_CHROnnn.DAT
Binary chromatogram data file. One file per recorded channel (e.g.
_CHRO001.DAT, _CHRO002.DAT). Contains a time-series of (RT, value)
pairs for a single instrument channel (pump pressure, flow rate,
temperature, etc.). The channels are described by _CHROMS.INF.
Status: Fully Decoded
File Layout
The file uses the same Waters Parameter Table structure as _FUNCnnn.STS:
[32-byte file preamble]
[2 × 48-byte descriptor records] (always exactly 2)
[n_records × 8-byte data records]
Total header = 32 + 2 × 48 = 128 bytes. data_offset at preamble byte 0
is always 0x80 = 128.
File Preamble (32 bytes)
| Offset | Type | Value | Description |
|---|---|---|---|
| 0x00 | u16 | 0x0080 (128) | data_offset - byte offset to first data record |
| 0x02 | u16 | 1 | Format version |
| 0x04 | u16 | 8 | Bytes per data record |
| 0x06 | u16 | 2 | Number of descriptor records (always 2) |
| 0x08-0x1F | - | zeroes | Padding |
Descriptor Records
Both are always present with the same structure (unk=3 = f32 encoding):
| Index | seq | name | code | encoding | Description |
|---|---|---|---|---|---|
| 0 | 1 | Time | 0 | f32 | Retention time (minutes) |
| 1 | 2 | Intensity | 4 | f32 | Channel value (units from _CHROMS.INF $CC$ string) |
Data Records (8 bytes each)
| Offset | Type | Description |
|---|---|---|
| 0 | f32 | Retention time (minutes) |
| 4 | f32 | Channel value in instrument-specific units |
The sampling rate is independent of the MS scan rate. LC channels are typically sampled at 1-10 Hz; the number of CHRO records per MS scan varies accordingly.
CHRO File Numbering
CHRO files are numbered 1-based and correspond to the 85-byte channel records
in _CHROMS.INF, starting immediately after its 128-byte descriptor header.
The Flags and Description descriptors are fields inside that header and do
not have companion CHRO files.
| CHROMS.INF channel index | CHRO file |
|---|---|
| 0 | _CHRO001.DAT |
| 1 | _CHRO002.DAT |
| 2 | _CHRO003.DAT |
Observed Values
| File | Dataset | Channel | n_records | RT range (min) | Value range |
|---|---|---|---|---|---|
| CHRO001 | CtpA.raw | BSM System Pressure | 7201 | 0.002-12.002 | 4753-6782 |
| CHRO002 | CtpA.raw | BSM Composition A | 721 | 0.017-12.017 | 94.7-95.0 (%) |
The first channel in the public 213-byte PSU metadata file is column
temperature. Its _CHRO001.DAT has 900 points, starting at 0 minutes with
approximately 40 degrees C, consistent with the channel name and units.
The four-channel MTBLS701 LCT Premier acquisition maps pressure, composition,
sample temperature and column temperature to CHRO001..CHRO004 in that order.
Units Lookup
The units for each channel's value field are stored in _CHROMS.INF as the
$CC$ spec string for the matching record. See 05-chroms-inf.md
for the $CC$ parsing rules.
Reference Sources
- Corpus samples:
- PXD068881/20220517_CtpA_1076_2h_1.raw (7 CHRO files, 7 channels)
- PXD075602/DHPR_11257-1.raw (5 CHRO files, 5 channels)