Ok, I have feedback on the 0.1N sulfuric acid standard from Amazon. I mixed up 1.5L of reagent using the Amazon product rather than OEM. I dumped the remnants of the previous reagent just to get a clear test. My last 4 measurements from the previous 24 hours, before swapping in the new reagent, were 7.70, 7.64, 7.70, 7.67. After the new reagent was used, I ran 2 extra measurements. They were 7.56, 7.53. The 0.2 difference between the reagents made from the OEM and Amazon standard is probably caused by a slight mixing error. I overshot on the amount of RODI by 12 ml and tried to add an offsetting amount of acid and then a final correction of RODI, because I overshot on the acid correction . I suspect I either miscalculated, or my scale was is not sensitive enough to small volume changes. Similar discrepancies after slight mixing snafus have happened in the past with the OEM version as well, so I don't consider it relevant.
I think the Amazon 0.1N sulfuric acid is a great alternative to the OEM and plan to use this going forward.
Dennis
This one