| Measurement principle | An infrared beam enters an ATR crystal and undergoes internal reflection, producing an evanescent wave that interacts with the sample surface. | Suppliers should provide clear optical documentation, validated accessories, and application guidance for solid, liquid, and semi-solid samples. | Material identification, contamination checks, polymer analysis, pharmaceutical testing, and quality control. |
| Typical mid-infrared range | Approximately 4,000–400 cm−1, depending on the instrument, beamsplitter, detector, and ATR crystal. | A wider usable range can improve access to functional-group and fingerprint-region information. | Organic compounds, coatings, elastomers, oils, solvents, powders, and biological materials. |
| Routine spectral resolution | 4 cm−1 is common for routine identification; 2 cm−1 or 1 cm−1 may be selected for better separation of narrow bands. | Higher resolution may improve peak discrimination but can increase acquisition time and data size. | Research spectroscopy, mixture analysis, reaction monitoring, and library matching. |
| ATR penetration depth | Typically about 0.5–5 μm, depending on wavelength, incidence angle, crystal refractive index, and sample refractive index. | The technique is highly surface-sensitive; suppliers should explain sampling depth and its effect on layered or coated materials. | Surface contamination, thin coatings, films, paints, laminated materials, and heterogeneous solids. |
| Diamond ATR crystal | Very hard and chemically resistant; suitable for many solids, powders, liquids, and abrasive samples. | A strong general-purpose option with low maintenance and good resistance to routine mechanical wear. | Polymers, pharmaceuticals, minerals, rubber, food materials, and industrial samples. |
| Zinc selenide crystal | Good infrared transmission across much of the mid-IR region; softer and more chemically vulnerable than diamond. | Useful for routine liquid and soft-sample measurements, but chemical compatibility and cleaning procedures must be confirmed. | Liquids, oils, solvents, polymers, and non-abrasive laboratory samples. |
| Germanium crystal | High refractive index and relatively shallow sampling depth; commonly used when surface sensitivity is important. | Can reduce the contribution from bulk material and is useful for strongly absorbing or high-refractive-index samples. | Thin films, coatings, dark samples, carbon-filled polymers, and surface analysis. |
| Number of ATR reflections | Single-reflection designs are common; multiple-reflection designs can increase effective interaction and sensitivity. | The supplier should match the reflection design to sample contact, expected concentration, and required throughput. | Single-point identification, low-level component analysis, liquids, and continuous testing. |
| Sample preparation | Usually minimal or unnecessary; the sample must make adequate, uniform contact with the crystal. | Efficient workflows reduce solvent use, preparation time, and operator variability. | Incoming inspection, production-line checks, forensic screening, and rapid laboratory testing. |
| Pressure-control accessories | Adjustable pressure devices help maintain reproducible contact for solids, powders, and rough surfaces. | Consistent contact improves repeatability and reduces differences between operators. | Powders, pellets, textiles, rubber, composites, and irregular solid parts. |
| Atmospheric compensation | Software may compensate for atmospheric water vapor and carbon dioxide features; purge systems can further reduce interference. | Important for low-concentration measurements, long scans, and laboratories with changing humidity. | Quantitative analysis, spectral library creation, and regulated quality-control workflows. |
| Detector options | DTGS detectors are widely used for routine work; cooled detectors can offer improved sensitivity for demanding applications. | Detector selection should reflect signal strength, scanning speed, spectral range, and sensitivity requirements. | Routine identification, rapid screening, trace-level measurements, and time-resolved experiments. |
| Validation and reference standards | Method documentation can reference recognized practices such as ASTM E1252 for obtaining and interpreting infrared spectra. | Documented validation, calibration, repeatability, and audit trails are important for regulated or quality-critical environments. | Pharmaceuticals, food testing, petrochemicals, environmental analysis, and manufacturing QA. |
| Software and data integrity | Key functions include background correction, ATR correction, baseline processing, library search, export, user permissions, and audit trails. | Software capability often determines workflow efficiency and suitability for electronic-record requirements such as 21 CFR Part 11 environments. | Regulated laboratories, multi-user facilities, remote review, and automated reporting. |
| Service and lifecycle support | Relevant factors include installation, training, preventive maintenance, spare parts, crystal replacement, software updates, and technical response time. | Long-term support can have a greater effect on total ownership cost than the initial instrument price. | Central laboratories, production facilities, contract testing, universities, and distributed global operations. |