What follows is a short list of problems, "observations" followed by a list of areas that should be investigated, as appropriate in parenthesis (), to troubleshoot common problems seen when using the analytical technique of capillary electrophoresis, CE, CZE.
Observation (Investigate for cause):
Excessive Baseline Drifting up or down
· Temperature is not stable (stabilize room and/or capillary temperature).
· Fouling of capillary (replace or clean and wash capillary with fresh, filtered solution).
· Current levels unstable (loose connections, partial obstruction in capillary or running out of buffer solutions).
· Capillary may have poorly cut ends resulting in poor connections or flow (replace capillary).
Excessive Signal Noise
· Detector has air in flow cell (purge capillary and wash flow path).
· Current level may be too high (reduce current).
· Detection parameters, wavelength and bandwidth, may be inappropriate for buffer solution (select appropriate detection settings which are appropriate for the buffer used and selective for the analyte).
Loss of Signal
· Voltage/Current has turned off (turn ON or investigate if system is in “alarm” state due to an error).
· Detector parameters not selected.
· Capillary has not been fully equilibrated (equilibrate capillary and auto-zero the scale).
· Baseline offset may be off-scale (after equilibration, adjust scale or auto-zero).
· Detector lamp(s) off, not ignited or due for replacement (verify lamp operation).
Signal Peak Shape Issues
· Truncated, clipped or ‘square’ peaks (sample overload, reduce concentration 10x, shorten load time and re-evaluate).
· Tailing peaks often result from very high current or when the concentration of buffer is too high (lower the current and/or reduce the buffer concentration, then re-evaluate).
· Sampling rate may be too low (measure the peak width in units of time (i.e. seconds), then configure the detector to insure that the sampling rate allows for at least 20 points to be collected per average peak width (30 points is a better target # to use).
· No peaks observed (Many possible causes, including: Partially or fully obstructed capillary, broken capillary, out of buffer, no injection, detector settings inappropriate for analysis, current too low, pressure too low. Look for a small peak from the injection along the start of the baseline to confirm that an analysis was started, then troubleshoot the method and settings).
General Stability and Noise Issues
· When the CE system has not been used in a few days, salts from the buffer solution(s) may deposit on and clog the capillary line, flow cell and/or sensors. To avoid these problems, be sure to thoroughly clean, flush and wash down the flow path before use. Take the time to prepare fresh filtered solutions (each day) and allow time for the system to equilibrate. Taking these basic steps will avoid many hours/days of frustration.
