2D 1H-1H COSY

2D Gradient Enhanced COSY

The following figure is the gradient based 2D COSY pulse sequence with the main parameters displayed (NMR500).

Gradient COSY Sequence

Procedure (on NMR600)

Lock and shim your sample as usual. Keep lock at ~80% after shimming by increasing lock gain or power.
Find proper sw and tof to use. Note that the whole signal region must be enclosed in the spectral window.
Under exp1 (type jexp1 to go there), collect a standard 1H spectrum with nt=1, process and reference the spectrum. Alternatively, you can also load a previous 1H experiment of this sample and process it.
Put the box cursor (two cursor lines) to enclose the signal region and to include ~10% flat baseline area at each end of the peak region. Type movesw. This command sets a new spectral width sw and spectrum center tof.
Run another 1H spectrum with nt=1 with the new setting. Reference the spectrum carefully or enter setref.
Load standard 2D COSY data file
Join a different experiment (i.e. jexp2 or create it with cexp(2) if it doesn't exist).
From exp2, type mf(1,2) to move fid from exp1 to exp2. Type wft f full to display spectrum. Check reference.
Type setexp('gcosy') su to load standard gcosy parameters. Solvent, spectral width, and center are copied over from 1D spectrum.
Enter time to display experiment duration.
Use default parameters values (~20 mins experiment) in most cases. The following can be optionally adjusted:
For a concentrated sample, set nt=2 for quicker experiment. For a dilute sample, increase nt (nt=8 or 16, ... ).
Optionally, for better quality data (may results in longer data collection time):
Enter time to display experiment duration.
Type go to collect data.
Watch for ADC or receiver overflow:
In arrayed experiments such as 2D's, a fixed gain (not autogain) must be set. Watch the receiver overflow light on the VT monitor next to the workstation and the ADC overflow error message immediately after the experiment starts. The default (gain=36) works most of the time unless there is an extremely strong 1H signal in your sample. With a gain above 20, it makes only small differences.
If the receiver overflows (red light blinks on VT display) or ADC overflow message is seen above the command area anytime during the experiment except during the dummy scan period, it is likely the data are ruined. Stop the experiment (aa), check the current gain (gain?) and reduce gain by 2-4 at a time (gain=32, etc), enter go, repeat the process until the overflow disappears.

Default parameters

The default setting (modified from Varian's default values) in our parameter set uses the following for a quick 2D COSY:

ni=256 (256 real points along indirect dimension. For better resolution, set ni bigger, ie. ni=400 or ni=512)
d1=1 (recycle delay between scans is 1 sec)
ss=16 (16 dummy scans before actual data collection)
nt=4 (4 scans)
phase=1 (absolute-value mode in indirect detection)
gain=36 (reduce it by 2-4 at a time if receiver or ADC overflows)
sspul='y' (removal of XY-plane signal after acquistion.)

Data Processing

You can use vnmrJ to process the data, but vnmrJ's graphics display for 2D spectrum leaves much to be desired. A separate program is strongly recommended for detailed processing and analysis. Mnova and nmrPipe/nmrDraw are installed on NMR600 and the data processing station.

NOTE: do not phase any absolute-value or magnitude mode spectrum such as COSY or HMBC setup here.

Example spectrum

Data collected October 2010 (~20 mins)
Processed and displayed with nmrPipe/nmrDraw
Absolute-value mode

2D absolute-value COSY

Expansion of the 1.0ppm to 4.7ppm region:

2D COSY

H.Zhou updated Apr 2012