Fluorocarbon, a generic term for organic compounds with carbon-fluorine (C-F) bonding, is a chemical material used as a refrigerant in refrigerators and freezers and air conditioners in cars, buses, other vehicles and buildings. It’s also used as a cleaning agent for electronic components and precision parts.

Hydrofluorocarbon (HFC), the most common type of organofluorine compound, is classified as a non-ozone-depleting chlorofluorocarbon (CFC) substitute and is used as a gas for semiconductor etching and electronic component cleaning. High-purity HFC is utilized in the semiconductor and electronics industries; confirming its purity requires measuring the concentration of impurities.

Shimadzu Scientific Instruments’ (Columbia, Md.) gas chromatographs are commonly used to test for these impurities. In recent years, demands for higher sensitivity and trace quantity analyses have increased. Examples include impurity analysis on the order of a few ppm for materials used in fine chemical products, and gas purity analysis for semiconductor manufacture. A recent applications report from Shimadzu Scientific Instruments introduces an example of analyzing trace quantities of CO₂ impurities in high-purity HFC using a high-sensitivity gas chromatograph.

Gas chromatograph system
The system used for this analysis incorporates a barrier ionization discharge (BID) detector, which generates a 17.7-eV helium (He) plasma that ionizes all compounds except neon (Ne) and helium (He). A newly designed quartz dielectric chamber allows for a lower discharge current and higher operating temperature. The BID is a universal detector with sensitivity greater than 100 times that of a thermal conductivity detector (TCD).

The technology arises from Shimadzu Scientific Instruments’ investigations of plasma detection technology as a means for increasing sensitivity stability and the detectable concentration range. The concept was developed through collaborative research with Dr. Katsuhisa Kitano at the Center for Atomic and Molecular Technologies, Osaka Univ., Japan, resulting in three U.S. patents and four patents pending.

BID technology improves on TCDs and flame ionization detectors (FID) that serve as general-purpose detectors used in conventional gas chromatographs (GCs). A TCD detects a variety of inorganic and organic compounds, excluding the carrier gas component, but the sensitivity is insufficient. An FID, meanwhile, is capable of detecting trace components at the ppm level, but can only detect organic compounds. As a result, analysis has required complex systems incorporating a variety of detectors to suit the target component.

The BID eliminates this complexity, allowing high-sensitivity detection of both organic and inorganic compounds, while providing excellent durability. This capability makes BID an optimal detector for trace levels of permanent gas, water, volatile fatty acids and light hydrocarbons.

Principles for detection
In operation, BID generates a plasma by applying a high voltage to a quartz dielectric chamber, in the presence of helium. Compounds that elute from the GC column are ionized by this He plasma, then captured with collection electrodes and described as peaks. The photon energy of He is extremely high (17.7 eV). Therefore, it’s possible to detect every compound except Ne and He with high sensitivity.

Table 1: CO2 quantitative results

Sample	Quantitative Conc. (ppm)	S/N
#1	5.09	1043.5
#2	1.93	250.7
#3	0.31	43.14

Experimental process
The instrument used in this analysis include Shimadzu Scientific Instruments’ Tracera GC system, which is built from the GC-2010 Plus platform and includes a BID-2010 Plus detector. Introduced in 2013, Tracera was designed by Shimadzu Scientific Instruments to detect trace organic and inorganic compounds at the 0.1 ppm level. Conventional analytical techniques require a system configuration with multiple detection schemes to analyze for permanent gases and light hydrocarbons. The use of a methanizer and flame ionization detector (FID) is often required to detect ppm levels of CO and CO₂. However, the BID replaces the hardware and allows for the highly sensitive detection of mixtures of inorganic gases and light hydrocarbons.

Complementing the Tracera GC is the MGS-2010 gas sampler and LabSolutions software.

Analysis conditions
The columns used for the analysis are the PoraPLOT Q, made by Agilent Technologies. These columns are noted for repeatable retention times not influenced by water in the sample, and are suited for column switching systems that analyze polar and apolar volatile compounds.

For the analysis, column temperature was first maintained at 30 C for 5 min, then increased at a 40 C/min rate to finish at 100 C for 8.25 min. The elapsed analysis time was 15 min in total, using 40 cm/sec of He gas in constant linear velocity mode. The injection port temperature was 150 C, and the detector was maintained at 200 C. The MGS-2010 gas sampler utilized an injection volume of 1 mL and He was discharged at 50 mL/min.

The initial column temperature (30C) can be set at a room temperature of 25C or lower, but itisn’t possible to separate air components (N₂, O₂ , Ar) or CO under these analysis conditions.

Analysis results
Multiple high-purity HFCs were analyzed. Figure 2 shows the resulting chromatograms, and Table 1 shows the quantitative results for CO₂. The CO₂ concentration in sample #3 was very low at only 0.3 ppm. The signal-to-noise ratio was approximately 43.

Analysis conclusion
Conventional analysis of trace levels of CO₂ requires using an FID and a methanizer. However, Shimadzu Scientific Instruments has demonstrated how a simply configured GC system, incorporating a rugged, sensitive, universal detector, can analyze trace amounts of CO₂ with high sensitivity.