Objective  To improve the national standard.method for the detection of hydrogen cyanide in the air of workplace.

Method  Because the abnormal color reaction of samples was caused by improper pH value, the preparation of isonicotinic acid-barbituric acid, the chromogenic agent, and the buffer reagent of original method were improved. The concentration of hydrogen cyanide in the air of workplace was detected by spectrophotometry.

Results  The minimum detection limit of the method was 0.05 μg/mL;the lowest detection concentration was 0.05 mg/m³ (in 2 L air samples); the range of detection was in 0.05~2 μg/mL; the regression equation of standard curve was y=0.332x+0.0169; and the correlation coefficient was r=0.9998. The relative standard deviation (RSD) of standard addition at low, medium and high levels (0.20 mg/m³, 0.70 mg/m³ and 1.20 mg/m³) were 4.5%, 1.7% and 1.3%, respectively.

Conclusion  The color reaction of sample was normal after the method being improved, and the results were stable and satisfactory.