As foods are mixtures of various compounds, qualitative analysis of the components requires a separation stage by high-performance liquid chromatography (HPLC) or gas chromatography (GC).
An example of compositional analysis of foods by preparative LC-FTIR is introduced below. Red wine was filtered through a membrane filter and injected into an HPLC. The isolates at peaks A to C were sampled and the IR spectrum measured using the diffuse reflectance method.

LC Chromatogram of Red Wine	IR Spectrum of Peak A (T: Tartaric Acid Peaks)

The IR spectrum of peak A is shown at the right. Despite the superimposed absorbance of coexisting compounds, the tartaric acid peaks (T) are plainly discernable.

Fourier Transform Infrared Spectrophotometer (FTIR)

Infrared Spectrophotometer (FTIR)

The qualitative analysis of food components requires a separation stage by high-performance liquid chromatography (HPLC) or gas chromatography (GC). Due to column load considerations, it is difficult to inject large sample volumes. The amount of the target component contained in a single chromatogram peak is roughly several micrograms (µg) at most. However, FTIR permits qualitative analysis of these components, producing clear IR peaks even for trace volumes.