Detector Control
Recording Absorbance Spectra

The Dionex UltiMate 3000 VWD-3x00 detectors allow you to record the absorbance spectra of substances used in an analysis, and thus to identify optimum wavelengths or to detect peak impurities. Spectrum scans can be triggered manually by executing a command or in a sample Program. For a program example, refer to  Recording Absorbance Spectra: Program Example.

Before you can record an absorbance spectrum, an intensity spectrum of the baseline must have been recorded, using the same wavelength settings. The baseline spectrum is saved in memory until the ClearBaseline command is executed or until a new baseline spectrum is recorded. Record a new baseline spectrum whenever you change the wavelength settings.

How to record an absorbance spectrum

 Tip:

The duration of the scanning procedure depends on the wavelength range to be scanned (ScanStartWavelength and ScanEndWavelength) and on the ScanSpeed. You can add an LED or a color box to the Control Panel (linked to UV.Ready) to visually indicate whether a scan is running.

  1. Open a control panel and connect it to the Timebase in which a VWD-3x00 detector is installed.

  2. Press F8 to open the Commands dialog box. Under UV, determine the settings for the ScanStartWavelength, ScanEndWavelength and ScanSpeed parameters. The settings apply to both baseline and absorbance spectrum scans. The following settings are available for the scan speed:

     

    Setting

    Scan Speed

    Required time from 200 to 900 nm

    Slow

    (1 nm/s)

    700 sec.

    Medium

    (5 nm/s)

    140 sec.

    Fast

    (10 nm/s)

    70 sec.

    Max

    (33 nm/s)

    22 sec.

     Note:

    Use identical ScanStartWavelength and ScanEndWavelength settings when recording the baseline spectrum and recording the absorbance spectrum. Do not change these parameters in-between the two scans.

    Different scan speeds can be selected for baseline scan and absorbance scan, except when Slow is selected. However, it is recommended using the same speed for both scans.

  3. Execute the ScanBaseline command and wait until the baseline scan is completed. The resulting spectrum is saved in memory and overwritten with each new baseline recording.

  4. Execute the Scan command.

 Tip:

To interrupt the scanning process, execute the StopScan command.

To retain the data, Chromeleon saves both spectra automatically to a Spectra Library named VWD3x00.lib. The spectra library is saved to the manual acquisition directory of the associated timebase (or to the sequence directory of the current sample, if a sample program is running). The location where the spectra are saved is also indicated in the Sample Audit Trail.

To open a recorded spectrum, double-click the spectra library named VWD3x00.lib. The recorded spectra can be viewed in Chromeleon.

 

Caution:

A network error may result in an abort of the sequence when recording absorbance spectra using the Scan command (for example, ScanBaseline, ScanEmission). In this case, Network Failure Protection (NFP) will not be activated!