Water for Gas Chromatography
Impact of Water
GC methods do not use a lot of water. If it does, it is usually for sample preparation. If the sample being analyzed is aqueous, water is also used to prepare blanks and standards.
- Particles
Particles may plug injector and column.
- Organics
Volatile organics will come out as extraneous peaks. If the organic contaminant is also a compound being investigated, the analyte peak will be erroneously larger than it should.
Example illustrating the impact of water quality in VOC analysis by GC-MS
GC-MS is the preferred method for the analysis of volatile organics (VOCs) in water. Figure 2A is mass chromatogram of tap water analyzed for VOCs. Concentrations of chloroform, bromodichloromethane, dibromochloromethane, and bromoform were between 4 - 19 ppb. This water is then fed to a pretreatment system (Elix®) and a polishing unit (Milli-Q® IQ 7000) with a point-of-use purifier (VOC-Pak®) specifically targeted to remove VOCs. As Figure 2B shows, this ultrapure water is VOC-free.Figure 2A.
Analysis of VOCs by GC-MS. Mass chromatogram of Tap water. Peak identities: 1 = chloroform, 2 = bromodichloromethane, 3 = dibromochloromethane, 4 = bromoform. Note: peaks from left to right, 1 through 4.
Bottled water that is commonly used as reference water in VOC analyses was analyzed and compared with ultrapure water purified by a VOC-Pak®. Figure 2B is an overlay of the mass chromatograms of the two types of water.
Figure 2B
Figure 2B. Mass chromatograms of bottled water (blue trace) and ultrapure water (black trace)
For more detailed information about VOCs, click here.
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