Pharma QC Guide

The resolution is represented as a numeric value, such as 0.8, 1.0, or 3.0. But what is the relationship between the number representing the resolution and the actual peak separation?  At a resolution of 1.0, if the two peaks are assumed to have a Gaussian distribution and have the same peak height and peak width, then the difference in retention time from equation  become 1.0W, or 1.0 × 4σ = 4 σ.  In the case of a Gaussian distribution, 4 σ encompasses 95.4 %, such that the peaks overlap by 2.3 % ((100 % - 95.4 %)/2).  This indicates that 2.3 % of the peak intrudes into the other peak from a perpendicular line drawn in the trough.  Similarly, a resolution of 1.5 indicates a difference in retention time of 1.5× 4σ = 6σ, which corresponds to an overlap of 0.15 % ((100 % - 99.7 %)/2).

The resolution is the separation of two components in a mixture, calculated by: Resolution = 2 × (tR2 − tR1)/(W1 + W2)  where tR2 and tR1 are the retention times of the two components; and W2 and W1 are the corresponding widths at the bases of the peaks obtained by extrapolating the relatively straight sides of the peaks to the baseline.  Where electronic integrators are used, it may be convenient to determine  the resolution, by the equation:  Resolution = 1.18 × (tR2 − tR1)/(W1,h/2 + W2,h/2) What relation Resolution and Peak seperations?

Relative retention time (RRT) is the ratio of the retention time of analyte peak relative to that of another used as a reference obtained under identical conditions. RRT = (T analyte / T reference)  Wher T = Retention time As per USP Relative retention time (RRT): Also known as the “unadjusted relative retention”. Comparisons in USP–NF are normally made in terms of unadjusted relative retention, unless otherwise indicated. RRT = tR2/tR1 The symbol rG is also used to designate unadjusted relative retention values. The use of the relative retention time (RRT) reduces the effects of some of the variables that can affect the retention time. What is Retention time?

Retention time (RT) is a measure of the time taken for a solute to pass through a chromatography column. Retention time (RT) is calculated as the time from injection to detection. The RT for a compound is not fixed as many factors can influence it even if the same instrument and column are used.  These include: The flow rate Temperature differences in the oven and column Column degradation Column length What is RRT?

Chromatography Chromatography  is a  laboratory technique  for the  separation of a mixture .  The mixture is dissolved in a fluid called the  mobile phase, which carries it through a structure holding another material called the  stationary phase. The various constituents of the mixture travel at different speeds, causing them to separate.  The separation is based on differential partitioning between the mobile and stationary phases.  Subtle differences in a compound's  result in differential retention on the stationary phase and thus affect the separation. Chromatography is based on the concept of partition coefficient .  Any solute partitions between two immiscible solvents. When we make one solvent immobile (by adsorption on a solid support matrix) and another mobile it results in most common applications of chromatography. If the matrix support, or stationary phase, is polar (e.g. paper, silica etc.) it...