Mixed complexing eluents

There is increasing interest in copolymer systems, which, due to their chemical heterogeneity, may require very complex eluent systems in order to dissolve the sample and ensure that the separation ensues hy a pure size exclusion mechanism. In these examples, the PLgel is also compatible with eluent systems containing mixed solvents of different polarity (including water as a cosolvent up to 10% hy volume) and in organic solvents modified with acids or bases (e.g., acetic or formic acid, triethanolamine) as it is stable in the pH range of 1-14. 

On-line GPC-MALDI MS On-line hyphenation of MALDI-MS with GPC is not as straightforward because of the incompatibilities associated with the complex sample preparation schemes required for MALDI and the intrinsically pulsed nature of the laser source with a continuous beam of eluent from GPC. Fei and Murray first demonstrated on-line GPC-MALDI-TOF MS by mixing the eluent from the GPC with a matrix solution, and by irradiating the resulting spray with a laser to promote MALDI. (349... 

A new approach to the resolution of sulphoxides 242 was recently reported by T oda and coworkers282. It takes advantage of the fact that some sulphoxides form crystalline complexes with optically active 2,2 -dihydroxy-l, 1-binaphthyl 243. When a two-molar excess of racemic sulphoxide 242 was mixed with one enantiomeric form of binaphthyl 243 in benzene-hexane and kept at room temperature for 12 h, a 1 1 complex enriched strongly in one sulphoxide enantiomer was obtained. Its recrystallization from benzene followed by chromatography on silica gel using benzene-ethyl acetate as eluent gave optically pure sulphoxide. However, methyl phenyl sulphoxide was poorly resolved by this procedure and methyl o-tolyl, methyl p-tolyl, s-butyl methyl and i-propyl methyl sulphoxides did not form complexes with 243. 

Fig. 3 Typical chromatograms of mixed sample containing (1) chloride, (2) bromide, (3) nitrate, and (4) sulfate. Anion-ex-change groups (a) H(bpa-ODP) and (b) Cd(bpa-ODP) are from the bpa-ODP, protonated, and complexed with Cd(II), respectively. Bpa-ODP is A,A-bis(2-pyridylmethyl)octadecyl-amine-coated octadecylated poly (vinyl alcohol). Eluent 5 mmol/L benzenesulfonate (pH 5.0). (From Ref. [4].)...

Improved performance is achieved with a more complex operation and layout of the process, which requires precise process design and control - especially when a recycling of the section IV outlet is applied and a second point of mixing at the desorbent port is implemented. An open-loop operation without eluent recycling between sections I and IV is more robust, especially when regeneration of the adsorbent is necessary. 

Complexones such as EDTA (complexone III) [1-3] and DCTA (complexone IV) [4,5] are suitable eluents, but other complexing agents, such as citrate [3,6] and sulphate [7] are also applied. Barium has been separated from strontium and other metals by cation-exchange chromatography using mixed HCl-organic solvent eluents [8]. Strontium has been enriched and determined in sea water [5] and in milk [2]. 

In a similar manner, elements that form anionic fluoride complexes can be separated from others and from each other on an anion exchanger by eluting with eluents containing HF plus HQ [24, 25]. Extensive studies of metal ion behavior on anion-exchange columns have also been carried out with eluents containing mixed H2SO4/ HF [26,27],... 

Complex gradients can be obtained without a mixing chamber by mixing independently selected streams of solvents A and B. For this purpose, a solenoid valve selects periodically solvent A or solvent B for the pump feed, as shown in Fig. 5. For the Linton gradient former, two valves are used, one being opened while the other is closed. The eluent flow consists of short variable lengths of... 

Syntheses of cw,m-[Co(CN)2(C03)(NH3)2] and w,cHCo(N02)2(C03)(NH3)2]+ are described as examples. The action of KCN on the green solution of [ 0(003)3] at room temperature gives a deep red solution containing c -[Co(CN)2(C03)2p as the main product. After neutralization with aqueous HCIO4, ammonium j r-chlorate and concentrated aqueous NH3 are mixed to the solution. After some time at a mild temperature, the concentrated solution is subjected to ion-exchange chromatography (Dowex 1-X8 in Cl form, 0.3 mol/dm NaCl eluent) to collect the desir complex species in a fraction of yellow-orange, from which cis,cis-Na[Co(CN)2(C03)(NH3)2] 2 HjO is obtained. 

Alternatively, leciystallise it from cyclohexane, chromatograph it on alumina with n-hexane as eluent, and reciystallise two more times [Saltiel et al. J Am Chem Soc 109 1209 1987. Anthracene is fluorescent and forms a picrate complex, m 139", on mixing the components in CHCI3 or but decomposes on attempted... 

The complexity of MLC is much greater dmn that of conventional RPLC with aqueous-organic solvents, because of Ihe number of possible interactions with both mobile and stationary phases (Fig. 5.1). Hie solutes in the mobile phase can interact electrostatically with the charged outer-layer of ionic micelles, and hydrophobically with their lipophilic interior. The steric factor can also be important. The modification of the stationary phase by adsorption of surfactant monomers, which creates a "micelle-like" surface, gives rise to similar interactions with the solutes. The combination of these interactions cannot be duplicated by any traditional pure or mixed solvent system. While micellar solutions will never totally replace traditional aqueous-organic eluents, they offer several interesting alternatives to separation work. 

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