Objective

To establish quantitative conditions for standard solution 1H NMR using a known concentration of 4-pyrenebutanoic acid.

Procedure

A 0.2M solution of 4-pyrenebutanoic acid in THF was made in a 1mL volumetric flask. A small volume (200uL) of the solution was dissolved in DMSO-d6 (500uL) and a standard HNMR was obtained and processed on a 500MHz Varian Unity Inova instrument using "default" parameters. Subsequently another HNMR was run on the same sample with the suggested "qHNMR parameters for varian" . The spectra were then analyzed for concentration determination using SAMS spreadsheets.

Results

ONSCExp103-1A-defpar 0.2M solution.
Spreadsheet for 1A def par

ONSCExp103-1A-qHNMR --FID

ONSCExp103-2A-defpar
Spreadsheet for 2A defpar

ONSCExp103-2A-qHNMR -- FID
ONSCExp103-2A-T1 -- FID


ONSCExp103-2A-d1=50
Spreadsheet for 2A-d1=50

ONSC-EXP103ratios [Ratios of aromatic to methylene Hs JCB]

Discussion

The purpose of this experiment was to verify if HNMR could be used to perform quantitative measurement of solutions, especially for solubility purposes. Unfortunately spectra obtained by using suggested "qHNMR parameters for varian" on either solutions (103-1A and 103-2A) could be be loaded using Jspecview, therefore those spectra were discarded and the data could not be used.

Two spectra for solution 103-2A obtained using different relaxation delay-d1 (a) default setting 0.3s and (b) d1=50s, were compared to check how the peak integrations for aromatic peaks (7.84-8.415 ppm) measured to that of a selected methylene peak (2.34- 2.44 ppm). Percent difference in integrations per proton calculated, can be found in the spreadsheet ONSC-EXP103ratios. The results are summarized in the table below (Table Exp103-i).

Table Exp103-i
Percent difference in the Peak Integration d1=0.3s vs d1=50s
Relaxation delay d1
d1 0.3s
d1 50s
full aromatic vs methylene
16.83
-0.79
One aromatic H (7.84-8.415ppm) vs methylene
8.71
0.05
One aromatic H (8.07 8.132ppm) vs methylene
18.38
-0.07
One aromatic H (7.894 7.94ppm) vs methylene
15.87
1.22
Increasing the relaxation delay d1 from 0.3s to 50s resulted in uniform peak integrations per proton over the entire spectrum.
Peaks in the aromatic region usually under integrate compared to peaks in the non aromatic region. This experiment proves that increasing the relaxation delay (d1) solves that issue.
Molar ratio for solute to THF based on ONSCExp103-2A-d1=50 spectrum was measured to be 0.086 (average value); which is very close to the actual value, 0.1. The difference could be due to experimental error involving THF pipetting.
Peak integrations, I believe also depend on the way the peaks are processed; more specifically line fitting and curve fitting. These issues do not seem to be of concern in the spectra used in this experiment.
[I would suggest doing 2-phenylbutanoic acid next to see if your new settings eliminate the difference between the methyl and methine Hs JCB]

Conclusion

It has been demonstrated that in order to obtain a spectrum with uniform peak integrations per proton, a prolonged delay time should be used. In general d1=50s could be used as a default value.
[very nice analysis! JCB]

Log

2009-06-16

13:10 Weighed out 4-pyrenebutanoic acid (58.1mg; 0.2mmol) in a clean and dry 1mL volumetric flask.
13:20 Added a small amount of THF to the volumetric flask and dissolved the solid by vortexing it. Then made-up the solution up to the 1mL mark on the flask. Homogenized the solution by mixing it well.
13:40 A capped, clean and dry NMR tube was tared on balance, pipetted out DMSO-d6 (500uL, 564.9mg w/cap).
13:45 Added the 200uL of the 0.2M acid/THF solution to the NMR tube, on the balance (tared). Weight of 200uL of the solution added was 190.2mg. The solution in the tube is now called 1A
13:47 The solution in the NMR tube was throughly mixed and the cap was prafilmed tightly.
14:00 Obtained an HNMR spectrum (ONSCExp103-1A-defpar) of the 1A with 'default' parameters on a 500MHz Varian Inova instrument.
14:30 Changed the following parameters on the instrument- these parameters were obtained from qnmr.org ->qNMR Resources->Varian->Varian.
Table1
Parameter
default
Changed to
d1
0.3
10
at
1.892
2.0
fn
not used (65536)
262144
dn
1H
C13
dpwr
30
43
dmm
c
ccg
dm
nnn
nny
14:40 With the above parameters set, obtained another HNMR (ONSCExp103-1A-qHNMR) of the sample.
15:45 Weighed out 4-pyrenebutanoic acid (35.7mg, 0.12mmol) in a clean and dry NMR tube, zeroed the balance with the tube on it, pipetted out DMSO-d6 (700uL, 796.5mg) and throughly mixed the solution. Zeroed the balance again with the NMR tube on it and then pipetted out THF (100uL, 96.1mg, 1.23mmol) in to it. Mixed the solution well and parafilmed the cap of the NMR tube. This solution in the NMR tube is now called 2A.
16:00 Obtained an HNMR of the 2A (ONSCExp103-2A-defpar)
16:10 Loaded again above changed parameters (see Table 1) and obtained another HNMR (ONSCExp103-2A-qHNMR).
16:20 Following the procedure laid out here with the macro dot1, to determined the longitudinal relaxation time (T1), performed an 'Inversion Recovery' experiment with sample 2A.-> set Maximum Expected T1=5 and Minimum Expected T1=1.
16:30 Obtained an array of spectra with variable d2 (0.125, 0.25, 0.5, 1, 2, 4, 8, 16, 32); performed Exponential data analysis on 40 peaks by setting a threshold on the last spectrum (9th) from the array. A copy of the spectrum with the peak frequencies can be found here. An fid of the spectra can be found here (ONSCExp103-2A-T1.fid)
17:10 Using default parametere, except for d1, which was now set to 50, obtained another HNMR spectrum of the sample 2A (ONSCExp103-2A-d1=50). This was done assuming the longest T1 was almost 7---

NOTE :Unable to process the qHNMR spectra with standalone jspecview (JSV_jars_2009_04_26)..therefore fids of the problem files have been listed in the results section
.References
1) http://www2.chemistry.msu.edu/facilities/nmr/handouts/T1%20Measurement.pdf
2) http://www.spectroscopyeurope.com/NMR_19_5.pdf