Symmetry Shield phases

HPLC condition — A Waters reversed-phase HPLC column (Symmetry Shield RP Cl8, 5 pm, 2.1 x 50 mm) was used in conjunction with a Regis SPS guard column (ODS, 5 pm, 100 A,... 

FIGURE 2.5 Separation of flavanoids on a classical RP and on a shielded phase. Columns Symmetry CIS symmetry shield RPIS (150x4.6mm). Mobile phase ACN/lOmM PO4 buffer pH 3, 30/70 v/v, 40°C. 

FIGURE 2.12 Influence of pH value on retention of basic analytes. Samples A,A-dimethyl aniline A-ethyl aniline. Column symmetry shield CIS mobile phase acetonitrile-20 mM phosphate buffers-water, 35-35-... 

FIGURE 2.18 Separation of polar and acidic solutes on a classical RP and on shield phases. Columns Symmetry C8 and symmetry shield C8. Mobile phases 20% ACN, 10% HjO, 70% lOmM phosphate buffer pH 3 (v-v-v). 30% MeOH, 70% lOmM phosphate buffer pH 3 (v-v). Samples 1, 4-hydroxyisophthalic acid 2, acetylic salicylic acid 3, salicylic acid 4, phenol 5. methylparaben 6, dimethylphthalate. 

Figure 4-1. Effect of column type on selectivity. Mobile phase Low pH. (A) 0.1 v/v % TFA. (B) 0.1 v/v% TFA in MeCN. Linear gradient from 5% B to 80% B in 40min, 220nm. Temperature, 40°C flow rate, l.OmL/min column dimensions, 150 x 3.0mm particle sizes, 3.5 pm for Symmetry Shield and Atlantis and 3.0pm for YMC ODS AQ. (Courtesy of Markus Krummen, Novartis Pharmaceuticals.)...

A reverse phase ion-pairing HPLC method was developed by the submitters for analysis. Chromatographic conditions A 10-pL sample (0.1 mg/mL in acetonitrile) is injected onto a suitable liquid chromatograph equipped with a Waters Symmetry Shield RP18 column, 250 x 4.6 mm, 5 pm particle size at 40°C with a mobile phase of 0.404 g/L heptanesulfonic acid, sodium salt -i- 0.1% phosphoric acid (Component A, pH 2.2) and acetonitrile (Component B) at a flow rate of 1.0 mL/min, programmed with a linear gradient from 95 5 A B (v/v) to 30 70 A B (v/v) over 20 min. Detection is achieved by UV at 300 nm. The retention time is approximately 10 min. 

Hot water and enzymatic extracts were analyzed by IP chromatography on a Waters Symmetry Shield RP8 column using water-methanol (99 1) mobile phases that contained different perfluorinated carboxylic acids as ion-pairing agents. 0.1% HFBA in the mobile phase allowed the separation and ICP-MS detection of >20 Se compounds in 70 min. 

HPLC Conditions Columns Reverse phase, and particularly CIS columns such as Waters Symmetry Shield RP18, are most frequently used (Li et ah, 2003 Soars et ah, 2002 Zhang et ah, 2002). 

Figure 9 serves to demonstrate this equalizing of the stationary phases in the presence of buffers even for non-ionic analytes. In Fig. 9a, the separation of the isomers of nitroaniline on four rather different stationary phases with the help of an alkaline acetonitrile buffer is shown. Apart from small differences in the retention time, the separation of the three peaks looks rather similar on each of the four columns. Fig. 9b shows the separation of the nitroanilines on Symmetry Shield and on Zorbax Bonus in a methanol/water mixture. The chromatograms look absolutely different even an inversion of the elution order is observed. This means that to exploit the individual properties of the stationary phases in the realm of ultimate selectivity, one should dispense with buffers, which is not easy to realize in routine work, where reproducible retention times are required. Nevertheless, one should remember this in the case of orthogonal tests see below. These phenomena are observed even with simple, polar, non-ionizable analytes such as ketones (see Fig. 10). 

Zorbax Bonus is more hydrophobic than Nucleosil Nautilus, and this in turn is more hydrophobic than Prontosil ACE. The most polar embedded phase with a long alkyl chain is Symmetry Shield, with carbamate as the embedded polar group. 

However, a comment on the expected clustering of two different types of phases is first necessary. In Chem. 24, two clusters are obvious. The upper cluster. Symmetry Shield to Nucleosil Nautilus, contains embedded phases. The lower cluster, XTerra MS to Chromolith Performance, contains phases with a classical coverage. 

All r values are small, which refleds the minor difference between the stationary and mobile phases with respect to this interaction. The r values of the polar embedded phases (symmetry shield) are dearly higher than those of all the other columns, confirming the n-/jr-electron activity of the incorporated carbamate moieties. The nitrile phase also shows a relatively prominent r parameter, which is easily traceable from the electronic structure of the surface groups. Whilst all other parameters of the cyano phase resemble those of the C4 and Cg phases, the r parameter indicates a higher contribution of electron interactions than with any other of the tested columns. Nevertheless, the nitrile phase r parameter is the smallest in its parameter set, whereas its n parameter is 5.5 times the size. It can be concluded that the Zorbax SB 300 CN column mainly behaves as a reversed phase in the given system. 

The dipolarity/polarizability parameter s closes the list of the interaction parameters from Eq. (5). Again, the data show a negative sign, indicating more pronounced dipole or induced-dipole activity in the eluent than in the stationary phase. Principally, phases with higher carbon load show weaker dipolar interactions and thus more strongly negative s parameters. As expected, the polar embedded phases and the cyano phase exhibit smaller values. The difference between Symmetry Shield Cjg and Cg reflects the differences in the steric effects of the alkyl chains. 

Rocuronium bromide Verapamil (i.s.) Column Symmetry Human plasma Shield RP18 cartridge (50 x 2.1 mm) Detector ESI-MS Mobile phase linear gradient from 10% to 90% of ACN in water containing 0.1% TFA/ applied in 15 min. Column was then washed for 3 min at final gradient condition and set back to initial condition in 1 min and equilibrated for 5 min Single ion recording Rocuronium bromide m/z 265 and m/z 529 Verapamil m/z 455... 

More recently it has been shown that in addition to Pi the nephe-lauxetic ratio )3 [)3 = B/Bg, Bg is the B value for the free ion in the gas phase and is equal to 1120 cm for Co(III) (173) ] has an effect on the shielding experienced by the cobalt nucleus. Juranic (179, 180) and Bramley et al. (173) found that there is a linear relationship between the chemical shift and )3 vi. The correlation is rather good for cubic complexes (Oh symmetry of donor atoms) but does not hold as well for distorted complexes (such as the tris-chelates). Co NMR data are shown in Table III. 

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