Peak Shape and Recovery Problems for Polar Opiates
Instrument experiencing poor recoveries as some of the analyte molecules eluted as “breakthrough” peaks far ahead of their expected retention times.
1. Change starting gradient conditions from 5 or 10% methanol to 100% aqueous mobile phase. Figure 1 shows how the elution and shapes of polar opiates changed by this step.
Figure 1: Gradients start with 95% aqueous + 5% methanol
2. Ensure completed column equilibration with 100% aqueous mobile phase. Figures 2 and 3 show column pressure traces typical of insufficient and sufficient equilibration.
Figure 2: PFP column pressure trace showing insufficient equilibration
Figure 3: PFP column pressure trace showing sufficient equilibration
3. Change autosampler method by introducing an air gap between washes and samples.
4. Ensure that no residual Wash 2 remained in injection ports after washes. Excessive needle gaps during rinses with organic wash caused peak problems.