SimultaneousDeterminationof Neoptenn and Creatininein Serum with Solid-Phase Extraction and On-Line ElutionLiquidChromatography

This is a method for the simultaneous determination of neoptenn, a product of interferon-gamma-activated macrophages, and creatininein serum.Acidified,butnotdeproteinized serum is applied to a 4-propylbenzene sulfonic acidmodified silica sorbentcartridge, whichquantitativelyretains the analytes but not the serum proteins.The retained analytes are then eluted from the cartridge directly onto the liquid-chromatographycolumn. Elutionfrom the cartridgeis facilitated by a pulse of 0.4 mol/L, pH 6.8 potassiumphosphate buffer. On isocratic elution from an octadecylsilica column with potassium phosphate buffer (15 mmol/L, pH 6.0), neoptenn is detectedby itsnativefluorescence,creatinineby ultravioletabsorption. Detection limits are 0.5 nmol/L for neopterin,1 Lrnol/Lfor creatinineat a samplevolumeof 100 jL. The standardcurve is linearover the rangeof concentrationsencounteredin sera. For both neopterinand creatinine inserum,concentrationsso measuredagree wellwithresults by establishedmethods.