Flagged as an outlier and excluded from subsequent analysis

Furthermore, the mean coefficient of variation across 104 samples—each analysed in triplicate—was 1.46%, corresponding to an error ±5.8 mg/g for a sample with a nominal tebuthiuron content of 400 mg/g. This supported the reproducibility of the HPLC method for measuring tebuthiuron content in the Regain samples. In addition, the routine use of triplicate analyses for the assessment of tebuthiuron content allows for the detection and removal of any outlier results.

#### *3.2. Observations on Moisture Content*

The standard deviation (i.e., laboratory error) of the triplicate moisture analysis was found to be 0.42% *w*/*w* (Table 1), with a coefficient of variation of 3.9%, indicating acceptable analytical error.

In the samples of Regain400, a moderate negative correlation between the tebuthiuron and moisture content was found (Figure 6); however, this relationship was very weak (R<sup>2</sup> = 0.05).

**Figure 6.** Relationship between the tebuthiuron content and the moisture content of the Regain400 samples.

#### *3.3. Assessment of Spatial Variation in the Sample*

The results from the sample variation experiment indicated a moderate amount of spatial variation in the tebuthiuron content, with the mean content of each sampling replicate ranging from 412.3–421.0 mg/g (Table 4). The mean content was 416.1 ± 3.3 mg/g, giving a coefficient of variation of 0.79%. The results are also shown visually in Figure 7.

**Table 4.** Assessment of the variation in tebuthiuron content between different portions of one Regain400 sample.

