3. Summary of Test Method
3.1 This test method is based upon a photometric determi- nation of the 1,10-phenanthroline complex with the iron(II) ion. The sample is dissolved in a suitable solvent and the iron is reduced to the divalent state by the addition of hydroxy- lamine hydrochloride. The color is then developed, by the
1 This test method is under the jurisdiction of ASTM Committee E15 on Industrial and Specialty Chemicals and is the direct responsibility of Subcommittee E15.01 on General Standards..
Current edition approved April 10, 2000. Published July 2000. Originally published as E 394 – 70. Last previous edition E 394 – 94.
addition of 1,10-phenanthroline. After a short reaction period, the absorbance of the solution is measured at approximately 510 nm using a suitable photometer. The absorbance of the solution, once the color is developed, is stable for at least several months.
4. Significance and Use
4.1 This test method is suitable for determining trace concentrations of iron in a wide variety of products, provided that appropriate sample preparation has rendered the iron and sample matrix soluble in water or other suitable solvent (see 10.1 and Note 6).
4.2 This test method assumes that the amount of color developed is proportional to the amount of iron in the test solution. The calibration curve is linear over the specified range. Possible interferences are described in Section 5.
5. Interferences
5.1 Fortune and Mellon5 have made a comprehensive study of the interferences of various inorganic ions in this determi- nation. Table 1 and Table 2, taken from their report, show the effects of various cations and anions on the determination of 2.0 ppm iron. If the maximum level of 500 ppm does not interfere, it is very likely that the ion will not interfere in any quantity. The data were obtained under slightly different conditions than those specified in the present test method, but the interferences should be similar. For a more detailed description of interferences, the original literature should be consulted.
5.2 Aldehydes, ketones, and oxidizing agents interfere by consuming the hydroxylamine hydrochloride added as a reduc- ing agent.
6. Apparatus
6.1 Photometer, capable of measuring light absorption at 510 nm and holding a 5-cm or 1-cm cell.