¹H One-Pulse Experiment 3/4/94

To optimize the standard One-Pulse experiment:

1. Collect a FID using the standard parameters.

2. Observe the FID and estimate the T2 relaxation time constant: determine the time when 95% of the FID has decayed (essentially the end of the FID), and divide by 3. See Measuring Relaxation Time Constants.

3. Process the spectrum using the standard paramters.

4. If peaks are unintentionally folded, set sw=7600 and start again at step 1.

5. Using the interactive display, position the spectrum so that the left-most and right-most peaks lie about 1 ppm from the spectrum edges. Type movesw to automatically update sw and tof .

6. Set np to 5056, 8256, 16448, 32832, or 65600. np should be ³ 2pT₂sw. If you can't decide between two valuesfor np, choose the larger value. Use Table 1 as a guide:

A. Choose the column with sw higher than your sw determined from step 5

B. Choose the row with T2 larger than your T2 in the column selected in step A.

C. Set np to the value in the left column of the row selected in step B.

Table 1. Relationship between sw, T2, and np.
	sw (hertz)
np	2000	2400	2800	3200	3600	4000	4400	5200	6000	6800	7600
2K	£0.18	£0.15	£0.13	£0.11	£0.10	£0.09	£0.08	£0.07	£0.06	£0.05	£0.05
5056	£0.35	£0.29	£0.25	£0.22	£0.19	£0.17	£0.16	£0.13	£0.12	£0.10	£0.09
8k	£0.69	£0.57	£0.49	£0.43	£0.38	£0.34	£0.31	£0.26	£0.23	£0.20	£0.18
16k	£1.37	£1.14	£0.98	£0.86	£0.76	£0.69	£0.62	£0.53	£0.46	£0.40	£0.30
32k	£2.74	£2.28	£1.95	£1.71	£1.52	£1.37	£1.24	£1.05	£0.91	£0.80	£0.72
65600	³2.74	³2.28	³1.95	³1.71	³1.52	³1.37	³1.24	³1.05	³0.91	³0.80	³0.72
	T2 (seconds)

7. Set d1 » (T1_estimate) - (at). T1_estimate can be estimated from table 2. d1 is an additional delay for relaxation after the FID has been detected. For molecules < 1000 a.m.u., d1 is approximated to be 0 if the previous steps have been followed.

8. Type ernst(T1_estimate,90_pulse), where T1_estimate (in seconds) can be estimated from Table 2, and 90_pulse is the value of the 90° pulse listed at the spectrometer.

Table 2: T1 for optimized one-pulse experiment
molecular weight	multiply T2 by	molecular weight	multiply T2 by
£1000 a.m.u.	1	2000	2.01
1200	1.05	4000	2.44
1400	1.12	6000	2.92
1600	1.42	8000	3.49
1800	1.71	³10,000	4.32

9. Set nt to a multiple of 4. For maximum signal-to-noise, set nt to the largest number that time permits. Type time to display the total experiment time. nt can be set to fill the remainder of your spectrometer reservation by typing time(hours,minutes). The spectrometer then calculates nt; round down this calculated nt to the nearest multiple of 4. For instance, if I type time(0,15), and the spectrometer sets nt to 362, I then type nt=360.

10. Set ss=2 pad=0

11. To decouple a signal, run a standard ¹H one-pulse spectrum and reference it. Place the cursor on the peak to be decoupled and type sd homo='y' dm='y' dpwr=10. The dpwr can be varied from 5 to 49.

12. Recheck all experimental parameters. Parameters listed below are from standard parameters for ¹H spectroscopy in chloroform.

13. Type go or ga to start your experiment. Type aa, sa, or halt to stop the experiment before completion. Type ra to resume acquisition stopped with sa.

Parameters shown by typing dg:

sfrq=399.952 spectrometer frequency

tn=H1 transmitter nucleus

at=1.862 acquisition time, change np and sw instead

np=16448 number of points, see step 6

sw=4400 spectral width, see step 5

fb=2500 filter band width, signals farther than fb from the center of the spectrum are

filtered out. Set by spectrometer based upon sw.

bs=16 block size, number of transients to collect before data is stored and processed

ss=0 or 2 steady state transients (no data collected) before nt acquisitions, see step 10

tpwr=55 transmitter power, ranges from 0 (no power) to 63 (maximum power)

pw=26.3 pulse width, see step 8

p1=0 not used in this experiment

d1=0 relaxation delay, see step 7

d2=0 not used in this experiment

tof=-426.0 transmitter offset, adjusts sfrq to set center of spectrum, higher numbers moves

center to higher frequencies (higher ppm), see step 5

nt=4 number of transients, see step 9

ct completed transients, set by spectrometer at end of acquisition

Processing Parameters Relevant to Acquisition:

werr=wft performs function upon error, such as aa (abort experiment)

wexp=wft performs function (wft in this example) at end of experiment

wbs=wft performs function (wft in this example) at end of bs transients

wnt=wft performs function (wft in this example) at end of nt transients

Flags:

il='n' interleaved experiment, not used in this experiment

in='n' checks sample spinning at beginning of experiment

dp='y' double precision

hs='nn' homospoil not used in tins experiment

temp=not used see Setting the Variable Temperature Unit

priority=5 used by spectrometer to prioritize tasks

Parameters not shown:

dw=0.0001136 dwell, time between collection of data points of FID, change sw instead.

pad=0 pre acquisition delay, not used in optimized experiment

rof2=10 alfa=20 sum of rof2+alfa is delay between pulse and acquisition

gain='n' gain automatically set by spectrometer

gain='y' allows manual setting of the gain

gain? displays gain setting

gain=x sets gain to value of x, ranging from 0 to 59.

Interesting Functions:

number of points: np ³ 2pT₂sw

digital resolution: dr = sw/fn

dwell: dw = 1/2sw

acquisition time: at = dw*np = np/2sw ³ pT₂

pulse width: pw = [90° pulse listed at spectrometer][cos^-1{exp(-at/T₁)}]

minimum line width at half-height = 1/pT₂

A. Spectrum recorded with standard parameters.

B. Spectrum recorded with sw set too small. The TMS peak at 0 ppm has been folded and appears at 9.05 ppm with distorted phase.

C. Spectrum recorded with optimized sw and tof, as described in step 5.

D. Spectrum recorded with optimized sw and tof for the aliphatic region. Normally the aromatic peaks would fold into the spectrum. However, the filter bandwidth (fb) was automatically set to 900 Hz. Thus, any signals greater than 900 Hz from tof (greater than 4.50 ppm or less than -0.90 ppm) are strongly attenuated. Since the benzene signals resonate 2364 Hz from tof, these folded peaks are not visible. This spectrum is a very unique example.

A. sw=4400

tof=-426.0

B. sw=3800

tof=-426.0

C. sw=3300

tof=-964.3

fb=1900

D. sw=1473.9

tof=-1881.8

fb=900