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.