Liquid chromatography-mass small molecules

Bakhtiar, R., and Majumdar, T. K. (2007). Tracking problems and possible solutions in the quantitative determination of small molecule chugs and metabolites in biological fluids using liquid chromatography-mass spectrometry. J. Pharmacol. Toxicol. Methods 55 227-243. 

Over the past two decades, capillary electrophoresis (CE) and related techniques have rapidly developed for the separation of a wide range of analytes, ranging from large protein molecules to small inorganic ions. Gas chromatography has been considered as a powerful tool due to its sensitivity and selectivity, especially when coupled with mass spectrometry. Nevertheless, liquid chromatography is the most used method to separate and analyze phenolic compounds in plant and tissue samples. 

Consider one small molecule, phenylalanine. It is an essential amino acid in our diet and is important in protein synthesis (a component of protein), as well as a precursor to tyrosine and neurotransmitters. Phenylalanine is one of several amino acids that are measured in a variety of clinical methods, which include immunoassay, fluorometry, high performance liquid chromatography (HPLC see Section 4.1.2) and most recently MS/MS (see Chapter 3). Historically, screening labs utilized immunoassays or fluorimetric analysis. Diagnostic metabolic labs used the amino acid analyzer, which was a form of HPLC. Most recently, the tandem mass spectrometer has been used extensively in screening labs to analyze amino acids or in diagnostic labs as a universal detector for GC and LC techniques. Why did MS/MS replace older technological systems The answer to this question lies in the power of mass spectrometer. 

Smyth WE, Brooks P. 2004. A critical evaluation of high performance liquid chromatography ionization-mass spectrometry and capillary electrophoresis-electrospray-mass spectrometry for the detection and determination of small molecules of significance in clinical and forensic science. Electrophoresis 25 1413. 

Hsieh, Y, Merkle, K., Wang, G., Brisson, J. M., and Korfmacher, W. A. (2003). High-performance liquid chromatography-atmospheric pressure photoionization/tandem mass spectrometric analysis for small molecules In plasma. Anal. Chem. 75, 3122—3127. 

The applicability of LC LC to the (ultra) high-molar-mass polymers. Contrary to liquid chromatography under critical conditions, LC LC likely exhibits no upper limit of the sample molar mass [234]. On the other hand, if the difference in elution rates of the barrier forming small molecules and the oligomeric species is too small, the LC LC separation becomes insufficient. As a result, LC CC and LC LC may be considered mutually complementary from the point of view of their applicability in the... 

In this chapter we focus primarily on calibration of LC-MS where the mass spectrometer is operating at unit resolution, resolution that is sufficient to separate two peaks one mass unit apart. This kind of low-resolution mass filter covers almost 90 percent of the instruments commonly used for qualitative and/or quantitative analysis of small molecules. Batch-to-batch qualification testing of the instrument is also described. For the calibration of high-resolution mass spectrometers such as magnetic sector, TOF, or FTICR coupled with liquid chromatography, readers are referred to specific publications. 

More recently, butterfat composition has been analyzed by capillary GC on polarizable liquid phases (122,123), reversed-phase high-performance liquid chromatography (124,125), and GC and HPLC with mass spectrometry (MS) (126), as well as by MS-MS (127). These studies have led to an extensive resolution of butterfat triacylglycerols, but the possible presence of small amounts of positional and reverse isomers as well as of species containing two or three short-chain acids per molecule has not been addressed. 

Herniman, J. M., Bristow, T. W. T., O Connor, G., Jarvis, J., and Langley, G. J. (2004). Improved precision and accuracy for high-performance liquid chromatography/Fourier transform ion cyclotron resonance mass spectrometric exact mass measurement of small molecules from the simultaneous and controlled introduction of internal calibrants via a second electrospray nebuliser. Rapid Commun. Mass Spectrom. 18 3035-3040. 

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