Table 2.

AF4 system: Factors studied by a Full Factorial Design (FFD) for the optimisation of the AF4 system with the JRCNM0-1004a material at three levels which show the studied range. The instrumental factors are: cross-flow (CF), detector flow (DF), focusing time (Ft) and the exponential decay of the cross-flow (CF_exp). The statistical assessment showed that exclusively CF and DF turned out to be significant and therefore only these parameters were included in the CCD.

	FFD levels
CF (ml min–1)	0.5–1.5–2.5
DF* (ml min–1)	0.2–0.35–0.5
Ft (min)	3–5–7
CFrate (%)	0.2–0.6–1

Note: CF and DF factors employed in the CCD.