Chromatography mass spectrometer inlet

The mass spectrometer inlet system for liquid chromatography, often termed the interface between the two component techniques, must therefore remove as much of the unwanted mobile phase as possible while still passing the maximum amount of analyte into the mass spectrometer. This must be done in such a way that the mass spectrometer is still able to generate aU of the analytical information of which it is capable. 

The availability of stable isotope-labeled PA makes an accurate quantitative determination of this imino acid possible. A short high-performance liquid chromatography (HPLC) run prior to the mass spectrometer inlet will result in a discrete peak of PA. For the definitive diagnosis of AASA dehydrogenase deficiency, a simultaneous determination of AASA would be preferred. The absence of a commercially available labeled standard leaves this analysis in the experimental stage. 

Practical inlet systems for attaching a high-pressure liquid chromatography (HPLC) column to a mass spectrometer utilize atmospheric-pressure ionization (see Chapters 8 and 11). 

In addition to GC/MS, high performance liquid chromatography (HPLC/MS) has been used to analyse natural resins in ancient samples, particularly for paint varnishes containing mastic and dammar resins [34]. A partial limitation of chromatographic techniques is that they do not permit the analysis of the polymeric fraction or insoluble fraction that may be present in the native resins or formed in the course of ageing. Techniques based on the direct introduction of the sample in the mass spectrometer such as direct temperature resolved mass spectrometry (DTMS), direct exposure mass spectrometry (DE-MS) and direct inlet mass spectrometry (DI-MS), and on analytical pyrolysis (Py-GC/MS), have been employed as complementary techniques to obtain preliminary information on the... 

Liquid chromatography (Waters, Alliance 2695 pump, Milford, MA, USA) is performed using a prevail carbohydrates ES 54 column (250x4.6 mm, bead size 5 pm, Alltech). An isocratic eluent of 50% acetonitrile/water is used, with the column kept at room temperature. The flow rate is set to 1 ml/min and is split after the analytical column in a ratio of 1 5, resulting in an inlet flow into the tandem mass spectrometer of 200 pl/min 10 pi of sample is injected onto the column and the total run time is 6 min. 

The several components of the less volatile fraction were separated by vapor phase chromatography using a Perkin-Elmer Model 154C instrument. The 6-ft. column was packed with di-n-decyl phthalate on firebrick and was maintained at 90° C. with a helium flow rate of 53 ml./min. Since fractions were expected to be too small to be collected individually, the effluent stream was fed directly into the inlet of a Bendix time-of-flight mass spectrometer. In one fraction, mass peaks at 57 (C4H9) and 71 (C4H9N2) units were observed, in relative intensities identical to those found in azoisobutane (IV). 

For example, little is known about the isotopic composition of formaldehyde in the atmosphere. Formaldehyde is a chemical intermediate in hydrocarbon oxidation. The carbon (8 C) and hydrogen (8D) isotopic composition of atmospheric formaldehyde is analyzed using continuous flow gas chromatography isotope ratio mass spectrometry." Isotope ratios were measured using GC-IRMS (Finnigan MAT 253 stable isotope ratio mass spectrometer, single-sector field with electron impact ion source and multiple ion collection) with a precision of 1.1 and 50%(lo ) for 8 C and 8D, respectively. The accuracy of the online continuous flow isotope technique was verified by calibrating three aliquots of the gas phase standard via the offline dual inlet IRMS technique. The concentration of formaldehyde in ambient air was determined on IRMS major ion peak areas (i.e., mass 44 for 8 C and mass 2 for 8D)." ... 

Gas chromatography (GC) is another widely used analytical technique for phytochemical determination. Similar to HPLC, GC requires sample preparation, which may include lipid extraction and/or extraction of phytochemicals. Once the sample is prepared, it enters the inlet system, flows through the column, and then reaches the detector. In the case of phytochemical analysis, the detector is often a flame ionization detector, which is suitable for all organic particles, or more commonly, the sample passes through the column directly to a mass spectrometer, which serves as the detector. 

Gas-Chromatography Mass Spectral (GC-MS) Analyses. Several different studies were carried out. The main study was done using a Finnigan MAT 4500 series quadrupole mass spectrometer and a 60 m X 0.32 mm l.d. DB-1 bonded fused silica capillary GLC column. The column was programmed from 25-250°C at 4° per minute with an inlet pressure of 14 psi. Chemical ionization (Cl) mass spectra on some of the components were also obtained using a VG Micromass 70/70 mass spectrometer with Isobutane as the reactant gas. 

The first step is the priming of the NRPS active site and a subsequent limited tryptic digest of the protein. The digested sample is loaded on a reverse-phase liquid chromatography (RPLC) C18 column, which is directly connected to the inlet of an FT mass spectrometer. During online LC separation, the eluent is analyzed by MS and MS2 on an LC timescale. In the mass spectrometer the eluent is first analyzed by broadband Fourier transform mass spectrometry (FTMS). Then, peaks in the resulting broadband FT mass spectrum are... 

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