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Marine Geochemistry - Laboratory Methods

Sulfate and Chloride detection using ion chromatography
method Sulfate and chloride are detected using a HPLC system with an anion separation column and indirect UV-detection. The eluent has a high UV adsorption which is "diluted" by chromatographically separated ions. Detection is performed at approximately 288nm. Chromatograms examined by integrator or PC-integrator.
setup Autosampler HPLC pump TSPUV photometer KNAUERtemperature controlled column box thermoconstant water circulationcomputer interface
pump Thermo Separation Products P100
flow 2 ml/min
detector KNAUER variable wavelength monitor @ 288nm
autosampler KNAUER Autosampler 7500
column WESCAN Anion-R 10 µm, 250 x 4.1 mm
capillary UPCHURCH, 1.6x0.5 mm I.D PEEK
peak integration KNAUER Eurochrome 2000 software and interface box (1V integrator output to RS 232)
solutions  
eluent KHP potassium-hydrogen-phtalate, 3mM, pH 6.8, methanol (p.a.) 5ml/L added for sterilization

standard stock

seawater standard (Cox & Culkin 1966)
work standards standards with lower concentration are prepared by diluting seawater standard with sulfate-free artificial seawater.
sample dilution both samples and work standards are diluted 1 : 20 with pure water
retention time approx. 8 min for sulfate
analysis time approx. 10 min per sample
tips + tricks standards have to be adjusted to expected concentrations. Chloride is measured but usually only used for correction. Other anions are below detection limit due to chloride peak tailing and 1:20 dilution necessary for sulfate detection

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