As you ask for precisely....the methods for chemical elements calculation may differe but for relative approximation and state of elements....xps can help you....after deconvolution of curve you can identify possible states nd area under the curv will give you proportion...but this is not absolute method.

Dear ilker, what you are looking for is so called "Chemical Speciation" in analytical chemistry. Wide variety of instrumental and classical strategies have been proposed for simultaneous determination and speciation of chromium (lll) and (Vl) which UV/Vis spectrophotometry, Ion chromatography, electrochemical techniques, atomic absorption spectrophotometry, modified ICP-OES, ICP-MS are just to name a few. However, choosing a method among all of these techniques depends on the instruments that you have access to, your sample matrix (other existing species in your sample), sensitivity, detection limit and some other analytical parameters that you should specify in advance. But, since you are looking for a method to monitor the concentration of chromium in a removal process, an straightforward strategy is the selective spectrophotometric detection of chromium VI complex with diphenylcarbazide with max abs. at 540nm. You can then determine the total concentration of chromium species by atomic absorption spectroscopy and subtract the Cr(VI) conc. to calculate the Cr(lll) content. This method is usually used in chromium removal researches. However, as I told you, everything depends on the available instruments in your department and the parameters I stated above. The following review article is concerning various speciation methods reported for the chromium.

https://www.tandfonline.com/doi/abs/10.1080/10643389.2010.534029

Below you can also find an example of using the strategy I explained above in the removal of chromiun contamination research.

https://pubs.acs.org/doi/10.1021/es052057x

Good luck,

Dear İlker Acar

To answer your first question, hexavalent chromium is yellowish in colour usually and water-soluble, so your visual observation should give the first impression. Even if you have a solid sample containing a trace amount of Cr(VI), you can leach it out in water solution and utilize diphenylcarbadize method (presence of Cr(VI) should impart pink colouration). Thereafter, you can measure the absorption at 540 nm, as Mahdi mentioned, and I agree with the approach he stated.

Again, XPS and XRD are other semi-quantitative tools for that matter besides more precise methods like UV-vis, ICP and so on.

Thanks & regards

MN

Thank you very much guys, Jignesh G. Hirpara, Mahdi Ghamsari and Mithun Nath for your comprehensive explanations and guidance. I think a combination of atomic absorption and XPS works for me.