Relative retention times, various

Webster s definition for database is a large collection of data in a computer, organized so that it can be expanded, updated, and retrieved rapidly for various uses. An LC/MS database established for drug impurities contains multi-dimensional information such as relative retention times, UV spectra, molecular mass and substructural information. In order for the information to be updated and expanded, the methods used for information collection need to be unified. A generic LC/MS method allows relevant information to be collected in a consistent... 

Gas chromatographic analyses are obtained at about 120° with a 2 m. X 7 mm. column packed with a suspension of 5% (by weight) of silver nitrate and 15% (by weight) of Carbowax 6000 (polyethylene glycol) on either Chromosorb P or Celite 545. With this column the relative retention times of the various possible components in the reaction mixture are cyclododecane, 1.00 trans,trans,trans-, S,9-cyc ododec tnene, 1.20 trans-cyclo-dodecene, 1.13 m-cyclododecene, 1.33 ci5,iraw5-l,5-cyclodode-cadiene, 1.51 m, m 5-/raw5-l,5,9-cyclododecatriene, 1.72. The reaction should be stopped when the rate of reduction of cis,trans-1,5-cyclododecadiene to cw-cyclododecene has become approximately equal to the rate of conversion of the as-monoolefin to cyclododecane. 

Table III. Relative Retention Times of Various Pesticides or Their Methyl Esters (M.E.) on a SE-54 Capillary Column...

The arrays of products from the various methyl ester fractions do not show the distinctive grouping noted for the methyl ethers. In contrast to the methyl ethers, the alkaline oxidations produced many acidic products having methyl esters with relative retention times less than 0.931. Methyl esters from alkaline nitrobenzene and nitric acid oxidations, present in more than trace amounts, were distributed more widely than esters from the oxygen reactions. In the latter instance most products with a relative retention time greater than 1.000 were present in small amounts. 

The procedures for sample preparation and the operating conditions of the GC-MS system have been described elsewhere (9-12. 14-16 ten Haven et al., Proc. ODP. Sci. Results. 112. in press). All GC-MS data had been stored on magnetic tapes, but in some cases could not be retrieved. In these cases, indicated by an asterisk in Table I, old hardcopy files were checked for the occurrence of OSC. Mass chromatograms of characteristic ions (m/z 87, 97, 98, 101, 111, 115, 125, 129, 139, 195, 265, 331, 341), in combination with published information on relative retention times (3-5. g), were used to identify the various compounds. 

A typical chromatogram obtained using this method is shown in Figure 12, and the retention times (Rt) and the relative retention time (Rrt) for pantoprazole sodium and some of its related compounds are shown in Table 6. The calibration curve for the assay determination, obtained over a concentration range of228-670 pg/mL, was found to be linear with a correlation coefficient of0.999. The recovery and relative standard deviation for various assays were 97.3-101.5 and 1.1, respectively. A calibration curve was also developed for pantoprazole sodium related compounds, covering a concentration range of 1 to 3 pg/mL, and which was found to be linear with a correlation coefficient of more than 0.999. The limits of detection and limits of quantitation were calculated as 0.15 pg/mL and 0.49 pg/mL, respectively. 

Moisture-Equivalent—Briggs and McLane (1907) made extensive physical studies on what has been termed moisture-equivalent — that is, the percentage of water retained by a soil, when the moisture content is reduced by means of a constant centrifugal force until it is brought into a state of capillary equilibrium. While King s procedure yields specific information on the relative retentiveness of various soils only after considerable time, the method of Briggs and McLane is rapid,... 

The chromatographic technique separates various PAH compounds such that each may be tentatively identified by a comparison of its relative retention time with those of known standards. In principle, this HPLC method is applicable to the analysis of any PAH for which acceptable resolution and peak area are achieved. 

Comparison of various halogenated acyl derivatives verifies that the typical properties of the ECD apply also for steroids [355]. Table 5.13 compares the relative retention times and responses of different derivatives of testosterone and cholesterol obtained on... 

