How to use a LOTUS spreadsheet

There are many spreadsheets available. One of the best known ones is LOTUS-1-2-3 (ref. 3) and we will use this to show how the spreadsheets can be used. 

For instance, suppose one measures the optical absorption of a solution in a colorimetric procedure. This procedure specifies that the measurement should be carried out at pH 2.5 and room temperature. On verification, it is found that a clearly different result is obtained at pH 2.4 and that differences are also observed when the temperature is 20°C and 25°C. The method will display higher variability between laboratories and between days than expected, because it is not rugged. 

Ruggedness is measured by imposing small variations on the experimental parameters and recording the results. Let us suppose we have developed an. AAS method and we want to test its robustness. The following seven parameters have been identified as possible sources of variation amount of water, reaction time, distillation rate, distillation time, n-Heptane, Aniline, and status of the reagent. For short, we will call these 7 variables or factors as AoW, Rt, Dr, Dt, n-H, Anl, SoR and perform a partial factorial experiment consisting of 8 experiments. The partial factorial experiment is described in Table 2.2. 

The + and - signs denote levels of the factors AoW, Rt, Dr, Dt, n-H, Anl, SoR. They are called the nominal and the extreme values, respectively. The nominal value ( +) is the value specified in the procedure of which one wants to evaluate the ruggedness. For instance, if the amount of water is 2, the nominal (+) value of AoW is 2 and the extreme (-) on could be 5, while the nominal value ( +) of SoR is new and the extreme one (-) might be used (Table 2.3). The third experiment, for example, is carried out in such a way that factors AoW, Dr, and n-H take their nominal values while the others are at the extreme level. 

One observes that the + and - signs do not have their usual meaning since the value for AoW - is higher than for AoW +. 

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