correlation coefficient (R2) was 0.9963. The within-assay and between-assay precision was <10.0% for four levels of quality control samples. No significant variation in BTD activity was detected due to hemolysis, icteric, and lipemic samples. The newly developed method eliminates the potential interference due to the presence of aromatic amines and significantly reduces the false positive results observed with the colorimetric method. It is simple, specific, sensitive, faster in sample preparation, and requires a small sample volume. The newly developed HPLC method was used in our laboratory as a secondary tier test for initial positive BTD samples from newborn screening programs. To our knowledge, no similar HPLC method has been reported to date.

Determination of nicotinamide and 4-aminobenzoic acid in pharmaceutical preparation by LC.

A rapid, precise and time saving high performance liquid chromatographic method has been developed and validated for the simultaneous determination of nicotinamide and 4-aminobenzoic acid in pharmaceutical preparation. The method involves isocratic elution of mobile phase through column in a reverse phase chromatography with UV detection at 254 nm. The ranges of quantification for nicotinamide and 4-aminobenzoic acid were 11-34 microg ml(-1) and 37-113 microg ml(-1), respectively. Investigating specificity, linearity, precision, accuracy, robustness and ruggedness performed the validation of the method.