Evaluation of urinalysis methods used in 35 Israeli laboratories.

The sample-preparation procedure presented here is a little more complicated than adding the internal standard would be, but offers a number of distinct advantages over previously reported methods. The solvent denaturation followed by centrifugation removes protein to such an extent that no precolumn is required to protect the separating column. No tedious sample preparation such as membrane filtering (3) or solvent extraction (5) is required, and no routine, timeconsuming column regeneration is required to maintain the resolving power of the column. Throughout the study we noted no increase in column pressure, which is a harbinger of plugging. We regenerated the column occasionally according to Whatman’s recommendations, to determine if any change in the column was occurring, and noticed none. The day-to-day precision was such that it is obvious that ambient temperature variations have negligible effects on the quantitation, and operation of the column at ambient temperature is in itself a benefit.