THE DETERMINATION OF INORGANIC SULFATE IN SERUM AND SYNOVIAL-FLUID BYHIGH-PERFORMANCE ION CHROMATOGRAPHY

A method for the determination of inorganic sulphate based on high per formance ion chromatography is presented. The separation was performed on an anion-exchange column with a 1.8 mmol/l sodium carbonate/1.7 mm ol/l sodium hydrogen carbonate-buffer, pH 10.35. Conductivity of the e luate was monitored after suppression of the background conductivity c aused by the eluent-buffer. Serum and synovial fluid samples were prep ared by ultrafiltration through membranes with a molecular mass cutoff of M-r 10000. The viscosity of the synovial fluids was reduced by tre atment with hyaluronate lyase before ultrafiltration. The method showe d a linear response for sulphate concentrations between 0.5 and 1000 m u mol/l. The limit of detection was 1 mu mol/l for aqueous standards. For serum the coefficient of variation within-run was 2.3%-2.4%, the c oefficient of variation between days 2.9%-3.1%. For synovial fluids th e coefficient of variation within-run was 3.1%-3.4%, the coefficient o f variation between days 4.6%-5.7%. Standard recovery experiments perf ormed by spiking pools of human sera containing low sulphate concentra tions with sulphate concentrations between 5 mu mol/l and 40 mu mol/l showed recoveries between 98.9% and 100.6%. The corresponding experime nts with pools of synovial fluids showed recoveries of 98.3% to 100.9% . As determined from 127 serum samples the reference range for sulphat e was 262 mu mol/l-420 mu mol/l, with a mean value of 314 mu mol/l. No dependence on age or sex was observed. The sulphate concentration in 36 synovial fluids from knees affected by inflammatory processes showe d a mean value of 424 mu mol/l and a standard deviation of 70 mu mol/l . In 41 synovial fluids from knees affected by chronic degenerative jo int disease, the sulphate concentrations were statistically significan tly lower, with a mean of 374 mu mol/l and a standard deviation of 58 mu mol/l. The concentrations of sulphate in the synovial fluids were s tatistically significantly higher than those in the serum samples used for determination of the reference range. Following the oral applicat ion of a subtoxic single dose of acetaminophen (32.5 mg/kg body weight -62.5 mg/kg body weight) to 4 healthy volunteers, there was a signific ant decrease in the concentration of sulphate in serum with a minimum at 4-5 h after application of the drug. The cumulative concentration d ecrease of sulphate in serum and the kinetic constant of the sulphate depletion were not correlated with the applied acetaminophen dose norm alized for body weight.