Hi
I ANALYSISED anion and cation of water ( ca, Mg, Na,K, NO3,SO4, F,PO4,Cl) using ICP and IC. I got the ion balance error is higher than 5%. I don't why this happened? Could you give me your idea ?
Did you measure pH or EC? These may hold the answer. Otherwise, it is simply analytical error, which is not uncommon.
Sum of the three major cationic constituents (Ca, Mg, and Na) in meq/L and sum of the three major anionic constituents (HCO3, Cl and SO4) in meq/L must be equal. There may be some percentage of difference which can not be more than 5%.
What were the absolute concentrations like? Very high or very low? Either way, 5% error (as Paul Milham said) is hardly worth stressing about as the propagation of measurement errors across all of these components could easily explain this difference.
If the water was somewhere between hypersaline and snowmelt then maybe your measurements are indeed accurate and there may be other anions or cations (as Pavel N Nesterenko suggests) which you haven't measured that may contribute to this difference. I would add to Md. Mahabub Alam 's suggestion that phosphate and potassium may also be important to some environments.
A deviation of the ion balance by 5% is not acceptable: Either the laboratory's quality control is insufficient, or the analysis is incomplete. In your analysis, Nazanin, it is particularly noticeable that the components of the carbonate system were not determined. In natural waters, they typically play a significant role and must not be neglected under any circumstances. Determining the pH during sampling is therefore crucial. If you obtain a deviation of the ion balance of approximately 2%, the ion balance is acceptable, but the analysis may still be incorrect. Therefore, quality control in chemical analyses also includes a plausibility check, in your case suggesting that HCO3-CO3 were likely "overlooked."
I'd like to ask how did you measure the Ca and Mg? if you followed the EDTA titration as CaCO3 method, then you expect to have much of deviation from accuracy. Even if you used the Flame Photometer you need to make sure that the quality monitoring was there. Secondly, what ions are more than the others ? according to the answer you need to give more attention to the analysis of each with thinking a bit more about dilution if any. Finally, if you can put the results here it might be useful to the readers to understand the issue, or otherwise at least mention the water source if it is surface or ground water or wastewater if any.
Hello Nazanin,
In addition to the previous responses, if the the anion sum is < 3.0 meq/L, then the acceptable cation-anion difference can be up to +- 0.2 meq/L.
You can use the sign of the R.E. for speculating wether an unknown cation or anion has not been analyzed.