Errors and Significant Figures

As seen in the previous section, measured values are not absolute, but are obtained with a certain degree of uncertainty. The uncertainty is caused by the combined effect of several error sources. Four major sources for data uncertainty were described in the previous section reproducibility, accuracy, resolution, and limit of detection. To these may be added other factors instability of instrumentation, contamination, accuracy in preparation of standard solutions, etc. The sum of all uncertainties is called the analytical error. The analytical error is a cumulative outcome of all errors 

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The sum of cations equals the sum of anions in each solution. The deviation from such an equality provides another way to assess data quality. The equation used is 

The reaction error is thus expressed as a percentage of the total ion concentration. Positive reaction errors indicate cation excess negative errors indicate anion excess. Reaction errors are caused by the analytical errors of the individual parameters and the fact that not all possible ions are commonly measured. 

In certain cases it is worthwhile to enlarge the list of ions analyzed in order to lower the reaction error, for example, to include NO/, Fe3+, or P044.  

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