Retention time, chromatography

Peracid Classification. Peracids can be broadly classified into organic and inorganic peracids, based on standard nomenclature. The limited number of inorganic peracids has required no subclassification scheme (4). However, the tremendous number of new organic peracids developed (85) has resulted in proposals for classification. Eor example, a classification scheme based on Hquid chromatography retention times and critical miceUization constants (CMC) of the parent acids has been proposed (89). The parent acids are used because of the instabiHty of the peracids under chromatographic and miceUization measurement conditions. This classification scheme is shown in Table 1. 

Micyus, N.J., Seeley, S.K., Seeley, J.V. (2005). Method for reducing the ambiguity of comprehensive two-dimensional chromatography retention times. J. Chromatogr. A 1086(1-2), 171-174. 

B., 37, 362 (1995). The authors claimed that acetone solutions (5, 10 and 20%, specifically) of a sample that had gel permeation chromatography retention time close to that of a linear polystyrene of 1.1 x 106 molecular mass, had four decades lower viscosity than the corresponding solutions of flexible-chain linear poly(butyl methacrylate). However, in our opinion, neither the examined sample was characterized satisfactorily enough to be referred to as a dendrimer, nor the rheology was described sufficiently enough to draw any conclusions about the solution s flow behavior. Therefore, we refer to this paper here only for reasons of curiosity. 

Gas chromatography retention time of PCB congener relative to the retention time of the reference standard octachloronaphthalene on a capillary column of SE-54. Gas chromatography peak area response of PCB relative to peak area of 1 ng octachloronaphthalene. 

Allyl disulphide (diallyl disulphide) [2179-57-9] M 146.3, 58-59°/5mm, b 79-81°/20mm, 138-139°/atm, d 1.01, no 1-541. Purified by fractional distn until their molar refractivities are in uniformly good agreement with the calculated values [JACS 69 1710 7947]. Also purified by gas chromatography [retention times JOC 2A 175 1959 UV JCS 395 7949]. 

Fig. 5 Discovery metabolite profiling of brain tissue, where mass ion intensity ratios (FAAH / / FAAH+/+) of metabolites are presented on three-dimensional surface plots. Global view of the relative levels of metabolites in FAAH / and FAAH+/+ brains, plotted over a mass range of 200-1,200 m/z and liquid chromatography retention times of 0-105 min (plot shown for negative ionization mode). FAAH / brains possessed highly elevated levels of A-acyl ethanolamines (NAEs) (lipid group 4) and an unknown class of lipids (group 5), identified as A-acyl taurines (NATs). Other lipids, e.g., free fatty acids (group 1), phospholipids (group 2), and ceramides (group 3) were unaltered in these samples...

Figures 1,2, and 3 are provided to illustrate one protocol often used to evaluate sink materials [20,32,42-47] however, other methods are also used. For example, Krebs and Guo [48] reported on a unique method involving two test chambers in series. The first chamber is injected with a known concentration of a pollutant (in this case, ethylbenzene). The outlet from the first chamber provides a simple first-order decay that is injected into the inlet of the second chamber that contains the sink material (gypsum board). Thus, this method exposes the sink test material to a changing concentration typical of many wet VOC sources. The sink adsorption rate and desorption rate results are comparable to one-chamber tests and are achieved in a much shorter experimental time. Kjaer et al. [31] reported on using a CLIMPAC chamber and sensory evaluations coupled with gas chromatography retention times to evaluate desorption rates. Finally, Funaki et al. [49] used AD PAG chambers and exposed sink materials to known concentrations of formaldehyde and toluene and then desorbed the sinks using clean air. They reported adsorption rates as a percentage of concentration differences.

There have been numerous attempts to determine HLB numbers from other fundamental properties of surfactants, e.g., from cloud points of nonionics (Schott, 1969), from CMCs (Lin, 1973), from gas chromatography retention times (Becher, 1964 Petrowski, 1973), from NMR spectra of nonionics (Ben-et, 1972), from partial molal volumes (Marszall, 1973), and from solubility parameters (Hayashi, 1967 McDonald, 1970 Beerbower, 1971). Although relations have been developed between many of these quantities and HLB values calculated from structural groups in the molecule, particularly in the case of nonionic surfactants, there are few or no data showing that the HLB values calculated in these fashions are indicative of actual emulsion behavior. 

HPLC/RT = high-pressure liquid chromatography/retention time IH = correction factor for hydrogen bonding in Eq. 1-38 Kcw = cyclohexane/water partition coefficient in Eq. 1-38... 

In liquid chromatography, retention times and co-chromatography with standard compounds must be used, but for a definite identification these must be combined with other methods. 

In reverse phase chromatography, retention times increase with increase in chain length of the bonded phase. Longer solute retention generally provides for enhanced resolution and thus varying chain length of bonded phase is a further aid to optimising the resolution. 

Normal-phase solvents are especially volatile. This is an advantage for preparative chromatography, but also can cause trouble, if this is not taken into consideration in analytical chromatography. Retention times can shift as a result of selective evaporation of some components of the mobile phase. Also, safety should be considered. Some normal-phase solvents, especially hydrocarbons, are highly flanunable others have adverse health effects. Consult the applicable matoial safety data sheets. All containers including waste containers should be closed. When not in use, the mobile-phase container should be sealed. 

Proton and Nuclear Magnetic Resonance Signals and Molecular Assignments for the Methyl Ester Product with Gas Chromatography Retention Time of 18 min... 

Zinc and a nickel complexes have been tested as stationary phases for ligand-exchange gas chromatography. Retention time and selectivity were affected greatly by simply coating about 5% of material on Chromosorb. These compounds were found suitable to separate efficiently polycyclic aromatic hydrocarbons and dialkylsulfides. ... 

ADyldisuffide (diallyl disulfide) [2179-57-9] M 146.3, b 58-59 /5mm, 79-81 /20mm, 138-139"/atm, d 5 1.01, n 1.541. Purify the disulfide by fractional distillation until the molar refractivity is in uniformly good agreement with the calculated value [Small et al. JAm Chem Soc 69 1710 1947. It has also been purified by gas chromatography [retention times Carson Wong J Org Chem 24 175 1959, UV Koch J Chem Soc 395 1949], It is present in garlic. [Beilstein 1IV 2098.]... 

AC CHROMATOGRAPHY RETENTION TIME 12.830 min AC MASS SPECTROMETRY MS TYPE MS AC MASS SPECTROMETRY ION MODE POSITIVE... 

Table 4.10 Gas chromatography, retention times for organic peroxides ...

---