INSTRUMENT MAINTENANCE
PRACTICAL TASK P13. UV/VIS PHOTOMETRIC ACCURACY Outline Photometric accuracy means how close to the correct value is the measured absorbance of a sample. Not surprisingly, this requires a material of exactly known absorbance. Surprisingly, this most common material used is a 60 mg/L solution of potassium dichromate in 0.005 M sulphuric acid. Why surprisingly? A solution has to be made up from the solid, hence leading to potential errors and variations. Procedure (Cary 1/Cary 5000/Philip 8625) For each wavelength specified in the table below: 1.
Set the instrument to the test wavelength 2.
Fill a pair of quartz cells zero with 0.005 M H2SO4 and zero the instrument. 3.
Measure the absorbance of the 60 mg/L dichromate standard. Expected absorbances Wavelength (nm) Absorbance Wavelength (nm) Absorbance 235 0.747 313 0.292 257 0.864 350 0.640 Reporting Requirements Use the standard Performance Check reporting sheet. Report each wavelength’s variation from the correct value. The absorbance at each wavelength should be within ±0.05 of the specified values.