12. An STE buffer contains 20% sucrose, 100 mMTris and 10 mM EDTA. Given the stock solutions – 50% sucrose,
1 M Tris, and 200 mM EDTA, the volumes of the stock solutions required to make 1 litre of the buffer
solution are respectively:
1. 400 ml, 100 ml, 100 ml
2. 200 ml, 50 ml, 100 ml
3. 400 ml, 100 ml, 50 ml
4. 200 ml, 100 ml, 50 ml
Preparing an STE Buffer Solution: Calculating Stock Solution Volumes
To prepare a STE buffer containing 20% sucrose, 100 mM Tris, and 10 mM EDTA, we need to calculate the required volumes of stock solutions of sucrose, Tris, and EDTA. Let’s break down the preparation process step-by-step.
Components of the STE Buffer:
-
Sucrose: 20% w/v (weight/volume)
-
Tris: 100 mM
-
EDTA: 10 mM
Given the following stock solutions:
-
Sucrose stock: 50% w/v
-
Tris stock: 1 M (1000 mM)
-
EDTA stock: 200 mM
We need to determine the volumes of each stock solution required to prepare 1 liter of STE buffer.
Step 1: Calculating the Volume of Sucrose Stock Solution
The desired concentration for sucrose is 20% w/v in 1 liter of buffer:
Required sucrose=20%×1000 ml=200 g of sucrose\text{Required sucrose} = 20\% \times 1000 \text{ ml} = 200 \text{ g of sucrose}
Using the 50% sucrose stock solution, we can calculate the volume needed:
\text{Volume of 50% sucrose stock} = \frac{\text{Required sucrose}}{\text{Concentration of stock solution}} = \frac{200 \text{ g}}{0.5} = 400 \text{ ml}
Step 2: Calculating the Volume of Tris Stock Solution
The desired concentration for Tris is 100 mM in 1 liter of buffer:
Required Tris=100 mM×1 L=100 mmol\text{Required Tris} = 100 \text{ mM} \times 1 \text{ L} = 100 \text{ mmol}
Using the 1 M Tris stock solution (which is 1000 mM), we can calculate the volume needed:
Volume of 1 M Tris stock=Required TrisConcentration of stock solution=100 mmol1000 mM=0.1 L=100 ml\text{Volume of 1 M Tris stock} = \frac{\text{Required Tris}}{\text{Concentration of stock solution}} = \frac{100 \text{ mmol}}{1000 \text{ mM}} = 0.1 \text{ L} = 100 \text{ ml}
Step 3: Calculating the Volume of EDTA Stock Solution
The desired concentration for EDTA is 10 mM in 1 liter of buffer:
Required EDTA=10 mM×1 L=10 mmol\text{Required EDTA} = 10 \text{ mM} \times 1 \text{ L} = 10 \text{ mmol}
Using the 200 mM EDTA stock solution, we can calculate the volume needed:
Volume of 200 mM EDTA stock=Required EDTAConcentration of stock solution=10 mmol200 mM=0.05 L=50 ml\text{Volume of 200 mM EDTA stock} = \frac{\text{Required EDTA}}{\text{Concentration of stock solution}} = \frac{10 \text{ mmol}}{200 \text{ mM}} = 0.05 \text{ L} = 50 \text{ ml}
Final Volumes:
-
Sucrose: 400 ml of 50% sucrose stock
-
Tris: 100 ml of 1 M Tris stock
-
EDTA: 50 ml of 200 mM EDTA stock
Thus, the correct volumes of the stock solutions required to make 1 liter of the STE buffer are:
✅ Correct Answer:
(3) 400 ml, 100 ml, 50 ml
Conclusion:
To prepare the STE buffer with the required concentrations, you need to mix 400 ml of 50% sucrose, 100 ml of 1 M Tris, and 50 ml of 200 mM EDTA. This type of calculation is commonly used in biochemistry and molecular biology when preparing buffers for experiments involving DNA/RNA extraction, electrophoresis, or enzyme assays. Understanding how to use stock solutions efficiently can save time and reduce waste in laboratory setting
