Optimization of the extraction procedures was performed with the aid of Design Expert 8® software, which suggested 58 different experiments. 
Design Expert 8
Response surface optimization of a vortex-assisted dispersive liquid-liquid microextraction method for highly sensitive determination of repaglinide in environmental water by HPLC/UV.A vortex-assisted dispersive liquid-liquid microextraction (DLLME) method, mated to chemometrics and combined with HPLC/UV detection was optimized and validated for enrichment and determination of repaglinide in environmental samples using nateglinide as an internal standard (IS). 
HPLC/UV