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| Author(s): |
Tatiana Monaretto
Total Authors: 1
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| Document type: | Master's Dissertation |
| Press: | São Carlos. |
| Institution: | Universidade de São Paulo (USP). Instituto de Química de São Carlos (IQSC/BT) |
| Defense date: | 2015-07-15 |
| Examining board members: |
Luiz Alberto Colnago
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| Advisor: | Luiz Alberto Colnago |
| Abstract | |
Longitudinal (T1) and transverse (T2) relation times have been often used in time domain NMR (TD-NMR) to obtain physical and chemical properties of the food, polymers, petroleum and pharmaceutical materials. The Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence is the standard method to measure T2 because it is a fast and accurate method. On the other hand, pulse sequences for T1 determination, as Inversion Recovery (IR) e Saturation Progressive (SP), is not common, such require long time. Under these circumstances, several authors developed two-dimensional (2D) fast methods to determine relation times and/or T1/T2 ratio. However, these methods require pulse sequences that are more sophisticated and difficult data processing than one-dimensional (1D) method. This way, recently, fast 1D techniques, based on Steady State Free Precession (SSFP), has been developed to determine simultaneous T1 and T2.These methods are named the Continuous Wave Free Precession (CWFP) and Carr-Purcell Continuos Wave Free Precession (CP-CWFP). The main disadvantage of these methods is that they require the adjustment of the offset frequency and the time between pulses (Tp) in order to obtain a precession angle odd multiple of π. Therefore, in this study, it proposed to use CWFP technique with π phase alternation (PA), which in resonance are Tp independent, when Tp<T2∗. These pulse sequences were named CWFPx-x, CP-CWFPx-x. They are similar to CWFP and CP-CWFP, however with π PA between refocusing pulse (x\' and -x\'). In addition, other pulse sequence, named CPMG90y-y will be analyzed. It is similar to CPMG90, however, the refocusing pulses have PA (y\' and -y\'). In these pulse sequences, the relaxation times are determine by the signal amplitude immediately after the first pulse |M0| and in the stationary state |Mss|, as wells as the exponential time constant T∗. T1 and T2 determine by the π PA sequences were similar those one obtained by standard methods, IR and CPMG. Nevertheless, among the sequences with or without PA, show in this study, the CP-CWFPx-x proved be the best sequence for T1 and T2 determination, because of its highest dynamic range of the quasi-stationary state to stationary state. Thus, it provides the relaxation times determination independent of the T1/T2 ratio and can be use in cases of the low-reason signal to noise ratio. (AU) | |
| FAPESP's process: | 13/03770-1 - Development and applications of pulses sequences with alternating phases in the time domain NMR |
| Grantee: | Tatiana Monaretto |
| Support Opportunities: | Scholarships in Brazil - Master |