Comparison of Ion Chromatography Conductivity Detector with

 Comparison of Conductivity Detector and UV Detector in Ion Chromatograph and the Comparison of Different Mobile Phase in UV Detection
In the chromatographic method, the components to be tested are separated by a separation column and passed into a detector (a suppressor is added to the ion chromatographic suppression conductance detection), thus selecting an appropriate one depending on the nature of the component to be tested and the characteristics of the actual sample The detector is an important step in the establishment of chromatographic analysis. For ion chromatography, ions in the aqueous solution with conductivity, so the conductivity detector from the beginning is the most commonly used ion chromatography detector, versatility is strong; some ions at a certain wavelength with a strong UV absorption, Can also use the UV detector to detect it, which is very close to high performance liquid chromatography; different ions maximum absorption wavelength is different, the absorption intensity is not the same, so the UV detector is a selective detector. I use NO2- as an example, the ion chromatographic conductivity detector and UV detector and UV detection of different mobile phase were compared.
Instruments and reagents:
PR-SA type anion suppressor, PR-CD type conductivity detector, PR-UV1000D type UV detector, PR-SA-4A anion separation column (250mm × 4.6mm), into the Sample volume 25ml
Reagents: Na2CO3, NaHCO3, NaNO2, Na2SO4, analytical grade; pure water (resistivity greater than 18.2 MΩ / cm)
Solution configuration:
1.92 mM Na2CO3 + 1.80 mM NaHCO3 solution 1 L; 2.0 mM Na2SO4 solution 1 L;
1000mg / LNO2-solution 100ml, and gradually diluted to get 0.2mg / L, 2.0mg / L, 5.0mg / L, 10.0mg / L and 20.0mg / L of NO2-solution;
Comparison of Conductivity Detector with UV Detector
The mobile phase consisted of 1.92 mM Na2CO3 + 1.80 mM NaHCO3 as the mobile phase. The NO2-standard solution series was analyzed by adding an ion chromatograph in the order of concentration from low to high. The minimum detection limit is calculated at 3 times the signal-to-noise ratio (S / N = 3). The linear range, linearity, correlation coefficient and minimum detection limit of NO2- are shown in Table 1, where Y is the peak height and X is the mass concentration of the component (mg · L-1). Table A for the inhibition of conductance test results, B for the UV test results (detection wavelength 205nm)
Table 1 Comparison of Ion Chromatography Conductivity Detection and UV Detection Analysis of NO2-
 
Linear range (mg · L-1)
Linear equation
Correlation coefficient / R2
Detection limit / mg · L-1
NO2-
0.2 to 20.0
A: Y = 2786X-536
0.9994
8.5
B: Y = 8807X + 1618
0.9997
2.9
It can be seen from the table, under the same conditions, 205nm wavelength UV detection NO2-than inhibition of conductance detection response is higher, higher sensitivity, which can be seen from the coefficient of X in the linear equation.
UV detection of different mobile phase contrast
In the use of UV detector, I found that in addition to the spectrum of NO2- peak, there is a negative peak, the negative peak is likely due to Na2CO3, NaHCO3 at 205nm wavelength with a certain UV absorption. I believe that in the chromatographic flow corresponding to the detector response value as low as possible, the use of UV detector Na2CO3 / NaHCO3 is not the best mobile phase. In the case of consistent other conditions, the author will 1.92mM Na2CO3 / 1.80mMNaHCO3, 2.0mMNa2SO4 two mobile phase elution ability, especially the background absorption were compared, the results shown in Table 2.
Table 2 Comparison of different mobile phases in ion chromatography by ion chromatography
 
Linear range (mg · L-1)
Linear equation
Retention time / min
Correlation coefficient / R2
Detection limit / mg · L-1
NO2-
0.2 to 20.0
A: Y = 8807X + 1618
3.7
0.9997
2.9
B: Y = 9355X + 1205
4.5
0.9996
1.4
    As can be seen from the table, compared with 1.92 mM Na2CO3 + 1.80mM NaHCO3 mobile phase, 2.0mMNa2SO4 mobile phase leaching ability is weaker but NO2-response value is higher, the sensitivity is higher. It was found that the Na2SO4 mobile phase was smaller than the 1.92mM Na2CO3 + 1.80mM NaHCO3 mobile phase when observing the chromatogram, indicating that the background of Na2SO4 mobile phase was low.
Conclusion
    Chromatography according to the nature of the material to be tested and the characteristics of the sample can choose a different detector. In the ion chromatogram conductivity detector is a versatile detector, UV detector has a certain selectivity, is necessary to add the conductivity detector. When using the ion exchange column for the determination of NO2-, the UV detector (205nm) is higher than the response value of the conductivity detector. When using the UV detector, using Na2SO4 as the mobile phase is lower than the Na2CO3 / NaHCO3 mobile phase background, Higher sensitivity, more suitable as UV detection NO2- when the mobile phase. In the use of UV detector, the deuterium lamp must be preheated for two hours to be used for testing; long time without UV detector, the flow must be used before the flow phase with deionized water, etc. are in the Use and maintain the UV detector must pay attention to matters.