ASTM E260 Standard Practice for Packed Column Gas Chromatography
15. Recommended Form for Writing Gas Chromatographic Methods
15.1 General - Not all of the steps outlined in this section may be needed to describe adequately a method. A number of variations in procedure format are shown in the publication, ASTM Standards in Chromatography. Ideally, the procedure should be written so that it can be followed by a person with the equivalent of a high school-chemistry understanding or six to twelve months of practical laboratory experience. Critical steps should be identified along with any reasons that show why this step is necessary to achieve a successful analysis. Any involved procedures should be written in an Appendix so that the main points in the procedure can be read more easily.

15.2 Recommended Form:
15.2.1 Title - The title should be concise, but complete enough to identify the component(s) analyzed, the nature of themethod (gas chromatography), the detector, and the materials to which it is applicable. Select words that easily lend themselves to indexing.

15.2.2 Scope - State as clearly as possible the range of application of method. In a separate paragraph, note interferring substances or any significant limitations of the method. This material could be placed in a later section (15.2.5), if an involved description is necessary.

15.2.3 Pertinent Documents or References:
15.2.3.1 ASTM Standards.

15.2.3.2 Other Standard Methods - Include any standard methods.

15.2.4 Summary of the Method - Describe the method in a general way, without going into details of the procedure. It may be appropriate to touch briefly on the following points: sample introduction technique, column dimensions and type of tubing material, nature of the packing material, mesh size of support or adsorbent, liquid phase loading (if a liquid phase was used), isothermal or programmed temperature and detector type (thermal conductivity, flame ionization, electron capture, etc.).

15.2.5 Significance and Application - Use this section for a more detailed discussion than can be fitted in the Scope.

15.2.6 Definitions - Include special definitions in this section. General chromatographic definitions are already available in Practice E 355, to which reference can be made.

15.2.7 Interferences - Use this section for a more detailed discussion than can be fitted into the Scope.

15.2.8 Special Comments - Use this section to include a description of special requirements needed to achieve a successful analysis.

15.2.9 Safety Precautions - If the method involves hazards, insert a warning to this effect. Point out the nature of the hazards, and describe precautionary measures which must be taken. Refer to the latest OSHA regulations regarding all materials used in this procedure.

15.2.10 Gas Chromatographic System - List and describe the apparatus. Describe the essential features of the apparatus that are necessary to achieve the desired analysis. Avoid the use of trade names. Include schematic drawings or photographs if they are needed to clarify or supplement the text. The gas chromatographic conditions can be either summarized in a table, as in Table 6, or in the text as follows:
15.2.10.1 Sample Injection Port - Construction: stainless steel, glass liner, fitted for on-column injection with a glass or metal column, etc. Temperature at which used.

15.2.10.2 Column Oven - Isothermal or temperature programmed operation: give temperatures and programming rates required.

15.2.10.3 Detector - Type (flame ionization, thermal conductivity, etc.), temperature of operation, sensitivity required. Detector gases used and flow rates.

15.2.10.4 Recorder - Operating range (in millivolts), chart speed, time for full-scale deflection of pen.

15.2.10.5 Integrator - Note operating characteristics of integrator and parameters used.

15.2.11 Preparation and Installation of the Chromatographic Column:
15.2.11.1 Tubing Material - Note the type of material, as stainless steel, nickel, glass, or glass-lined tubing, as well as the dimensions (outer diameter and inner diameter, or wall thickness and length). Any pretreatment of the column material, solvent washing, or silanization should be mentioned.

15.2.11.2 Partitioning Phase - Solid adsorbent, if used (type and mesh size). Coated support if used (liquid phase, percent loading and coating procedure, support type and pretreatment, and mesh size). Note sources for special materials in footnotes. Provide preparation and purification method for materials not commercially available. In an Appendix, note other liquid phases that have been successfully used in this analysis.

