Mass spectrometry is an analytical technique that provides valuable compound identity information, particularly for substances present at low concentrations that may be difficult to obtain using other methods. Unfortunately, mass spectrometry instrumentation is often expensive, usually requires skilled and trained personnel to operate, and generally occupies a large amount of bench space. For many analytical chemists, therefore, mass spectrometry isn’t practical. Many who do require mass spectral data must send their samples out for analysis, either to a dedicated mass spectrometry laboratory within their company or, alternatively, to an outside laboratory. That could mean long turnaround times and missed deadlines in addition to higher costs. To address the continuing challenges in separations science with mass spectral information, Waters Corporation has developed a mass detector that overcomes the barriers to adoption of mass spectrometry by analytical chemists. The new mass detector is not only affordable, but it can be directly integrated with various chromatographic systems, to provide high quality mass spectral data at the touch of a button.
Real need for simple and affordable mass detection
“Across numerous markets, including pharmaceuticals, we found that people working in labs, whether in methods development, sample profiling, synthesis, or purification, there is a real desire for access to mass detection capabilities, but without the cost and complexity of a traditional mass spectrometer,” notes Gary Harland, director for mass spectrometry product management at Waters Corporation. “What is really needed,” he continues,” is a mass detector that is complementary to their existing optical detection techniques, can be easily and repeatedly used, and maintained without extra work. In sum, they want to obtain mass spectral data using a chromatographic-like detector.”
In liquid chromatography method development, mass spectroscopy is not routinely used by most. While separation techniques have improved significantly in recent years, there are still challenges, according to Harland. A validated chromatographic method is one that completely separates the components of a sample from one another and that identifies components based on their retention time. To develop such a method requires extensive expertise and experience, particularly when there may be a coelution of structurally related compounds and when numerous chromatographic peaks must be completely baseline-resolved. Sample profiling also relies on the accurate identification of compounds in very complex matrices, such as foods and pharmaceutical formulations, that are often at very low concentrations. For synthetic chemists who often rely on mass spectral data to test reactions and verify the intended products or those reactions, the waiting time for mass spectrometry results can be quite long since samples must often must be sent to another lab and analyzed by someone with the proper expertise. Finally, according to Harland, ultraviolet-visible (UV-vis) methods are often used to detect compounds during downstream purification steps. That means that every fraction must be analyzed in order to determine which ones are of interest.
In all of these cases, access to immediate mass spectral data could significantly improve the efficiency of the analytical process.
A mass detector for the chromatographer
To address the need for easy-to-use mass detection as part of a separations system, Waters developed the ACQUITY QDa detector. Based on the same ion physics as a conventional single quadrupole mass spectrometer, it is specially designed for a small footprint and to work synergistically with a variety of chromatographic separation systems, such as liquid chromatography (LC) ultra-performance LC (UPLC) supercritical fluid chromatography (SFC) and conventional detection systems, such as UV-vis spectroscopy and photodiode array (PDA) systems, and do so at a cost closer to those detectors.
“When developing this technology, our key goals were to create a mass detector that would provide quality mass spectral data but operate with the familiarity of a PDA detector,” Harland notes. In addition, the detector needed to be reliable, require little maintenance, and be compatible and complementary with other chromatographic systems, which meant covering the mass range for the types of molecules that are separated and detected with LC/UV methods. Furthermore, the acquisition speeds needed to match that of very fast UPLC systems, and the ionization of the molecules could not impact the performance and operation of the other separation systems.
Two key features, according to Harland, are its push-button operation and automatic calibration. “Once the system is turned on, it boots up within 30 seconds and is under vacuum within five minutes and pressure tested and ready to use within six-and-a-half minutes. For a cold start, the system also goes through automated calibrations, so it takes a little longer, but operators are still up and running within 20 minutes. At that point, the detector is ready to use in the same time as it takes a PDA to be ready.”
Significant advances in technology were needed to achieve these goals. Many patents have been filed that are related to advances in ease of use and affordability, according to Harland, without compromising the high-quality mass spectral data required. “We had to engineer many new systems in order to achieve robust, high-quality mass detection at a reasonable price.” Two examples include a single-piece, zero-adjustment probe capillary that not only eliminates all the optimization normally required but also minimizes dispersion and preserves the high resolution chromatographic separation, and a new sample cone assembly featuring an inexpensive and disposable sample aperture. “Conventional sample cones for mass spectrometry are expensive, can be damaged if dropped or mishandled, and require regular cleaning involving disassembly and sonication to prevent degradation of the sensitivity of the instrument, which is a time-consuming process. The new disposable system is easy to replace and only needs replacing about as often as the column gets replaced, which saves both time and money while maintaining consistent performance,” Harland observes.
Key advantages for all chromatographic separations
With the ability to obtain optical and electrospray (ES) ionization mass spectral data simultaneously, it is possible for scientists to identify compounds at low concentrations in complex mixtures, including co-eluting substances. They can also detect compounds that are “transparent” to UV detectors because they lack chromophores. “For methods development, having access to mass spectral data will enable faster methods development and allow for more rapid and robust methods as well,” asserts Harland. “We expect that, because scientists can get mass spectra immediately, it will have the biggest impact in methods development applications,” he continues.
He also believes that the mass detector will provide greater sensitivity and selectivity for sample profiling, which includes quantifying impurities or additives often at low levels in complex matrices. Meanwhile, synthetic chemists who have tested the detector are considering expanding the use of LC–MS systems for more immediate results, which can significantly speed up new compound synthesis. In purification processes, the ability to identify the compounds in each fraction means that only the fractions that contain the desired compound need to be processed, which leads to more efficient separations and greater productivity, according to Harland. He adds that there is also interest in the new mass detector from academia, both for research and for undergraduate education.
The mass detector also has potential applications in the pharmaceutical manufacturing setting. Some possible uses include the profiling of active pharmaceutical ingredients and related compounds, the determination of batch-to-batch variations, and the determination of extractables and leachables.
Customer collaboration key
The initial development of the new mass detector began about three years ago, according to Harland. At that time, Waters was working with key customers to determine the key properties of the new system. In the last year, that program expanded significantly to include numerous customers across many different markets. “This testing initiative was our largest beta-testing program ever because we wanted to be certain that we would have a very high level of confidence that the mass detector would meet the operability and data performance needs of all possible groups of scientists that could benefit from the technology,” he observes. The program was very valuable, and refinements were made to the detector based on input from these users before it was determined ready for commercial sale. “We definitely want to thank all of the participants in the testing program. They were definitely a key factor in the successful development of the new technology.”