Coping with un-dilution of SOLUTION_SPREAD chemical compositions

[peterwadeuk]

Greetings, Sterling Comrades,

I wish you very well.

I am faced with a problem. I am routinely asked to do charge balances and other calculations involving chemical analytical data in large spreadsheets that are sent to me in the following format:

pH and Alkalinity are measured at site of sampling, or less than 24 hours after sampling.

Elements are determined by ICP on solutions that were diluted 4x (four times) with deionised water.

Anions are determined by IC on the same solutions diluted 4x.

How may I multiply all the ICP and IC data by 4, and then associate the resulting matrix with pH and Alkalinity, inside PHREEQC? I am doing this all outside PHREEQC and reading in the resulting database/matrix using SOLUTION_SPREAD, but this manipulation is inconvenient for people who will be taking over my work.

All the best,
Peter

[dlparkhurst]

One way that should work is to redefine the gram formula weights of the cations and anions in a SOLUTION_MASTER_SPECIES data block. If your data are mg/L, then decreasing the gram formula weights by a factor of 4 should increase the molalities by a factor of 4.

You would need to be very careful to make clear what you are doing. I would probably add the data block to the input file each time (rather than modifying the database) just to make it clear how the conversions were done. You could use an INCLUDE$ file to import the data block.

If you need to have a variable dilution factor, it could be possible to have a USER_PUNCH data block that generates the SOLUTION_MASTER_SPECIES data block, or you could generate the SOLUTION_MASTER_SPECIES data block within your spreadsheet.

[peterwadeuk]

Thank you David