| ATR Crystal Cleaning | After every sample | Remove residue with a lint-free wipe and a solvent compatible with the crystal and sample. Allow the surface to dry completely before the next measurement. | Unusual peaks remain in the background or appear in the next sample spectrum. | Sample carryover, film formation, or incomplete drying. | Repeat cleaning using a suitable solvent. Collect a fresh background after the crystal is clean and dry. | Routine |
| Crystal Protection | Every use | Use only sample-contact materials and pressure accessories that are appropriate for the ATR crystal. Avoid scratching, impact, and excessive force. | Reduced signal intensity, scattered baseline, or visible surface damage. | Scratched crystal, incompatible chemicals, or excessive pressure. | Stop using the damaged accessory and have the crystal inspected. Replace it if the optical contact surface is permanently damaged. | Service |
| Background Spectrum | At the start of a session and after major changes | Collect a background with the clean, dry ATR surface and the same instrument configuration used for the sample. | Strong atmospheric peaks, unstable baseline, or poor sample-to-background comparison. | Moisture or carbon dioxide changes, contaminated crystal, or a mismatched configuration. | Clean and dry the ATR surface, confirm the accessory is correctly installed, and collect a new background. | Check |
| Sample Contact | Every measurement | Place enough sample on the active crystal area to cover it fully. For solids, powders, and low-contact samples, apply consistent pressure when appropriate. | Weak absorbance bands, variable spectra, or poor repeatability. | Insufficient contact, uneven sample coverage, or inconsistent pressure. | Reposition the sample, increase coverage, and standardize pressure and contact time for replicate measurements. | Check |
| Liquid Samples | Every liquid measurement | Apply a sufficient volume to cover the crystal without overflowing into the instrument. Check for bubbles and remove them before collecting data. | Distorted bands, irregular intensity, or poor repeatability between replicates. | Air bubbles, inadequate coverage, evaporation, or sample spreading. | Reapply the liquid, remove bubbles, keep the contact area covered, and measure promptly when volatility is a concern. | Check |
| Pressure Application | For powders and hard solids | Use consistent, moderate pressure only when the accessory is designed for it. Do not force the pressure arm beyond its normal travel. | Large intensity differences between repeated measurements or mechanical resistance. | Variable contact pressure, unsuitable sample geometry, or overloading of the pressure mechanism. | Standardize the pressure procedure, use a smaller or flatter sample, and inspect the pressure accessory if movement is abnormal. | Check |
| Moisture Control | Daily in humid environments | Keep the instrument area stable and minimize prolonged exposure of hygroscopic samples and the ATR surface to ambient air. | Variable water vapor bands near approximately 3,400 and 1,600 cm-1, or changing background levels. | Ambient humidity, wet samples, or insufficient purge and equilibration time. | Allow the system to equilibrate, use appropriate environmental control, and collect backgrounds under stable conditions. | Check |
| Spectral Range and Resolution | Before each method or workflow | Confirm the selected spectral range, resolution, number of scans, apodization, and sampling mode match the measurement objective. | Missing bands, excessive noise, or spectra that cannot be compared with previous data. | Incorrect method settings or a changed accessory configuration. | Load the validated method, verify the accessory and optical path, and repeat the measurement using consistent parameters. | Check |
| Signal-to-Noise Ratio | When noise increases | Check sample contact, crystal cleanliness, source warm-up, background quality, and the number of co-added scans. | Random fluctuations obscure small peaks or replicate spectra show excessive variation. | Poor contact, insufficient scans, unstable background, or an optical or detector issue. | Improve contact, clean the ATR, collect a new background, increase scans if appropriate, and escalate persistent problems for service. | Check |
| Baseline Stability | Each operating session | Review the baseline before analyzing samples and allow the instrument to reach a stable operating condition. | Sloping, wavy, or drifting baseline across repeated measurements. | Temperature changes, purge instability, contaminated optics, or an unsuitable background. | Wait for thermal equilibration, verify environmental conditions, clean the sample interface, and recollect the background. | Check |
| Carryover Test | After strongly absorbing or hazardous samples | Clean the ATR surface and measure a blank or background check to confirm that no meaningful sample features remain. | Characteristic peaks from a previous sample appear in the blank spectrum. | Persistent residue, porous contamination, or solvent incompatibility. | Repeat cleaning with a compatible procedure. If residue remains, isolate the accessory and arrange inspection. | Check |
| Data Quality Review | Before reporting results | Confirm peak positions, baseline quality, replicate agreement, sample identification, and measurement conditions. | Unexpected peaks, shifted bands, saturation, or disagreement with known material behavior. | Contamination, incorrect sample preparation, poor contact, or an inappropriate interpretation. | Repeat the measurement with a clean interface and documented conditions. Compare with a qualified reference spectrum. | Check |
| Instrument Exterior and Accessories | Weekly or when visibly contaminated | Remove dust and spills from accessible exterior surfaces. Keep liquids away from vents, connectors, and internal components. | Residue buildup, blocked ventilation, or difficult accessory movement. | Accumulated dust, sample spills, or improper cleaning materials. | Power down when required by the operating procedure, clean accessible areas with approved materials, and do not open the instrument unnecessarily. | Routine |
| Performance Verification | According to the laboratory quality schedule | Run a suitable reference material or certified check standard and compare key peak positions, intensities, and noise with acceptance limits. | Reference spectrum fails established wavelength, intensity, or noise criteria. | Optical alignment change, source or detector degradation, accessory problem, or environmental instability. | Repeat the verification after checking cleaning, configuration, and background. If it still fails, remove the instrument from routine use and request qualified service. | Service |
| Software and Method Records | After method changes and periodically | Maintain controlled methods, sample identifiers, background conditions, spectral settings, and maintenance records. | Results cannot be reproduced or measurement settings are unclear. | Uncontrolled parameter changes, incomplete metadata, or outdated procedures. | Restore the validated method, document deviations, and restrict method editing to authorized users. | Routine |