With the SC-CSRS®, nonlinear response can be overcome by converting the weak base analyte to a fully ionized salt form, thus extending the linear response. The SC-CSRS suppressor is designed to make this conversion and provide linearity up to three orders of magnitude.
- Increased linearity for ammonium and amine
- Increased sensitivity for ammonium and amine
Low background and noise
When to the Use SC-CSRS
Dionex has developed the SC-CSRS for applications where an extended linear range or increased response for weak bases such as ammonium and amines are required. A linear response increases the accuracy at higher concentrations, requiring fewer calibration check standards over the calibration curve. Reduced calibration requirements increase sample throughput for industries with high sample workloads such as the power generation industry. The SC-CSRS should be used in industries where regulated methods require a linear response, for example, Boiler Industrial Furnace Compliance Monitoring. The SC-CSRS may also be beneficial for amine determinations where the increased conductivity response improves sensitivity for these analytes.
Increased Linearity for Ammonium and Amines
When using the SC-CSRS, the response at varying concentrations is linear because the analyte is detected as fully dissociated methanesulfonic acid. The figure below shows the linear calibration plots for ammonia comparing the SC-CSRS and the CSRS® ULTRA over three orders of magnitude (0.1–100 mg/L). When using the SC-CSRS, the response at varying concentrations is linear because the analyte is converted to and detected as fully dissociated methanesulfonic acid.
Increased Sensitivity for Ammonium and Amines
The SC-CSRS improves ammonium and amine response to the conductivity detector. Because the analytes are actually detected as fully dissociated methanesulfonic acid, which has a higher equivalent conductance, the sensitivity is increased. The greatest increase in response is observed at higher concentrations, as illustrated in the figure above for ammonium. The figure below shows a comparison of separations of inorganic cations and ammonium using a SC-CSRS. The concentrations in chromatogram A in this figure are 1 ppm for each analyte and the concentrations in chromatogram B are 0.1 ppm. The SC-CSRS increases ionization and therefore has a larger effect at higher concentrations.
Method detection limits for Group I and II cations, ammonium, and amines using the SC-CSRS are equivalent to those achieved using the CSRS ULTRA.
The SC-CSRS improves the analyte response to the conductivity detector because the analytes are detected as fully dissociated methanesulfonic acid, which has an equivalent conductance of 399 S cm2 mol–1. In contrast, sodium detected as Na+OH– has an equivalence conductance of only 249 S cm2 mol–1. Ammonium detected as NH4+ OH– has an equivalent conductance of only 273 S cm2 mol–1. The figure below shows a comparison of separations of inorganic cations, ammonium, and amines using a SC-CSRS. The concentrations in chromatogram A of this figure are 1 ppm for each analyte and the concentrations in chromatogram B are 0.1 ppm. The SC-CSRS increases ionization and therefore has a larger effect at higher concentrations. Method detection limits using the SC-CSRS are equivalent to those achieved using the CSRS ULTRA.
SC-CSRS Background and Noise
The SC-CSRS suppressor effluent contains a low background concentration of methanesulfonic acid. Due to this low background concentration of methanesulfonic acid, the expected background is slightly higher than when using a CSRS ULTRA. The expected noise is also slightly higher due to the increased background. For a 20 mM MSA eluent suppressed using the SC-CSRS, the typical background conductance is 5 µS and the typical noise is less than 3 nS.
