Multiple Gas Analyzer #5 GC

• TCD, HID and FID-Methanizer detectors
• Two 10-port gas sampling valves
• Two on-column injector
• 5-meter HayeSep D column
• 2-meter HayeSep D column
• 2-meter Molecular Seive 5A column
• Built-in “whisper quiet” air compressor
• 6-channel PeakSimple data system
• Options/Upgrades: additional gas sampling valve, additional detectors, additional columns and additional injector

System Overview:

Unfortunately, there is no single column that can separate: Hydrogen, Oxygen, Nitrogen, Methane, Carbon Monoxide, Carbon Dioxide, Ethane, Water, Propane, Butane, and Pentane. Over the years, SRI Instruments has devised several solutions to this analytical problem, starting with the MultipleGas#1 configuration and evolving to the present MultipleGas#5 configuration.
The Thermal Conductivity Detector can detect all the gases listed above, besides Hydrogen, from 200ppm to 100% concentration. The Flame Ionization Detector can detect Hydrocarbons down to 1ppm, and with the Methanizer attachment, CO and CO₂ down to 1ppm.
This model, is highly customizable, as are most of our GCs. It can be modified to have a third valve, more detectors like a second TCD, FPD, and FID for liquid analysis, and more columns.

This picture shows an MG#5 with additional TCD, 10-Port Valve, backflush over precolumn, and extra carrier stream. This is needed if Oxygen and Hydrogen must be measured down to a low level of ppm in the same run. The best choice to measure Hydrogen is Argon as a carrier and Hydrogen as a carrier to measure Oxygen.

The schematic above shows the 4 steps in the MG#5 analysis after the sample has been loaded into the loop of each valve.

STEP 1: Valve 1 is turned to the INJECT position (Relay G on). The carrier gas pushes the sample out of the valve loop onto the 5-meter HayeSep D column. H₂, O₂, N₂, CH₄, and CO migrate through the 5-meter HayeSep D column very quickly and land on the 1-meter MS5A column.

STEP 2: Valve 1 is turned back to the LOAD position (Relay G off). Carrier gas continues to push the H₂, O₂, N₂, CH₄, and CO molecules through the MS5A column toward the detectors. Also, carrier gas backflushes any remaining molecules backward through the 5-meter HayeSep D column out to the vent (not through the detectors). The molecules which remain on the 5-meter column are CO₂, Water, and C₂ and higher hydrocarbons. These molecules would get stuck on the MS5A column if they were allowed onto the MS5A column. However, they easily backflush out of the HayeSep D.

STEP 3: Valve 2 is turned to the INJECT position (Relay F on). The carrier gas pushes the molecules in the loop of Valve 2 onto the 2-meter HayeSep D column in the “forward” direction. H₂, O₂, N₂, and CO elute from the column very quickly as one peak, followed by the CH₄ peak, the CO₂, water, and the hydrocarbons from C₂-C₆.

STEP 4: At some point in the analysis Valve 2 is returned to the LOAD position. This reverse (back-flushes) the flow direction in the HayeSep D column. Any peaks which have not yet exited the HayeSep D column now back out of the column and into the detector. If for example, the analysis had no peaks after CO₂ (or you did not care about any peak after CO₂), then you would backflush after the CO₂ peak. Any peaks remaining in the HayeSep D column would come out in a “lump”.

The following is a typical chromatogram of H₂, O₂, N₂, CH₄, CO, CO₂, C₂H₂, C₂H₄ and C₂H₆ at 1% in Nitrogen.

The screen on the right shows the oven temperature program used.

STEPS 1 and 2 occur while the column oven is at 50°C. After 1 minute, the column temperature increases to 90°C and stays there until after STEP 3. Then the column temperature increases to 270°C.

At some point, while the column temperature increases, STEP 4 occurs, backflushing any un-eluted molecules.

The channel 1 Event table is shown on the right. At time 0.05 Relay G turns on. This initiates STEP 1. At time 0.4, Relay G turns off. At time 4.00 Relay F turns on initiating STEP 3. At time 8.0 Relay F turns off backflushing the HayeSep D column to the detectors.

The exact times may change if the carrier flows rate changes or if a different carrier gas is used. The backflush time (STEP 4) especially may change depending on what molecules are in the sample.

MG#5 GC System’s Schematic: