Liquid detectors, coupling

One example of normal-phase liquid chromatography coupled to gas chromatography is the determination of alkylated, oxygenated and nitrated polycyclic aromatic compounds (PACs) in urban air particulate extracts (97). Since such extracts are very complex, LC-GC is the best possible separation technique. A quartz microfibre filter retains the particulate material and supercritical fluid extraction (SPE) with CO2 and a toluene modifier extracts the organic components from the dust particles. The final extract is then dissolved in -hexane and analysed by NPLC. The transfer at 100 p.1 min of different fractions to the GC system by an on-column interface enabled many PACs to be detected by an ion-trap detector. A flame ionization detector (PID) and a 350 p.1 loop interface was used to quantify the identified compounds. The experimental conditions employed are shown in Table 13.2. 

Ultraviolet spectroscopy is not as useful in detecting the -NC function. Despite its limitation, coeluting isothiocyano compounds are UV active ( 250 nm, e 1200) [27c]. Thus, a UV monitor can be interfaced with an LH-20 or silica column to detect column fractions containing -NCS compounds. Final resolution of enriched mixtures of previously fractionated isonitrile-related compounds is achieved by examining the responses generated by UV and RI detectors coupled in liquid chromatography. 

GC-FID gas chromatography with flame ionization detector, HPLC-UV high performance liquid chromatography with UV detector, LC-MS liquid chromatography coupled with mass spectrometry, GC-FPD gas chromatography with flame photometric detector... 

Brinkman, F.E., Blair, W.R., Jewett, K.L., and Iverson, W.P. Application of a liquid chromatograph coupled with a flameless atomic absorption detector for speciation of trace organometallic compounds, J. Chrom. Sci. 15, 493-503 (1977). 

The opportunity to measure the dilute polymer solution viscosity in GPC came with the continuous capillary-type viscometers (single capillary or differential multicapillary detectors) coupled to the traditional chromatographic system before or after a concentration detector in series (see the entry Viscometric Detection in GPC-SEC). Because liquid continuously flows through the capillary tube, the detected pressure drop across the capillary provides the measure for the fluid viscosity according to the Poiseuille s equation for laminar flow of incompressible liquids [1], Most commercial on-line viscometers provide either relative or specific viscosities measured continuously across the entire polymer peak. These measurements produce a viscometry elution profile (chromatogram). Combined with a concentration-detector chromatogram (the concentration versus retention volume elution curve), this profile allows one to calculate the instantaneous intrinsic viscosity [17] of a polymer solution at each data point i (time slice) of a polymer distribution. Thus, if the differential refractometer is used as a concentration detector, then for each sample slice i. 

In order to minimize noise and Li migration, the solid-state detector should be cooled, usually to 80 K. This can be done using liquid nitrogen but it is quite inconvenient to have a cryogenic container mounted on the detector arm, especially since the container needs to be refilled every few days. Thus, solid-state detectors coupled with thermoelectric coolers have been developed and commercialized, and successfully used in powder diffraction. 

A solvent module (Varian model No. 5000) with a UV detector coupled to an on-line Nal(Tl) detector was used for high performance liquid chromatography (HPLC) analysis. For radioactive measurements, a dose calibrator (Capintec CRC-7, USA), a solid scintillation counter (ORTEC, USA) with a plane (7.62 cm x 7.62 cm) Nal(Tl) detector, an automatic well type gamma counter (Compac-120, Picker, USA) and a multichannel analyser coupled to a Nal(Tl) detector (7.62 cm x 7.62 cm) were used. 

Several methods have been developed for the determination of arsenic species, involving different extraction, derivatisation, separation and detection steps [13] these include hyphenated techniques based on liquid chromatography coupled to detectors such as ICP-MS or ICP-AES, and hydride generation in line with QFAAS and UV degradation followed by ICP-AES detection. The techniques that were selected in the certification campaign are listed in Table 7.8. 

Deng, Y. et al., Quantitation of drug metabolites in the absence of pure metabolite standards by high-performance liquid chromatography coupled with a chemiluminescent nitrogen detector and mass spectrometer, Rapid Commun. Mass Spectrom., 18, 1681, 2004. 

The prepared solutions were monitored by liquid chromatography coupled with a diode array detector (DAD) and with an electrospray mass spectrometry (ESI-MS) detector. Isolation of the formed pigments was achieved by HPLC at the semipreparative scale. 

