I'll explain the steps to calculate phosphorus concentration (ppm) in a plant sample using the common colorimetric method with a spectrophotometer:

1.Sample Preparation

-Dry the plant material thoroughly

-Grind sample to fine powder

-Weigh a precise amount (usually 0.5-1.0g)

-Ash the sample at 500°C for 4-6 hours

2.Extraction Process

-Dissolve ash in dilute acid (usually HCl)

-Filter the solution

-Dilute to a known volume (e.g., 50 or 100 mL)

3.Colorimetric Analysis

-Take an aliquot of the prepared solution

-Add vanadomolybdate reagent

-Allow color development (usually 30 minutes)

-Measure absorbance at 430-470 nm wavelength

4.Calculation Formula

CopyP (ppm) = (C × D × V) / (W × 1000)

Where:

C = Concentration from standard curve (mg/L)

D = Dilution factor

V = Total volume of extract (mL)

W = Weight of plant sample (g)

5.Standards and Calibration

-Prepare standard solutions (0-10 ppm P)

-Plot standard curve

-Use curve equation to determine unknown concentrations