What is meant by stock solution (or) standard solution? What is meant by working standard?
- Stock Solution (or Standard Solution):A stock solution or standard solution refers to a highly concentrated form of a solution used as a preparative reference in laboratories. It is often prepared to a known concentration and then diluted to achieve lower concentrations for various experiments or procedures. The main advantage of maintaining a stock solution is that it provides a consistent starting point for preparations, ensuring reproducibility and accuracy in experimental work.
- Working Standard: A working standard, often referred to as a working solution or working reference, is a dilution of the stock or standard solution. It’s prepared from the stock solution to a concentration suitable for actual experimental work or analytical measurements. Working standards are used in routine analysis, ensuring that the concentration is within a range optimal for a given analytical method or instrument. They are typically used for a short period and may not be stored for extended times, unlike stock solutions, which can often be stored longer.
In the context of calibration and quality control in analytical chemistry, a stock solution might be a primary standard (a compound of known purity). In contrast, a working standard would be a secondary standard (a solution prepared from the primary standard). The primary standard is used to prepare the secondary standard, and the secondary standard is then used for routine calibration and measurements.
Comparison Table
| Feature | Stock Solution (Standard Solution) | Working Standard |
|---|---|---|
| Purpose | To serve as a reservoir for making dilutions. | Used directly in experiments or analytical procedures. |
| Concentration | Typically high (concentrated). | Typically lower than the stock solution, suitable for actual use. |
| Volume | Typically prepared in larger volumes to be used over time. | Prepared in smaller volumes as needed. |
| Storage | Stored for longer periods. Proper storage conditions are essential to prevent degradation. | Often prepared fresh and used immediately or stored for short periods. |
| Preparation | Requires accurate weighing and dilution to ensure the correct concentration. | Prepared by accurate dilution from the stock solution. |
| Use in Experiments | Not used directly in most experiments due to its high concentration. | Used directly in experiments or analytical procedures. |