4In order to determine benzoylecgonine (Cocaine) amount in a urine sample, stand

Question

4In order to determine benzoylecgonine (Cocaine) amount in a urine sample, standard solutions of “known” benzoylecgonine concentration has been prepared and corresponding absorbance data at 280 nm has been obtained using UV-VIS spectroscopy. The following data has been collected.

concentartion (mg/ml) Signal (absorbance@280)

0.00 0.005->Blank

2.00 0.201

4.00 0.399

6.00 0.601

8.00 0.799   

10.00 0.999

Plot a calibration curve and determine the actual concentration of this drug in the collected urine, if its Absorbance at 280 nm is 0.434.

Explanation / Answer

Prepare a calibration curve by plotting concentration of benzoylecgonine along x-axis and absorbance along y-axis as below:

Plot of absorbance vs concentration of standard (known) benzoylecgonine.

Use the regression equation and place the corrected value of absorbance for the unknown solution. Note that we say corrected value, since we need to subtract the absorbance for the blank from the absorbance for the unknown.

Corrected absorbance for the blank = (0.434 – 0.005) = 0.429

Plug in y = 0.429 in the regression equation and obtain the concentration of the unknown.

0.429 = 0.0995x + 0.0031

===> 0.0995x = 0.4259

===> x = 4.2804 4.28

The actual concentration of the drug is 4.28 mg/mL (ans).

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