[stdacet]

I am analyzing the water soluble phosphorous in soil samples by molybdenum blue method.

Suppose I make five working standards with concentration of 0.04 mg/L, 0.08 mg/L, 0.12 mg/L, 0.16 mg/L and 0.20 mg/L.

For preparation of calibration curve, I use 50 ml of the working standard each for color development by the molybdenum blue method and subsequent recording of absorbance.

I use 100 ml of water to extract the phosphorous from 1 gram soil sample. Next, I used  the entire extract (which is about 92 ml due to filtration) for color development and read the concentration from calibration curve.

I am confused with regard to reading the concentration from calibration curve as I used 50 ml volume for standard and 100 ml for extract.
If i consider the concentration of the working standard as 0.002 mg/50 ml, 0.004 mg/50 ml, 0.006 mg/50 ml, 0.008 mg/50 ml and 0.01 mg/50 ml, and determine the concentration of my 100 ml unknown soil extract as x mg/ 50 ml from the calibration curve, will it be ok?
Next I will convert x mg/50 ml to x mg/L and then to mg/kg.

I want to clear the point that this strategy is correct, if I have used different volumes of working standard and samples, as volume will definitely affect the color development.

Thanks

[chenbeier]

Think: you have calibrations curve Absorbance to concentration in mg/l. You measure the absorbance of your sample and you get also a result in mg/l . So what does it mean for the volume of your sample?

[stdacet]

As the absorbance is based on color development, higher amount of phosphorous in 100 ml will lead to higher colored product absorbance as compared to that in 50 ml.

[chenbeier]

The 50 ml doesnt matter. Important is your concentration in mg/l !!! The curve is made by obtaing results in mg/l. Your sample reading is also mg/l Now you have 92 ml. What does it mean?

[stdacet]

The volume of extract was reduced to 92 ml due to filtration so the final extract that was used in color development reaction was 92 ml.

So it does not matter that the volume of standards that I used was 50 ml in color reaction and sample volume was 92 ml???

Thanks