Micro high pressure liquid chromatography

Wheeler, G. L., Lott, P. F. Rapid determination of trace amounts on selenium(IV), nitrite and nitrate by high pressure liquid-chromatography using naphthalene-2,3-diamine. Micro-chem. J. 19, 390(1974)... 

Wang J, Du Z, Yu W, Qu S. Detection of seven pesticides in cucumbers using hollow fibre-based liquid-phase micro-extraction and ultra-high pressure liquid chromatography coupled to tandem mass spectrometry. J Chromatogr A 2012 1247 10-17. 

High performance liquid chromatography was performed with a high pressure liquid chromatography apparatus equipped with a U.V. detector (280 nm). The U.V. monitor has an 8 pi flow cell. The chromatographic column was a 20 cm x 2.1 mm (internal diameter) pre-packed stainless-steel Micro-Pack" column (Varian, Palo Alto, Calif.,... 

High-pressure liquid chromatography Analysis was performed by reverse-phase utilizing a Waters Associates chromatograph equipped with 30 cm X 4 mm i.d. micro Bondapak C g columns with 254-and 280-nm detectors at a flow rate of 60 ml/hr, using water-acetonitrile-acetic acid as a solvent system. 

Kwon, J. and Moini, M. Analysis of underivatized amino acid mixtures using high performance liquid chromatography/dual oscillating nebulizer atmospheric pressure micro-wave induced plasma ionization-mass spectrometry. J. Am. Soc. Mass Spectrom. 2001, 12, 117-122. 

The mass spectrometer is a very sensitive and selective instrument. However, the introduction of the eluent into the vacuum chamber and the resulting significant pressure drop reduces the sensitivity. The gas exhaust power of a normal vacuum pump is some 10 ml min-1 so high capacity or turbo vacuum pumps are usually needed. The gas-phase volume corresponding to 1 ml of liquid is 176 ml for -hexane, 384 ml for ethanol, 429 ml for acetonitrile, 554 ml for methanol, and 1245 ml for water under standard conditions (0°C, 1 atmosphere). The elimination of the mobile phase solvent is therefore important, otherwise the expanding eluent will destroy the vacuum in the detector. Several methods to accomplish this have been developed. The commercialized interfaces are thermo-spray, moving-belt, electrospray ionization, ion-spray, and atmospheric pressure ionization. The influence of the eluent is very complex, and the modification of eluent components and the selection of an interface are therefore important. Micro-liquid chromatography is suitable for this detector, due to its very small flow rate (usually only 10 p min - ). 

Toluene disproportionation was carried out in a high-pressure continuous flow micro reactor. Granular catalyst (32-64 mesh, 2.5 cm ) was loaded into a stainless steel tube reactor. Toluene was fed at a rate of 10 cm h (liquid) in the flow of H2S(0.2vol.%)/H2 mixture gas (200 cm min b at 623K and 6MPa. The effluent was analyzed by gas chromatography (Shimadzu, GC-9A) by a flame ionization detector (FID). 

As mentioned earlier, that it is possible to simultaneously apply a high hydraulic pressure at the inlet vial to drive the solvent through the column and an electrical field. This hybrid method combining both pressure and electrodriven liquid chromatography was first introduced by Tsuda [46] and is referred to as pressure assisted CEC or field assisted micro HPLC. Verheij et al. [47] used this the technique to couple CEC with MS. These authors also proposed the name pseudo-CEC for this technique. 

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