[Direct determination of ammonia in plasma with indophenol method].

A new method for direct determination of ammonia in plasmas with indophenol reagent is described. It is shown that using sodium citrate as anticoagulant in phosphate buffer within pH 10.5-11.2, indophenol reagent reacts sensitively with ammonia in the plasmas to form a stable blue compound with a maximum absorption at 630 nm with low interference. The apparent molor absorptivity is 2.48 x 10(4) L x mol(-1) cm(-1) , and the linear range 0-1500 micromol x L(-1) (r = 0.9999) with a detection limit of 1.7 micromol x L(-1). The relative standard deviation is 1.13% (n=11) and the recoveries are in the range of 93.6%-101.6% with an average recovery of 97. 0%. The proposed method has been applied to detect ammonia in the plasmas from 43 healthy persons and 97 patients who suffered from liver diseases with satisfactory results.