Having done spectrophotometry for water quality analysis 40+ years ago I was somewhat surprised it was being used but it has some advantages: it's mechanistic and easy, without risking the integrity of the sample, but as the story here shows it depends on certainty of the solvents and related conditions under test (we had to use specific optical refractive index glass measurement vials with their own cleansing routine and there was a rigmarole around calibration i still suspect was hugely subjective. I would hope by now the human eyeball is replaced by some digital light sensor, I think my subjective view skewed the sampling method)