Chirascan™-plus Circular Dichroism Spectrometer

Benefits of the Chirascan-Plus

Chirascan-plus builds on the strengths of Chirascan by introducing a new high-performance, solid-state detector with advanced intelligent electronics to provide significant improvements in productivity, sensitivity and capability over traditional photomultiplier-based instruments.

High detector Sensitivity

The sensitivity of the new solid-state detector is significantly superior to that of a photomultiplier tube, common used in UV/Vis circular dichroism (CD) spectrometers, at all wavelengths. This is because of the very high quantum efficiency of the solid-state detector as illustrated in the figure below.

Quantum efficiency* of Chirascan Plus solid state detector and a typical photomultiplier detector

In the region of 180-260 nm, the most common range for many circular dichroism applications, there is an approximate two-fold increase in signal-to-noise (S/N). This extends to several orders of magnitude increase in signal to noise in the red regions. For an explanation of how detector quantum efficiency increases the S/N performance please consult this tutorial.

The signal-to-noise improvement translates to a 4-fold decrease in time-taken to collect data of equivalent quality as the already high-sensitivity Chirascan.

• This means a significant increase in productivity in all CD applications. For laboratories with a high demand on CD instruments, such as pharmaceutical labs working in biotherapeutic characterisation, we recommend Chirascan-plus.
• The increased sensitivity allows new approaches to experimental design not possible with previous generation machines. An example of this is the information-rich technique of dynamic multimode spectroscopy (DMS).
• The signal-to-noise gains are important for kinetic applications, such as stopped-flow CD spectrophotometry, where a significant reduction in sample volume can be obtained.

High performance optical design

Chirascan-plus uses the same innovative optical design as Chirascan, which provides very high light throughput, particularly at far-UV wavelengths. High light throughput equates to improved signal-to-noise, for an explanation of how light throughput increases the signal-to-noise performance please consult this tutorial. Shown below are calibrated radiometric scans of the light flux of Chirascan at various bandwidths.

 

The photon flux for a 1nm bandwidth is in excess of 1013 per second for all UV wavelengths from 360nm to 180nm. Should more light be required, a bandwidth of up to 4nm can be maintained down to 178nm (equivalent to a 16-fold increase in light-flux), a feature that is unique amongst prism-based CD spectrometers and derives directly from the innovative optical design of Chirascan. It means that for Chirascan, where the photon flux at 1nm bandwidth is already superior to that of other CD spectrometers, there is more than a further order of magnitude of light flux in reserve.

The superior light throughput of the Chirascan family of instruments translates directly to superior quality of measurement for a given measurement time or, equivalently, a measurement of a given quality can be completed much more quickly. Coupled with the performance of the new solid-state detector, the high light throughput means the Chirascan-plus has by far the highest sensitivity and highest productivity of any commercial circular dichroism spectrometer.

Rugged detector

The detector of the Chirascan-plus is solid-state and consequently physically rugged. This detector is coupled with intelligent electronics that can detect potentially damaging conditions, such as excessive light, and automatically protects the detector. In normal use, the detector will last the lifetime of the instrument.

Extended Wavelength range

The high quantum efficiency of the Chirascan-plus from the far-UV into the Near infrared results in a large extended wavelength range. This is illustrated below in the single spectrum of a single sample.

Single spectrum of nickel tartrate from 1100nm to 215nm, acquired on Chirascan-plus, inset of 300-400nm region

Accurate simultaneous Absorbance and CD measurement

The standard Chirascan can simultaneously measure absorbance with circular dichroism, but requires calibration of the gain of the photomultiplier tube. This adds in a small amount of inaccuracy to the measurement. The electronics in the Chirascan-plus have a known absolute gain, consequently Chirascan-plus can measure absorbance simultaneously with CD, as accurately as a high quality single beam spectrophotometer. This has a number of advantages:

• Allows accurate quantification of a sample at the same time as the CD analysis.
• Very easy to identify when the CD signal is likely to be compromised by a large absorbance of the sample, allowing easy validation of a measurement.
• Increased data content from a single experiment, in applications like DMS.

Flatter baseline

Birefringence in stressed optical elements in the light path is the major cause of baseline offsets in Circular Dichroism spectrophotometers. A significant contributor to this in conventional photomultiplier based instruments is the window of the vacuum tube of the photomultiplier itself. The solid-state detector on Chirascan-plus does not have a window and so doesn’t contribute to the baseline.

Insensitive to stray magnetic fields

The solid-state detector of Chirascan-plus is impervious to magnetic fields up to 5 tesla. This makes the detector ideal for the specialist technique of Magnetic Circular Dichroism (MCD) using either the MCD.3 accessory or home-built MCD systems, where stray magnetic fields can interfere with accurate measurements using photomultiplier detectors.

 

* Footnote: quantum efficiency is the defined as the percentage of photons hitting the detector that result in electron-hole pairs. Single deep UV photons have sufficient energy to form more than one electron hole pair, and so it is possible to have quantum efficiencies higher than 100%.

 

Chirascan plus- the next generation in CD spectrophotometers