Robustness parameter Coumarin** o-coumaric acid** Dihydrocoumarin** Syringaldehyde** Recovery% RSD% T test (p value) Recovery% RSD% T test (p value) Recovery % RSD% T test (p value) Recovery % RSD% T test (p value) Methanol Confidence interval =  99.26 to 100.74%  99.22 to 100.78%  99.50 to 100.35%  98.78 to 101.22% 29% 99.97 0.09 0.9434 99.88 0.13 0.1497 99.69 0.18 0.5152 100.72 0.57 0.2363 30%* 100.00 1.0000 100.00 1.0000 100.00 1.0000 100.00 1.0000 31% 100.14 0.1578 100.14 0.4428 99.72 0.9222 99.59 0.4535 Acetonitrile Confidence interval =  99.22 to 100.78% 99.83 to 100.17% 99.92 to 100.08% 98.80 to 101.20% 4.9% 99.88 0.10 0.8205 99.83 0.09 0.0979 99.98 0.03 0.6991 99.25 0.39 0.2811  5%* 100.00 1.0000 100.00 1.0000 100.00 1.0000 100.00 1.0000 5.1% 99.79 0.6671 99.86 0.2287 99.94 0.4384 99.79 0.6951 Formic Acid Confidence interval =  99.28 to 100.72 99.64 to 100.36% 99.68 to 100.32% 98.64 to 101.36% 0.9% 100.08 0.11 0.5945 100.21 0.16 0.1736 100.24 0.11 0.2182 99.80 0.22 0.6903 1%* 100.00 1.0000 100.00 1.0000 100.00 1.0000 100.00 1.0000 1.1% 99.87 0.5493 99.89 0.4676 100.05 0.6255 100.24 0.7796 Temperature Confidence interval =  98.7 to 101.24% 99.84 to 100.16% 99.71 to 100.29% 97.86 to 102.14% 23°C 99.92 0.06 0.3947 99.87 0.08 0.1057 100.11 0.06 0.5152 99.77 0.18 0.6206 25°C* 100.00 1.0000 100.00 1.0000 100.00 1.0000 100.00 1.0000 27°C 100.03 0.8861 99.84 0.1058 100.02 0.9222 100.12 0.5696 Flow Rate Confidence interval = 97.83 to 102.17% 97.99 to 102.01% 96.58 to 102.46% 98.02 to 101.98% 0.98 mL min-1 102.03 1.96 0.9434 101.88   2.3933-5 101.73   6.4554-5 102.28   8.6387-6 1.0 mL min-1 100.00 1.0000 100.00 2.00 1.0000 100.00 1.06 1.0000 100.00 2.30 1.0000 1.02 mL min-1 98.11 8.3198-5 97.88 9.5319-8 97.69 1.9681-6 97.68 1.5826-6

Data: *Optimized conditions; **Standard concentration: Coumarin, 25.0470 µg mL-1; o-coumaric acid, 24.8805 µg mL-1; dihydrocoumarin, 24.9480 µg mL-1; syringaldehyde, 24.8490 µg mL-1

Table 5: Accuracy and precision by recovery test for robustness analysis (n=6).