General

Import data

The data to be imported has three components

1. The model. This can be imported from an HQD file or created from new. If HySS was used to find titration conditions, the model can be taken from the file created in HySS.
2. The instrumental data. Once the data have been collected they will be stored in a file as detailed on the experimental pages.
3. The titration conditions, amounts of reagent, burette concentration etc.

The data import routines are designed such that all the necessary data can be imported and/or edited. The new data will be stored in an HQD file, which may be the same file as was created in HYSS. The project will be ready for stability constant determination.

Manual fitting

Each program has a manual fitting routine. Though details differ, the principle is the same. The objective of manual fitting is to reduce the systematic differences between the observed data points and the points calculated with a set of stability constant values and given concentrations. Since the calculation of stability constants uses an iterative procedure it is important that starting values of the stability constants produce a reasonably good fit of the data. In manual fitting systematic differences between observed and calculated data are reduced, while in the refinement process both the systematicand random differences are reduced.

Adjuster

The adjuster, shown above, may be used to adjust stability constant values interactively by pressing to decrease or to increase a value. The stability constant to be adjusted may be selected either by clicking on the speciation curve or from the drop-down box in the adjuster.

Another feature of manual fitting is that it should provide confirmation that the model may allow a good fit of the experimental data to be obtained. If a species is missing from the model there will probably be large differences between observed and calculated quantities.

Species concentrations

The concentrations of the species at a the point under the cursor are shown in a table. The table shows the proportion, as a percentage, of each species relative to the total concentration of the chosen reagent, whose free concentration is highlighted in green. The reagent may be changed by clicking on another reagent name.

Note that by default the chosen reagent will be the first in the list if reagents. This means that the hydrogen ion should not normally be the first reagent in the list, as concentrations relative to the hydrogen ion are not helpful.

Data selection

The data points to be used for the determination of a stability constant should be those points where the species concerned is in equilibrium with other species. For example, when determining protonation constants by titrating a solution of an acid with alkali, the points which may be obtained after all the protons have been removed should be flagged to be ignored, as there is no equilibrium after the final end-point.

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