Separator column counterions

The solvent or solution used for the sample to be introduced into the separation column has to be compatible with the aqueous mobile phase. If it is too strong an eluent and injected in relatively large volumes, peak deformation may occur as in other kinds of chromatography. The addition to the sample solution of a hydrophilic counterion or a strongly competing ionic component of the same charge as the ionic solute may give severe peak distortion, but peak compression under optimized conditions. Column deterioration is probably no more pronounced in ion pair LC than in other systems with bonded stationary phases and mixtures of aqueous buffer solutions and... 

In pharmaceutical development, the determination of APIs and counterions are two important assays. Due to the charge and/or hydrophobicity differences, APIs and counterions are usually analyzed by different chromatographic techniques that require different separator columns and/or detection methods. For example, reversed-phase liquid chromatography is most commonly used for analyzing APIs with intermediate to higher hydrophobicity, but it fails to provide adequate retention for hydrophilic counterions. In contrast, ion chromatography provides a selective and highly sensitive solution for the analysis of counterions. 

Figure 7.9 Comparison of the chromatographic behavior of pharmaceuticai counterions between Acclaim Trinity PI (a) and ZIC-HILIC (b). Separator columns lOOmmxSmm i.d. Acclaim Trinity PI, 3 pm, and 150mmx4.6 mm i.d. ZIC-HILIC, 5 pm coiumn temperature 30 °C eiuent (A) 60 40 (v/v) MeCN/0.02 moi/L NH4OAC, pH 5 and eiuent (B) 80 20 (v/v) MeCN/0.015 moi/L NH4OAC, pH 5 flow rates ...

Figure 7.11 Comparison of the chromatographic behavior of a hydrophobic acidic API and its counterion between Acclaim Trinity PI (a) and ZIC-HILIC (b). Separator columns ...

Figure 8.65 Simultaneous separation of a basic drug and its counterion utilizing UV and ELS detectors in series. Separator column Acclaim Trinity PI, 3 pm column dimensions 50 mm X3 mm i.d. column temperature 30°C eluent 20 80 (v/v) MeCN/30 mmol/L...

Figure 8.77 Simultaneous measurement of (a) diclofenac and its sodium counterion, and (b) chloride impurity. Separator column Acclaim Trinity PI, 3pm column dimensions 50mm X 3 mm i.d. column temperature 30 °C eluent 75 25 (v/v) MeCN/200 mmol/L ammonium...

Figure 8.117 LC-MS for simultaneous analysis of ionic liquids, counterions, and impurities. Separator column Acclaim Trinity PI, 3 pm column dimensions 100mmx2.1 mm i.d. eluent MeCN/5 mmol/L NH4OAC, pH 5.2 gradient 55% MeCN (v/v) for 0-2 min, to 60% (v/v) in 8 min, and then to 90% (v/v) in 1 min and isocratic for 7min flow rate 0.4mL/min detection MS (Thermo Scientific MSQ Plus) source voltage 1 kV needle temperature ...

Figure 10.272 Separation of chloride and bromide counterions in a multisymptom cold/flu medication. Separator column lonPac ASM column dimensions 250 mm x 4 mm i.d. eluent 35mmol/L Na2CO3-l-0.8mmol/L NaHCOi flow rate 1.2miymin detection suppressed...

Figure 10.276 Separation of sulfate counterion and anionic impurities in Humatin by gradient anion-exchange chromatography. Separator column lonPac ASII-HC-l-guard column dimensions 250 mm x 2 mm i.d. column temperature 30 °C eluent KOH (EG) gradient 1 mmmol/Lfor 0-5 min, 1-5mmol/L for 5-9 min, 5-38 mmol/L for 9-20 min,...

Figure 10.283 Analysis of ferf-butylamine as a counterion of a pharmaceutical drug. Separator column lonPac CS14 eluent 10 mmol/L methanesulfonic acid/MeCN (99 1 v/v) flow...

It is usually a plot of peak intensity of the separated species over time, column The main component of the chromatographic separation. It is typically a tube containing the stationary-phase material that separates the species and an eluent that elutes the species off the column, counterions The mobile phase contains a large number of ions that have a charge opposite to that of the surface-bound ions. These are known as counterions, which establish equilibrium with the stationary phase, dead volume Usually refers to the volume of the mobile phase between the point of injection and the detector that is accessible to the sample species, minus the volume of mobile phase that is contained in any union or connecting tubing. 

Sugar analysis by hplc has advanced greatly as a result of the development of columns specifically designed for carbohydrate separation. These columns fall into several categories. (/) Aminopropyl-bonded siHca used in reverse-phase mode with acetonitrile—water as the eluent. (2) Ion-moderated cation-exchange resins using water as the eluent. Efficiency of these columns is enhanced at elevated temperature, ca 80—90°C. Calcium is the usual counterion for carbohydrate analysis, but lead, silver, hydrogen, sodium, and potassium are used to confer specific selectivities for mono-, di-, and... 

The ionic or polar substances can be seperated without any reaction on specially treated chromatographic columns and detected refractometrically. This is necessary because alkyl sulfosuccinates show only small absorption in the UV-visible region no sensitive photometric detection can be obtained. Separation problems can arise when common steel columns filled with reverse phase material (or sometimes silica gel) are used. This problem can be solved by adding a suitable counterion (e.g., tetrabutylammonium) to the mobile phase ( ion pair chromatography ). This way it is possible to get good separation performance. For an explanation of separation mechanism see Ref. 65-67. A broad review of the whole method and its possibilities in use is given in an excellent monograph [68]. 

Ion-exchange chromatography (lEC) is used mainly for the separation of ions and easily ionized substances (e.g., substances that form ions by pH manipulation or complexation) in which one of the principal contributions to retention is the electrostatic attraction between mobile phase ions, both sa le and eluent, for immobilized ion centers of opposite charge in the stationary phase. The sample ions are separated based on differences in their relative affinity for the stationary phase ion centers compared to that of the mobile phase counterions in a dynamic exchange system, in which sample ions and eluent ions interact with multiple stationary phase ion centers as they pass through the column. Ion-... 

The PO mode is a specific elution condition in HPLC enantiomer separation, which has received remarkable popularity especially for macrocyclic antibiotics CSPs and cyclodextrin-based CSPs. It is also applicable and often preferred over RP and NP modes for the separation of chiral acids on the cinchonan carbamate-type CSPs. The beneficial characteristics of the PO mode may arise from (i) the offset of nonspecific hydrophobic interactions, (ii) the faster elution speed, (iii) sometimes enhanced enan-tioselectivities, (iv) favorable peak shapes due to improved diffusive mass transfer in the intraparticulate pores, and last but not least, (v) less stress to the column, which may extend the column lifetime. Hence, it is rational to start separation attempts with such elution conditions. Typical eluents are composed of methanol, acetonitrile (ACN), or methanol-acetonitrile mixtures and to account for the ion-exchange retention mechanism the addition of a competitor acid that acts also as counterion (e.g., 0.5-2% glacial acetic acid or 0.1% formic acid) is required. A good choice for initial tests turned out to be a mobile phase being composed of methanol-glacial acetic acid-ammonium acetate (98 2 0.5 v/v/w). 

According to some recent literature, typical conditions for biogenic amine determination are precolumn derivatization with Dnsl-Cl followed by separation on C8 or C18 column with gradient elution with mobile phases consisting of water or phosphate buffer and acetonitrile (or methanol) or postcolumn derivatization with OPA and gradient elution with mixtures of sodium acetate buffer and methanol (or acetonitrile). In the latter case, a counterion (such as hexanesulfonic or octansulfonic acid) is usually added in the mobile phase. 

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