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2D processing

2D processing

2D Processing

2D data must be processed differently depending on how it was acquired (magnitude, TPPI, hypercomplex, echo-antiecho) or States-TPPI). See also: description of 2D display, phasing 2D data, overlaying multiple 2D spectra.

Magnitude (not phase-sensitive) data are the simplest to process. A typical sequence of commands for processing magnitude data (such as COSY or HETCOR) is:

IM – import the data
MS 0 – apply sine multiplication (may want to apply this twice, for sine squared)
FT
TD – transpose data, for processing the indirect dimension
MS 0
ZF – zero-fill (may want to apply this more than once)
FT
MC – magnitude calculation
TD – transpose again, to view direct dimension horizontally
SA – save processed data

For hypercomplex data, 2 FIDs are acquired at each t1 time point, in which odd numbered slices contain only cos t1 terms, and even numbered slices contain only sin t1 terms. To display the data properly, the "pairwise" mode must be turned on (command "pairwise on"). When the data are transposed, the data quadrants must be swapped to keep the correct complex pairs matched up. For hypercomplex data, the transpose must be executed with command "TDhyper". Failure to do so will cause the data to appear distorted. Be sure to turn off pairwise mode if subsequent data are magnitude mode data.

A typical sequence of commands for processing hypercomplex data is:

IM – import the data
pairwise on
MS 90 – apply cosine multiplication, which is a sine function with a 90 degree phase shift (may want to apply this twice, for cosine squared)
FT
phase the data (eg, PH)
TDhyper – transpose data, for processing the indirect dimension
MS 90
ZF – zero-fill (may want to apply this more than once)
FT
phase the data (eg, PH)
TDhyper – transpose again, to view direct dimension horizontally
SA – save processed data

For echo-antiecho data, 2 FIDs are acquired at each t1 time point, and must be combined correctly to obtain pure phase data. These phase-sensitive experiments are run such that each slice contains both sine and cosine terms in t1. Pairs of slices must be added and subtracted to separate the sine and cosine terms. This is done after the direct dimension FT, using the command asPairs (Add/Subtract pairs). To display the data properly, the "pairwise" mode must be turned on (command "pairwise on"). The data must be shuffled differently during transpose, so requires the command TDecho for every transpose operation.

A typical sequence of commands for processing echo-antiecho data is:

IM – import the data
pairwise on
MS 90 – apply cosine multiplication, which is a sine function with a 90 degree phase shift (may want to apply this twice, for cosine squared)
FT
asPairs – to combine the slices properly
phase the data (eg, PH)
TDecho – transpose data, for processing the indirect dimension
MS 90
ZF – zero-fill (may want to apply this more than once)
FT
phase the data (eg, PH)
TDecho – transpose again, to view direct dimension horizontally
SA – save processed data

TPPI data is phase-sensitive, but it is not "pairwise" data – only one FID is acquired per t1 value. The additional quadrants need to be generated containing zeroes. To do this, after processing in the direct dimension, exeucte the command

tppi2pairwise

This fills out the other half of the data with zeroes and enters the pairwise data display mode.

Note that the transpose needs to be done with TDhyper, as with hyercomplex data.

Process in the indirect dimension using "ft real", which performs a real FT, rather than a complex FT, because the imaginary half of the data is all zeroes.

A typical sequence of commands for processing TPPI data is:

IM – import the data
MS 90 – apply cosine multiplication, which is a sine function with a 90 degree phase shift (may want to apply this twice, for cosine squared)
FT
phase the data (eg, PH)
TPPI2pairwise
TDhyper – transpose data, for processing the indirect dimension
MS 90
ZF – zero-fill (may want to apply this more than once)
FT REAL
phase the data (eg, PH2D)
TDhyper – transpose again, to view direct dimension horizontally
SA – save processed data

Data can also be acquired as States-TPPI, not to be confused with the method of States, et al, (also called hypercomplex) or TPPI (Time Proportional Phase Incrementation).

For States-TPPI, you need to invert every other data point in the indirect dimension "fid", or equivalently, every other slice in the direct dimension. This is done after FT and phasing in the direct dimension. To do this, execute the command invert. Use TDhyper for transposing data.

IM – import the data
MS 90 – apply cosine multiplication, which is a sine function with a 90 degree phase shift (may want to apply this twice, for cosine squared)
FT
phase the data (eg, PH)
invert – inverts every other slice
TDhyper – transpose data, for processing the indirect dimension
MS 90
ZF – zero-fill (may want to apply this more than once)
FT
phase the data (eg, PH2D)
TDhyper – transpose again, to view direct dimension horizontally
SA – save processed data


Last updated: 1/29/09