DSS standard.

• For a DSS sample in deuterated water
  
• Set the temperature and load the sample.
• Starting from a suitable shim files, shim using the lock signal as usual.
• Tune and match the proton probe as usual.
• If you haven't already, make a specialized version of calib1h with edc (eg. 1d_dss.xxx)  set TD to 8K.
• Take spectrum (zg), transform (ef), and phase.
• The spectrum will have two tall peaks with 3 short peaks in between.  The one on the left is deuterated water (ie. ^[1]H in HDO); the one on the right is the relevant DSS resonance.  Ignore the short peaks.
• Zoom on the rightmost DSS peak. Click <utilities> and <O1>.  Position the cursor on the peak top and read the absolute frequency from the information window.  For 300 K, it would be 500.1312532.  Be careful not to middle click, else you will change a carrier frequency setting in the active dataset.
• Use <calibrate> to set this peak to zero, and then get the chemical shift to deuterated water as above.  For 300 K (true), it would be 4.7396.  This is the value to use for the center position shift of hydrogen.
• To get center positions for nitrogen or carbon, multiply the absolute DSS frequency by the relative chemical shift constant for that nuclei to get the extrapolated reference frequency.  The relative chemical shift constants are given in the Markley et al. paper cited above and are based on choosing reference values (ppm = 0) for the other nuclei at a constant proportion to the hydrogen DSS standard under all conditions.  The nitrogen reference is 0.10132918 times the hydrogen reference.  The carbon standard is 0.251449530 time the hydrogen reference.
• For nitrogen: Look in the pulse program and see on what channel nitrogen.  For hsqc_fb.ref, it is channel f3.  The carrier frequency will be found in parameter SFO3 = 50.683840.  Take the difference between the carrier and the nitrogen reference frequency and divide by the  reference frequency to get the center position for nitrogen. So for ^[15]N, the reference frequency is 500.1312532 * 0.101329118 =  50.677859.  The center position offset is (50.683840-50.677859)/50.677859 =118.05 ppm.
•  ^[13]C is calculated similarly except that the carrier frequency may be a little more complicated to identify.
• In some cases involving ^[13]C, The frequency is switched among several different frequencies.  If this is the case, there will be a list of frequencies listed specified by the parameter F2LIST.  The pulse program will advance through this list each time it exectues an "O2" command, cycling back to the beginning of the list as necessary.  Only one of these frequencies will be used as the ^[13]C carrier with respect to evolution of the ^[13]C  magnetization in te indirect dimension.  The other frequencies are used for decoupling.  It may not be obvious to the casual user which frequency on the frequency list is the correct one to use for the carrier position.  In this case, there should be a comment in the header of the pulse program clarifying which frequency to use.  As a rule of thumb, always read the comments in the pulse program first.
• For example, suppose that you establish that the ^[13]C carrier was at = 125.764214.  500.1312532 * 0.251449530 = 125.757769.  (125.764214 - 125.757769)/125.757769 = 50.12 ppm