NOx contamination in laboratory ware and effect of countermeasures

Contamination of various types of laboratory wares with NOx (NO2- and NO3-) was assessed systematically and the effect of extensive washing as a count ermeasure was evaluated. Mean NOx contamination arising from a model proced ure for NOx determination in plasma was 0.93 muM (range, 0.35-1.49 muM). Th e major source of contamination included conical tubes (54.8%) and pipette tips used for transfer of solution (12.3-16.3%). Except for soft glassware, most NOx contamination could be washed out by pure water. Although NOx con tamination in respective laboratory wares could be reduced below detection levels by extensive washing, summation of the contamination through the mod el procedure could not be completely abolished (but the effect of washing p ersisted at least 10 days), Heavy contamination was noted in glassware (esp ecially soft glass) and ultrafiltration units, which was difficult to remov e. Several types of vacuum blood sampling tubes contained various levels of NOx. Our results indicated that a small but significant amount of contamin ation remained in laboratory ware even after extensive washing, and that it is advisable to avoid the use of glassware (soft glass), ultrafiltration u nits, and vacuum blood sampling tubes during the processing of clinical sam pling for the measurement of NOx. (C) 2000 Academic Press.