FAST SPECTROPHOTOMETRIC DETERMINATION OF Fe~(3+) AND Fe~(2+) IN COMMERCIAL GLASS

摘要

Total iron and FeO/Fe_2O_(3tot) ratio in the glass can be obtained by spectrophotometry. A fourth derivative calculation and the conventional procedure are respectively applied for the determination of Fe~(3+) and Fe~(2+) concentrations.The shape of the fourth derivative in the 360-400 nm range recorded with the same spectrophotometer was similar for analysed samples with different Fe_2O_3 concentrations but with the same glass system (soda-lime, borosilicate). By a simple linear regression the peak height of the fourth derivative can be correlated with the known Fe~(3+).In the case of flat polished samples the sole spectrophotometric measurement allows total iron and FeO/Fe_2O_(3tot) ratio to be obtained with an accuracy comparable to wet chemical analysis. The sensitivity of the spectrophotometric method allows the measurements of not chemically detectable Fe~(3+) and Fe~(2+) concentrations.The method can also be directly applied to the finished glass product. In this case the absorption curves of Fe~(2+) and Fe~(3+) should be recorded without removing the sample from the spectrophotometer so that the evaluation of Fe~(2+)/Fe~(3+) ratio is independent from the thickness irregularity of the sample, the planarity and roughness of its surfaces, etc.