The authors of the article cited above respond:

[摘要] Dr. Schmidt’s comments give the false impression that our recently published HPLC method (1) is unable to identify the presence of the C-3 epimer apart from 25(OH)D3 or 25(OH)D2. We routinely achieve levels of chromatographic resolution illustrated in Fig. 1⇓ . Chromatogram A displays elution of the C-3 epimer alone. Chromatogram B shows separation of 25(OH)D3 and its C-3 epimer, a scenario that would be observed for samples from infants <1 year old. Chromatogram C is from a patient receiving vitamin D2 as a supplement. Here the compounds are not baseline resolved, but each has a different retention time, and clearly they do not coelute. Most importantly, the C-3 epimer is not mistaken for 25(OH)D2. Our method has detected the C-3 epimer in nearly 25% of the average 650 samples we test each month. Concentrations of the C-3 epimer are usually <10 μg/L. Thus, we can analyze samples from …

[学科分类] 过敏症与临床免疫学