Can anyone explain this method? Especially the last statement where it says only at 1.5 to 2.5mins was the MS/MS connected to the UPLC. How is that possible, is it a feature in this specific brand?
Ivermectin was analysed on a modular UPLC system from Shi-madzu (Kyoto, Japan) containing a system controller (CBM-20A),four pumps (LC-30AD), a degasser (DGU-20A5), a column oven(CTO-20AC), and an autosampler (SIl-30ACMP), which was cou-pled to an API 5500 QTRAP tandem mass spectrometer (AB Sciex,Framingham, MA, USA).A Kinetex C8 analytical column (2.6 m, 100 A, 50 × 2.1 mm)was installed in the 55◦C tempered column oven. A filter frit (SS0.5 m 0.62 × 0.65, Ercatech AG, Bern, Switzerland) was used toprolong the lifetime of the analytical column. Mobile phase A wasan aqueous solution of 20 mM ammonium formate supplementedwith 0.1% formic acid (pH 3.5). Mobile phase B was methanol plus0.1% formic acid. The column was conditioned at 2% mobile B duringthe first 0.25 min of each analytical run. Afterwards, the mobile Bconcentration was linearly increased to 75% over 0.5 min and to 95%within 1.75 min. 95% mobile phase B was kept constant for 0.75 min.The run was terminated by reconditioning the column for 0.5 minat 2% mobile B. The flow rate was set to 0.6 ml/min and the injec-tion volume was 10 L. Ivermectin eluted after 1.9 min, therefore the UPLC system was only connected during minute 1.5 and 2.5with the mass spectrometer to avoid superfluous contamination of the system.
In the described method, an HPLC system is connected to a mass spectrometer only between 1.5 and 2.5 minutes to focus solely on the elution of Ivermectin. This is achieved using a diverter valve that directs the flow to waste outside this window, preventing contamination and unnecessary data collection. The flow is switched to the mass spectrometer during this time frame to capture the target compound while keeping the system cleaner. This time-based switching is a standard feature in modern LC-MS systems, including the one used in the study, ensuring accurate and efficient analysis.
As Dr Balamurugan Krishnamoorthy said, it is most likely that the LC flow was going to the MS during this particular time window and diverted to waste otherwise.
However, the wording from the original authors could have been a little better. Technically, LC and MS instruments are connected during the whole analysis. The "disconnection" of LC and MS is not done by manually disconnecting the cables or capillaries, but by a software-controlled diverter valve which does this by switching flow from the MS to waste and vice-versa. It does this much faster than you could ever do it by hand.
Connecting an HPLC to a Mass Spec at specific time points is possible using "timed switching." This technique directs LC eluent to the MS only when the analyte of interest elutes, reducing contamination and improving data quality. It's a common feature in modern LC-MS systems, controlled by the instrument software.
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