HB 20056.1-2011 "Sn-bismuth alloy platings and Eletroplating tin-bismuth alloy solution analysis method, Part 1: Spectrophotometric method, spectrophotometry for the determination of bismuth content in tin-bismuth alloy platings" stipulates the use of Spectrophotometric method, spectrophotometry principle, reagents, instruments, analysis steps and result calculation method. This part is suitable for the determination of bismuth content in tin-bismuth alloy platings. Measurement range is 0.18%~ 2.20%. During the analysis, bismuth forms a stable water-soluble complex with thiourea in acidic medium. Absorbance at a wavelength of 440 nm is measured, and its content is calculated according to the working Linear dispersion of bismuth. This standard refers to the "Spectrophotometric method, spectrophotometry for chemical analysis of metallurgical products" (GB/T 7729), which requires the use of a spectrophotometer that meets its requirements for analysis.