Use of complexing reagents as additives to the eluent for optimization of separation selectivity in high-performance chelation ion chromatography

This paper details a study of the selectivity characteristics of high-performance chelation ion chromatography when separating a range of metal ions with a number of complexing eluents. It shows that exploitation of competitive metal complexation between ligands in the eluent and surface bonded chelating groups allows a wide range of control over the retention order and selectivity coefficients of groups of metal ions for specific applications. An indication of the metal separation characteristics found for simple non-complexing eluents on iminodiacetic acid (IDA) silica bonded substrates is given first, followed by an illustration of the selectivity changes that can be achieved by using complexing eluents. Using a novel approach, plots of logbeta(1) of the metal complexes of a chosen eluent ligand against the surface bonded IDA metal complexes were found to be useful indicators of which metals may show unusual selectivity changes during separation. Example chromatograms of metal separations are given for three selected complexing eluent reagents, namely, oxalic acid, picolinic acid, and chloride, either singly or in admixture. For special mention it was found that very specific retention control could be achieved for Cu(II) with picolinic acid, Fe(III) and Fe(II) speciation with oxalic acid, Pb with dipicolinic acid and Cd with chloride.     

Determination of beryllium in a stream sediment by high-performance chelation ion chromatography

High-performance chelation ion chromatography (HPCIC), involving a chelating silica substrate bonded with aminomethylphosphonic acid, has been developed as a novel technique for the quantitative determination of beryllium in complex matrices. An isocratic separation method, using an eluent containing 1 M KNO3, 0.5 M HNO3 and 0.08 M ascorbic acid, allowed the Be2+ to elute away from the sample matrix peak in under 6 min in a sample containing in excess of 800 mg l(-1) matrix metals. A detection limit of 35 microg l(-1) Be(II) was found using a post-column reaction involving Chrome Azurol S (CAS), 1 M hexamine and 10 mM EDTA buffered at pH 6. The standard addition curve gave excellent linearity (R2>0.999). The procedure was applied to the determination of trace beryllium in a certified sediment sample. The results obtained compared well with the certified value for beryllium.     

Recent developments in the high-performance chelation ion chromatography of trace metals

There have been a number of significant developments in the high-performance chelation ion chromatography (HPCIC) of trace metals in recent years. This review focuses on these developments, while giving important information on the fundamental parameters controlling the chelation sorption mechanism, including type of chelating group, stability constants, kinetics, and column temperature. The discussion pays particular attention to the types and properties of efficient chelating stationary phases which have been fabricated for certain groups of metals. The review also describes a number of major improvements in postcolumn reaction detection including the use of the latest reagents and noise reduction strategies to improve sensitivity and reduce LOD. In the final section, an indication of the applicability of HPCIC to a range of complex sample types is given with some key examples and chromatograms using the latest high-efficiency chelating phases.     

Iminodiacetic acid functionalised monolithic silica chelating ion exchanger for rapid determination of alkaline earth metal ions in high ionic strength samples

Iminodiacetic acid has been covalently bonded to a bare silica monolith to produce the first reported high-performance monolithic chelating ion exchange column. Using the new column, separation and determination of traces of alkaline earth metal ions (low ppm) in high ionic strength samples (up to 2 M NaCl and KCl brines), could be achieved in under 40 s. At an eluent flow rate of 4 mL min(-1) retention time precision was < 1.2% (n = 9) for Mg(II) and Ca(II), with detector linearity (n = 5) over the range 2-10 mg L(-1) of between R2 = 0.985 and R2 = 0.995. In 1 M KCl and NaCl brine samples, detection limits of 0.2 mg L(-1) were possible.     

Tunable separation of anions and cations by column switching in ion chromatography

A convenient ion chromatography method has been proposed for the routine and simple determination of anions (Cl⁻, SO₄²⁻ and NO₃⁻) and/or cations (Na⁺, NH₄⁺, K⁺, Mg²⁺ and Ca²⁺) using a single pump, a single eluent and a single detector. The present system used cation-exchange and anion-exchange columns connected in series via two 6-port switching valves or a single 10-port valve. The connection order of the ion-exchange columns could be varied by switching the valve(s). The present system therefore allowed the separation of either cations or anions in a single chromatographic run. While one ion-exchange column is being operated, the other ion-exchange column is being conditioned, i.e., the columns are always ready for analysis at any time. When 2.4 mM 5-sulfosalicylic acid was used as the eluent, the three anions and the five cations could be separated on the anion-exchange column and cation-exchange column, respectively. In order to obtain the separations of the target ions, the injection valve was placed between the two columns. Complete separations of the above anions or cations were demonstrated within 10 min each. The detection limits at S/N = 3 were 19-50 ppb (μg/l) for cations and 10-14 ppb for anions. The relative standard deviations of the analyte ions were less than 1.1, 2.9 and 2.8% for retention time, peak area and peak height, respectively. This proposed technique was applied to the determination of common anions and cations in river water samples.     

