Application Editorial

Accurate Preparation of Standards

Application Editorial

For Chromatographic Analysis

Chromatographic techniques like HPLC or GC are commonly applied in analytical R&D and QC labs for identifying, quantifying and purifying the individual components of the mixture. The purity, concentration and composition of these components has a major influence on the quality of the final product, its efficiency, safety, shelf-life, and many other important product features.

To run a chromatographic analysis, many identical samples must be prepared and run through the whole analytical method to see whether the necessary details can be determined. HPLC and GC methods employ the use of known reference substances as standards, to gain traceable results from the evaluation. Therefore, reference standard preparation is a common daily task in most analytical laboratories.

This application note presents a quick and easy way to prepare accurate reference standards for HPLC and other chromatographic (analytical) methods. The method enables using less substance and solvent, ultimately significantly saving time and money.

Types of Reference Standards

Reference standards are used to identify or determine the concentration of an analyte in a sample of unknown concentration. The reference standard is prepared with a known concentration, so the unknown sample can be compared to it, in order to determine the actual concentration of the sample. There are two different types of standards:

 

Internal StandardsExternal Standards
Added to the unknown sample and analyzed at the same timeAllows highly accurate monitoring of the compounds based on residence time
Used for calibration, by simply plotting the ratio of the analyte signal to the internal standard signal, as a concentration functionUsed for calibration by preparing various concentrations of the external standard, and creating a calibration graph
Allows highly accurate monitoring of the compounds on the basis of residence timeUsed to determine the exact concentration of a compound in the sample

 

Note: Some companies refer to reference standards that were purchased from other companies as external standards, while standards from within the company are then called internal standards.