Chemical Forums

Chemistry Forums for Students => Analytical Chemistry Forum => Topic started by: pieka on January 26, 2010, 06:23:25 AM

Title: spectrophotometry calculations
Post by: pieka on January 26, 2010, 06:23:25 AM

 Solution D contains a mixture of ADP and CMP. These compounds both absorb light in the same range of the spectrum and are often found together in biological extracts. The molar extinction coefficients of these compounds are: At 260nm: ADP, 15.4x103; CMP, 7.5x103 litres/mole.cm At 280nm: ADP, 2.5x103; CMP, 13.0x103 litres/mole.cm

If the following optical densities were measured in a 1 cm cuvette:
At 260nm 1.45
At 280nm 1.89

Calculate the concentrations of ADP and CMP in Solution D, explaining the principle involved.

I have no idea how to do this... any suggestions?
thanks :)

Title: Re: spectrophotometry calculations
Post by: deuterium on January 27, 2010, 06:17:29 AM

You must solve system of two equation:

1.45=15.4x103*C1+7.5x103*C2
1.89=2.5x103*C1+13.0x103*C2

C1-concentration of ADP
C2-concentration of CMP

Title: Re: spectrophotometry calculations
Post by: Train on January 30, 2010, 09:45:55 AM

Or alternatively you could plot (absorbance sample/absorbance ADP std) vs. (absorbance CMP std/absorbance ADP std) over many wavelengths to obtain a line with slope (conc. CMP in samle/conc. CMP in std) and intercept (conc. ADP in sample/conc. ADP in std).

Title: Re: spectrophotometry calculations
Post by: xoto on February 16, 2010, 04:52:15 PM

exactly what deuterium has done. go ahead and get the answers

Title: Re: spectrophotometry calculations
Post by: sc414 on January 26, 2011, 12:01:59 PM

Having completed the calculation I was wondering if anyone could clarify my answers. For C1 [ADP] I got a concentration of 25.75um and for C2 [CMP] I got a concentration of 140.5 um. Any feedback would be much appreciatied!

Title: Re: spectrophotometry calculations
Post by: cjf30 on January 26, 2011, 05:41:27 PM

Quote from: sc414 on January 26, 2011, 12:01:59 PM

Having completed the calculation I was wondering if anyone could clarify my answers. For C1 [ADP] I got a concentration of 25.75um and for C2 [CMP] I got a concentration of 140.5 um. Any feedback would be much appreciatied!

I have a deadline for this experiment tomorrow and cannot do the equations for this question. How did you get those figures?
Chaarrs

Title: Re: spectrophotometry calculations
Post by: cjf30 on January 26, 2011, 07:35:17 PM

Quote from: cjf30 on January 26, 2011, 05:41:27 PM

Quote from: sc414 on January 26, 2011, 12:01:59 PM

Having completed the calculation I was wondering if anyone could clarify my answers. For C1 [ADP] I got a concentration of 25.75um and for C2 [CMP] I got a concentration of 140.5 um. Any feedback would be much appreciatied!

I have a deadline for this experiment tomorrow and cannot do the equations for this question. How did you get those figures?
Chaarrs

OK i figured it out and got 25.76 and 140.4, so virtually identical answers!