Effects of solvent suppression using two different probes on the same sample.

<p>The spectra were acquired utilizing the identical NMR pulse sequence as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0085732#pone-0085732-g001" target="_blank">Figure 1</a>, with the exception that (<b>A</b>) was acquired using a 5 mm probe on a 600 MHz spectrometer at the University of Alberta and (<b>B</b>) was acquired using a 3 mm HX probe with Z-axis pulsed field gradients on a 500 MHz spectrometer at the University of Michigan. The decibel value of both settings for excitation and saturation were maintained between probes. However, due to probe design differences, the resulting pulse width for the 3 mm probe was 120° (same instrument decibel setting), and the saturation power for this probe resulted in a γB1-induced field of 226 Hz or 8 dB. The difference in metabolite intensities (<i>e.g.</i>, urea at ∼5.8 PPM, and sharp peaks at ∼4.0 and ∼3.75 PPM) in the same urine sample is readily evident. This inspired our extensive investigation to identify which experimental parameters were responsible for these differences, and to determine how the sensitivity of the metabolite resultants changed in response to several common NMR parameters (see text for details). The large arrows designate urea peaks, the small arrows indicate trigonelline (which was not observed in the 3 mm probe spectrum), and the red dashed-line boxes represent a region of the spectra that exhibited marked peak suppression, particularly around 4.5 PPM, near the water region.