I have the equation of the line; the unknown sample is diluted to 250 ml and to process it for UV spectrophotometer I will get 5 mL of it add the necessary reagents and dilute it to 50 mL, my question is how to calculate the unknown concentration?
it Is not possible for anyone to answer the question with the information provided, but here are some general guidelines using some algebra where necessary.
First I assume by ‘line‘ you mean some sort of standard curve. The key thing to consider is how the samples used to prepare the standard curve were handled, and whether the unknown sample was treated DIFFERENTLY. If not, then the absorbance value obtained for the unknown sample is read directly off the standard curve to get the concentration. In reality, rather than reading off the curve, your graphing software will probably calculate x values for any unpaired y values.
In your question you say the unknown sample is diluted to 250ml. As we do not know the volume at the start, I will assume it to be ‘v’ ml. Dilution factor is therefore v/250.
You also refer to further dilution of 5ml of this sample by addition of various reagents and diluting to 50ml. This is a 1/10 dilution. It seems likely however that the standard curve samples would have been treated in this way too?
To give an example calculation I will assume that the v/250 dilution did not apply to samples used to make the standard curve, but that the 1/10 dilution did.
Therefore the concentration of the undiluted sample = x value from standard curve x 250/v.
Yes, the sample are prepared similarly to the standards, the only difference is the sample is from a 250 mL volumetric flask, while the standard is a known analyte concentration plus the reagents diluted to 50 ml volumetric flask. Nick Gee
For example I get a x = 2 from solving the standard curve equation, calculating it further:
2 mg/50 mL × 10 = 0.4 mg/ml
Is that the concentration of the unkown sample from the 250 ml volumetric flask?
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