How to compare and overlay several HPLC runs

Comparing a sample with a standard, checking retention time drift over a sequence, or spotting an extra peak: all of it starts with putting several chromatograms in one plot. Without the data system at hand, that usually means exporting every run by hand.

Open all runs at once

1. Open Nagura Lab, click Open data and pick Folder. Choose the folder that holds your .D runs, or drag the folder onto the page. Every run inside is opened.
2. Each run gets its own entry in the run list, and the first chromatogram of every run is plotted straight away.
3. To add runs from another folder, or .dx, .cdf and other files, use Add more.

The files are decoded on your computer and never uploaded.

Choose what to compare

• Tick signals in the run list to add or remove them, from the same run or across runs. Each trace is labeled with its run, for example red.D · DAD1B.ch 280 nm. Up to eight traces fit in one plot.
• A wavelength that was not saved as a signal: for runs with full diode-array data, open the spectrum map and add the chromatogram at any recorded wavelength. See chromatogram at any wavelength.
• Zoom: drag across the chart to zoom into a time range; Reset zoom goes back to the full run.

Absolute or % of range

Absolute shows every trace in its own unit, which is right for runs from the same detector. % of range scales each trace from its lowest point (0%) to its highest (100%), so a run with a higher baseline or a smaller injection still lines up for comparing peak positions and shapes.

When the traces are in different units, for example mAU from a DAD and pA from an FID, the plot switches to % of range by itself and says so.

Export the overlay

• Download CSV gives every plotted trace in one file. Traces sampled at the same times share one time column; otherwise each trace gets its own time and value columns, so nothing is interpolated.
• Download PNG gives the figure with its legend.
• Table view shows the values under the chart.

For many runs at once (a whole sequence exported as CSV, or the retention time, height and area of a peak in every run in one table), see the batch tools on the page, available as Pro early access.

In Python

With the open-source rainbow library (LGPL), one CSV per run, ready to overlay in a spreadsheet:

import csv, glob
import rainbow as rb

for path in sorted(glob.glob("*.D")):
    run = rb.read(path)
    f = next(d for d in run.datafiles if d.name.upper().startswith("DAD1") and d.name.upper().endswith(".CH"))
    with open(f"{path[:-2]}_{f.name}.csv", "w", newline="") as out:
        csv.writer(out).writerows(zip(f.xlabels, f.data[:, 0]))