Lub hauv paus ntsiab lus tseem ceeb yog kev zom sai sai spectrophotometric, nrog rau txoj kev poov tshuaj dichromate yog feem ntau siv.
Ib qho kev paub txog cov tshuaj potassium dichromate yog ntxiv rau cov qauv. Nyob rau hauv ib tug muaj zog sulfuric acid nruab nrab, siv nyiaj sulfate raws li ib tug catalyst, tus qauv yog digested nyob rau hauv high kub (feem ntau rhuab mus txog 175 degree). Tus nqi COD yog txiav txim siab spectrophotometrically. Thaum tus nqi COD hauv cov qauv yog nyob nruab nrab ntawm 100 mg / L thiab 1000 mg / L, qhov nqus ntawm trivalent chromium (Cr3+) tsim los ntawm kev txo cov poov tshuaj dichromate yog ntsuas ntawm lub wavelength ntawm 600 nm ± 20 nm. Tus nqi COD nyob rau hauv tus qauv yog ncaj qha proportional rau qhov nce nyob rau hauv absorbance ntawm trivalent chromium (Cr{10}}). Lub absorbance ntawm trivalent chromium (Cr{12}}) yog ces hloov mus rau hauv tus nqi COD ntawm tus qauv.
Thaum tus nqi COD nyob rau hauv cov qauv yog li ntawm 15 mg / L mus rau 250 mg / L, tag nrho absorbance ntawm ob chromium ions-tsis txo hexavalent chromium (Cr6+) thiab txo trivalent chromium (Cr{4}})- yog ntsuas ntawm lub wavelength ntawm ± 40 nm. Tus nqi COD nyob rau hauv tus qauv yog ncaj qha proportional rau qhov txo nyob rau hauv absorbance ntawm hexavalent chromium (Cr6+), qhov nce nyob rau hauv absorbance ntawm trivalent chromium (Cr{10}}), thiab txo nyob rau hauv tag nrho absorbance. Tom qab ntawd tus nqi absorbance tag nrho yog hloov mus rau COD tus nqi ntawm tus qauv.
