Elution systems

DALLUGE J J, NELSON B c, THOMAS J B and SANDER L 0 (1998) Selection of column and gradient elution system for the separation of catechins in green tea using high-performance liquid chromatography , J Chromatogr A, 793, 265-74. 

WANG H, HELLiwELL K and YOU X (2000a) Isocratic elution system for the determination of catechins, caffeine and gallic acid in green tea using HPLC ,Pood Chem, 68 (1), 115-21. 

Nowak, M. and Seubert, A., Application of experimental design for the characterization of a novel elution system for high capacity anion chromatography with suppressed conductivity detection, /. Chromatogr. A, 855, 91,1999. 

The limit of detection for this instrument is about 10 pg/ ml for polystyrene in 2-butanone,163 which is close to two orders of magnitude higher than that of the deflection-type DRI. Moreover, the response of the ELSD is linear over only two decades in concentration.163 The ELSD is a useful backup detector when the DRI or UV detectors are not appropriate, e.g., when the UV absorbance or RI change is a function of copolymer composition as well as concentration or in gradient elution systems where changes in solvent composition cause drift in baselines of the UV and DRI detectors. Compounds about as volatile as the solvent are poorly detected by ELSD. 

Liquid chromatography is carried out in columns. The common columns are packed using reversed-phase ( jx-bonded silica gel as stationary phase. Elution systems are... 

If you use only one liquid, either neat or as a mixture, the entire chromatogram is said to be isochratic. There are units that can deliver varying solvent compositions over time. These are called gradient elution systems. 

Four basic types of elution system are used in HPLC. This is illustrated below by the systems offered by LKB, Sweden. 

The rise in popularity of HPLC is due in large part to its high-performance nature and the advantages offered over the older, noninstrumental open-column method described in Chapter 11. Separation and quantitation procedures that require hours and sometimes days with the open-column method can be completed in a matter of minutes, or even seconds, with HPLC. Modern column technology and gradient solvent elution systems, which will be described, have contributed significantly to this advantage in that extremely complex samples can be resolved with ease in a very short time. 

A parallel study [94] was performed by the same authors on the retention of model compounds (tryptophan, erythro- and t/ireo-P-methyltryptophan, A-carbobenzyloxy-tryptophan, A-(3,5-dinitro-2-pyridyl)-tryptophan, l-[5-chloro-2-(methylamino) phenyl]-l,2,3,4-tetrahydroisoquinoline, and y-phenyl-y-butyrolactone) on a ristocetin A-based CSP, using the three RP, POM, and NP elution systems. Also, in this case, the natural logarithms of the retention factors (In k) of the investigated compounds depended linearly on the inverse of temperature (1 /T). 

A comprehensive study on the temperature effect was done in 2004 for 71 chiral compounds on four glycopeptide CSPs TE, TAG, ristocetin A, and vancomycin phases, using the three RP, POM, and NP elution systems [95]. The separations were studied in the 5 5°C temperature range. Peak efficiencies always increased with temperature, but in only 17% of the separations studied, a small increase of the resolution was observed. In the rest of the cases, the resolution decreased or even vanished when temperature increased. All van t Hoff plots were linear, showing that... 

Another screening strategy using the same type of columns but with normal-phase gradient elution has been proposed by the pharmaceutical group Lilly.In this strategy, each compound is screened on four columns, i.e., Chiralcel OD-H, Chiralpak AD, Chiralpak AS and Chiralcel OJ. An n-hexane/2-propanol and an n-hexane/EtOH gradient elution system are... 

Dams et al. [19] determined seven different opium alkaloids and derivatives in seized heroin using fast LC-MS analysis. Analytes were separated in 5 min on a monolithic silica column with a gradient elution system and an optimized flow of 5 mL/min. Detection was carried out using a sonic spray ion source [20] a modified ESI source were ionization is achieved using a nebulizer gas at sonic speed instead of applying an electrical field. 

Brunborg, G. Holme. J.A.. Soderlund, E.J., Omichinski. J.G. Dybing. E. (1988) An automated alkaline elution system DNA damage induced by 1.2-dibro mo-3-chloropropane in vivo and in vitro. Anal. Biochem.. 174. 522-536... 

When performing HPLC (see Basic Protocol 2) the time of analysis will depend on the conditions used—i.e., isocratic versus gradient. Isocratic separation of the individual betacyanins, as shown in Figure F3.1.2, requires 20 min, compared to 9 min using a gradient elution system. 

In the beginning, the refractive index detector was the most used detection system, although it has two important drawbacks (1) solvent gradients cannot be used, and (2) it has low sensitivity and different responses to saturated and highly unsaturated TGs (112). Moreover, use of the ultraviolet (UV) detector is difficult, because the most adequate solvents also absorb in the same range and therefore cause an important baseline drift with gradient elution systems (106). 

Demopoulos et al. demonstrated that PL separation can be accomplished by using a cation-exchange column with an isocratic elution system of AIM/ W (300/150/35). Thus, most PLs, such... 

Figure 10.9 HPLC trace of standard pigments using gradient elution system, (a) standard mixture (1) monitored at 415 nm (b) standard mixture (2) monitored at 490 nm and 590 nm. Conditions column 5 pm ( IS 150 X 4.6 mm, using diode array detection at 450 nm and gradient elution solvent A = 0.02 M ammonium acetate, Solvent B = acetonitrile gradient profile 0 min 95% A, 20 min 50% A, 25 min 95% A flow rate 1.0 ml/min.

Rhizodeposition is affected by many biotic and abiotic factors of plant and soil (Jones et al., 2004). A simple and efficient technical solution for the collection of rhizodeposits in a soil environment consists of small boxes in which plants are grown and from which the rhizodeposits are leached by a siphon-elution system (Kuzya-kov and Siniakina, 2001). In the past five years, this was applied to a large number of rhizopeposits from maize (Zea mats L.) (e.g., Melnitchouck et al., 2005 Fischer et al., 2007) and potato (Solarium, tuberosum L.) (e.g., Melnitchouck et al., 2006 Schlichting and Leinweber, 2008). 

Freeze-dried DOM samples collected with the siphon-elution system (Kuzyakov and Siniakina, 2001) for the first time showed diurnal dynamics in the molecular-chemical composition of maize rhizodeposits (Kuzyakov et al., 2003). In a forthcoming study with maize, Melnitchouck et al. (2005) showed that amino acids, especially aspartic acid, asparagine, glutamic acid, phenylalanine, leucine and isoleucine contributed to the more intensive rhizodeposition during daytime than during nighttime. Furthermore, the maximum of thermal volatilization of peptides at low pyrolysis temperature in Figure 14.8 indicates the rhizodeposition or microbial formation of free amino acids rather than amino acids bound in peptides or trapped in soil humic substances. 

Fig. 1.1 Elution systems supplied by LKB, Sweden (a) isocratic bioseparation system (b) basic system ...

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