Low-Level GC/MS for Semivolatiles in Drinking Water
Excellent Responses at 10ng On Column, Using an Rxi-5ms Column
- Inert, ultra-low bleed column improves low level analyses.
- Excellent peak shapes and responses for active analytes.
- Drilled Uniliner inlet liner minimizes sample breakdown in the injector.
Semivolatile organic chemical contaminants in drinking water are target compounds in many analytical methods, worldwide. US EPA Method 525.2, for example, is a general purpose solid-phase extraction/GC/MS procedure for identifying and quantifying a wide range of semivolatile compounds. Analytes, and introduced internal standards and surrogates, are extracted from a 1-liter water sample by passing the sample through a solid phase extraction disk containing a bonded C18 phase (e.g., Resprep-C18, cat. #24004). Target compounds are trapped on the disk, then eluted in a small amount of solvent. The extract is concentrated by evaporating the solvent, and the sample components are separated, identified, and quantified by GC/MS.
As is true for many other semivolatiles methods, the extensive target compound list for Method 525.2 encompasses numerous classes of analytes. These diverse compounds present varying difficulties in the analysis, including differing modes of degradation. Coupled with the continual need for lower levels of detection, these challenges make extreme demands on the chromatography column, and the analysis requires an inert, thermally stable, low-bleed stationary phase. To meet these needs, we recommend a 30 meter, 0.25mm ID, 0.25µm Rxi-5ms column. Enhanced surface deactivation provides Rxi-5ms columns with exceptional inertness and ultra-low bleed, ensuring resolution and symmetric peaks for these difficult analytes.
Figure 1 shows the total ion chromatogram for semivolatiles commonly analyzed in drinking water, and listed in US EPA Method 525.2, at 10ng each on an Rxi-5ms column. Resolution and peak shapes are exceptionally good.
To minimize analyte degradation in the injection port, and discrimination among analytes by molecular weight, we recommend installing a Drilled Uniliner inlet liner in the injection port. This liner forms a Press-Tight seal with the inlet end of the column, eliminating contact between the sample and the hot metal surfaces in the injection port and assuring near-complete sample transfer. The small hole in the wall of the liner allows the liner to be used with split/splitless injections. As an additional precaution to minimize analyte breakdown, we use a pulsed splitless injection (50psi / 0.3 min.; 1µL sample) to reduce the time the analytes spend in the injection port.
Exceptional inertness and ultra-low bleed enable an Rxi-5ms column to perform exceptionally well in analyses of complex mixtures of semivolatile compounds. We recommend pairing an Rxi-5ms column with our recently revised reference mixes for semivolatile pollutants in water. Restek can provide all the materials needed for a semivolatiles analysis: extraction disks, reference materials, and a column capable of excellent responses for all target analytes at low on-column concentrations.