How do I perform a total Chromium analysis in plant, soil, and water using Diphenyl Carbazide method while keeping low detection limits?

I have tried methods a few methods, see attached, but in each they require at least a 5x dilution of the sample before analysis and then again a dilution in color preparation. When I try to avoid diluting with distilled water and using highly concentrated basis to increase the pH of digested sample the color quickly dissapears upon addition of diphenyl carbazide. See methods I have been working on attached and in "Determination of total chromium in tannery waste water by inductively coupled plasma-atomic emission spectrometry, flame atomic absorption spectrometry and UV – visible spectrophotometric methods". Also I do not have access to a chromatography column so am trying to do this without preconcentration and isolation by chromatography.
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    ABSTRACT: Existing methods for the colorimetric determination of microgram quantities of chromium with diphenylcarbazide gave poor recovery, unstable colors, and unreliable results. Investigation revealed that the methods of oxidizing the chromium to the required hexavalent state and of destroying the excess oxidizing reagent were of critical importance. Oxidation in alkaline media was subject to losses because of precipitation, while oxidation in acid media with energetic agents such as persulfate or bismuthate could generate traces of hydrogen peroxide which would later reduce chromium recoveries. A new method was developed for oxidizing chromium in acid medium with permanganate; the excess oxidant was destroyed with sodium azide. The color with diphenylcarbazide was stabilized by the addition of a phosphate buffer. The procedure is conveniently applied to air, water, and urine samples, yielding excellent recovery and color stability, with a sensitivity of 0.03 microgram of chromium in a volume of 25 ml. The method should be applicable in many fields.
    No preview · Article · Jun 1952 · Analytical Chemistry