Industry expert Tony O'Lenick examines the difference between separation science and instrumental methods in the following C&T Today exclusive:
Analytical chemists are often presented with complex formulations and asked for information leading to duplication. There are two fundamentally different types of analysis that can be performed with such complex mixtures. The first relates to analysis conducted on the complex solution itself. This type of analysis gives information on colligative properties; that is, properties of the entire formulation. This type of analysis can include Fourier Transform Infra-Red (FTIR) analysis in which infrared radiation is passed through a sample.
With FTIR analysis, some of the infrared radiation is absorbed by the sample and some of it is passed through (i.e., transmitted).1 The resulting spectrum represents the molecular absorption and transmission of the entire formulation, creating a formula fingerprint. While very helpful, this technique results in a determination of the functional groups in the entire formulation, not for each molecule. For example, if the FTIR reveals a hydroxyl group and an ester group, it cannot be assumed they are on the same molecule but could just as well be on a mixture of the two.
The full analysis will require separation science. Separation science most commonly uses chromatographic separation, including GPL, HPLC, GPC and TLC. These techniques allow for separation of the formulation into its pure components based upon physical interactions between the molecules and another material. Once the materials are separated and the quantity of each component is determined, the FTIR can be run on each individual component. The FTIR will identify the same groups as above, only now it will analyze pure materials.
Analysis of both colligative properties and those of separated materials is important to the formulation chemist. The former is a very powerful quality control technique, and the latter a powerful analytical tool. The formulator should use both types of analysis.
References
1. http://mmrc.caltech.edu/FTIR/FTIRintro.pdf
