The biphenyl stationary phase offers advantageous selectivity compared to a C18 column for drugs of abuse panels, but choosing the right column dimension is key to obtaining robust and accurate data. Every column dimension can be advantageous in different scenarios, but generally clinical labs are all working towards the same goals: high throughput, low sample volume, good sensitivity, and low cost. In this work, the advantage of 2.1 mm internal diameter (ID) columns is discussed and demonstrated for the analysis of drugs of abuse by LC-MS/MS.
Two methods were developed to analyze common isobars in drugs of abuse panels on Raptor Biphenyl columns: one method used a 50 x 2.1 mm, 2.7 μm column with a flow rate of 0.6 mL/min and the other used a 50 x 4.6 mm, 2.7 μm column with a flow rate of 0.9 mL/min. The two methods were compared for efficiency, sensitivity, resolution (Rs), consumption of mobile phase, and robustness. Buprenorphine was used to demonstrate sensitivity differences between the two different column dimensions. It was found that the 2.1 mm ID column produced twice the signal response of the 4.6mm internal diameter column when injection volume is held constant. Twice the amount of sample had to be injected on the larger-bore column to produce the same signal response, thus introducing the chromatography to greater matrix effects with more impact to instrument cleanliness.
In summary, the 2.1 mm ID column was able to demonstrate superior sensitivity while consuming less resources and minimizing impact to the MS while still providing adequate resolution of isobars and excellent column robustness.
