How to get a chromatogram at any wavelength from Agilent DAD data

Forgot to add 254 nm to the method? Found an impurity that absorbs best at 320 nm? If the run stored full spectra (DAD1.UV), every wavelength was recorded and you can pull out its chromatogram after the fact.

In your browser

1. Open Nagura Lab and drop the .D folder.
2. Click on the spectrum map where your compound shows up. The wavelength field fills in with the wavelength you clicked; you can also type one.
3. Press Add chromatogram. It appears on the main chart next to your original signals, and you can add several wavelengths to compare.
4. Press Download CSV to export them side by side.

Nagura Lab takes the nearest recorded wavelength. With 2 nm steps, asking for 255 nm gives 254 or 256 nm; the trace label shows which.

In Python

import rainbow as rb

uv = rb.read("sample.D").get_file("DAD1.UV")
trace = uv.extract_traces(254)[0]   # absorbance at 254 nm over time
times = uv.xlabels                  # minutes

How it compares to a signal set in the method

• Bandwidth. A method signal such as Sig=254,4 averages 4 nm around 254 nm, and may subtract a reference wavelength. A trace taken from the spectra is a single stored wavelength, so it can be slightly noisier and its baseline can differ.

For identification and screening this rarely matters. For quantitation, keep using the calibrated method signal where you have one.