| | Home | Industrial Measurement | Radiation Protection | Life Sciences | Molecular Imaging | | | About | Contact Us | |
EG&G Berthold first produced a Radio HPLC detector nearly 25 years ago. Over the years improvements have been made in the performance of the instruments resulting in the latest detectors with higher 3H and 14C sensitivity.
The Detector The new detector is available as either a "stand alone" version with compatible outputs to conventional "UV type" data stations or as a fully PC driven system under the control of Berthold's WinFlow software.
The Flow Cell EG&G Berthold has a large selection of flow cells available. Solid or liquid scintillator cells and special cells for high pressure HPLC/MS, preparative chromatography, SFC and microbore applications can be supplied.
The ScintillatorPump For admixture applications where a liquid scintillator is continuously mixed with the column eluate a mixing pump is required. The pump is separate from the main detector to eliminate the possibility of scintillator leaks into the detector and associated electronics. It is also possible to split the eluate stream prior to mixing.
The PC Software...WinFlow A complete mass and radiochromatography package WinFlow provides control of the detectors and provides full data reduction. The software provides facilities for control of pumps and data capture from mass detectors (UV, fluorescence etc.). Network systems are available for the larger laboratory.
The key to a good HPLC detector is to obtain the lowest level of detection which is a function of background (B) and efficiency (E) or "Figure of Merit" E2/B. EG&G Berthold has optimised both these aspects of the detector to provide the lowest detection limits available. The latest innovation is the Optimised Coincidence Time (O.C.T.) to produce an improved figure of merit as compared to previous detectors. The flow cell is positioned between the photocathodes of two photomultiplier tubes operating in coincidence in the same way as a conventional liquid scintillation counter. The column eluate flows through the cell and the radioactive label is detected.
Electronic methods utilising pulse timing have proved unreliable with increased suppression of the true count rate as the activity increases. This results in inaccurate percentage calculations of metabolite peaks. For this EG&G Berthold has optimised the detector design to eliminate the cause of background as much as possible. Cosmic radiation is reduced by a lead shielding, electronic noise by the selection of only the very best photomultiplier tubes. Cross talk between the tubes is virtually eliminated by using ground convex front windows.
In continuos flow monitoring applications such as RadioHPLC flow detectors, luminescence is often created as the eluate flows over the solid scintillator or is mixed with the liquid scintillator. Special selection of chemiluminescence resistant solid a liquid scintillator is important to minimise this phenomenon.
As an added benefit the detector is equipped with a novel compensation circuit that distinguishes between a radioactive and a chemiluminescent event and "strips" the luminescence spectra from the chromatogram.
The efficiency is not just a function of the detector but also of the scintillator. The liquid scintillator must be carefully selected to provide the optimum sensitivity for a given solvent system (see application note H-0100, available from EG&G Berthold). For solid scintillator the proven YG material unique to EG&G Berthold provides the ultimate in efficiency/background performance. The detector is equipped with the most sensitive 2" photomultiplier tubes operating in coincidence. The coincidence time for each type of scintillator will vary and by using automatic Optimised Coincidence Time (O.C.T.) the best E2/B is achieved. Automatic optimisation of the electronics to capture the complete energy spectrum of the isotope is also performed to ensure all detectable events are monitored.
A wide variety of flow cells are available for all types of radioisotopes and applications. The measuring cells are distinguished according to their method of application. The heterogenious method requires no liquid scintillator, hence the eluate is available for subsequence processing at the cell exit. With the homogenous "admixture" method, the column eluate is mixed with the liquid scintillator and the resulting cocktail is passed through the measuring cell. After having passed through the cell the eluate is only available as a mixture unless the eluate splitter has been used.
This homogeneous method is equivalent to continuos liquid scintillation measurement. Memory effects are excluded and counting efficiencies are high. The liquid scintillator must be carefully selected for optimum performance.
These cells consist of a very thin Teflon hose filled with fine scintillator grains. The cells have been specially designed to withstand backpressures due to eluate viscosity and flow rate. The YG cells offer exceptional efficiency yields and are very inert. Surface treated (YG-S type) cells are also available to minimise memory effects seen when analytes stick to the scintillator.
High pressure cells with test pressures upto 350 bar have been developed for special methods such as HPLC/MS and SFC.
Preparative cell with surface treated scintillator for high activity and upto 20 ml/min.
The Cherenkov cell requires no scintillator and allows high efficiency counting of 32P and other high energy beta emitters.
Special Cells for 125 I and all other gamma(PET) emitters.
Low volume solid cells with minimum dead volume for low flow rate methods such as microbore HPLC.
Solid scintillator cells can not always be used. Compounds with molecular weighs of more than 600 have a tendency to stick to the scintillator. 3H has a poor efficiency with solid scintillator and the higher efficiency of the homogeneous methods is often preferred. The scintillant flow can be started, stopped and regulated during a chromatographic run. Optimum mixing is always maintained. Initial equilibration is achieved by running the pump at maximum flow for a short period before the measurement starts.
Splitting of the eluate before mixing with scintillator is achieved by using valveless splitters, allowing part of the eluate to be diverted to a fraction collector. As only part of the eluate is radioactive, a waste valve diverts the radioactive peak to a fraction collector and the non radioactive waste to a low activity waste container.
The detector is available either as a "stand alone" microprocessor version or can be controlled by the flexible PC Windows software WinFlow. This allows the user to select the best solution for their laboratory. Measurement of all radio-labelled compounds is possible with control of scintillator pump, fraction collector, auto-sampler and waste valve to divert active waste to a separate container from the "cold" waste.
For those users who already have a chromatography data station or work with a standardised software package throughout their company the stand alone version is the correct choice. The output of the detector is compatible with UV type signals. Most RadioHPLC detectors simply convert the digital pulse rate to an analog signal and because the count interval is long (seconds rather than ms) this approach gives rise to a stepped analog output. Most "UV" chromatography data stations will see these steps as individual peaks and integration will be performed on non existent peaks. Digital filtering of the analog output helps to reduce this problem but at the expense of smoothing out real peaks. EG&G Berthold have adopted "16-bit oversampling" which mathematically fits the analog signal to the digital data resulting in a smooth output without any loss of resolution. The measurement parameters of the microprocessor option are entered via the soft-key linked interactive display. Fraction collector control and on-line peak detection is supported.
For those users who require a dedicated radiochromatography software which include the calculation of DPM, half life correction and radioactive background subtraction then the WinFlow PC software is the best option. WinFlow however is not just a RadioHPLC package. It will meet all the demands of the UV, fluorescence data reduction methods. A large number of software drivers are also available for control of many commercially available pumps. As the software is Windows based it is also possible to run other Windows pump control packages at the same time, eliminating the need for tow PC's. For those users who purchase the microprocessor stand alone version and find they want the WinFlow software at a later date then it is possible to buy an upgrade PC software version.
With Life Sciences Enquiries (Luminometers, Night Owl, HPLC) please email:
| Australia & South East Asia | berthold@berthold.com.au | |
| USA | usbio@berthold.com.au | |
| Europe | eurobio@berthold.com.au |