1:2 ratio (1 sample: 2 DI) is the acceptable dilution factor. This means that a sample volume as small as 2 ml can be diluted in 4 ml of Deionized water (DI) for a total of 6ml, when measured in a 50ml tube using the TitraPro3 pH electrode.  Note that since the sample is diluted, the pH should not be reported as the sample initial pH value.  Only undiluted samples should be measured and reported for initial pH. Dilutions factors that are greater, for example 1 part sample to 3 parts DI, were found to produce incorrect, lower alkalinity results.  It was also noted that on higher dilutions, the pH dropped below 7, indicating a change over to the acidic side.