For a hydrogeochemistry project, I want to calculate the molar masses of some compounds. I came across a problem when encountering species like (6)UO2+2D (aq) and (6)UO2OH+D(aq). I don't know what the (6) and the +2D mean.

I started off with IPC-MS results for several trace elements and fed them to VMinteq for the speciation modelling. I tried to google the species, but that query produced no useful results. I am no chemist and I don't know "how" or "where" to search efficiently for an answer.

EDIT: another (6) appeared in FA1-UO2(6)(aq)

  • $\begingroup$ Welcome to the Chemistry SE! You should take the tour and, if you have any further questions about the site, visit the help center. I'm unfamiliar with the topic, are you saying you got these species from the modeling program or you saw them in a paper? Best of luck in getting an answer! $\endgroup$
    – Tyberius
    Mar 28, 2017 at 16:44
  • $\begingroup$ I'm completely unfamiliar with both those (6) and +D notations. Must be field-specific. $\endgroup$
    – hBy2Py
    Mar 28, 2017 at 16:47
  • $\begingroup$ Those species were produced by vMinteq, the modeling program. Thanks for the links, I'll make sure to study the help sites to cozy into the mores and fashion of chemSE. $\endgroup$
    – thymaro
    Mar 28, 2017 at 16:48
  • 2
    $\begingroup$ $m/z$ is the ratio between the mass and the charge of a particle hitting the MS detector. That would allow to guess whether the (6) means "six of these fragments", or "a fragment that has six of these things in it" $\endgroup$
    – hBy2Py
    Mar 28, 2017 at 16:53
  • 3
    $\begingroup$ The (6) for uranium in this Minteq output refers to the valence number for uranium here (+6), which means that $\ce{UO2}$ is really $\ce{UO2^{2+}}$. The D is very likely deuterium, but I cannot confirm that from the user's manual. $\endgroup$ Mar 28, 2017 at 17:28

1 Answer 1


These notations signify someone performed calculations in Visual MINTEQ accounting for dissolved organic matter (DOM) using a NICA-Donnan modeling method. From the manual nicadonnan.pdf bundled with the installer:

In Visual MINTEQ, a “D” suffix is used to identify a diffuse-layer species such as a Donnan species.


The numbers 6, 7, 8 and 9 have no conceptual significance; they are only used by Visual MINTEQ to distinguish different humic components, and they reflect the order in which the components appear on the NICA-Donnan menu (with 6 as the starting number).

Considering the default numbering layout

enter image description here

and that FA1 and FA2 refer to fulvic acids containing carboxylic (FA1) and phenolic groups (FA2), OP's species can be interpreted as such:

(6)UO2+2D(aq): Weakly (electrostatically) bound uranyl $\ce{UO2^2+}$ to fulvic acid in the aqueous phase.

(6)UO2OH+D(aq): Weakly (electrostatically) bound uranyl monohydroxide $\ce{UO2(OH)+}$ to fulvic acid in the aqueous phase.

FA1-UO2(6)(aq): Organically complexed uranyl $\ce{UO2^2+}$ to carboxylic fulvate in the aqueous phase.

Several examples from the manual:

FA1-Zn(aq), FA2-Zn(aq): Organically complexed Zn to dissolved fulvic acid. Sites 1 and 2 refer to carboxylic and phenolic functional groups, respectively.

FA1-Zn(s), FA2-Zn(s): Organically complexed Zn to fulvic acid in the solid phase.

HA1-Zn(s), HA2-Zn(s): Organically complexed Zn to humic acid in the solid phase.

(8)Zn+2D: Weakly (electrostatically) bound Zn to dissolved fulvic acid.

Zn+2D(s)(6): Weakly (electrostatically) bound Zn to fulvic acid in the solid phase.

Zn+2D(s)(7): Weakly (electrostatically) bound Zn to humic acid in the solid phase.


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