When preparing diluted calibration standards from a stock standard, which of the following should you use for the most precise measure?

Using a Class A volumetric flask and a Class A volumetric pipet for preparing diluted calibration standards provides the most precise measurement due to the high accuracy and reliability of these tools. Class A volumetric glassware is specifically designed to deliver precise volumes with minimal error, adhering to strict manufacturing tolerances.

The volumetric flask has a well-defined volume mark, ensuring that any liquid filled to that line is exactly the specified volume, which is crucial for preparing accurate dilutions. The Class A volumetric pipet further enhances precision because it is calibrated to deliver a very specific volume, which minimizes the variability in your dilution process.

In contrast, other options, such as a graduated cylinder or measuring cups, do not offer the same level of precision and accuracy. Graduated cylinders can have more significant graduated markings making it easier to misread the liquid level. Measuring cups are typically designed for approximate volume measurements in cooking rather than laboratory precision. Plastic disposable pipettes, while convenient, often lack the precision required for accurate dilutions and can vary in delivering the correct volume.

Therefore, using Class A volumetric equipment is essential for tasks like preparing diluted calibration standards where precision and repeatability are critical for achieving reliable analytical results.