15.2.11.3 Column Preparation - Describe the procedure used to pack the column. Note the amount of packing in the column.

15.2.11.4 Column Installation - Note if the column is set up for back-flushing, if a sample fraction is removed on a pre-column, or other special column arrangement.

15.2.11.5 Column Conditioning - Provide the column conditioning procedure.

15.2.11.6 Column Evaluation - Give the procedure for evaluating the column. Calculation of the resolution between two components in a standard mixture will often be sufficient. Provide some estimate of column life and signs of degrading column performance (loss of resolution, peak broadening, or tailing). Provide examples of good and bad chromatograms.

15.2.12 General Apparatus - Volumetric flasks and pipets, microsyringes for sample introduction, balance (capacity and sensitivity), heat lamps, hot plates, etc.

15.2.13 Reagents and Materials:
15.2.13.1 Chemicals and Reagents - Include derivatizing reagents. Note purity, or purification methods, if required.

15.2.13.2 Calibration Standards - Note purity required.

15.2.13.3 Gas (or Gases) - Carrier gas, fuel gases for flame ionization detector, special gas for electron capture detector, etc. Note purity required.

15.2.14 Calibration - Describe in detail the calibration procedure. State whether pure components or standard mixtures are used and the basis of measurement. Include equations and describe the preparation of any calibration charts. Show the calibration curve. If a trace method is described, provide a chromatogram of the lowest detectable amount. Lengthy procedures, such as the development of complex equations, or the preparation of standard mixtures, should be placed in a section of an Appendix.

15.2.15 Procedure - Include, in proper sequence, directions for carrying out the method. Refer to the pertinent parts of the calibration procedure in 15.2.14. Do not repeat these steps here. Possible subheadings are as follows:
15.2.15.1 Final Conditioning and Adjustment of the Gas Chromatographic System - This section is intended to include adjustment and verification of the state of the chromatographic system before analytical use.

15.2.15.2 Sampling - Careful attention must be given to the sampling techniques since representative samples are essential to achieve successful analysis. Include special directions that may be required for taking samples, for preservation of samples, and for special treatment of samples prior to injection.

15.2.15.3 The remainder of the steps leading to the chromatogram.

15.2.15.4 Typical Chromatogram - Show, in a figure, a plot of the retention time (in minutes) versus the detector response. Label the known peaks (including the dead volume or unadsorbed gas peak) and indicate in parentheses the attenuation for each peak.

NOTE 8 - When determining the retention time of the unadsorbed peak, the retention time of air is used for thermal conductivity detectors, methane for flame ionization detectors, and methylene chloride lead space vapors for ECDs.

15.2.15.5 Retention Time Data - Include a table listing retention times and relative retention times for all compounds of interest, for all recommended columns. Identify the unadsorbed peak and the reference material used for relative retention time calculations.

15.2.16 Calculation - State the reference point on which the calculations are based (for example, sample as received), the terms in which the results are finally obtained (weight, volume, or mole percent), and whether or not these values are normalized. Present the calculations in equation form, using letter symbols to designate variable values and numerical values of constants. Define the letter symbols in a legend immediately following the calculation equation.

15.2.16 Report - Show limits to be reported.

15.2.17 Precision - Limiting values for precision should be based on cooperative test results. Judgment as to the acceptability of results (95 % probability) should be based on the following criteria.
15.2.17.1 Repeatability - The following wording should be used: Duplicate results by the same operator should not be considered suspect unless they differ by more than the following amounts: (insert determined limits in tabular form).

15.2.17.2 Reproducibility - The following wording should be used: The result submitted by each of two laboratories should not be considered suspect unless the two results differ by more than the following amounts: (insert determined amounts in tabular form).

15.2.18 Appendixes - Supplementary information may be included in one or more Appendixes to the report. Examples of such information are: technique to improve column life, directions to clean the apparatus, leak check procedures, procedures to optimize column performance, development of equations used in the calculations, and precautions to avoid common causes of errors, etc.

16. Keywords
16.1 gas chromatography; GC; packed columns