PeakWright / Guides / Inside a .D folder
What is inside an Agilent .D folder
The single most common thing that stops people is this: a .D is a folder, not a
file. Nothing will open it, because there is nothing to open. The run is in the files inside.
On Windows a .D usually behaves like an ordinary folder and you
can double click straight in.
On a Mac it can appear as one item. Right click it and choose Show Package
Contents to see what is really there.
The files you will find
The exact set depends on the instrument, the detector and the software version, so treat this as a map rather than a checklist. Nothing is wrong if some of these are missing.
| File | What it holds |
|---|---|
| *.ch |
One signal against time. This is the chromatogram for a single detector channel, and it
is the file most people are looking for. Several channels means several
.ch files.
|
| *.uv | Diode array data: a full spectrum at every time point rather than one number. Much larger, and the one free tools handle worst. |
| *.ms | Mass spectra, where the instrument had an MS detector. |
| *.reg | Processed results: integration output, peak tables and the settings used to produce them. Not the raw signal. |
| *.mth or ACQ* | A copy of the acquisition method, so the run carries the conditions it was collected under. |
| RUN.LOG, *.txt, report files | What the software did and what it printed. Useful for reconstructing what happened, not for reading data. |
Which one has your chromatogram
A .ch file, in almost every case. If there is more than one, they are separate
channels: different wavelengths on a UV detector, or different detectors on the same run. The
file names are often unhelpful, so the fastest way to tell them apart is usually to open them
and look, since each one carries its own description in its header.
If you find a .uv and no useful .ch, you have diode array data, and
that is a different problem. See
reading .uv DAD data.
Why there are several .ch files
A single injection can produce several signals. A UV detector set to monitor four wavelengths writes four channels. A system with both a UV and an ELSD writes one for each. They are all the same run, sharing a time axis, and the reason to open more than one is to overlay them.
That overlay is often the point. A peak that appears at one wavelength and not another tells you something a single trace cannot.
What to copy when you take a run with you
Copy the whole folder. A single .ch is enough to see and export
that one channel, because the scaling and the sample information live in its own header. But
the other files carry the method, the other channels and the processing history, and you
cannot recover any of it later from a machine you no longer have access to.
Zip the folder before you move it. It is many small files, and copying it as one archive avoids the case where a folder arrives with its contents missing.
The .D that arrived empty
A frequent and frustrating case: someone sends you a .D and it contains nothing,
or contains only a report. This normally means the folder was copied by something that treated
it as a file, or a cloud sync moved the wrapper and not the contents.
There is no way to recover the data from an empty folder. Go back and ask for it zipped. More on this and the other failure cases in when a ChemStation file will not open.
What about a .dx file
A .dx is an OpenLab archive: one container holding what a .D folder
would otherwise spread across many files. If a tool cannot open it directly, treat it as an
archive and look inside, because the familiar files are usually in there.
Converting the whole folder
Once you know which file you want, the next question is usually how to get the numbers out of
it. That is covered in getting ChemStation data into CSV, and
the readers that handle a whole .D at once are listed on the
tools compared page.
Open one of the files
Go into the folder, find a .ch, and drop it in. The viewer reads it in your
browser with nothing installed, and tells you what channel it is.
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