Instrumentation And Basis Of Analysis

Instrumentation for MS-MS screening consists of a triple quadrupole mass spectrometer controlled by a computer system, an electrospray ionization (ESI) interface, and a liquid chromatograph equipped with an autoinjector.

A mass spectrometer is a ''mass'' detector by which gas-phase ions can be analyzed.[1] The masses of ions are recorded as ratios of molecular weight to charge (m/z). Through an ESI device, ionic compounds in the liquid phase can be introduced into MS as gas-phase ions. ESI plays an important role in MS-MS screening by the sequential introduction of sample solutions, which are injected automatically into the continuous flow of a liquid chromatograph at 2-min intervals without chromato-graphic separation.

A triple quadrupole MS system comprises two mass analyzers, which are separated by a collision chamber that induces the fragmentation of ionic compounds by the introduction of argon gas. Using a computer algorithm, the intensities of the masses of ionic compounds in the first mass analyzer (precursor ions) and those of their fragment ions in the second mass analyzer (product ions) are recorded in synchronized manners. In acylcarnitine analysis, a fragment ion of m/z 85, which characterizes the structure of butylester derivatives of acylcarnitines (Fig. 1), is monitored in the second mass analyzer, whereas the masses of ionic compounds are analyzed in the first mass analyzer. In amino acid analysis, the masses are analyzed synchronously in both mass analyzers to record the intensities of the masses of fragment ions produced from the precursor ions after the loss of 102 atomic mass units (Fig. 2). Thus, without chromatographic separation of the sample mixture, the information on the characteristic fragmentations enables the measurement of acylcarnitines and amino acids with high specificity. Quantification is performed using stable isotope-labeled compounds as internal standards.

Data are recorded by class-specific analysis or target compound analysis.[2] In the latter analysis, called selected or multiple reaction monitoring, a certain transition of the precursor to the product is monitored to analyze a single compound. The degree of fragmentation can be optimized to improve sensitivity by controlling both the amount of argon gas in the chamber and the energy of the compounds entering the chamber and argon. If target disorders in MS-MS screening are restricted, the latter analysis allows for monitoring of the selected compounds.

Fig. 1 Fragmentation of acylcarnitine butyl esters in a collision chamber by collision-induced dissociation (CID).

Fig. 1 Fragmentation of acylcarnitine butyl esters in a collision chamber by collision-induced dissociation (CID).

specimens have been tested. If the values are very abnormal, a full metabolic workup is initiated immediately.

Getting Started With Dumbbells

Getting Started With Dumbbells

The use of dumbbells gives you a much more comprehensive strengthening effect because the workout engages your stabilizer muscles, in addition to the muscle you may be pin-pointing. Without all of the belts and artificial stabilizers of a machine, you also engage your core muscles, which are your body's natural stabilizers.

Get My Free Ebook


Post a comment