Development of low-pressure ion chromatography for the separation of anions
Victory, Danielle (2005) Development of low-pressure ion chromatography for the separation of anions. Master of Science thesis, Dublin City University.
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Ion chromatography on short permanently coated monolithic columns has been investigated with the aim of developing a low-pressure chromatographic method for the separation of inorganic anions. Both lon-chromatography and anion-exchange chromatography were studied as were three modes of detection namely, direct UVVis using a post-column reaction method, indirect UV-Vis and suppressed conductivity detection.
Initially, the investigation of different monolithic columns with the later application of these to low-pressure anion-exchange separations was considered. Traditional analytical columns used m chromatographic separations have high backpressures associated with them. The introduction of commercial polymeric and silica based has effectively reduced the backpressure restriction associated with the traditional chromatographic stationary phase. Hence, the use of short monolithic silica based anion exchange columns (25 mm and 10 mm column lengths) for the low-pressure separation of inorganic anions (fluoride, chloride, nitrite, bromide, mtrate and sulphate) was investigated. The instrumental set-up consisted of a basic FIA manifold using simple peristaltic pumps, but incorporated a short low pressure anion exchanger. The use of direct conductivity and indirect UV detection was examined
for the determination of these inorganic anions using various concentrations of phthalate and /?-hydroxybenzoate eluents. Suppressed conductivity was also possible within the FIA/IC system by incorporation of a second low-pressure cation exchange column in the acid form after the short monolithic analytical column. This approach significantly reduced the background conductance of the /?-hydroxybenzoate eluent, resulting in improved detection. limits for the above inorganic anions. A two peristaltic pump system was then developed which allowed gradient separations to be carried out with suppressed conductivity detection. The potential significance and advantages of this work in relation to low cost portable ion chromatography was evident.
Finally, the development of another low-pressure ion chromatographic system (LPIC) using monolithic columns coated with DDMAU surfactant (N-dodecyl-N, N- (dimethylammomo) undecanoate) was also considered The column coating showed excellent retention time reproducibility, even at elevated temperatures, over an
approximate 17,200 column volumes Using a combination of low-pressure pumps and short 1 cm monolithic columns, it was possible to separate and detect both silicate and phosphate in surface water samples using post-column reaction (PCR) and UV/Vis detection at 840 nm Linear range was established between 1 and lOmg/L phosphate with this PCR method Total backpressures associated with this system were < 100 psi. The possibility of using a near infrared LED device as the detection mode was also investigated for further miniaturisation of system components.
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