Relative retention time (RRt) is defined as the ratio of the analyte and the reference compound s retentions. The RRt of sterols relative to cholesterol and cholestane, stearyl acetates to cholesteryl acetate, estrogen derivatives to cholestane, estrogen TMS ether to cholestane on various packed columns was described by Heftman. The RRt of some estrane, androstane, and pregnane derivatives was also reported. ... 

Baker et al. reported the identification of various drugs by means of their relative retention times in combination with the absorbance ratio, calculated from the peak heights observed with 254 and 280 nm UV-detection. 

The retention times of 17 monovalent anions on resins with different functional groups but with almost identical exchange capacities (average 0.027 mequiv/g) were compared with the use of a solution of a monovalent anion (sodium benzoate) as the eluent [8]. Relative retention times were calculated by dividing the measured retention times by that of chloride. Data for resins with various trialkylammonium groups are presented in Table 3.1. 

Determination of Relative Reaction Ratios of Olefins Comparison of relative reaction rates was done by gas chromatographic analysis of reaction mixtures with addition of a suitable internal standard such as biphenyl. A mixture of the olefin to be compared and norbornene (both olefins in excess) were readed with a defidency of ethyl mercaptoacetate at various temperatures. Relative retention times were compared with those of independently prepared and characterized mercaptoacetate-olefin adducts. Comparison of the relative amounts of each product in the reaction mixture gave the relative, competitive reaction rate. The independently synthesized adducts were also examined to determine that... 

The method described is identical to the lUPAC method 2.403 (Paquot, 1979b). The AOCS method Ce 3-74 (AOCS, 1978) describes a method for the gas chromatographic determination of tocopherols and sterols in soya sludges and residues. In this method, the sample is saponified and the extracted unsaponifi-able matter is reacted with butyric anhydride. The butyrate esters of the tocopherols and the sterols present in the unsaponifiable matter are subjected to gas chromatographic analysis and determined quantitatively. Relative retention times for the various tocopherol and sterol butyrates are given. 

After fractionation, some relationships between various components are immediately apparent. Both the chain-length and the number of double bonds in each fatty acid derivative in the chromatograms are ascertained, while relative retention times can be correlated with those of constituents of the unfractionated material. By careful measurement of ECL values, it is then frequently possible to assign double bond positions. In this sample, the identities of nearly fifty different fatty acids in the fractions were confirmed by GC-mass spectrometry following conversion to the picolinyl ester derivatives (see Chapter 7). 

Finally, it should be noted that the retention indices given for the various derivatized drugs are not, nor were they intended to be, true Kovats Indices. These indices should be merely used as guides for determining relative retention times. However, it was determined that for several common underivatized drugs the retention indices were calculated to be within a few percent of the actual Kovats number. 

In Table 2 a series of (0-acylated) N-acylneuraminic acids isolated from various biological sources is presented (see also chapter B and C). These sialic acids have been analyzed by g.l.c./m.s. after esterification with diazomethane and trimethylsilylation (section II. 3) the Table includes relative retention times of the derivatives on g.l.c. and mje values of the fragment ions A-G. As was mentioned earlier, sialic acids predominantly occur in the p-anomeric form. However, on 3.8% SE-30 the a-anomer could sometimes be detected separately from the p-anomer (in most cases as a small shoulder). Mass spectra are depicted in Figs. 2 and 5-17. 

Partial 0-acetylation of NeuSAc methyl ester p-methyl glycoside led to the formation of several 0-acetylated compounds (Haverkamp et al. 1975, Van Halbeek et al. 1978). In Table 5 the relative retention times on g.l.c. and the m.s. data in terms of the fragment ions A-G of the various trimethylsilyl derivatives are summarized. Compared with the intensity of the peak at mje 175 (fragment F) in the mass spectra of the 9-O-acetylated compounds, this peak is observed only in a... 

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