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Comprehensive Analysis of Major Cations and Anions in Water Samples Using Advanced Techniques

This module outlines methods for determining major base cations such as Ca²⁺, Mg²⁺, Na⁺, and K⁺ using ICP-AES, as well as anions like Cl⁻, NO₃⁻, and SO₄²⁻ through Ion Chromatography (IC). It emphasizes the importance of conductivity and temperature measurements, pH determination, and total organic carbon analysis to achieve quality control in water sample analysis. The guidelines also cover calibration procedures, utilizing advanced equipment like Thermo Orion pH-meters and Shimadzu TOC analyzers, essential for accurate analytical chemistry in environmental studies.

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Comprehensive Analysis of Major Cations and Anions in Water Samples Using Advanced Techniques

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  1. Analyses planModule 19 • Major base cations to be determined by ICP-AES • Conductivity and temperature • {H+} determined using pH electrode • Al fractionation • Major anions to be determined by IC • Use of auto-pipettes • Total organic carbon • UV and Vis absorption

  2. Conductivity • Master student lab V160 • Ecoscan Con5 (Eutech instruments) conductivity meter. • The instrument is calibrated using 1000 and 1433 µS calibration solutions • The measurements are done for quality control purposes in order to compare measured and calculated conductivity

  3. {H+} determined using pH electrode • Analytical Chemistry lab Ø109 • Thermo Orion model 720 pH-meter with a Blueline 11-pH electrode. • The pH-meter is calibrated with pH = 4.00 and 7.01 buffer solutions

  4. Major base cations to be determined by ICP-AES • Ca2+, Mg2+, Na+, K+ • Method will be demonstrated in Module 24 • Appropriate calibration solutions are prepared by Masha • Conducted by Anne-Marie Skramstad

  5. Major anions to be determined by Ion Chromathograph (IC) • Analytical Chemistry lab Ø109 • Tot-F, Cl-, NO3-, SO42- • Principle • The sample is injected in a flow of eluent • The analyte ions are separated by different degree of binding to the active sites on the ion exchange material • Ions with opposite charge of the analyte is exchanged with H+ or OH- • The activity of the analyte is and accompanied H+ or OH- in the eluent stream is measured by means of a conductometer • Presented by Hege Lynne et al

  6. Total organic carbon • Analytical chemistry lab Ø 104 • High temperature (680C) catalytic combustion analysis on a Shimadzu TOC-5000A instrument • Principle: • The organic carbon is combusted to CO2 by high temperature and catalysis. The amount of CO2 produced is measured using av IR detector • Presented by Hege Lynne et al. • Analytes measured may include: TC, IC, TOC, NPOC, and POC

  7. Al fractionation • Master student lab V160 • Method presented as example in Lecture 1 (slide 15) • Download manual from • http://folk.uio.no/rvogt/KJM_MEF_4010/

  8. QC of data • After the analysis the data must be compiled and quality controlled by ion balance and agreement between measured and calculated conductivity • For this purpose you may use the Data compilation and QC worksheet available at http://folk.uio.no/rvogt/KJM_MEF_4010/

  9. Speciesin natural freshwaterCentral equilibriums in natural water samples KJM MEF 4010 Module 19

  10. Inorganic complexes • Major cations in natural waters • H+, Ca2+, Mg2+, Na+, K+ • Common ligands in natural systems: • OH-, HCO3-, CO32-, Cl-, SO42-, F- & organic anions • In anoxic environment: HS- & S2- • Dominating species in aerobic freshwater at pH 8 are:

  11. Hydrolysis • In aqueous systems, hydrolysis reactions are important • Hydrolysis reactions are controlled by {H+} • The higher the pH, the stronger the hydrolysis of metal cations • E.g. Aluminium • Al3+aq denotes Al(H2O)63+

  12. Concentrations of dissolved Fe3+ speciesTwo total Fe concentrations, FeT = 10-4M and FeT = 10-2M

  13. Dissolved Organic Matter • Low molecular weight (LMW) • < 1000Da (e.g. C32H80O33N5P0.3) • E.g.: • High molecular weight • 1000 - > 100 000Da • Humic substance • Very complex and coloured substances • Enhances weathering • The protolyzation of weak organic acids • Complexation of Al and Fe • Total congruent dissolution

  14. Concentrations and activities

  15. Activity • {X}=X · [X] • {X} is the activity to X • [X] is the concentration to X • X is the activity coefficient to X • X are dimensionless • It is determined by: • The diameter (å) of the hydrated X • Its valence (nX) • The ionic strength (I) Not possible to calculate further than I=0.1 n=1 n=2 n=3 n=4 •   when I  0 1 when I<10-5M Anions + cations

  16. Debye Huckel(DH) equation • For ionic strengths (I) < 0.1M the X can be calculated by means of e.g. the Debye Huckel equation: I < 0.1 I < 0.005 • 0.5 & 0.33 are temperature dependent table values • Presented values are for 25°C • åX is a table value for the specie in question

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