[dun13203171]

Hi guys,
           I am not mathmatically minded, so please bear with me. I finished of an experiment a few weeks ago, now I am just trying to plot a few graphs and come to conclusions, the finish line is close, or so I thought.

So a quick recap on what I was actually doing.

This was an experiment measuring the rate of dissolution of a drug.

A standard solution was made up for the active compound in the drug andserial dilutions were then made from this. They were then  placed into a UV vis spectrophotometer, absorbances were read and from this a calibration graph was made in excel, a line of best fit was made and from this I was able to plug in future absorbances from an experiment for it to automatically calculate the concentration for me. Hope this makes sense so far!!

For the experiment. the drug in question was then added to buffered solutions at ph2, ph8 and a control (water). At 30 min intervals, samples were taken and absorbances were read.

So I am getting some good absorbances, for the pH which was most suitable for the drug to dissolve, so I can use the calibration graph to calculate the concentration for these absorbances and then plot concentration against time. However for the pH's which were less suitable for the drug, the absorbances were of course low, I was hoping to be able to plot some sort of graph for each variable but I am not sure how I would go about it with negative values being produced. I am also getting these sort of values from excel, 2.1985E-05, which is confusing me.

I have never used excel for this sort of work before, so if someone could help me that would be great. I just want to get this finished and put to bed!

thanks

[Borek]

2.1985E-05 means 2.1985×10^-5.

You can't assume the same calibration curve to work for different pH values.

[dun13203171]

Thankyou for your reply borek.

Absorbances were taken at different pH's, ie. the drug was addded to a solution buffered to pH2, a solution at pH8 and a control (water). Absorbances taken for each.

These are my serial dilutions (absorbances) . 0.15893, 0.30546, 0.44073, 0.56860 and 0.70560.

wheras I have absorbances from the experiment at varying pH's, from as little as 0.0164545 to a maximum of 0.9807235.

But it shouldn't make a difference if they fall outside of this range of serial dilutions or would it? as the line of best fit should be able to calculate it in excel?

I am only getting some negative values when I add low absorbances to my calculation  using (TREND) in my excel document, so negative concentration values.

For example when I add the absorbance 0.0154250, I get the following concentration "-1.13544E-05"

I am not very mathmatically minded, so please bare with me.

thanks