Chelation retention time

A normal-phase HPLC separation seems to be useful to separate major chlorophyll derivatives, but it is not compatible with samples in water-containing solvents an additional extraction step is required to eliminate water from the extract since its presence rednces chromatographic resolution and interferes with retention times. Besides that, the analysis cannot be considered quantitative due to the difhculty in transferring componnds from the acetone solution into the ether phase. On the other hand, an advantage of the normal-phase method is its efficacy to separate magne-sinm-chlorophyll chelates from other metal-chelated chlorophyll derivatives. ... 

Competing amines such as triethylamine and di-rc-butylamine have been added to the mobile phase in reversed-phase separations of basic compounds. Acetic acid can serve a similar purpose for acidic compounds. These modifiers, by competing with the analyte for residual active sites, cause retention time and peak tailing to be reduced. Other examples are the addition of silver ions to separate geometric isomers and the inclusion of metal ions with chelating agents to separate racemic mixtures. 

Here, R is the radius of the sphere, q is the coefficient of viscosity, kB is Boltzmann s constant, and T is temperature. Equation (4) implies that rR should vary linearly with volume, or mass, in the range where the Stokes-Einstein equation is valid. Figure 5 shows the roughly linear behavior of rR for these compounds, and illustrates why polymeric conjugates of Gd3+ chelates remain a very attractive method of modulating both rR and the intravenous retention time (t1/2) of BPCAs. 

The present section and Section IV.A.4 complement each other. The GC of metal chelates derived from monothio-/3-diketones, /3-diketones, -dithioketones and /3-keto-enamines was reviewed. The discussion includes column phenomena, analytical improvements and limitations and various applications . A study of the GC behavior of Group 13 /9-diketonates 37 shows that when the chelate contains a Mef group its volatility is enhanced, while a Ph group tends to decrease it. When R and R are alkyl groups the retention time of the chelates increases with the molecular weight, but it does not depend on the volatility however, the retention time of the chelates containing a Mef group is almost inversely correlated with the volatility . ... 

The reaction of [Pt(cis-dach)(H20)2] with sodium ascorbate gives a white precipitate that contains two isomeric forms of the [Pt(cis-dach)-(ascorbato-C, 0 )] chelate (due to a lack of rotational symmetry in the cis-dach ligand). The two isomers have different HPLC retention times and solubility properties, and may be separated by using the following method. 

Gas chromatographic studies of ethers, ketones, alcohols, esters, olefins, and alkanes, using columns with liquid phases containing P-diketonate complexes in squalane, revealed that the more nucleophilic organic substrates reacted more strongly with the P-diketonates than the less basic ones. Er complexes of fluorinated P-diketones (especially 3-trifluoroacetyl-d-camphor-ate, facam) reacted more strongly with these nucleophiles than did similar non-fluorinated Er complexes. The retention time of THE increased exponentially with the inverse of metal ionic radius in the facam chelates of a variety... 

Gas chromatography experiments (injection port 150°, column 60°) on the chelates in hfaa solutions gave two distinct peaks, the first presumably due to the solvent, and the second that of the chelate. However, the retention times of the individual chelates (with the columns so far used) did not differ sufficiently to make quantitative determinations possible. No third peak which might be attributed to acetone from the addition product was observed. 

A series of eight substituted 3-hydroxypyridin-4-one (e.g., A -methyl-2-methyI-, A -ethyl-2-ethyl-, A -methyl-2-amide-6-methyl-) iron chelates were separated on a PRLP-S column (A = 280 nm) using a 20-min 98/2 - 65/35 water (5mM sodium heptanesulfonate to pH 2.0 with HCl)/acetonitrile gradient [926]. Note that HCl is very aggressive toward stainless steel components and another acid should be tried to replace it here. Baseline resolution and excellent peak shapes were obtained. The retention times for 22 other analogs are also tabulated. ... 

Separations of metal cations are best carried out with a carboxyhc acid stationary phase. The mobile phase contains a chelating reagent, such as citric, ojaUc, or 2,6-pyridinedicarboxylic acid (PDA). The concentration and pH of the mobile phase are adjusted so that metal ions in the sample will be in an equilibrium between the cationic form, M, and a neutral or anionic metal ligand complex form. The rate at which a metal analyte moves down the column wiU depend on the fraction that remains in the free cationic form. A greater degree of complexa-tion results in a shorter retention time. 

Divalent ions, such as the transition metals Fe, Co, Ni, Cu and Zn +, are most commonly used. The affinities of many retained proteins and their respective retention times, such as in the IDA chelator, are in the following order Cu > Ni > Zn > Co. The loss of metal ions at lower pH values leads to reduced adsorption capacity of the sorbent and can also cause damage to the target proteins by metal-catalyzed reactions. 

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