I support what Kanhaiya Lal said, first draw a calibration curve using known conc. of dye solution

I support what Kanhaiya Lal shared.

Hi Renu-

If you know what dye it is, as mentioned above you will prepare a stock solution of that dye in a solvent that does not absorb at the wavelength of your dye of interest. Do a series of dilutions on the stock solution to make your calibration standards.

If further isolation or concentration of dye is necessary in your wastewater sample, or if you experience interference, think about adding a Solid Phase Extraction (SPE) step in the procedure to get better results. This would be necessary if the concentration of dye in the wastewater is lower than your instrument detection limits. Also if you had multiple dyes that you wanted to separate/fractionate from each other.

Dear colleague, if you are working with one specific dye dissolved in water, I believe the answer given by our colleague Kanhaiya Lal is very appropriate. However, if you have a real textile wastewater sample, I believe that would be a much more complex situation, since you will probably have a mix of different types of dyes, as well as other organic and inorganic components dispersed in the medium. A way to know if your process is really effective to remove the dyes from your wastewater sample would be using the parameter color (Hazen units), so you could evaluate the color of your sample before and after the treatment. There are other important parameters you can evaluate if you are working with real textile wastewater, such as turbidity, Chemical Oxygen Demand (COD), and conductivity. I hope that is helpful. Good luck with your project!

If I understand your question correctly you have a UV/visible spectrum of your WW sample, but you don't know which dye you are dealing with. So, all of the answers regarding how to prepare a calibration curve really don't help you at all, since you don't know which dye you have. The UV/visible spectrum is somewhat characteristic of your dye but is not specific. You might be able to find published typical UV/vis spectra for common dyes, which may help you narrow down the identification of your dye.

As Caroline pointed out, you probably have a mixture of dyes. You can find out by performing solid phase chromatography (using SPE cartridges) or thin layer chromatography. Either one will give you multiple color bands if you have a mixture. There is a good AOAC method for water soluble colors (988.13) that you could easily modify to meet your needs, or you can use HPLC/UV if you have that available to you.

Good luck!

You depend Kanhaiya Lal answer