VMA-SKREEN |
SUMMARY
| The VMA-Skreen procedure is a quantitative test for the measurement of VMA in urine. VMA is a major urinary metabolite of epinephrine and norepinephrine, and is excreted in increased amounts in almost all cases of pheochromocytoma and neuroblastoma. The VMA-Skreen technique eliminates most substances that have been sources of interference in VMA methods that do not use a TLC purification step. Purification is achieved by using a silica gel column. Twenty-eight samples can be analyzed in approximately 2 hours (45 minutes tech. time) using the 28 place Multi-Prep work station. PRINCIPLE The method involves a pre-extraction of 3 ml urine (pH 1-2) with ethyl acetate to isolate VMA from metanephrines, and most urinary metabolites that are not strongly acidic. After adsorption of the ethyl acetate fraction on the VMA-Skreen Column, interfering substances such as vanillic acid and 3-methoxy, 4-hydroxy phenylethylene glycol are removed with a simple washing step. VMA is eluted with deionized water and reacted with diazotized p-nitroaniline. The colored complex is further purified by extraction into ethyl acetate. The characteristic violet color is read at 570 nm. Other similar compounds not previously removed, fail to react significantly (pale yellow, yellow-green, green) or react (yellow, yellow-orange, salmon-pink) without producing the characteristic violet color.
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