Estimate the amount of protein in the given solution by Lowry's method.

1. 1 · Aim. To estimate the protein in the given solution by Lowry's method using BSA as the standard.
2. 2 · Principle. Cu2+ binds peptide bonds in alkali (biuret step); the copper complex and tyrosine and tryptophan reduce Folin-Ciocalteu reagent to a blue colour read at 660 nm, proportional to protein.
3. 3 · Requirements. Reagents A, B, C (alkaline copper), D (Folin-Ciocalteu, 1:1); BSA working standard 200 µg/mL; test tubes, pipettes with bulb, colorimeter, graph paper.
4. 4 · Procedure.
   • 0.2-1.0 mL standard and 0.2, 0.4 mL sample; make up to 1 mL with water; blank with water.
   • 5 mL reagent C, 10 minutes.
   • 0.5 mL reagent D, mix at once, 30 minutes in the dark.
   • Read at 660 nm against the blank.
5. 5 · Observation. [Table of tubes and absorbance; standard graph of absorbance against µg BSA, with the test marked]
6. 6 · Calculation. Graph: 0.39 → 130 µg in 0.4 mL of a 1-in-10 dilution. 130 ÷ 0.4 × 10 = 3250 µg/mL = 3.25 mg/mL.
7. 7 · Result. The given solution contains ____ mg protein per mL (____ g/100 mL).
8. 8 · Precautions. Fresh reagent C; mix D at once; same timing for all tubes; stay within the standard range; gloves, goggles, no mouth pipetting.

Scoring tip: A neat graph with labelled axes, units and the test point marked is worth several marks on its own.