Check the APHA 'Standard Methods of Water and Wastewater'.

There are a few USEPA Methods that use this approach. Check out 218.6 for waters and 7196 for waters and solids. You should consider employing ion chromatography separation if you anticipate interferences in the samples you are testing. EPA Methods 218.7 and 7199 both utilize this approach. The most specific and sensitive approach however is ion chromatography coupled to ICP-MS. 

Diphenylcarbazide is oxidized by Cr VI to Diphenylcarbazone and Cr VI is reduced to Cr3+.

Cr3+ with Diphenlycarbone gives a red-violet coloration (measurement at 550 nm).

There are many methods which use this principle:

Tube tests: for instance HACH LCK313, no standard at this time,

Classic manual method:  DIN 38405-24 or EN ISO 18412,

Discrete analyzer: no standard at this time,

Continuous Flow Analysis (CFA) or Flow Injection Analysis (FIA): EN ISO 23913

we are try cr6+ in spectro metric method,and qulitative and quanitative

could you check this paper:

http://onlinelibrary.wiley.com/doi/10.1002/3527600418.am1854029stae0004/pdf

also you can download APHA BOOK FOR WATER AND WASTEWATER ANALYSIS FROM HERE:

https://www.mwa.co.th/download/file_upload/SMWW_1000-3000.pdf

KIND REGARDS,