Investigations on the Effects of NMR Experimental Conditions in Human Urine and Serum Metabolic Profiles
Studying on the effects of the experimental conditions to the spectra data are very important for NMR-based metobonomics since the resonance signals were sensitive to the experimental conditions. In this paper, NOEPER and NOEPER-CPMG pulse sequences are adopted to acquire the 1H NMR spectra of the human urine and serum samples respectively, and two important parameters, i.e., the experimental temperature and the saturation power of NOEPER sequence, are investigated. Resonance peaks shifting and signal intensity changing can be observed in both the urine spectra and the serum spectra when the experimental temperature was changed. For example, intensity of resonance signal of LDL, VLDL, valine and choline would increase obviously in the serum spectra with the experimental temperature increasing. Those evidences implied that it is important to acquire the 1H NMR spectra of the samples in the same temperature. In addition, water suppression profiles of the NOEPER pulse sequence are obtained with several different values of saturation power, in which signals whose chemical shifts are closed to that of water would decrease their intensity with the saturation power rising. Those results demonstrate that trade-off between the water suppression and signal decrease must be taken into consideration. As a matter of experience, lower saturation power is recommended if the water signal has been suppressed enough.