The obtained results were similar in both cases. For the analytical method, the Cpm and Cpk indices were computed. Therefore, the process needs to be revised especially, a greater control in the process variation is necessary. The unitary process does not satisfy the minimum capability requirements for Cp and Cpk indices when the specification limit and control limits are equal in breath. We applied different criteria to establish the specification limits (i.e., analyst/customer requirements) for fixed method or process performance (i.e., process or method requirements). The traditional x-chart and moving range chart confirmed both analytical method and process are in control and stable and therefore, the process capability indices can be computed. All these aspects were analyzed using real data from unitary processes and analytical methods. Different control charts in combination with the process capability indices, Cp, Cpm and Cpk, as part of the control strategy, were evaluated, since both are key elements in determining whether the method or process is reliable for its purpose.
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