Frey, B.M. Frey, F.J. Simultaneous measurement of prednisone, prednisolone and 6p-hydroxypredni-solone in urine by high-performance liquid chromatography coupled with a radioactivity detector. J.Chromatogr., 1982, 229, 283-292... 

Earlier methods used to determine mercury in biological tissue and fluids were mainly colorimetric, using dithizone as the com-plexing agent. However, during the past two to three decades, AAS methods - predominantly the cold vapor principle with atomic absorption or atomic fluorescence detection - have become widely used due to their simplicity, sensitivity, and relatively low price. Neutron activation analysis (NAA), either in the instrumental or radiochemical mode, is still frequently used where nuclear reactors are available. Inductively coupled plasma mass spectrometry (ICP-MS) has become a valuable tool in mercury speciation. Gas and liquid chromatography, coupled with various detectors have also gained much importance for separa-tion/detection of mercury compounds (Table 17.1). 

Liquid chromatography coupled with a photodiode array detector, electrospray ionization, collision-induced dissociation, and tandem mass spectrometry (LC-DAD/ESI-CID-tandem MS) on a triple quadrupole has been used to detect and characterize CGAs in green coffee beans [8,9]. Fragmentation in the quadrupole MS stages is different from that in the ion-trap instrument. 

The simplest way of giving pervaporation the character of a continuous separation technique is its coupling to a dynamic manifold for assistance of both donor and acceptor chambers. In the first instance, when the samples are liquid, the coupling with the manifold (usually a flow-injection (FI) arrangement) is mandatory for driving the sample either by injection or aspiration to the donor chamber. In addition, (bio)chemical and/or physical steps, namely, reactions that convert the analyte into the most appropriate form for being evaporated, physical dispersion, etc., can also be developed in the manifold prior to the arrival of the sample to the donor chamber meanwhile, a detector can be located in postpervaporator position in order to monitor nonvolatile species. When the sample is a solid, the... 

Dugo, R, M. Herrero, T. Kumm, D. Giuffrida, G. Dugo, and L. Mondello, 2008. Comprehensive normal-phase X reversed-phase liquid chromatography coupled to photodiode array and mass spectrometry detectors for the analysis of free carotenoids and carotenoid esters from mandarin. L Cfmmgtogi 1189 196-206. 

Yu and co-workers [59] discussed liquid chromatographic interfaces for bench-top single quadruple LC-MS. The two most popular interfaces are particle beam and atmospheric pressure ionisation types. The system was applied to the analysis of additives in PP. Dilts [60] used a photodiode array detector coupled with particle beam LC-MS to characterise the degradation of Isonox 129, Irganox 1010, Ii anox 1076, andirgafos 168 in polyolefins. Sidwell [61] examined extractables from plastic and rubber components of medical products by LC-MS and GC-MS. 

Jones and co-workers [228] used particle beam liquid chromatography coupled with a MS detector to determine styrene oligomers up to the w-18 oligomer of PS. Bryant and Semiyen [229] analysed cyclic oligomers of polybutylene terephthalate using column chromatography GPC (size exclusion), fast atom bombardment mass spectrometry, and tandem mass spectrometry (MS-MS). They obtained molecular weight distributions. 

The use of detectors other than UV for the analysis of tropane alkaloids has been reviewed previously [15, 24, 27]. In contrast to conventional detectors such as UV, RI, fluorescence, and ELSD coupled with LC, the MS detector provides information on the molecular structure of the separated compotmds (Fig. 31.3). Over the past decade, liquid chromatography coupled with mass spectrometry (LC-MS) has undergone tremendous technological improvement and is now one of the most powerful tools for the investigation of natural compotmds. 

HPLC is designed to separate compounds from complex mixtures based on polarity, solubility, and size properties of each compound. High-pressure liquid chromatography coupled with a photodiode-array detector (HPLC-DAD) provides extensive information on polyphenol stmctures [6, 110]. 

Zhang, L., Xu, L., Xiao, S.-S. et al. (2007). Characterization of flavonoids in the extract of Sophora Jlavescens Ait. by high-performance liquid chromatography coupled with diode-array detector and electrospray ionization mass spectrometry. Journal of Pharmaceutical and Biomedical Analysis, 44, 1019-1028. 

LC-MS tandem apparatus equipped with ESI and APCI in both PI and NI modes was evaluated [133]. This study investigated the effects of matrix interferences on the analytical performance of a triple-quadrupole detector coupled to various reversed-phase liquid chromatographic. In Table 19.8, selected LC and GC methods for assaying herbicides and fungicides in water are listed. 

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