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Analyses plan Module 19. Conductivity and temperature {H + } determined using pH electrode UV/VIS MAS Sample pre-treatment Sample filtration Total organic carbon Major anions and cations to be determined by IC UV oxidation. Conductivity.
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Analyses planModule 19 • Conductivity and temperature{H+} determined using pH electrode • UV/VIS MAS • Sample pre-treatment • Sample filtration • Total organic carbon • Major anions and cations to be determined by IC • UV oxidation
Conductivity • 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
{H+} determined using pH electrode • 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
Major anions and cations to be determined by Ion Chromatograph (IC) • 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 along with H+ or OH- in the eluent stream are measured by means of a conductometer
Total organic carbon • Analytical chemistry lab Ø 104 • High temperature (680ºC) 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 an IR detector • Analytes measured may include: TC, IC, TOC, NPOC, and POC
Al fractionation • Fractionation of monomeric aluminium from polymeric forms is accomplished by 20 sec. complexation with 8-hydroxyquinoline at pH 8.3 with subsequent extraction into MIBK organic phase • Organic bound monomeric aluminium is separated from inorganic aluminium (mainly labile) by trapping the latter fraction on an Amberlight IR-120 ion exchange column • The Al concentrations in the organic extracts are determined photometrically • Download manual from • http://folk.uio.no/rvogt/KJM_MEF_4010/
P fractionation - The oxidation by UV is intended to mimic the photooxidation occurring in the lake during ice free season. - Filtration through 0,45μm filter (or rather 0,2μm) filter removes algae.
P determination • - Orthophosphate reacts with ammoniummolybdate to a yellow-coloured phosphorousmolybdate acid, that is reduced with ascorbic acid in the presence of antimony to a strongly blue coloured complex. This colour is measured photometrically as described in Norwegian Standard (NS 4724).
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/
Speciesin natural freshwaterCentral equilibriums in natural water samples KJM MEF 4010 Module 19
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:
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+
Concentrations of dissolved Fe3+ speciesTwo total Fe concentrations, FeT = 10-4M and FeT = 10-2M
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
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
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 because • 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