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May 28, 2015

Homework Help: Chemistry/lab math

Posted by Anonymous on Tuesday, August 20, 2013 at 10:06pm.

For an AST determination, 0.2 mL of serum was used. The change in absorbance (ΔA) was measured at 340 nm with a 3 mL reaction mixture. The initial reading was 0.54 A, the reading after 5 minutes was 0.32 A. Report the AST value in IU.

Equation to use when time is other than 1 min.;
IU/L = ΔA/min x Vt/6.22 x Vs x 1000 x 1/T

Vt is the total volume and Vs is the volume of serum

My math;
= 0.22/5 min x 3.2 / 6.22 x 0.2 x 1000 x 1/5
= 22.6 IU

Do I divide the change in absorbance by the time of 5 min. or is min. just listed as is per the equation? I'm a little confused now on that. And for total volume, would you add together the volume of serum used and the 3mL reaction mixture or would it just be the volume of the reaction mixture to take into account?

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