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More Rapid Extractable & Leachable Analyses with Advanced Mass Spectrometers
Mass spectrometry (MS) is an analytical technique that provides valuable compound identity information, particularly for substances present at low concentrations such as extractables and leachables (E&Ls) that are often difficult to detect using other methods. In fact, detection of extremely low levels of E&Ls in large-volume parenteral formulations is testing the limits of conventional analytical techniques, and as a result there is growing interest in MS for this application, according to Patrick Bennett, marketing director for pharmaceuticals and biopharmaceuticals at Thermo Fisher Scientific. Advances in technology are not only improving the sensitivity and accuracy of MS analyses, they are also helping to reduce the cost of MS instruments and, therefore, are driving greater use of MS for E&L analysis
Orthogonal methods including MS are essential
Many of these latest analytical techniques used for E&Ls determinations are improvements on current technologies; more modern equipment and electronics offer greater sensitivity, while advances in computer technology and computer software capabilities enable the analysis of much more complex data, observes Daniel L. Norwood, a distinguished research fellow with Boehringer Ingelheim Pharmaceuticals. For Dennis Jenke, a distinguished scientist in the Technology Resources Division of Baxter Healthcare Corporation, the coupling of high-efficiency chromatographic techniques with information-rich detectors is proving very useful for E&L analysis. In particular, he notes that the coupling of ultra high-performance liquid chromatography (UHPLC) with high-resolution MS detectors capable of providing accurate mass information enables the determination of the empirical formulas for otherwise unidentified E&Ls is a noteworthy recent advance.
Benefits of MS for E&L analysis
The use of reliable/accurate exact mass instruments has also reduced the time it takes to analyze and identify E&L compounds. “In the past, it would take significant time, because the unknown compounds first had to be isolated before they could be characterized, which was very time-intensive. With the sensitivity and accuracy of the instruments available today, this time can usually be significantly reduced because structure elucidation is now possible without the need to perform laborious isolation work for the individual unknowns,” Rushing explains.
Choice of MS instruments for data generation
Exact mass instruments are used for the determination of the chemical formula of E&Ls while fragmentation instruments are used for the determination of functional groups and the structure of analytes. TOF and quadrupole TOF (QTOF) provide exact mass and formula information, with QTOF having high accuracy and sensitivity. Ion trap, on the other hand, provides fragmentation data for the determination of functional groups and chemical structure. Single quad systems provide basic mass information. Triple quads (MS/MS) also provide fragmentation data and are frequently used for quantitation and compound identification; Orbitrap MS systems, meanwhile, offer this functionality at high-resolution accurate mass (HRAM) levels. Matrix-assisted laser-desorption ionization (MALDI)–TOF is useful for large organic molecules and matrices where sample preperation is problematic. “Of all of these instruments, the Orbitrap could be considered the instrument of choice for most E&L work,” Rushing says
It should also be noted that the same type of instruments from different suppliers will provide slightly different results. This fact should not be surprising, according to Norwood, given that the ion sources are based on proprietary technology and as a result compounds may ionize differently even though the process is nominally the same. Furthermore, some instruments are much more robust than others, and are thus more suited to initial sample analyses. “For example, we will screen samples on a more rugged instrument, such as a triple quadrupole, and only use the fourier transform mass spectrometry (FTMS) ion cyclotron resonance instrument with an ion trap for pure samples that require extremely high sensitivity. Injection of samples with large quantities of contaminants is problematic on the FTMS system, and cleaning results in significant downtime for the instrument. TOF MS also tends to be used with UHPLC because it enables the rapid scans required for this very fast chromatographic technique,” Norwood comments.
As a result, most laboratories that do trace analysis work have several different types of mass spectrometers and several of the same types but from different manufacturers to ensure they possess the greatest possible analytical capabilities.
Advances in technology
Cyclotrons, ion traps, and triple quadrupole instruments produce data that used to be very difficult to obtain. However, it is not only advances in ion sources and ionization methods that have enabled the types of E&L analyses commonly seen today. “Without the advances in computer and software technology that have taken place in the last few decades, we would not be able to process the data generated by these mass spec instruments,” Norwood emphasizes. “Computers and software really should be considered analytical tools in their own right,” he adds.
Jenke also cautions that the data obtained from accurate MS analyses must be considered in context. “Accurate mass is not always able to give a single definitive empirical formula. Oftentimes several viable candidates are identified and it is not possible, based on the accurate mass data alone, to establish which candidate formula is the correct one. There can be literally hundreds of compounds with a certain empirical formula but only a few may be toxic. It is necessary to know the structure in order to reach the ultimate end game for E&L, which is safety assessment. Accurate mass can therefore, help shore up a tentative identification and may provide insight into a compound’s identity, but it is only one piece of several pieces of necessary information for elucidating and confirming an identification,” said Jenke.
Wishes for the future