Optimum Integration Path

A chromatogram that was recorded at a fixed wavelength usually does not have an optimum Signal-to-Noise Ratio for all peaks. The selected wavelength is often a compromise that allows you to "see" all substances.

It would be preferable to detect, for example, peak 1 at 230 nm, peak 2 at 254 nm, peak 3 at 320 nm, etc.

This is possible when you perform Wavelength Switching (if the wavelength switch points are known) or when you record a 3D Field using the Photodiode Array Technology and subsequently determine the optimum integration path.

Definition

The optimum integration path is characterized by

This means that the integration path must pass through the absorption maximum of a peak, without being influenced by another peak. As the recording precision in relative maxima and minima is higher than it is in steep spectra edges (this is especially true for large optical bandwidths of a detector), the largest relative absorption maximum should be used instead of the absolute maximum. In addition, the absolute maximum of UV spectra is frequently located in the low UV range, i.e., near 200 nm. In this range, the detector sensitivity usually decreases, while interferences, such as solvent absorption or humidity, increase.

When dealing with large substance quantities, as in preparative chemistry, total absorption should be below 2 AU. For optimum precision, select a relative spectra extremum for recording.

For unresolved peaks, it makes sense to record each channel at a point where the other peak has its absorption minimum, or ideally, is inhibited entirely.

How does it work?

Chromeleon automatically calculates the course of the optimum integration path and displays the path in the 3D Field. Wavelength switching takes place in the center between the peak end of one peak and the peak start of the other peak. That is why peak end, peak start, and switch time may coincide for neighboring peaks.

You can extract the result, i.e., the switch times for the Wavelength signal parameter, to a Program, using the Extract: Opt.Int.Path to clipboard command.

 Tip:  

Chromeleon ignores rider peaks (Type (Peak Type): Rider) when calculating the optimum integration path.

For more information, refer to Analyzing the Peak Purity  Selecting the Optimum Integration Path.