field methods of monitoring aquatic systems unit 9 – ion-chromatography copyright © 2006 by dbs
TRANSCRIPT
Field Methods of Monitoring Aquatic Systems
Unit 9 – Ion-Chromatography
Copyright © 2006 by DBS
Suppressed IC System
• Chromographic separation of inorganic anions– Provides analysis of many ions at once
– Organic polymer column (10-25 cm, 3-5 mm ID) and CO32-/HCO3
- elluent
• Detection via conductivity – Eluent ions must be removed (background conductivity) (Na+ replaced by
H+, CO32-/HCO3
- converted to CO2)
– Suppresor removes all buffer ions via ion exchange or continuous suppression) electolysis
Eluent reservoir Pump
Analytical column
Ion Supressor
Conductivity detector
Injection system
Chromatographic Separation
Principles
1. Mobile phase – eluent carries the mixture through the column
2. Stationary phase – compounds adsorb to ion-exhcange resin in the column. Stickier compounds require more elution time
3. Force pushes the mixture through the column – pump
4. Separation depends on retention time (ion charge and size)
• Column is covered in +ve binding sites - N(CH3)3+
• As sample passes over the resin, anions in the sample replace bicarbonate ions bound to the resin
[Resin]+-HCO3- +Cl- [Resin]+-Cl- + HCO3
-
• Eventually sample anions are displaced again by new eluent (bicarbonate) and washed off the column
Kegley, 1998
IC Chart
Conductivity
Conductivity ~ concentration
Compare peak area of unknown with that of a standard
Procedure
In environmental waters samples require filtration (0.45 μm)
Standardization
1. Inject standards one at a time to obtain peak areas at different concentrations
2. Plot concentration vs. peak area for each component and obtain a calibration graph for each component
Sample Run
1. Inject the filtered sample and use the calibration for each ion to obtain concentrations of anions
2. If anion peaks go off-scale dilute the sample using pipets and volumetric flask.
3. Determine concentrations in mol L-1 and ppm.
4. Determine total moles of negative charge.
Dionex ICS-1000
• Chromeleon software• Continuous electrolytic
suppression
Question
Use the following data to draw a calibration curve and calculate the concentration of the sample.
12 ppm
Procedure
• Pump window– 0.1 mL normal flow, increase to program flow (e.g. 1.2 mL
for SO42-)
• Anion.qnt– Adjust file– Check 10 mM CO3
2-/1 mM HCO32-
• Batch– Must be run on samples (add to batch)
• Peak assignment– Assign retention times to peaks in software
Text Books
• Rump, H.H. (2000) Laboratory Manual for the Examination of Water, Waste Water and Soil. Wiley-VCH.
• Nollet, L.M. and Nollet, M.L. (2000) Handbook of Water Analysis. Marcel Dekker.
• Keith, L.H. and Keith, K.H. (1996) Compilation of Epa's Sampling and Analysis Methods. CRC Press.
• Van der Leeden, F., Troise, F.L., and Todd, D.K. (1991) The Water Encyclopedia. Lewis Publishers.
• Kegley, S.E. and Andrews, J. (1998) The Chemistry of Water. University Science Books.
• Narayanan, P. (2003) Analysis of environmental pollutants : principles and quantitative methods. Taylor & Francis.
• Reeve, R.N. (2002) Introduction to environmental analysis. Wiley.
• Clesceri, L.S., Greenberg, A.E., and Eaton, A.D., eds. (1998) Standard Methods for the Examination of Water and Wastewater, 20th Edition. Published by American Public Health Association, American Water Works Association and Water Environment Federation.