Directive 2005/55/EC of the European Parliament and of the Council (repealed)Show full title

1.3.1. Gas chromatographic method (GC, Figure 9) U.K.

When using the GC method, a small measured volume of a sample is injected onto an analytical column through which it is swept by an inert carrier gas. The column separates various components according to their boiling points so that they elute from the column at different times. They then pass through a detector which gives an electrical signal that depends on their concentration. Since it is not a continuous analysis technique, it can only be used in conjunction with the bag sampling method as described in Annex III, Appendix 4, Section 3.4.2.

For NMHC an automated GC with a FID shall be used. The exhaust gas shall be sampled into a sampling bag from which a part shall be taken and injected into the GC. The sample is separated into two parts (CH₄/Air/CO and NMHC/CO₂/H₂O) on the Porapak column. The molecular sieve column separates CH₄ from the air and CO before passing it to the FID where its concentration is measured. A complete cycle from injection of one sample to injection of a second can be made in 30 s. To determine NMHC, the CH₄ concentration shall be subtracted from the total HC concentration (see Annex III, Appendix 2, Section 4.3.1).

Figure 9 shows a typical GC assembled to routinely determine CH₄. Other GC methods can also be used based on good engineering judgement.

Components of Figure 9 U.K.

PC Porapak column U.K.

Porapak N, 180/300 μm (50/80 mesh), 610 mm length × 2,16 mm ID shall be used and conditioned at least 12 h at 423 K (150 °C) with carrier gas prior to initial use.

MSC Molecular sieve column U.K.

Type 13X, 250/350 μm (45/60 mesh), 1 220 mm length × 2,16 mm ID shall be used and conditioned at least 12 h at 423 K (150 °C) with carrier gas prior to initial use.

OV Oven U.K.

To maintain columns and valves at stable temperature for analyser operation, and to condition the columns at 423 K (150 °C).

SLP Sample loop U.K.

A sufficient length of stainless steel tubing to obtain approximately 1 cm³ volume.

P Pump U.K.

To bring the sample to the gas chromatograph.

D Dryer U.K.

A dryer containing a molecular sieve shall be used to remove water and other contaminants which might be present in the carrier gas.

HC U.K.

Flame ionisation detector (FID) to measure the concentration of methane.

V1 Sample injection valve U.K.

To inject the sample taken from the sampling bag via SL of Figure 8. It shall be low dead volume, gas tight, and heatable to 423 K (150 C).

V3 Selector valve U.K.

To select span gas, sample, or no flow.

V2, V4, V5, V6, V7, V8 Needle valve U.K.

To set the flows in the system.

R1, R2, R3 Pressure regulator U.K.

To control the flows of the fuel (= carrier gas), the sample, and the air, respectively.

FC Flow capillary U.K.

To control the rate of air flow to the FID.

G1, G2, G3 Pressure gauge U.K.

To control the flows of the fuel (= carrier gas), the sample, and the air, respectively.

F1, F2, F3, F4, F5 Filter U.K.

Sintered metal filters to prevent grit from entering the pump or the instrument.

FL1 U.K.

To measure the sample by-pass flow rate.