Thymol is a suitable preservative for uric acid standards in the uricase technique.

336 CLINICALCHEMISTRY, Vol.25,No. 2, 1979 capillary, the nine negative specimens were sampled and processed. This experiment was repeated with a plastic capillary. With the glass capillary, the first specimen was positive as expected, but the next eight specimens were also positive. The last specimen was negative. For the plastic capillary, the first specimen was positive and the next three originally negative specimens were now positive. The last six negative specimens were still negative. These experiments clearly demonstrate that carryover of HB9Ag is significant enough to give an erroneous result on a number of successive specimens, depending upon the type of capillary used. We did another experiment to determine how feasible it would be to wash the capillary with several water rinses before sampling the next specimen. Even though our first experiment indicated that counts were reduced to background after six washes with glass capillaries and after three washes with plastic capillaries, as many as 10 rinses, in some cases, did not prevent a negative specimen following a positive specimen from also being positive. Twenty washes did, however, eliminate the problem. In HB5Ag testing it is not practicable to wash 20 times between each specimen; the best solution is to use a new tip or capillary for each specimen.