Determination of total iron in circulating water
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Previously, we used the sulfosalicylic acid method to determine the total iron content in circulating water; currently, the standard method is the o-phenanthroline method. However, we found that the values obtained through these two methods differ significantly, with the differences being more than double in some cases. The former method yields higher values, but it provides better reproducibility, while the latter method has poorer reproducibility. I wonder why everyone still uses that analysis method? But the sulfosalicylic acid method is not an ** or a chemical standard
Ophenanthroline spectrophotometry (-) The standard reference is the international standard ISO 6332-82 \"Determination of iron – Ophenanthroline spectrophotometry\". 1. Instruments and reagents； 1.1 Optical photometer: with an absorption cell of 3 cm thickness ； 1.2 Sulfuric acid: 1+35 solution ； 1.3 Ammonia water: 1+3 solution ； 1.4 Acetic acid-sodium acetate buffer solution: pH=4.5. Weigh 16.4 g of sodium acetate, dissolve it in an appropriate amount of water, add 8.4 mL of glacial acetic acid, then dilute to 100 mL with water, and adjust the pH using a pH meter. 1.5 Ascorbic acid: 20.0 g/L solution – Dissolve 10.0 g of ascorbic acid in 200 mL of water, add 0.2 g of disodium ethylenediaminetetraacetate (EDTA) and 8.0 mL of formic acid, dilute to 500 mL with water, mix well, and store in a brown bottle (validity period: one month) ； 1.6 Neophyrin: 2.0 g/L aqueous solution ； 1.7 Potassium persulfate: 40.0 g/L aqueous solution: Dissolve 4.0 g of potassium persulfate in water and dilute to 100 mL; store in a brown bottle at room temperature. This solution can remain stable for 14 days ； As can be seen from the above, the preparation of our solution has an impact on stability. Moreover, the transparency of the circulating water that you measured, as well as the effects of other components present in it, have they been taken into account? There is also the use of instruments
The reason for the discrepancy between the two methods used by the original poster is due to the sample processing process. The sulfosalicylic acid method involves color development with trivalent iron ions; during sample processing, an oxidant is required to oxidize iron into trivalent ions, and it is necessary to strictly control the conditions for color development (pH value and the elimination of the influence of certain interfering ions). The sample must first be adjusted to a stronger acidic condition before the buffer and color developer are added, in order to prevent trivalent iron ions from being converted into ferric oxide colloids. The o-phenanthroline method or the TPTZ method involve color development with divalent iron ions; during sample preparation, it is necessary to reduce the higher-valent iron ions so that they are all converted into divalent iron ions, after which color development occurs in an appropriate buffer medium. The poster simply needs to process the sample in strict accordance with the operational steps, and carry out the color development process following those same steps. Both of these methods are classic and reliable, but the operators need to have some experience as well as basic knowledge of analytical chemistry.
First of all, thank you. Our results using the yellow base salicylic acid method are higher compared to those obtained from the o-phenanthroline analysis, right? Was it because o-phenanthroline failed to fully reduce the trivalent iron to divalent iron? Sometimes, why does a turbid precipitate appear after boiling when potassium persulfate is added? ,
We have been using the o-phenanthroline method. Not bad. It is recommended to check the specific procedures to ensure that the details are accurate. For example, at one point our analysis results were extremely unstable, and it was then that we realized we had made a very basic mistake: we used an iron brush to clean the colorimetric tubes, which resulted in iron residues remaining at the sealing edges of those tubes.