UV-visible spectroscopy is widely used for the analysis of chromophores - groups of atoms characterised by strongly absorbing electronic transitions
Axiom Analytical, a supplier of sampling equipment, software, and integrated systems for vibrational spectroscopy, has announced the availability of its TNL-120EL high sensitivity UV-visible attenuated total reflectance (ATR) flow cells.
The attractiveness of UV-visible spectroscopy results from the relationship between the spectra and the molecular functional groups.
However, when using conventional transmission analysis, it is often necessary to dilute a sample by a factor of at least thousand in a suitable non-absorbing solvent.
This requirement is undesirable for a number of reasons.
The alternative is the use of attenuated total reflectance (ATR).
This approach provides an effective path length at least three orders of magnitude shorter than is practical in transmission analysis.
Until now, the most common sampling devices used for UV-visible chromophore analysis have been sapphire-tipped ATR probes.
These are often employed in such applications as pharmaceutical dissolution monitoring and the analysis of dyes and other strongly pigmented materials.
However, the available ATR probes are quite inflexible in that they are inherently restricted to three internal reflections at an incidence angle of typically 60deg.
This arrangement provides insufficient sensitivity for many applications.
Axiom's new TNL-120EL ATR flow cell overcomes the sensitivity limitations of sapphire ATR probes in three ways.
First, it uses fused silica as the ATR rod material, providing greater penetration depth per reflection than is available with the sapphire probes.
Second, its design allows the angle of incidence to be chosen to maximise sensitivity.
Third, the rod design allows the number of reflections to be increased considerably beyond the three which characterise the earlier probes.
When used to analyse aqueous samples, a nine reflection version of the new cell provides typically a factor of six greater sensitivity than is available with the sapphire probes.
The company envisions even greater sensitivity enhancement with cells employing longer ATR rods.
