Construction of phosphate Beer-Lambert Plot using standard phosphate solution
KH2PO4 (50 µg P / 1mL)
3 point calibration
- Label four 50mL volumetric flasks (blank, 2mL, 5mL, and 10mL of standard phosphate
solution).
- Place 10mL of Vanadate-molybdate reagent in each of the 50mL volumetric flasks.
- Pipette 2mL (0.1mg P), 5mL (0.25mg P), and 10mL (0.5mg P) of the standard
phosphate solution into the volumetric flasks, respectively. For blank, do not add any
standard phosphate solution.
- Add DI water into each flask (including blank) up to the 50mL mark.
- Compute final concentrations for each flask (Eg. For 2mL of standard solution,
0.1mg P/0.05L = 2 mg P /L).
- Wait for 10 minutes while reaction takes place.
- Place each solution into a cuvette.
- Blank as a blank
- Measure absorbance for each cuvette (you can pick a wavelength of 400 nm for all
measurements, since there will be no peak in the range between 400nm and 490nm).
- Construct a Beer Lambert plot with the concentration on x-axis and absorbance on yaxis.
- Save the Blank Solution for the sample determination.
Determining phosphate concentration in samples
-
Place 25mL of a sample into 50mL volumetric flask.
Add 10mL of Vanadate-Molybdate reagent and dilute to the mark with DI water
(1 to 2 dilution of original sample).
Wait for 10 minutes while reaction takes place.
Place the sample solution into a cuvette.
Blank
Dark
Measure absorbance for each cuvette (you have to pick the wavelength you used
for Beer-Lambert plot).
Find a concentration using BL plot and multiply it by 2 to get original
concentration.