9.7 : Instrument Calibration

Instrument calibration is essential for ensuring that instruments produce accurate and consistent results. It is vital in manufacturing, healthcare, testing laboratories, and scientific research. Calibration processes are specific to each instrument and help enhance data accuracy. Each instrument has a unique calibration process tailored to its design and function to improve data accuracy.

Analytical Balance Calibration

An analytical balance measures mass and requires regular calibration to maintain precision. Calibration is achieved by comparing its measurements to known standard weights. These standard weights serve as references to ensure accurate mass readings. Analytical balance can be affected by external factors like air buoyancy, which makes a weighted object appear lighter than its actual weight in a vacuum. A buoyancy correction is applied to calibrate the balance, considering the object's density, air density, and calibration weights. By addressing the determinate error introduced by air buoyancy, the analytical balance provides a more accurate and reliable measurement of the object's true weight.

Spectrophotometer Calibration

Calibration for a spectrophotometer, an instrument that measures the absorbance of light by a solution, is different from mass measurement. It involves creating a calibration curve using standard solutions with known analyte concentrations. The process starts with preparing a series of standard solutions that typically range from low to high concentrations to form a broad calibration curve. Each standard solution is then measured for absorbance using the spectrophotometer. The spectrophotometer shines light through the solution and measures the amount of light absorbed by the analyte.

The absorbance values are plotted against the known concentrations. According to the Beer-Lambert law, this plot should form a straight line, showing a direct relationship between concentration and absorbance. Once the calibration curve is established, the unknown solution is measured for its absorbance. This absorbance value helps determine the corresponding concentration of the analyte in the unknown solution from the calibration curve.