Drug development projects are complex initiatives. Each stage of drug development requires a robust bioanalytical method to measure analytes in complex biological matrices. While measuring analytes in complex samples is challenging, assessing hundreds of study samples while ensuring the highest quality is even more challenging.
Combining liquid chromatography with mass spectrometry has helped fulfill many of the above demands. Liquid chromatography-mass spectrometry (LC-MS) is a highly versatile and efficient instrument and has now become a routine technique in most modern bioanalysis. The LC component physically separates the compounds while the MS unit detects them based on their mass-to-charge ratio. Besides, newer improvements in LC systems include coupling two mass analyzers in a series. LC-MS/MS analysis further provides additional accuracy and sensitivity in detecting and quantifying analytes.
Regardless of their applications, LC-MS method development and LC-MS/MS method development are crucial for reliable results. The following section highlights five critical differences between LC-MS and LC-MS/MS method development. For clarity, we shall first understand LC-MS analysis and then compare it with MS/MS development.
Differences between LC-MS and MS/MS development
The primary difference between LC-MS and LC-MS/MS method development is the coupling of two MS units in LC-MS/MS analysis. A wide variety of detectors are available for coupling with LC units. However, mass spectrometers have emerged as the ideal choice..
The LC system operates at ambient temperature. However, the MS unit operates under a vacuum. Hence, the two systems are joined through an interface. As the eluent enters the interface, the heat evaporates the eluent and the analytes are vaporized and ionized. This step is necessary as the MS units can only detect and measure gas phase ions.
As the analytes enter the MS unit, they are subjected to magnetic and electric fields. These fields deflect the analytes and thus separate them based on their mass-to-charge ratio. Once these analytes are separated, the mass detectors collect and detect the ions.
In tandem mass spectrometry or LC-MS/MS analysis, two MS units detect target analytes. Triple quadrupole mass spectrometers and quadrupole time-of-flight are the most common detectors used in LC-MS/MS analysis.
The triple quadrupole mass spectrometers have two quadrupole mass analyzers separated by a collision cell. Although the two mass analyzers scan or monitor over a range, the collision cell fragments the precursor ions isolated from the first analyzers using high-energy collisions. The triple quadrupole mass spectrometers can operate in four modes, namely precursor ion scan, product ion scan, neutral loss, and selected reaction monitoring.
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The quadrupole time-of-flight MS system has a quadrupole mass analyzer separated from the time-of-flight mass analyzer by a collision cell. The quadrupole system can either isolate specific precursor ions or transmit them forward, where the collision cell fragments the ions. Initially, a small fraction of ions is pulsed through the time-of-flight mass analyzer and then accelerated into a high-vacuum field-free area. Ions with different mass-to-charge ratio travel at different velocities and are thus separated from one another. Time-of-flight mass can scan large mass areas and offer a higher mass resolution.
