The biphenyl phase offers advantageous selectivity compared to a C18 column for drugs of abuse (DoA) panels but choosing the right column dimension is paramount to obtain 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.
Two methods were developed to analyze common isobars in drugs of abuse panels on Raptor Biphenyl columns using methanol and water modified with 0.1% formic acid and column oven set to 45 ⁰C. One method used a 50 x 2.1 mm column with a flow rate of 0.6 mL/min, and the other used a 50 x 4.6 mm column with a flowrate of 0.9 mL/min. Both methods used gradient conditions with a total cycle time of 9 minutes. A lifetime study was conducted by performing 1000 total injections of samples prepared through a common dilute-and-shoot approach on the 50 x 2.1 mm column dimension.
Both methods were compared for efficiency, sensitivity, resolution (Rs), consumption of mobile phase, and robustness, and 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.
