I've been asking and spending a lot of time looking up stuff.
Looking for info on the potential of a potentiometer:
source- chemist w. doctorate in physical chemistry. I asked, can chromium be detected with a potentiometer? His answer-"No."
I'm concerned about concentrations greater than 100 ppb, the EPA's drinking water limit.
Does 100 ppb means there are 100 chromium-6 atoms in (10)9 water molecules?
Or does it go by weight?
Note-I just want to know if a significant, over the limit amount of Cr is in the water-I don't need precision measurements. A certified lab will have to do that.
Looking for some ideas-
source: EPA website
Copy of a little of approved EPA method follows:
"1.0 SCOPE AND APPLICATION 1.1 Method 7196 is used to determine the concentration of dissolved hexavalent chromium [Cr(VI)] in EP/TCLP characteristic extracts and ground waters. This method may also be applicable to certain domestic and industrial wastes, provided that no interfering substances are present (see Paragraph 3.1 below). 1.2 Method 7196 may be used to analyze samples containing from 0.5 to 50 mg of Cr(VI) per liter. 2.0 SUMMARY OF METHOD 2.1 Dissolved hexavalent chromium, in the absence of interfering amounts of substances such as molybdenum, vanadium, and mercury, may be determined colorimetrically by reaction with diphenylcarbazide in acid solution. A redviolet color of unknown composition is produced. The reaction is very sensitive, the absorbancy index per gram atom of chromium being about 40,000 at 540 nm. Addition of an excess of diphenylcarbazide yields the red-violet product, and its absorbance is measured photometrically at 540 nm." (end copy)
Simplifying the preparation of a reagent stock solution:
"Dissolve 141.4 mg of dried potassium dichromate, K2Cr2O7 (analytical reagent grade), in reagent water and and dilute to 1 L water. 1 mL = 50 ug Cr"
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So, I reformulate my question: How does 50 ug/ mL translate into ppb?
Also, is diphenylcarbazide safe?
Is there a simpler way?
1. Methods for Chemical Analysis of Water and Wastes, EPA-600/4-82-055, December 1982, Methods 218.4 and 218.5.
2. Gaskill, A., Compilation and Evaluation of RCRA Method Performance Data, Work Assignment No.2, EPA Contract No. 68-01-7075, September 1986
OSHA's atmospheric testing method for Cr-6: