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Automatically running Spec8 or React with 100's of samples using bicarbonate as makeup ion


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In Spec8 and React, you can automatically speciate many samples at once using Cl as a make-up ion if a charge imbalance exists. However, it is not clear how one can do the same thing using bicarbonate as a makeup ion instead. I have 100's of samples that I need to run, so doing this by hand is not efficient. In Spec8, I read in the GWB manual that you can add additional arguments in the command pane found in the menu when selecting samples to run (accessed from the GSS file), however, it's not clear what kind of arguments can be input there or perhaps more importantly, what the variable name would be to set bicarbonate as the make-up ion. There are "header commands" and 
trailer commands" listed as additional input, just can't figure out what command initiates a bicarbonate charge balancing.

Along these lines, I was attempting to manually calculate charge imbalance so that I could use this information to manually calculate a new bicarbonate concentration, but I cannot seem to match the calculated charge imbalance values from GWB. I know that GWB uses the equation: 100*[(Sum cations-Sum anions)/(Sum cations+Sum anions)], but when I perform this calculation, I cannot recreate exactly the charge imbalance output. The concentration data of interest was converted to mEq/L and multiplied by the charges to sum the cations and anions. Part of this could be due to not fully understanding how GWB handles H+ in this calculation, but could you provide any further explanation as to how GWB exactly calculates charge imbalance? Are ALL major cations and anions in the GSS file always used to calculate charge imbalance, or are only the major cations and anions used in the calculation? Based on the forum information, it's not quite clear how exactly GWB deals with charge imbalance.


Any help would be greatly appreciated.

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Hello Jenna,

In SpecE8 and React, you can change the charge balancing ion by adding in that component in the basis and then click on the unit and select "balance species". You can also alternatively enter the command "balance on HCO3-" in the Command pane, assuming that you are using thermo.tdat. All commands recognized by SpecE8, React and other GWB apps can be found in the GWB Command Reference. You can open this from the Help menu under any app.

In GSS, you can set a charge balancing on HCO3- under Analysis -> Options....  Again, if you are using thermo.tdat (default database in the GWB), then the command would look like "balance on HCO3-". The header commands are at the top of the file and the trailer commands are placed at the bottom. In this case, I believe it does not matter if you place the balancing ion command in the header or trailer section. If you launch your samples from GSS in SpecE8 or React now, the programs will use HCO3- for charge balancing.

If you are looking to calculate charge balance for many water samples at once, you can use the calculated analytes feature in GSS. To do so, add all your water samples to your GSS spreadsheet, go to "+analyte", select "Calculate with SpecE8", select the "charge imbalance" and hit "Apply" or "Ok". You will see an extra row added to your spreadsheet for your newly calculated charge imbalance. Please see more about calculating with SpecE8 in section 3.3.7 in the GWB Essentials Guide.

The concentrations entered into GSS are bulk concentrations. The charge imbalance and charge imbalance error are calculated with all cation and anion species concentrations after chemical speciation. For more information regarding speciation, please see section 7.2 Equilibrium Models in the GWB Essentials Guide. To perform a manual calculation of charge imbalance, I would suggest launching a SpecE8 instant for one sample in your GSS spreadsheet. Then run the calculation and verify the charge imbalance by summing the total electrical equivalents for anions and subtracting it from the total equivalents of cations from concentrations, found under the variable type "Species concentration" in Gtplot. You can export the numerical values by going to Edit -> Copy as... -> Spreadsheet or Tab. Make sure all species concentration are plotted before exporting.

The equation 100*[(Sum cations-Sum anions)/(Sum cations+Sum anions)] is how the software calculates the percentage of charge imbalance error.

Hope this helps,

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