Electrospray interface HPLC

The pump must provide stable flow rates from between 10 ttlmin and 2 mlmin with the LC-MS requirement dependent upon the interface being used and the diameter of the HPLC column. For example, the electrospray interface, when used with a microbore HPLC column, operates at the bottom end of this range, while with a conventional 4.6 mm column such an interface usually operates towards the top end of the range, as does the atmospheric-pressure chemical ionization (APCI) interface. The flow rate requirements of the different interfaces are discussed in the appropriate section of Chapter 4. 

The advent of the electrospray interface has allowed the full potential of LC-MS to be achieved. It is now probably the most widely used LC-MS interface as it is applicable to a wide range of polar and thermally labile analytes of both low and high molecular weight and is compatible with a wide range of HPLC conditions. 

A triple-quadrupole mass spectrometer with an electrospray interface is recommended for achieving the best sensitivity and selectivity in the quantitative determination of sulfonylurea herbicides. Ion trap mass spectrometers may also be used, but reduced sensitivity may be observed, in addition to more severe matrix suppression due to the increased need for sample concentration or to the space charge effect. Also, we have observed that two parent to daughter transitions cannot be obtained for some of the sulfonylurea compounds when ion traps are used in the MS/MS mode. Most electrospray LC/MS and LC/MS/MS analyses of sulfonylureas have been done in the positive ion mode with acidic HPLC mobile phases. The formation of (M - - H)+ ions in solution and in the gas phase under these conditions is favorable, and fragmentation or formation of undesirable adducts can easily be minimized. Owing to the acid-base nature of these molecules, negative ionization can also be used, with the formation of (M - H) ions at mobile phase pH values of approximately 5-7, but the sensitivity is often reduced as compared with the positive ion mode. 

The MS/MS response for each analyte must first be optimized on the specific instrument to be used. This is usually done by infusing a solution of the analyte into the HPLC mobile phase without a column present. The composition of the mobile phase should match that expected at the time of analyte elution within 25%. The instrument is first operated in the LC/MS mode, and the settings for the electrospray interface are... 

For HPLC/MS/MS analysis, a triple-quadrupole mass spectrometer with an electrospray interface is recommended for achieving the best sensitivity and speciflcity in the quantitative determination of oxime carbamates and their metabolites. This allows... 

HPLC, ConstaMetric 3500 MS and ConstaMetric 3200 MS Mass spectrometer, TSQ 7000 with atmospheric pressure ionization (API) electrospray interface Robotcoupe, Model RSI 25 Syringes, Luer lock, 10-mL... 

The application of polymer monoliths in 2D separations, however, is very attractive in that polymer-based packing materials can provide a high performance, chemically stable stationary phase, and better recovery of biological molecules, namely proteins and peptides, even in comparison with C18 phases on silica particles with wide mesopores (Tanaka et al., 1990). Microchip fabrication for 2D HPLC has been disclosed in a recent patent, based on polymer monoliths (Corso et al., 2003). This separation system consists of stacked separation blocks, namely, the first block for ion exchange (strong cation exchange) and the second block for reversed-phase separation. This layered separation chip device also contains an electrospray interface microfabricated on chip (a polymer monolith/... 

The first reported case of timesharing for a mass spectrometer9 involved the design of an Ionspray interface with multiple sprayers to support the analysis of effluents from multiple columns. This approach led to the development of a multiplexed electrospray interface (MUX)10 using an LC/MS interface and multiple (identical) sprayers linked to a HPLC system and a spinning screen to allow the output of only a single sprayer to enter the MS (Figure 4.5). The injections of the HPLC systems... 

Interfacing HPLC and electrospray has permitted remarkable advancements in biomedical analysis however, the process of successfully coupling these two techniques has required considerable efforts to overcome the limitations imposed by their distinctive operating requirements. 

Several interfaces had been developed, but at present, mainly electrospray ionization (ESI) and atmospheric pressnre chemical ionization (APCI) are widely used. In the ESI interface, HPLC... 

This method allows a quantitative analysis of BAs present in biological fluids (free, and glycine- and taurine-conjugated forms) in a single chromatographic run, performed with an HPLC mass spectrometric system equipped with an electrospray interface [33]. 

BAs are analysed with an HPLC-MS system equipped with an electrospray interface. 

A full experimental design was employed to set the best conditions of a heated electrospray interface intended to couple quartz furnace AAS with HPLC... 

P. Rychlovsky, P. Cernoch and M. Sklenickova, Application of a heated electrospray interface for on-line connection of the AAS detector with HPLC for detection of organotin and organolead compounds. Anal. Bioanal. Chem., 374(5), 2002, 955-962. 

C18 reversed-phase column for HPLC separations of chlorophylls narrow-bore (2.1 -mm i.d.) column at flow rate of 50 to 300 p.l/min without splitting the flow, or analytical column (4.6-mm i.d.) at 1 ml/min with post-column solvent splitting of 5 1 (200 p,l/min entering the mass spectrometer) for APCI electrospray interfaces are available for use without solvent splitting over all flow rates from nl/min to 1 ml/min... 

Solvent selection for HPLC-NMR-MS has to be a compromise between the ideal requirements of each instrument. Thus, for HPLC-NMR the use of inorganic buffers, e.g. sodium phosphate, for pH modification is preferred because no additional signals are introduced into the NMR spectrum although this type of buffer system is currently incompatible with most HPLC-MS systems using an electrospray interface. An alternative acidic modifier is tri-... 

Ionization is accomplished in the electrospray interface by passing the HPLC effluent down a heated metal capillary tube along which an electric charge differential is applied. The evaporating liquid sprays out of the tube end as charge droplets rapidly decreasing in size. A gas nebulizer often... 

Micro- and nano-HPLC systems (Fig. 15.11) rely on small-diameter and capillary columns packed with high-efficiency packing materials and very slow flow rates to produce concentrated solutions and sharp chromatography peaks to feed electrospray interfaces for mass spectrometers. 

The interfacing HPLC with MS is problematic, as pointed out by the image proposed by Arpino of the coupling between HPLC-fish and MS-bird [72] one provides for the separation of neutral molecules in solution with high operating pressures, while the other responds to ions in the gas phase and requires high vacuum. The most widely used technique is electrospray ionization (ESI). It is suitable for analysis of highly polar compounds which are ionized in solution, such as... 

Today, mass spectrometry offers an attractive alternative as a detector to HPLC. Newer techniques for linking HPLC systems with mass spectrometers directly via atmospheric pressure chemical ionization (APCI) and electrospray interfaces should see an expansion of this analytical tool in the analysis of confectionery fats, a field in which it has not yet been applied. Triacylglycerols... 

In an interesting experimental protocol, Silvestro et al. (1993) utilized HPLC-mass spectrometry with an ion spray (electrospray) interface for determination of PAF and lysoPAF in human PMN (neutrophils). Both unstimulated and stimulated (with complement-activated zymosan) cells were used as starting material. The total lipids were isolated in the usual way, and the PAF was isolated and purified by a combination of thin-layer chromatography, HPLC, and silica chromatography. This final PAF preparation was subjected to a bioassay with the inclusion of 3H 16 0 PAF to monitor recoveries. 

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