Static Low-E Probes:
Changing Sample Coils and Observe Nucleus

Changing Observe Nucleus

Fig. 1.  Typical layout of chip capacitors that determine observe frequency. Not all chips require replacement. Actual probe may have smaller number of chips.

Our static low-E probes were designed with the ¹⁵N detection in mind but its observe channel X can be re-tuned to other nuclei. Re-tuning is done by replacing the detachable chip capacitors C8A, C8B, C7A, and C5A (where applicable). Typical locations of these chips are indicated in Fig. 1. To switch the observe frequency, use tuning table (go to individual probe's page) to determine which of these chip capacitors require replacement. Loosen the screws holding them in place enough to slide their leads out. Replace capacitors according to tuning table for each probe. For any unused screw terminal, make sure the screw is turned all the way in. When fastened, screws should be tight but be careful not to overtorque. People with large fingers should be careful due to their inherent ability to apply more torque. We also suggest using gloves when handling conductive parts inside the probe to prevent an unnecessary oxidation.

Changing Sample Coils

The static low-E probes feature replaceable sample coil assembly and can be used with different sample geometry. The low-E assembly can be made for large and small rectangular samples (Figs. 2A, 2C), and it can also be oriented at 90° to static magnetic field (Fig. 2B). Other shapes such as round coil for bicelle preparations can be arranged (Fig. 2D). To change sample coil assembly, fully unscrew the 4 brass screws on top of the Teflon plate inside the sample VT chamber (remove the 2 screws holding inner coil leads first). When installing the new coil assembly, fasten the outer ¹H resonator first, but do not tighten the screws. Insert 2 small head screws to align the leads of the inner solenoid. Tighten all screws starting from those holding the ¹H resonator. Attach correct tuning chips and REMEMBER to adjust your power levels for the newly installed sample coil assembly!!!

Fig. 2. (A) Standard 470 uL flat coil; (B) Same flat coil rotated 90 degrees; (C) Smaller flat coil for limited sample volumes; (D) Round 5 mm bicelle coil.

How to read the capacitance value on a chip?

Fixed value chip capacitors are normally marked in picoFarads (pF), using 2 significant digits. Another, third digit indicates the power of 10, and the letter after it normally specifies tolerance. Example: 150G means 15 x 10⁰ = 15 pF +/- 2%. If capacitor value is less than 10 pF, letter "R" is introduced in place of a floating dot. Example: 2R2B means 2.2 pF +/- 0.1 pF.