FAQ

• Required Equipment Status Before Formal Testing

  ● Before formal testing, the magnet temperature control of the NMR system must reach and stabilize within ±0.03℃ of the preset value. The typical preset is 32℃ (35℃ for the cross-link density analyzer);

  ● All other switches on the cabinet should be ON with indicator lights illuminated;

  ● Software launches normally;

  ● Use the calibration oil sample with the FID sequence to complete SF calibration and P1/P2 calibration.

• Sample Requirements and Recommended Sample Amounts

  ● Before NMR testing, no complex pretreatment is required. Solid samples should be cut to fit the holder, then weighed;
  ● Liquid samples must be sealed, e.g., bagged or bottled in capped glass vials;
  ● For vertical holders, the sample height should not exceed 2.5 cm and is not recommended below 1 cm;
  ● For horizontal holders, the sample length should not exceed 3 cm (for 60 mm bore systems, avoid lengths over 5 cm).

• Industrial PC Won’t Boot / Monitor Won’t Turn On

  ● First check whether the monitor cable is loose;
  ● If secure and still not working, reseat the RAM and interface boards in the PC;
  ● Possible poor contact;
  ● Open the NMR system’s PC chassis, locate the boards, and reseat them;
  ● Locate the RAM module(s) and reseat them;
  ● Do not use excessive force when reseating.

• During Calibration, FID Is a Flat Line or Very Noisy

  ● Confirm the RF unit is powered on;
  ● Ensure the probe contains the calibration sample;
  ● Verify SF and O1 match the factory report or a known-good configuration; adjust if they differ;
  ● Check rear-panel cabling for poor contacts; replace with a spare RF cable if needed.

• Suggested CPMG Parameters for Common or Special Samples

  In low-field NMR, suggested parameter presets:
  1) Dry powders / dry samples / plastics:
  T2: set TE to the minimum the instrument allows, i.e., slightly greater than (12*P1 + 6*P2) – P1 and P2 are shown in the left panel and vary by system; set NECH so the signal fully decays with a short flat tail; TW 500–2000 (tune per TW method); NS 16–64 depending on SNR (rule of thumb: highest initial point divided by the average of the last few points > 50); SW 200.
  2) Fresh meat / seafood / fruit:
  T2: TE 0.5–0.8 ms; NECH so the signal fully decays with a short tail (typically 10,000–18,000); TW 6000–8000; NS ≈ 4 depending on SNR; SW 100.
  3) Gels:
  T2: TE 0.4–0.6 ms; NECH to full decay with short tail (≈ 10,000–18,000); TW 8000–10,000; NS ≈ 4; SW 100.
  4) Rubber:
  T2: TE ≈ 0.2 ms; NECH to full decay with short tail; TW 500–3000; NS ≈ 8; SW 200.
  5) Liquids:
  Oils/fats: T2 TE 0.2–0.4 ms; NECH 4000–6000; TW 2000; NS 2–8 per SNR; SW 100.
  Pure water (DI/ultrapure): T2 TE ≈ 1 ms; NECH 18,000; TW 18,000; NS ≈ 2; SW 100.
  Ethanol: similar to water; slightly smaller TE/NECH/TW, e.g., TE 0.8 ms, NECH 15,000, TW 15,000.

• How to Judge If CPMG Parameters Are Appropriate

  ● After acquisition, the CPMG decay should fully attenuate and level off at the end;
  ● The decay should be smooth and exponential with no point dropouts; if not fully decayed, increase NECH (up to ~18,000) or TE — prioritize increasing NECH;
  ● Check the vertical scale: higher initial amplitude improves SNR; typically aim for thousands to tens of thousands;
  ● If the signal is weak, increase NS.

• How to Judge If IR Parameters Are Appropriate

  ● After acquisition, the IR recovery should complete with the last 2–3 points stable and no obvious upward trend; the curve should be smooth and exponential;
  ● If recovery is incomplete, increase TW and reset NTI;
  ● For better SNR, aim for a higher peak amplitude (typically > 100);
  ● If the signal is weak, increase PRG and NS as needed.

• Abbreviation Expansions and Meanings

  SEQ: sequence
  SF: spectrometer frequency
  O1: offset 1
  P1: pulse 1 [90° pulse]
  TD: time data
  DR: data radius
  PRG: pre-amp regulate gain
  SW: sampling bandwidth
  RFD: RF delay (regulate first data)
  TW: recycle delay (time wait)
  RG1: analog gain 1
  DRG1: digital gain 1
  NS: number of scans (sampling)
  P2: pulse 2 [180° pulse]
  TE: echo time
  NECH: number of echoes
  Peaks parity: peak picking