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Liquid Chromatography

Liquid Chromatography Overview

Liquid Chromatography (LC) measures non-volatile and semi-volatile organic analytes based on their relative affinity for a mobile and stationary phases.  This technique is commonly employed to measure relatively polar and/or heat sensitive analytes in a variety of sample matrices.

Methods

Galbraith's LC method is written to handle a wide range of sample types.  The method specifies a range of columns and allows for unspecified columns.  The method also allows for a range of mobile phase components.  Click below to view a copy of the method summary: LC-100-HPLC-Analysis-GLI-Method-Summary

Detectors

The following detectors are available for LC analysis:
  1. A Refractive Index Detector (RI) measures the change in the refractive index of the mobile phase during elution of an analyte.
  2. An Ultraviolet-Visible (UV-VIS) detector measures the change in the absorbance of ultraviolet or visible light by the mobile phase during elution of an analyte.
  3. A Diode-Array Detector (DAD) uses the same principle as the UV-VIS detector, yet it offers the ability to monitor multiple wavelengths during analysis.
Separate methods for each detector are not provided.  The detector will be chosen based on the identiy(ies) of the analyte(s).

Preparation

Each successful analysis begins by adequately dissolving the sample for analysis.  Many solvents may be used as long as they don't interfere in the analysis and sufficiently dissolve the sample.

Analysis

LC instruments are externally calibrated with the use of approximately 5 calibration standards.  Sample solutions are injected onto the column and are separated based on their relative affinity for the stationary (column) and mobile phases.  Components of the analysis solution are detected using one of the available detectors to provide a sample chromatogram.  The area under the desired (target) peak(s) is integrated and is compared to the calibration curve to provide the concentration.

Quantitation Limit

Unless otherwise evaluated, the quantitation limit (QL) depends on the concentration of the lowest calibration standard used to calibrate the instrument.  Results that read below the QL are reported as less than values, i.e <50 ppm.

Results

Results are reported using the mass of sample originally taken for the analysis.  Typical reporting units are ppm, mg/L, or %.  Other units may be reported.

Regulated Submissions

The general methodology is suitable for the analysis of regulated samples.  The method is considered validated to a reference substance, but not to the sample matrix unless a formal validation is conducted.  Click here to see more information on Method Validation.