Dear all,
I have made 10µM arsenite (As3) solution (1 Liter) from Sodium metaarsenite (NaAsO2) salt (KEBOS), molar mass 129.92. I have got concentration apprx 5000µg/L (ppb) in AAS analysis, whereas similar concentration (10µM/L) for Arsenate (As5), made with standard solution got 900 µg/L (ppb)
My question, why I have got it so high for arsenite? It should be similar range as like arsenate due to the molecular weight of these inorganic As species are same 74.
Thanks in advance!
Did you use the hydride generation-atomic absorption spectrometry? Anyway I think that different arsenic species may have different level of hydride generation or atomization. Arsenic(III) readily generated hydride-generation reaction. I guess your standard solution (standard curve) is arsenic(V). Therfore the high result of arsenic(III) concentration occurred.
Try oxidating the samples of arsenic(III) or using arsenic(III) to make the standard curve.
Hope it can help you!
Regards
Jie Ma
Hej Jie,
Thank you very much for your answer
Yes, I have used hydride generation for analysis of arsenite samples in AAS. But preparation of arsenite, I have used Sodium meta arsenite ( KEBOS) powder. and when I do analysis in total As in AAS, then i have used standard addition method and the standard is regular As standard (100ppm) for AAS analysis. It was not mentioned that which species it was.
Dear scholar,
I also had experienced the same problem you faced.
To my opinion, to measure any unknown concentration of As, we must calibrate the AAS with the known concentrations of the same arsenic-salt of which the solution with unknown strength is made. For example, if you use NaAsO2 for your study, you should also use the known As solutions of the same salt to get the calibration curve. Use of As2O3 would definitely not serve the purpose. The disassociation rate of As from various salts/ oxides should be different and hence you can not expect the same [As] for every salt. This is my opinion and I am eager to know your thoughts on it.
Thanks Dear Arpan,
We have used the standard solution for As in AAS measurement (1000mg/L) (merck). as we have measured the total As, not speciation, so we should not need to specific salt solution as standard addition. But
I agree with your comments totally 'The disassociation rate of As from various salts/ oxides should be different and hence you can not expect the same [As] for every salt.'
Lets see the opinions from all, then I can also post my outcome based on investigation
Dear, Arifin, I might not help but I too need your help on how to make 10µM arsenite (As3) solution (1 Liter) from Sodium metaarsenite (NaAsO2)
Thanks in advance.
Mawia A Musyoki, Here is the way, first check the formula weight of Sodium metaarsenite (NaAsO2), its 129,91g/mol. So, its like 2 step process for reduce error in chemical solution preparation;
1. make 1 L of 10,000µM solution of Sodium metaarsenite (NaAsO2) , where you should add 1.29 grams of Sodium metaarsenite (NaAsO2). So, this would be your stock solution.
2.Then you can dilute this solution using M1V1=M2V2 formula where, M1= stock soln. molarity (10,000µM) and V1=vol. of stock solution, M2=10µM (your desired concentration) and V2=1 Liter (your desired vol.).
So, these are the 2 steps.
Good Luck!
Cheers!
Arifin
The curve is not the same if you use standard As (III) or As(V) standard solution. My experience is that I will get the higher values of the As in samples if I use As(III) standard curve . I think that problem is kinetic of the reaction (of forming AsH3) of these two As forms.
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