Chromatographic Methods for Environmental Analysis - Fundamentals of Environmental Sampling and Analysis - page 284

connection) can result in the retention time shift. In HPLC, changes in mobile phase
flow rate and composition, small leaks, small air bubble, column aging and
deactivation, or not fully equilibrated system are common causes for the change in
retention time. In some cases, an increase in peak width, particularly in early eluting
peaks, is because of inappropriate tubing i.d. or mis-set nut and ferrule union. It is
almost essential for every HPLC user to have the basic skills in replacing and
connecting tubings and unions.
In addition to using chromatogram to guide troubleshooting, pressure in HPLC
system is another effective diagnostic tool. No or low pressure could be air bubbles,
mis-set backpressure regulator, leaks in unions and fittings, broken piston, or major
leaks around piston seal. High pressure could be because of clogged in-line filter,
clogged guard column/analytical column, or clogged connected tubing. High
pressure can also be because of the inadequate large flowrate, immiscible solvents,
or use of large percentage of high viscosity mobile phase such as isopropanol.
Fluctuated pressure may be because of damaged pump valves and/or worn seal, air
bubble in the pump head, or partially clogged pump inlet filter.
Practical tips
Skilled readers can further consult GC and HPLC troubleshooting guides such as
published by Agilent Technologies. As a beginner, you may attend the year-round
workshop held by manufactures in many large cities in the United States. Some
seminars are free, and others may have high cost. Many instrument manufacturers
provide online technical support, training/education and events, application notes,
and literature library. The web addresses of a handful of these are provided below.
Agilent Technologies, Inc.: http://www.chem.agilent.com
Alltech Association, Inc.: http://www.alltechweb.com
Dionex Corporation: http://www.dionex.com
Perkin Elmer, Inc.: http://las.perkinelmer.com
Shimadzu Corporation: http://shimadzu.com
Waters Corporation: http://www.waters.com
REFERENCES
Agilent Technologies, Inc. (2001), Maintaining Your Agilent 1100 Series HPLC System.
Agilent Technologies, Inc. (2001), Maintaining Your GC/MS System.
Agilent Technologies, Inc. (2002a), Maintaining Your Agilent GC System.
Agilent Technologies, Inc. (2002b), GC Troubleshooting Guide.
C HRISTIAN GD (2003), Analytical Chemistry, 6th Edition, John Wiley & Sons Hoboken, NJ.
F RITZ JS, G JERDE DT (2000), Ion Chromatography, 3rd Edition, Wiley-VCH Weinheim.
G ROB RL, B ARRY EF (2004), Modern Practice of Gas Chromatography, 4th Edition, Wiley-Interscience.
K ROMIDAS S (2004), Practical Problem Solving in HPLC. Wiley-VCH weinheim.
M ANAHAN SE (2004), Environmental Chemistry, 8th Edition, Lewis Publishers, Boca Raton, FL.