What is an electrochemical (EC) detector? An EC detector for a liquid chromatograph detects analytes based on their electrochemical properties. The detector either removes an electron from (oxidation), or donates one to (reduction) the analyte molecule . The amount of current generated by the redox reaction is proportional to the amount of analyte present. See PRINCIPLES OF EC DETECTION for a detailed explanation.
How do I know which analytes can be determined by LCEC? Published literature is a good source of information about routine analytes. BAS Application Capsules have specific information for determining many analytes. Electrochemical data for many other compounds are presented here. Finally, you may contract with BAS to determine the electrochemical properties of any molecule of interest.
How can I learn more about EC detection?Read our PRINCIPLES OF EC DETECTION tutorial.
How do I hook up this thing? It would be best to follow the detailed INSTALLATION instructions. Briefly, the epsilon detector is connected to the computer's serial port by a standard RS-232 cable. The cell leads plug into the back of the epsilon detector, and to the flowcell at the other end. The flowcell connections are coded by size, gender, and color, so there should be no confusion there. Finally, the flowcell is plumbed into the LC flow stream with standard 1/16" fingertight connectors.
Do I need to use your software? I have my own data-analysis software. You can use your own software for data collection and analysis. However, you will have to use BASi Control software to turn on and set the parameters of the epsilon detector. Instructions can be found here.
What is a working electrode? A working electrode is a piece of conducting material (glassy carbon, gold, platinum, etc.) embedded in a plastic block. It is positioned so the eluent from the column will flow across its surface. Electrical connections on the back side allow the electronics to apply a potential and measure the resulting current.
When should I polish the working electrode? Usually only when your analyte peaks have gotten smaller and you suspect that the surface of the electrode is coated with something nasty.
How do I polish the working electrode? The simplest way is to wipe it hard with a laboratory tissue wetted with methanol. If that doesn't help, mild abrasives and pads are provided in the polishing kit.
What is a reference electrode? A reference electrode is an electrochemical device that produces a known (reference) potential. Its functioning is critical because the potential applied to the working electrode is based on the potential of the reference electrode. A BAS reference electrode is a tube with a porous frit at one end, containing a silver-chloride-coated silver wire in a sodium-chloride gel solution.
How do I store the reference electrode? Because the reference electrode has a porous frit at one end, it is subject to drying out. To prevent this, carefully remove the rubbery shipping coat from the end of the electrode and store it with its tip immersed in 3M sodium chloride.
What potential should I use? In general you should use as high a potential as you need to oxidize or reduce your analyte. But the higher the potential you use, the higher will be your background, and the more extraneous compounds will be detected. BAS Application Capsules detail the required potentials for many analytes. Electrochemical data for many other compounds are presented here. Finally, you may contract with BAS to determine the electrochemical properties of any molecule of interest.
What is range? Range is the amplification of the detector, expressed as the amount of current produced by a peak. For example, a peak that generates 100 nanoamperes of current would be half scale on a range of 200 nAfs (nanoamperes full scale). And a range of 20 nAfs is ten times more sensitive than one of 200 nAfs.
What range should I use? Use a range that will keep your largest peaks on scale. When in doubt, use a less-sensitive range, because the data-analysis system can easily resolve small peaks. A peak that goes off scale, on the other hand, cannot be quantitated.
What is filter? A filter is an electronic way of filtering out unwanted noise in detector output. Most detectors have built in filtering, sometimes called rise time. BASi filters are calibrated in Hertz (Hz). Large Hz values give less filtering than small values.
What filter should I use? For challenging determinations, use the filter that gives you the best signal-to-noise ratio. This must be determined by trial and error. For routine determinations, 0.1 Hz works well.
What is background? Background is the electrochemical activity of your system when analytes are not passing through the detector. It has contributions from the mobile phase, contaminants, electrodes, etc. High backgrounds contribute to baseline noise.
How do I offset (zero) background? Use the zeroing functions of the epsilon detector. When not doing programmed runs, the detector can be zeroed through a button in the Detector Status box. During programmed operation you can still use the zero button, or you can insert automatic rezeroes in the EC Detector Schedule.
How do I import information about the samples?You need to enter this information in a special file called a RAN file, then tell ChromGraph Control to use this file.
What are all these files on my disk? There are a lot of files associated with instrument control, data acquisition, data processing, and results presentation. Here's a list of the files you may encounter:
FILES CREATED OR USED BY CHROMGRAPH CONTROL
|.mth||Method||Instrument control and data-collection options|
|.mth||Backup||Auto-backup of main Method|
|.dat||Data||Raw data and comments|
|.log||Log||Log of injection times, run numbers, etc.|
|.lok||Backup Log||Log file cleared and copied here when it gets > 100 KB|
|.baq||Queue||Advanced programming for on-the-fly changes in Methods|
|.ran||Ran||Import sample info and save with data file|
FILES CREATED OR USED BY CHROMGRAPH REPORT
|.met||Method||Instructions to identify and quantify peaks, print reports|
|.dat||Data||Raw data (generated by Control, used by Report)|
|.bln||Baseline||Graphical representation of each run|
|.rep||Report||Text file of results (peaks, retention times, areas, etc.)|
|.sta||Standards||Info about standards for quantitation of unknowns|
|.prn||PRN||Processed data for exporting to spreadsheets|
|.csv||CSV||Processed data for exporting to spreadsheets|
|.tab||TAB||Processed data for exporting to spreadsheets|
How can I make the graph from my UV detector read in AU? ChromGraph can receive range settings from the on-board EC detectors, but not from external detectors such as UV/Vis and Fluorescence detectors. This has no effect on quantitation, but graphs look better when the units are correct for the detector used. ChromGraph allows you to enter the relevant detector settings so the graph is correct.
How do peak heights and areas relate to amperes and coulombs? Peak heights are reported in counts, a digitized representation of detector response. Peak areas are counts summed over the width of the peak. Most people do not need to know about converting to amperes and coulombs, but if you do, the formulas are here.
What periodic maintenance is required? You should clean the fan filter every three months. The reference electrodes should be stored in fresh 3M NaCl and a fresh one switched with the one in the instrument occasionally (whenever convenient).
What's the best way to shut down the system? You should flush out the mobile phase (which can be corrosive, and will leave abrasive salt deposits as it evaporates), remove and cap the column, disassemble the flowcell and store the electrodes. Details in the SHUTDOWN section.
How do I reduce a high background? In LCEC, cleanliness is important. Details here.
What can I do about pump noise? See the extensive troubleshooting sections on baseline noise.
Why did my peaks get smaller? There are many possibilities. Did you make a dilution error? Are your standards fresh? Is the working electrode coated with nasty stuff? Is the reference electrode weak? Is the injector bad? Is the column losing efficiency? See the TROUBLESHOOTING section.
Why did my pressure go up? Has the temperature gone down? Did you change to a higher viscosity solvent such as methanol? If neither of these, there's likely a partial clog somewhere. Disconnect things one at a time, starting at the column and working back to the pump. In-line filters are a good possibility, as this is what they're supposed to do. See the TROUBLESHOOTING section.
How do I run an electronic self-test? This section pertains to the epsilon electrochemical detector only. The epsilon contains two built-in resistors that can be substituted for the flowcell, thus providing a known input for testing the electronic circuits. See the SELF-TEST section.