Diffuse Reflectance Accessories (DRAs)

Importance of Diffuse Reflectance Analysis

Diffuse reflectance measurements are vital in analytical chemistry for characterizing surfaces and bulk materials where light scattering dominates. By capturing both specular and diffuse components, researchers can accurately determine optical properties of powders, coatings, solar materials and turbid media. Integrating sphere attachments extend the capabilities of UV-Vis-NIR spectrophotometers, enabling reflectance, transmittance and absorptance studies that are otherwise challenging with conventional cuvette-based approaches.

Objectives and Overview

This application note reviews the design and performance of Agilent’s external and internal Diffuse Reflectance Accessories (DRAs) for the Cary 4000, 5000, 6000i and 7000 spectrophotometers. Key goals include:

• Summarize accessory configurations that support diffuse and total reflectance modes
• Compare internal versus external sphere geometries and their measurement reach
• Outline detector options and wavelength coverage for UV-Vis and NIR analyses
• Highlight practical applications in quality control, materials research and kinetics

Methodology and Instrumentation

The integrating sphere accessory features a hollow sphere coated with a diffuse reflector. Samples can be mounted on the wall or at the center, allowing for:

• Diffuse reflectance (excludes specular component)
• Total reflectance (includes specular component)
• Diffuse transmission and absorptance with center mounts

Two formats are offered:

• External DRA extends beyond the instrument footprint, accommodates unlimited sample dimensions in reflectance mode and supports small-spot, variable-angle and transflectance measurements.
• Internal DRA fits inside the sample compartment, providing compact geometry, higher signal-to-noise ratio and limited sample size bounded by compartment dimensions.

Detector choices include:

• DRA-900: PMT detector for low noise and wide photometric range (200–900 nm).
• DRA-2500: PMT plus PbS photo-detector, Peltier-cooled for extended NIR range to 2500 nm.
• DRA-1800: PMT plus narrow-band InGaAs detector for improved sensitivity up to 1800 nm.

Main Results and Discussion

Comparative evaluation shows external DRAs support a broader set of measurement modes, including large or highly granular samples, transflectance kinetics with reference beam access and small-spot analysis down to 5 mm. Internal DRAs deliver superior dynamic range and noise performance for low-volume powders and routine QA/QC. Wavelength coverage depends on spectrophotometer limits and detector choice. Both formats enable exclusion or inclusion of specular reflection, and variable-angle transmittance enhances analysis of scattering media.

Benefits and Practical Applications

Key advantages of integrating sphere DRAs include:

• Comprehensive optical characterization of matte and glossy surfaces
• Reliable analysis of powders in disposable cuvettes or powder cells
• Measurement of turbid liquids, coatings and solar cell materials
• Simultaneous reflectance and transmittance for absorptance studies
• High throughput QA/QC workflows with minimal sample preparation

Future Trends and Potential Applications

Advances in detector technology and sphere coatings may further extend spectral range into the SWIR region. Integration of automated sample changers and robotics will boost throughput for industrial QC. Emerging fields such as in-situ polymer curing studies, real-time monitoring of nanoparticle suspensions and advanced colorimetry in digital displays are expected to leverage refined diffuse reflectance methodologies.

Conclusion

Agilent’s external and internal DRAs for Cary spectrophotometers offer versatile and robust solutions for diffuse reflectance, transmission and absorptance measurements across the UV-Vis-NIR spectrum. Selection between formats hinges on sample size, dynamic range needs and measurement modes. Combined with tailored detectors, these accessories enhance analytical capabilities for research, quality control and industrial applications.

Instrumentation

Integrating sphere accessory (110 mm internal or 150 mm external), Cary 4000/5000/6000i/7000 spectrophotometers, detectors: DRA-900 (PMT), DRA-2500 (PMT/PbS), DRA-1800 (PMT/InGaAs).