Preparing Dextrose Solutions: A Practical Guide Using Alligation

The need to prepare a precise concentration of a solution is a common challenge in pharmaceutical and laboratory settings. This article will demonstrate how to prepare a 275 mL solution of dextrose 12.5 using available stock solutions of 5%, 10%, 20%, and 50%. The method of alligation, a useful technique in pharmacy, will be explained step-by-step, providing a practical guide for both educational and real-world applications.

Introduction to Alligation Method

When faced with the task of preparing a specific concentration from multiple stock solutions, the alligation method is an effective and systematic approach. This method is particularly useful in pharmaceuticals for mixing solutions of different concentrations to achieve a desired concentration. Let's explore how to prepare a 12.5% dextrose solution from a set of available concentrations.

step-by-step Guide to Using Alligation

Step 1: Set Up the Alligation

Start by identifying the concentrations of the available solutions and the desired concentration. In our case, we need to prepare a 12.5% dextrose solution using 5%, 10%, 20%, and 50% dextrose solutions.

[text{Concentration of 10 solution}: 10%]

[text{Concentration of 20 solution}: 20%]

[text{Desired concentration}: 12.5%]

Step 2: Calculate the Alligation

The next step is to calculate the differences between the desired concentration and the available concentrations. This will help establish the ratio in which the solutions should be mixed.

[text{Difference between the desired concentration and the lower concentration (10%)}: 12.5 - 10 2.5%]

[text{Difference between the upper concentration (20%) and the desired concentration}: 20 - 12.5 7.5%]

The ratio of the lower concentration (10%) to the upper concentration (20%) is then calculated as follows:

[text{Ratio} frac{2.5}{7.5} frac{1}{3}]

This indicates that for every 1 part of the 10% solution, 3 parts of the 20% solution are required.

Step 3: Calculate the Volumes

Let x represent the volume of the 10% solution, and 3x represent the volume of the 20% solution. The total volume needed is 275 mL:

[x 3x 275 text{mL}]

[4x 275 text{mL}]

[x frac{275}{4} 68.75 text{mL}]

Now, calculate the volume of the 20% solution:

[3x 3 times 68.75 206.25 text{mL}]

Step 4: Summary of Volumes

The volumes required to prepare the 275 mL solution of 12.5% dextrose are:

[text{Volume of 10% dextrose solution}: 68.75 text{mL}]

[text{Volume of 20% dextrose solution}: 206.25 text{mL}]

Conclusion: To prepare 275 mL of a 12.5% dextrose solution, mix:

[68.75 text{mL of 10% dextrose solution}]

[206.25 text{mL of 20% dextrose solution}]

Mix these volumes thoroughly to achieve the desired concentration.

Practical Considerations and Variations

While the exact volumes may not be easy to measure precisely, the method of alligation provides a reliable and accurate calculation. In real-life scenarios, where exact measurements are not feasible, a slight adjustment can be made. For instance, mixing 70 mL of 20% with 210 mL of 10% will result in a close approximation of the desired solution. The final 275 mL can then be used, with the remainder discarded.

This method of alligation is not limited to pharmaceutical applications; it is widely used in laboratory settings for preparing solutions of various concentrations. Understanding and mastering this technique can significantly enhance the efficiency and accuracy of solution preparation processes.

Key Takeaways

The alligation method is a proven technique for preparing solutions of specific concentrations from multiple stock solutions. Step-by-step calculations using differences and ratios provide a systematic approach to determining the correct volumes of each stock solution. Practical adjustments can be made when exact measurements are difficult, especially in real-world scenarios.

Further Reading and Resources

For more detailed information and practical examples on alligation and solution preparation, visit the following resources:

Pharmaceutical Journal BioCatalogue Pediatrics Net

By following the alligation method and understanding its principles, you can ensure accurate and consistent solution preparation in various applications.