Chapter 7 Data Explorer Examples

7.1.3Determining if a Peak is Background Noise

Overview

7

Subtracting spectral peaks

To determine if spectral peaks represent low-level components or if they are due to solvent contribution, you can:

•Subtract the spectral peaks from the chromatogram

•Create an extracted ion chromatogram for the spectral peaks

The following example uses the chromatograms and spectra from Section 7.1.2, Deconvoluting and Evaluating Unresolved Chromatographic Peaks. It illustrates how to subtract baseline and determine if the spectral peak observed at 391 Da (Figure 7-5 on page 7-7)is eliminated.

To subtract spectra:

1.Activate the first extracted ion chromatogram in Chromatogram window (see Figure 7-4 on page 7-6).

2.From the Process menu, select Add/Subtract Spectra.

3.Click , then right-click-drag over the peak in the extracted ion chromatogram.

The spectrum range is displayed in the Spectra To Be Added list in the Add and Subtract Spectra dialog box (Figure 7-6).

4.In the Add and Subtract Spectra dialog box, click anywhere in the Spectra To Be Subtracted list.

5.In the TIC, right-click over a region of baseline that does not contain any peaks.

NOTE: When selecting spectra to subtract, select from the TIC. The baseline in the extracted ion chromatograms is for a selected mass and does not represent all components which may be present.

7-8 Applied Biosystems