UV/VIS/NIR Absorbance Measurements

Why use fibre optic spectroscopy for Absorbance measurements?

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• Spectrometer range to cover most/all measurements i.e. High resolution, High sensitivity, cooled and non cooled

• Sample testing and/or demo/loan

• Accessories – Micro flowcells, fibre optic switch or beam combiner to measure light source drift

• Pre-sales support to prove the customer has the best set up e.g. Averaging, Smoothing, choice of accessories, fibre types etc.

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The absorbance (also called optical density) of a material is a logarithmic ratio of the radiation falling upon a material, to the radiation transmitted through a material. UV/VIS absorbance measurements encompass a wide variety of chemical and biochemical applications which involve many areas of research and industrial end uses. UV/VIS absorbance can be applied qualitatively and quantitatively in spectroscopic measurement applications ranging from blood parameters to chemical concentrations in process and reaction monitoring.

Fibre optic spectrometers offer a tremendous value proposition for UV/VIS measurements because of their relatively low cost, small size and ability to be introduced in harsh environments through the fibre interface. Combined with a fibre optic transmission dip probe, inline flow cells or the more traditional cuvette cell, a fibre optic spectrometer can accurately and repeatably measure over the range from 200-1100nm.

Small Instruments Come of Age
Scientists who are largely familiar with more traditional bench top spectrophotometers may have the perception that fibre optic instruments cannot provide the resolution or straylight rejection required for the most demanding applications. The truth is that fibre optic spectrometer technology has come a very long way and Avantes instruments are on the leading edge for this technology, and our instruments are capable of measuring at resolutions as high as 0.05nm in the UV. In terms of straylight rejection, we have developed a special optical bench called the ultralow straylight (ULS) , to provide optimal performance for our customers. AvaSpec-ULS spectrometers have straylight levels as low as 0.04%.

Typically, UV/VIS absorbance systems consist of a spectrometer, stabilised light source and fibre optics, which are connected to some form of sampling accessory which could be a probe, cuvette/cell, flowcel etc etc. Single fibre optic spectrometers can be configured for broadband measurements or narrow band (any range from 200-1100nm) depending upon the desired wavelength range and resolution. Avantes UV/VIS instruments are also fully compatible with our AvaSpec NIRLine spectrometers, which enable spectroscopic measurements out to 2500nm.

Common System Configurations
Avantes modular platform enables users to configure systems in a variety of ways and also allows the flexibility of changing the system configuration later to provide additional functionality. The typical UV/VIS absorbance system consists of an AvaSpec spectrometer, AvaLight fibre optic light source, fibre cables and a cuvette/cell holder. In the illustration above, the system configuration is shown with a cuvette cell holder, a dip probe and flowcell.

Our affordable AvaSpec-ULS2048-USB2 and AvaSpec-ULS2048L-USB2 provide excellent resolution (1.0 nm FWHM) over the entire range from 200-1100nm, or higher resolution for a shorter range configuration. For higher resolution (0.6 nm FWHM from 200-1100nm) the AvaSpec-ULS3648-USB2 is recommended. Users that demand higher signal/noise performance and higher sensitivity in the UV or NIR should consider Avantes SensLine instruments.

SensLine instruments include the AvaSpec-ULS2048XL which has a high performance backthinned CCD detector,and the AvaSpec-HS1024X58/122-TEC is Avantes highest sensitivity spectrometer with a thermo-electrically cooled CCD detector and a high numerical aperture optical bench. Any of our spectrometers can be combined with our AvaLight-DHS-BAL deuterium halogen source and a CUV-UV/VIS cuvette cell holder. The CUV-DA-DHS is a nice alternative, which enables directly coupling of the cuvette cell holder to the front plate of the light source to minimise the use of fibre optics. 

This same system configuration can be integrated into a single housing to provide an integrated spectrophotometer module with a common power supply for the light source and spectrometer. We also offer the AvaAbsorb-HAL, a complete system for Absorbance measurements.

Fibre Optics
One of the most valuable attributes fibre optic instruments is the ease with which measurements can be made inline or in-process using a fibre optic probes or accessories. We offer a variety of sizes and configurations of fibre optic transmission dip probes, which include special configurations for measurements in high temperatures (up to 500 °C), high pressure or vacuum. Also available are fibre optic flow cells for standard and micro-fluidic applications.

Instrument Control Software
Avantes proprietary AvaSoft software is a Windows-based 32- and 64-bit compatible software package which enables full instrument control and includes a basic chemometry add-on module, AvaSoft-CHEM. For users requiring more sophisticated analytical software, which enables model development and multi-variate analysis, Avantes instruments are fully compatible with Panorama-Pro software from LabCognition.