Paracetamol Standard Preparation

Step 1: Weighing

Weigh 100 mg of Paracetamol accurately.

Step 2: First Dilution

Transfer the weighed Paracetamol into a suitable volumetric flask.

Add 25 mL of methanol and dissolve it properly.

Step 3: Make Up Volume

Make up the volume to 250 mL with water.

Mix well.

Step 4: Second Dilution

Pipette out 5 mL from the above solution.

Transfer it into a 100 mL volumetric flask.

Step 5: Final Make Up

Make up the volume to 100 mL with water.

Mix the solution properly.

Step 6: Measurement

Measure the OD / absorbance at 240 nm using a UV spectrophotometer.

Final calculation from your standard preparation

1. Stock standard concentration

You weighed:

Paracetamol = 100 mg

Final volume:

250 mL

So,$$\text{Stock concentration} = \frac{100 \text{ mg}}{250 \text{ mL}}$$Stock concentration=250 mL100 mg​ $$= 0.4 \text{ mg/mL}$$=0.4 mg/mL $$= 400 \text{ µg/mL}$$=400 µg/mL

---

2. Final standard concentration

You pipette:

5 mL from stock solution

Dilute to:

100 mL$$\text{Final concentration} = \frac{400 \times 5}{100}$$Final concentration=100400×5​ $$= 20 \text{ µg/mL}$$=20 µg/mL

So, the prepared Paracetamol standard concentration is:

20 µg/mL

---

% Result calculation

To calculate final % assay/result, you need the sample absorbance and standard absorbance.

Basic UV formula:$$\% \text{ Assay} = \frac{\text{Sample OD}}{\text{Standard OD}} \times \frac{\text{Standard concentration}}{\text{Sample concentration}} \times 100$$% Assay=Standard ODSample OD​×Sample concentrationStandard concentration​×100

If your sample and standard are prepared at the same final concentration, then:$$\% \text{ Assay} = \frac{\text{Sample OD}}{\text{Standard OD}} \times 100$$% Assay=Standard ODSample OD​×100

Example

If:

Standard OD = 0.512
Sample OD = 0.498

Then:$$\% \text{ Assay} = \frac{0.498}{0.512} \times 100$$% Assay=0.5120.498​×100 $$= 97.27\%$$=97.27%

Final result in this example:

Paracetamol Assay = 97.27%

To give your exact final %, send me the sample OD and standard OD values.