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Volume IV - 5.3 Gas Chromatography

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Orientation and Training

Food and Drug Administration

DOCUMENT NO.:

IV-05
VERSION NO.: 1.3

Section 5 - Pesticides Analysis

EFFECTIVE DATE: 10/01/2003REVISED: 02/14/2013

5.3.1  Instrumentation and Apparatus

A.  Objective

To present an overview of basic gas chromatographic apparatus in the laboratory.

B.  Assignment

The trainer will introduce basic gas chromatographic apparatus for the various commercial units in the laboratory and explain its use in pesticide analysis. The locations of components, including carrier gas supply injection port, columns, detectors, electrometers, recorders, and data systems will be shown and discussed.

C.  Reference

  1. U.S. Food & Drug Administration, Center for Food Safety and Applied Nutrition, Office of Plant, Dairy Foods and Beverages. Makovi, C. M. (Ed.), McMahon, B. M. (Ed Emerita). (1994). Pesticide analytical manual-multresidue methods (3rd ed., Vol. I, chap. 5-Gas Liquid Chromatography, updated October 1999). R.O.W. Sciences, Inc.

D.  Instruction

Using a block diagram, illustrate the basic GC apparatus needed for pesticide analysis.

5.3.2  Injection Techniques

A.  Objective

To develop a reproducible and precise manual injection technique.

B.  Assignment

The trainer will demonstrate acceptable injection techniques. The training will include proper syringe handling and cleaning, and a discussion of injection volume.

Inject a standard in triplicate using each demonstrated technique. Make 10 injections and determine the coefficient of variation of the peak heights.

C.  Reference

  1. U.S. Food & Drug Administration, Center for Food Safety and Applied Nutrition, Office of Plant, Dairy Foods and Beverages. Makovi, C. M. (Ed.), McMahon, B. M. (Ed Emerita). (1994). Pesticide analytical manual-multiresidue methods (3rd ed., Vol. I, section 501-General Information, updated October 1999). R.O.W. Sciences, Inc.

D.  Questions

  1. What is the major consideration in using the "solvent flush" technique for GC injections?
  2. Generally, what causes bubbles or non-smooth draw up of solvent into a syringe?
  3. For acceptable practice, what are the practical volumes to inject using a 10 uL syringe? What is the desirable percentage relative standard deviation for repeated injections?
  4. What effects can be expected from a leaky septum?
  5. Explain the "blow-by" phenomenon.
  6. How is a syringe checked for "blow-by?"
  7. Explain available automated injection techniques e.g. split, split/splitless, on-column, and temperature programming.

5.3.3  Columns

A.  Objectives

  1. To introduce some representative gas-liquid chromatography (GC) columns commonly used in pesticide residue analysis.
  2. To present techniques and precautions for preparing columns; utilization of capillary columns and injection systems.
  3. To evaluate the separation characteristics of the commonly used pesticide columns.
  4. To obtain an understanding of performance criteria for acceptable GC columns.

B.  Assignment

The trainee will inject laboratory standard solutions onto different columns used for pesticide residue analysis. Evaluate peak efficiency, resolution, and symmetry for each compound. Compare the compound elution order from each column.

C.  References

  1. U.S. Food & Drug Administration, Center for Food Safety and Applied Nutrition, Office of Plant, Dairy Foods and Beverages. Makovi, C. M. (Ed.), McMahon, B. M. (Ed Emerita). (1994). Pesticide analytical manual-multiresidue methods (3rd ed., Vol. I, chap. 5-Gas Liquid Chromatograph, updated October 1999). R.O.W. Sciences, Inc.
  2. U.S. Food & Drug Administration, Center for Food Safety and Applied Nutrition, Office of Plant, Dairy Foods and Beverages. Makovi, C. M. (Ed.), McMahon, B. M. (Ed Emerita). (1994). Pesticide Analytical Manual Vol. I, section 302-Multiclass multiresidue methods, updated October 1999). R.O.W. Sciences, Inc.
  3. Internal laboratory GC methods and SOPs.

D.  Questions and Instructions

  1. How are retention times measured?
  2. What GC parameter has the greatest effect on relative retention times?
  3. Why are relative retention times used rather than absolute retention times?
  4. What GC conditions are required for acceptable performance using the DG-1 system for chlorinated compounds?
  5. Why is chlorpyrifos used as the reference pesticide for determining relative retention times?
  6. What are some of the indicators of a deteriorating column?
  7. Describe the effect of pesticide polarity on chromatography and on column selection. Describe how columns are conditioned to achieve linear response.