Nitrite determination in human plasma and synovial fluid using reactions of nitric oxide with 3,5-dibromo-4-nitrosobenzenesulphonate (DBNBS)

DBNBS (3,5 -dibromo-4-nitrosobenzenesulphonate) reacts with nitric oxide (N O) produced from nitrite ions in acid solution to give a radical with a cha racteristic electron spin resonance spectrum, attributable to a 'DBNBS-NO' product, and comprising a triplet with a(N) = 0.96 mT. This is identical wi th the spectrum obtained when NO, introduced from the gas phase, reacts wit h DBNBS. Under certain conditions, an additional signal is observed, attrib utable to oxidation of DBNBS to the radical cation, DBNBS.+ (a triplet with aN = 1.32 mT). Conditions are described for the determination of nitrite, which avoid this DBNBS oxidation. The height of the low-field signal from t he DBNBS-NO product is directly proportional to the nitrite concentration u p to about 0.08 mM nitrite. The method has been applied to the measurement of nitrite concentrations in whole blood, plasma and synovial fluid taken f rom rheumatoid arthritis patients. In order to avoid the oxidation of DBNBS when analysing biological samples of this type, it is necessary to treat t he specimen by ultrafiltration as soon as possible after collection and bef ore addition of DBNBS, (C) 1999 Elsevier Science B.V. All rights reserved.