Hi Pedro,
Sorry it took me so long to get back to you. Good question. I need to add that to the help files. For isocratic elution, sigma is calculated from:
double dSigma = Math.sqrt(Math.pow(dRetentionTime / Math.sqrt(m_dTheoreticalPlates), 2) + Math.pow(m_dTimeConstant, 2) + (1.0/12.0) * Math.pow((m_dInjectionVolume / 1000.0) / (m_dFlowRate / 60.0), 2) + dTubingTimeBroadening);
or in nonJava language:
sigma^2 = (RetentionTime/SQRT(N))^2 + TimeConst^2 + (1/12)(InjectVol/F)^2 + (Broadening from postcolumn tubing)
For gradient elution, peak broadening is calculated based on the k of the solute right as it elutes and injection volume doesn't affect peak width (we assume the gradient is steep enough and the solute retained enough for this to hold true). Therefore,
double dSigma = Math.sqrt(Math.pow((m_dVoidTime * (1 + kprime)) / Math.sqrt(m_dTheoreticalPlates), 2) + Math.pow(m_dTimeConstant, 2) + dTubingTimeBroadening)
or in nonJava language:
sigma^2 = ((t0(1 + kf))/SQRT(N))^2 + TimeConst^2 + (Broadening from postcolumn tubing)
where t0 is the dead time, kf is the retention factor at elution, and N is the number of theoretical plates.
I hope that answers your question. I'll answer more quickly next time.
Paul
