We've been digesting soil samples with heated NaCO3 and NaOH mixtures. The brown discolouration of the filtrate makes it difficult to use DPC under acid conditions to detect Cr6+. Yet people use this technique to detect Cr6+ using the UVPSM. How is the DPC coloration compatible with the brown tanning that occurs following the digestion?
Robert Thomas Bachmann
The discolouration may be due to humic substances. If so try digesting your sample with H2O2 and HNO3 to help oxidise the humics.
Instead of using UV SPM consider AAS or ICP-MS.
Check also out: https://www.researchgate.net/post/How_do_I_perform_a_total_Chromium_analysis_in_plant_soil_and_water_using_Diphenyl_Carbazide_method_while_keeping_low_detection_limits
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