Organic Geochemistry Research Group

Liquid Chromatography/Mass Spectrometry (LC/MS)

High-performance liquid chromatography, also called high-pressure liquid chromatography (HPLC), separates compounds on the basis of their interaction with the solid particles of a tightly packed column and the solvent of the mobile phase. Modern HPLC, such as the one used in this laboratory, uses a nonpolar solid phase, like C18, and a polar liquid phase, generally a mixture of water and another solvent. High pressures of up to 400 bar are required to elute the analyte through the column before they pass through a diode array detector (DAD). A DAD measures the absorption spectra of the analytes to aid in their identification.

To increase the selectivity and sensitivity of HPLC, it can be coupled with a mass spectrometer (MS), the setup is known as LC/MS. LC/MS allows for more accurate identification of compounds on the basis of their molecular mass and their fragment mass after decomposition. Although MS is often considered to be adequate for the identification of compounds, the combination of the DAD and MS helps assure the identity of the analytes.

LC/MS Analysis

Two Hewlett Packard (Agilent) complete systems of 1100 series liquid chromatographs equipped with diode array detectors and mass spectrometers are in use for research projects, methods development, and other analyses. Each LC system is further equipped with refrigerated sample compartments on the autosamplers to preserve sample integrity. There are Spark-Holland's Prospekt^TM "online" solid-phase extractors for each of the complete LC system with Triathlon autosamplers for large volume sample handling. All instrument systems are controlled by completers, as is the data collection.

An extracted calibration curve is included within each LC/MS instrument run along with blanks and duplicates. Extraction efficiencies are performed with each instrument run. Internal standards are added to each blank, standard and sample prior to injection into the LC/MS system. Prior to any preparation surrogate standards are added to each blank, standard, and sample to monitor the overall extraction and analysis in the method.

*The use of brand, trade, or firm names in this description is for identification purposes only and does not constitute endorsement by the U.S. Geological Survey.

Selected LC/MS References

1. Lee, E.A., Strahan, A.P., and Thurman, E.M., 2002, Methods of Analysis by the U.S. Geological Survey Organic Geochemistry Research Group-Determination of Glyphosate, Aminomethylphosphonic Acid, and Glufosinate in Water Using Online Solid-Phase Extraction and High-Performance Liquid Chromatography/Mass Spectrometry: U.S. Geological Survey Open-File Report 01-454.

2. Lee, E.A., Kish, J.L., Zimmerman, L.R., and Thurman, E.M., 2001, Methods of analysis by the U.S. Geological Survey Organic Geochemistry Research Group--Update and additions to the determination of chloroacetanilide herbicide degradation compounds in water using high-performance liquid chromatography/mass spectrometry: U.S. Geological Survey Open-File Report 01-10, 17 p.

3. Lindsey, M.E., Meyer, M.T., and Thurman, E.M., 2001, Analysis of Trace levels of Sulfonamide and Tetracycline Antimicrobials in Groundwater and Surface Water using Solid-Phase Extraction and Liquid Chromatography/Mass Spectrometry, Analytical Chemistry, v. 74, p. 4640-4646.