You want to measure the concentration of compound Q in a complex sample. Q react

Question

You want to measure the concentration of compound Q in a complex sample. Q reacts with reagent R to give a product that absorbs at 625 nm. Neither Q nor R by themselves absorb at this wavelngth. However, there might be other things in the sample that interfere. You decide to use standard addition. You add 1 ml of your sample to 2 tubes. To tube 1 you add 1 ml of 0.250 mM Q dissolved in distilled water. To other tube you add 1 ml of distilled water. To each sample you add 1 ml 5mM reagent R and let it incubate. You measure the absorbance at 625 nm against a suitable blank. For tube 1 you get 0.853 and tube 2 you get 0.425. What is the concentration of Q in your sample. (Note that each tube contains 3 mL of liquid).

Explanation / Answer

Tube 1) Q sample (1ml) +reagent(R) (1ml) (5mM) =0.853

2) dist water(1ml) + reagent (R) (1ml) ( 5mM) = 0.425

Q sample absorbance =0.853-.425

= 0.428

so concentration of Q sample=2.4X 10-4

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