Elution sequences

PMMA). Under these conditions, some inevitable peaks are observed in the low molar mass range. This area starts for an elution volume of Mpmma of about 600. Enclosing a further column for this low molecular size range generally improves the separation, but the elution sequence of oligomer and disturbing peaks remains constant. 

Procedure. Inject 1 fiL of the sample solution and obtain a chromatogram. Under the above conditions the compounds are separated in about 3 minutes, the elution sequence being (1) aspirin (2) phenacetin (3) caffeine. Measure peak areas with an integrator and normalise the peak area for each compound (i.e. express each peak area as a percentage of the total peak area). Compare these results with the known composition of the mixture discrepancies arise because of different detector response to the same amount of each substance. 

Selectivity of the separation in TLC is achieved by various of the aforementioned techniques (e.g. multiple development, gradient elution, sequence TLC, AMD, HPPLC or OPLC). Multidimensional TLC methods are described in Section 7.4.4. 

In the TLC of the toxins (lower part of Figure 5), Rf values are not presented because they show small variations and are potentially misleading. However, the relative elution sequence has proven to be highly reproducible, such that the two-dimensional composition maps produced by this method can be interpreted with a high level of confidence. 

Figure 6. Binding of ozonized lysozyme to CM-chitin. Samples of lysozyme (1.3 mg) ozonized at different pHs to > 95% inactivation were applied to a column of CM-chitin (1.5 X 4 cm). The elution sequence was firstly Tris-Cl and secondly 0.2N HAc.

RP-HPLC with nonaqueous solvents and UVD at 246 nm was developed for the determination of low level POVs of vegetable oils. These measurements are specific for conjugated diene peroxides derived from vegetable oils with relatively high linoleic acid content. These measurements may be supplemented by nonspecific UVD at 210 nm and ELSD for detection of all eluted species. The elution sequence of the triglycerides in a nonaqueous RP-HPLC is linearly dependent on the partition number of each species, Vp, which is defined as = Nq — 2Ni, where Nq is the carbon number and is the double bond number. In the case of hydroperoxides = Nq — 2Nd — Vhpo, where Vhpo is the number of hydroperoxyl groups in the molecule (usually 1 for incipient POV). For... 

Still the search continued. In 1954 several laboratories reported die isolation and study of elements 99 and lOO. A group at Berkeley gave some details of the discovery of 99 (96), and soon afterwards of 100 (97). Only minute amounts of these substances were obtained, but the elution sequences on ion-exchange resins served to identify them. Physical properties were reported from both Berkeley ( 98) and the Argonne Laboratories at Arco, Idaho (99). The authors of all those papers added notes to their reports stating that unpublished information still remained, and that no attempt should be made to prejudge questions of priority of discovery on the basis of the published papers. 

The distribution coefficient increases from La3+ to Lu3+ and then decreases with increasing Z. When citrate ion is used as eluant the elution sequence is the reverse of the order for cation exchange resins [50]. 

Solid-phase extraction effectively separates vitamin D from its more polar 25-hydroxy metabolite. In the analysis of human milk (64), the dried lipid fraction of milk was dissolved in 35% dichloromethane in hexane and then applied to a preconditioned silica cartridge. The sample was fractionated using the following elution sequence 9 ml hexane (discard), 3 ml 7% ethyl acetate in hexane (discard), 15 ml 7% ethyl acetate in hexane (vitamins D2 and D3), 25 ml 15% ethyl acetate in hexane (discard), and 9.5 ml 3% 2-propanol in hexane (25-hydroxyvitamin D2 and 25-hydroxy vitamin D3). 

Normal-phase HPLC is capable of separating isocratically all of the eight unesterified tocopherols (T) and tocotrienols (T-3) that occur in nature, and it has been utilized in determining the distribution of these vitamers in a wide variety of fats, oils, and foodstuffs. The elution sequence... 

Regarding the response signals of the lactate esters, the D-enantiomers showed stronger interaction with the L-polymer of Chirasil-Calix. This is in agreement with the elution sequence in GC. 

Any species with a retention time similar to that of the main ions can interfere. Large amounts of one of the ions may interfere by reducing the peak resolution of the next ion in the elution sequence. Sample dilution may then be necessary. In some systems the so-called negative water dip at the start of the chromatogram may interfere with the Cl determination. This can be avoided by adding a small amount of concentrated eluent to all samples and calibration standards to match the eluent concentration. 

The elution sequence was as follows 0.006M trichloroacetic acid (pH2.5), yielding first As(III) and then monomethylarsonate 0.2M trichloroacetic acid yielding As(V) 1.5M NH4OH followed by 0.2M trichloroacetic acid yielding dimethylarsinite. 

Neutral Lipids. The neutral lipid fraction, free of phospholipids, will give the following elution sequence with the indicated solvents ... 

Sehat, N., Kramer, J.K.G., Mossoba, M.M., Yurawecz, M.P., Roach, J.A.G., Eulitz, K., Morehouse, K.M., Ku, Y. 1998. Identification of conjugated linoleic acid isomers in cheese by gas chromatography, silver ion high performance liquid chromatography and mass spectral reconstructed ion profiles. Comparison of chromatographic elution sequences. Lipids 33, 963-971. 

Identity Description Elution Sequence of Peaks (and Typical Attenuation Settings)... 

An interesting and useful variant of reversed-phase HPLC is called ion-paired reversed-phase HPLC. In such a system the analytical columns are packed with the same material, but a compound such as tetrabutylammonium is added to the mobile phase. The separation of ATP and adenosine on such a system is shown in Figure 2.15. A comparison of this profile to that shown for the same compounds in Figure 2.14 immediately highlights the change in the elution sequence. Whereas without ion pairing, the order is ATP followed by adenosine, with ion pairing the order is adenosine followed by ATP. 

Haglund, P. Wiberg, K., Determination of the gas chromatographic elution sequences of the (+)-and (—)-enantiomers of stable atropisomeric PCBs on Chirasil-Dex J. HighResol Chromatogr. 1996, 19, 373-376. 

The nature of the counter ion is important because it establishes the exact value of the potential difference between the stationary phase and the bulk eluent, and also, if it exhibits suitable absorption characteristics, indirect photometric detection of UV-inactive analytes is feasible. Moreover, the choice of the counter ion of the potential determining ion allows a tailor-made separation of the analytes since adsorbophilic counter ions may compete with the analyte for interaction with the potential determining ion, thereby decreasing analyte retention. Different counter ions may alter the elution sequences of a series of analytes with potential advantage for resolution and identification purposes [143]. 

The electrified stationary phase carries the same charge status of the IL ion that shows the strongest adsorbophilic attitude. Furthermore, ionic interactions between the analyte ion and the IL anion and cation, respectively, are contradictory and concur to modulate analyte ion retention in a complicated way. It follows that by increasing IL in the eluent, overall retention of the analyte may potentially (1) decrease [4] or (2) increase [5,6], or (3) remain almost constant if the conflicting effects of the IL cation and anion balance each other [7], depending on the specific IL concentration in the mobile phase [8]. Furthermore a reversal of elution sequence with increasing IL concentration is possible [9]. The multiplicity of interactions in the presence of a mixture of these ionic modifiers offers wide versatility related to selectivity adjustment. 

Table V. Analyses and Element Ratios of Athabasca Asphaltenes (Cyclohexane Omitted from Elution Sequence)...

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