[STM]

Hello everyone,

I am working with an organic compound, a diphenyl phosphine compound linked to a fluorescein chromophore 2:1. I dissolve in DMF and then dissolve in seawater for analysis of my analyte. The % DMF in the final solution is 5%.

I observed that when I measure the absorbance of this compound in my medium (seawater), I observe an increase in absorbance value at 248 nm for about 5 min followed by a decrease in absorbance for another 5 min. This has made reading the absorbance value difficult for me.

I used seawater containing the same % DMF as blank and ensured homogenized mixture when the DMF-Organic compound was introduced into the seawater sample.

Please what could be responsible for the unstable absorbance reading I am observing?

Thank you

[kriggy]

Might be the seawater? You might try to run the expetiment in deionized water instead of seawater to see if there is any difference

[Arkcon]

If you can determine what's needed in seawater for your analysis, you can prepare a synthetic seawater containing just what you need.  For that matter:  Where do you get your sea water?  How is it stored?  How much do you have, and is it always a homogeneous sample -- i.e. does it act the same in a standard at all times?   Do you treat it in any way -- i.e. autoclave it to prevent algal growth?

[orgopete]

This seems a little unusual, but I'm thinking similarly to the other suggestions. So you are finding an "S" shaped curve. Questions that I'd have about it. Is it temperature and concentration dependent? Is this an oxygen (and algae) dependent reaction? Turbidity? Homogenization effect? A seawater effect not seen in distilled water or saline?