Water, suppression

One thing we can not prevent when carrying out presaturation or other water suppression experiments is the distortion or disappearance of solute signals which are very close to (within a few Hz of) the HOD signal ... 

WATERGATE Water suppression through gradient tailored excitation. 

Gadhe, J. B. Gupta, R. B., Hydrogen production by methanol reforming in supercritical water Suppression of methane formation. Industrial and Engineering Chemistry Research 2005, 44, 4577-4585. 

When water is combined with other additives, it can control and extinguish most petroleum fires. A water suppression system consists of a supply source, distribution system, and the end using equipment such as fixed spray systems, monitors, hose reels and hydrants. The objective of water suppression systems is to provide exposure cooling, fire control, suppression of fire incidents and may assist in the dispersion of flammable or toxic vapors. 

When water suppression systems are provided, due concern should be made for the disposal of the released water. Of primary importance are the capacity and location of surface drainage systems. Fire water usage usually places greater demands on a facility gravity sewer system than rainfall or incidental petroleum spillage effects. 

Various gasification schemes have been conceived for the direct production of H2 (and C02) instead of synthesis gas. Matsumura has reviewed the gasification of biomass with near- and super-critical water [42], The presence of liquid water suppressed the formation of char but not of tars. Full gasification proceeds in the presence of metal catalysts at 350-600 °C but also in absence of any catalysts at 500-750 °C. This subject is discussed elsewhere in this book [26],... 

Fig. 7.11 J modulation in a constant time HSQC in order to measure dipolar couplings. A Watergate pulse is introduced in order to optimize water suppression. The intensity of cross peaks is given by /(7") = C cos(nJT)exp(-T/T2) The right...

In water-suppressed muscle spectra, contributions of lipids, methyl and methylene groups of creatine (Crs, Cr2), trimethylammonium-containing compounds (TMA), including signals from carnitine (Ct), choline (Cho), and taurine (Tau) are well observable as demonstrated in Fig. 15. Furthermore, small signals of histidine protons of carnosine (Cs) can be sometimes identified... 

Fig. 13. Spectra from three volume elements recorded without water suppression. Measurement parameters STEAM, TE= 10 ms, TM= 15 ms, TR = 2 s, 40 acq., VOI...

Fig. 15. Comparison of a water suppressed muscle spectrum and a spectrum from yellow bone marrow containing almost pure fat (triglycerides). Measurement parameters STEAM sequence, TE=10 ms, TM=15 ms, TR = 2 s, 40 acq., VOI (11 X 11 X 20) mm. (a) Spectrum from TA muscle recorded after careful positioning of the VOI, avoiding inclusion of macroscopic fatty septa allows separation of extramyocellular (EMCL, broken lines) and intramyocellular lipid signals (IMCL, dotted lines) based on susceptibility differences. For this reason characteristic signals from fatty acids occur double. Signals of creatine (methyl, Crs, and methylene, Cr2) show triplet and doublet structure, respectively, due to dipolar coupling effects. Further signals of TMA (including carnitine and choline compartments), Taurine (Tau), esters, unsaturated fatty acids (-HC=CH-), and residual water are indicated, (b) Spectrum from yellow fatty bone marrow of the tibia with identical measuring parameters, but different amplitude scale.

In contrast to the water resonance, Cr3 did not show a considerable MT effect in the water suppressed spectra resulting in MTRcr lower than 1%. Significant MT effects on the creatine/phosphocreatine signal in skeletal muscle have exclusively been described in rats. ... 

Sugar content (water suppression) 4.7 single pulse and IRFT 13 ... 

Cho and co-workers reported that the amplitude of the sugar proton peak following water suppression with a T null sequence correlated well with the... 

The success of fixed water suppression systems depends on the following ... 

Tm = 250 ms. 32 scans were accumulated in each spectrum using an acquisition time of 1 s and a relaxation time of 4 s. Water suppression was applied in (a) but not in (b). (Reprinted with adaptation with permission from ref. [38]. Copyright 1993 ESCOM Science Publisher... 

Since water protons are not bound to or nuclei, the water signal is also suppressed by the spin-lock purge pulse. In practice, the suppression of the water signal is sufficient to record HSQC spectra of protein samples dissolved in mixtures of 95% H20/5% D2O without any further water suppression scheme [12]. For optimum water suppression the carrier frequency must be at the frequency of the water resonance. On resonance, the phase of the water magnetization is not affected by imperfections of the first 180°(ff) pulse, so that no solvent magnetization ends up along the axis of the spin-lock purge pulse. 

The use of spin-lock pulses for water suppression is illustrated with the NOESY and ROESY pulse sequences (fig. 5). Using the Cartesian product operator description [9], the effect of the NOESY pulse sequence of fig. 5(A) is readily illustrated ... 

Fig. 5. Pulse sequences of NOESY and ROESY with spin-lock purge pulses for water suppression. (A) NOESY pulse sequence. The spin-lock pulses are typically of length 0.5 ms and 2 ms, and r = 1/SW, where SW is the spectral width in the acquisition dimension. Phase cycle (pi = x,—x) 4>2 = 4 x,x,—x,—x) ...

Fig. 3. 2Q-HoMQC spectrum of apo-cytochrome c in 93% H2O at pH = 6 and 0.48 mM concentration. The spectrum was acquired with 30 ms 2Q excitation delay overnight on a Varian Unity/INOVA 600 MHz instrument using gradient MQ selection and no additional water suppression (I.P., unpublished). Equal spectral windows were set for both dimensions.

Experimentally, the retention time of ibuprofen was found in fact to be 12.23 min. This reflects the fact that the pATa of the drug may not be exactly as given in the literature under the conditions used for chromatography and the fact that the low dielectric constant of the mobile ptese in comparison with water suppresses ionisation so that the drug is less ionised than predicted. However, the calculation gives a reasonable approximation of the behaviour of ibuprofen. 

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