Development of fast ion chromatography
Connolly, Damian (2005) Development of fast ion chromatography. PhD thesis, Dublin City University.
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Fast ion chromatography has been applied to short (3 cm) silica based ODS columns with a view to achieving rapid determinations of selected inorganic anions. The use of smaller stationary phase particle sizes (3 |im) allowed higher flow rates (2.0 - 2.5 ml/min) to be used while maintaining chromatographic efficiency due to the favorable Van Deemter curves obtained as particle size decreases. Using ioninteraction chromatography and direct UV detection, eight anions were separated in under four minutes with the first five anions separated in < 50 seconds; this separation was subsequently applied to the rapid analysis of nitrite and nitrate in tap water. With the addition of a peristaltic pump and in-line filter, up to 60 analyses per hour could be carried out unattended using an on-line system, which matches the analysis rate possible with traditional FIA based methods. This mobile phase was further modified such that nitrate, nitrite and thiocyanate could be rapidly determined in urine samples as a means to quantitatively evaluate smoking behavior.
Subsequently, the same column was permanently coated using
didodecyldimethylammonium bromide (DDAB) and anion exchange chromatography used for the isocratic separation of nine common anions in 160 seconds, with the first seven anions, including phosphate, chloride and sulphate, separated within only 65 seconds using a simple phthalate eluent. The high capacity, highly hydrophobic ion exchange coating demonstrated excellent stability over time, even at elevated temperatures (45 °C). The developed chromatography was successfully applied to the rapid analysis of river water, tap water and relatively high ionic strength seawater samples with minimal sample preparation required.
Multi-valent eluents were briefly applied to this column with a view to achieving faster separations, with further studies also involved the use of dipicolinic acid eluents, which allowed the simultaneous separation of chloride, sulphate, nitrate, carbonate, magnesium and calcium, in less than 180 seconds.
Short monolithic silica ODS columns were used with a tetrabutylammoniumphthalate eluent and direct conductivity detection for the rapid analysis of six common inorganic anions in < 60 seconds. Van deemter curves for this monolithic column showed that considerably higher flow rates could be used without adversely affecting efficiency relative to 3 p,m particulate columns due to the improved permeability of these phases. Finally, two short Cis monoliths were coated with DDAB and DOSS and individually used to separate eight anions in 100 seconds and five cations in 100 seconds using a common phthalate/ethylenediamine eluent. By subsequently coupling the columns in parallel, the with the eluent delivered using a flow splitter from a single isocratic pump, the simultaneous analysis of anions and cations was also possible, based on a single conductivity detector.
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