GB 223.37-1989 Methods for chemical analysis of iron,steel and alloy The indophenol blue photometric methods for the determination of nitrogen content after distillation seperation (English Version)
2020GB/T 223.37-2020 Iron, steel and alloy—Determination of nitrogen content—Indophenol blue spectrophotometric method after distillation separation
1989GB/T 223.37-1989 Methods for chemical analysis of iron,steel and alloy--The indophenol blue photometric methods for the determination of nitrogen content after distillation separation
1985GB 223.37-1985 Methods for chemical analysis of iron, steel and alloys Distillation separation-volumetric determination of nitrogen content