Mechanistic studies on the separation of cations in zwitterionic ion chromatography

Electrostatic ion chromatography, also known as zwitterionic ion chromatography, has been predominantly used for the analysis of anions. Consequently, separation mechanisms proposed for this technique have been based on anion retention data obtained using a sulfobetaine-type surfactant-coated column. A comprehensive cation retention data set has been obtained on a C18 column coated with the zwitterionic surfactant N-tetradecylphosphocholine (which has the negatively and positively charged functional groups reversed in comparison to the sulfobetaine surfactants), with mobile phases being varied systematically in the concentration and species of both the mobile-phase anion and cation. A retention mechanism based on both an ion exclusion effect and a direct (chaotropic) interaction with the inner negative charge on the zwitterion is proposed for the retention of cations. Despite the relatively low chaotropic nature of cations compared with anions, the retention data shows that cations are retained in this system predominantly due to a chaotropic interaction with the inner charge, analogous to anions in a system where the C18 column is coated with a sulfobetaine-type surfactant. The retention of an analyte cation, and the effect of the mobile-phase anion and cation, can be predicted by the relative positions of these species on the Hofmeister (chaotropic) series.     

Ion-exchange separation of nucleic acid constituents by high-performance liquid chromatography

The high-performance liquid chromatographic separation of a large variety of nucleic acid constituents on a silica-based, weak-anion exchange column was accomplished. Using this technique it was possible to achieve some relatively difficult separations, such as the separation of 2'-, 3'-, and 5'-AMP, and the separation of a mixture of ribo- and deoxyribo-nucleosides and -nucleotides. A number of other separations are demonstrated by isocratic or gradient elution. These include the separation of a mixture of nucleoside monophosphates, the separation of a mixture of nucleoside mono-, di-, and triphosphates, the separation of a mixture of nucleosides and bases, and the separation of a mixture of nucleotide oligomers. These chromatographic separations were accomplished using relatively simple experimental procedures at ambient temperatures and involved relatively short analysis times. Excellent separations were obtained, in most cases, by adjustment of buffer concentration and pH, or by addition of an organic modifier. In some cases, it was necessary to use gradient elution to achieve optimum resolution.     

Non-trivial temperature effects on the cation exchange chromatography and chelation ion chromatography of metal ions

The effect of column temperature upon the retention of metal ions on sulfonated and mono-, di-, and amino-carboxylated cation exchange columns has been investigated. The retention of alkali, alkaline earth and transition metal ions on each of the above types of cation exchanger was studied over the temperature range 19-65 degrees C. A major difference between the behaviour of mono- and divalent metal ions was shown on each of the above stationary phases, with the monovalent alkali metals exhibiting clearly exothermic behaviour (a decrease in retention with increased temperature) under acidic eluent conditions and an apparent relationship between retention factor and the magnitude of the temperature effect. The effect of temperature upon alkaline earth metal ions was less defined, although strongly endothermic behaviour (increase in retention with temperature) could be seen on all stationary phases through correct choice of eluent. The transition metal ions studied showed endothermic behaviour on all four stationary phases, with the sulfonated column unexpectedly showing the largest increases in retention. The above behaviour can be partially explained through the dominance of the type of solute-stationary phase interaction governing retention. In several of the above columns, both ion-exchange and surface complexation interactions can occur, with the effects of temperature indicating which process dominates under specific eluent conditions.     

乙酰丙酮基聚苯乙烯在萃取金属离子上的应用

大孔的苯乙烯-二乙烯苯共聚物经氯甲基化后,分别与乙酰丙酮镍、乙酰丙酮钠和四正丁基乙酰丙酮铵三种不同的乙酰丙酮盐反应,可制得聚3-(p-乙烯苄基)戊二酮-[2,4]。其中以由乙酰丙酮镍制得的聚合物最好,除二乙烯苯外,78%左右的苯环乙酰丙酮化了。该聚合物螯合Fe~(3 )和Ni~(2 )的能力与β-二酮基高聚物相仿或稍优。还比较了此类高聚物的物理机械性能。     

Serial separation of cations and anions by ion chromatography using the peak parking technique and sulfosalicylic acid as the eluent

An improvement of the peak parking technique is described for the serial determination of cations (Na⁺, , K⁺, Mg²⁺, and Ca²⁺) and anions (Cl⁻, , and ) using a single pump, a single eluent and a single detector. The present system used commercially-available unmodified cation exchange and anion exchange columns, which were attached to each switching valve. When 1.75 mM 5-sulfosalicylic acid was used as the eluent, serial separation of the above cations and anions was achieved in less than 20 min. The proposed ion chromatographic method was successfully applied to the serial determination of cations and anions in tap water and river water samples. The limits of detection at S/N=3 for an injection of 20 μl were 16–68 ppb (μg/l) for cations and 15–28 ppb for anions.     

Simultaneous separation and detection of anions and cations in ion chromatography

An overview of new possibilities for the simultaneous determination of anions and cations by ion chromatography is presented. A short comparison of the characteristics of separation and detection methods for simultaneous anion–cation determinations of ions is given and applications are discussed.     

柠檬酸试剂中痕量无机阴阳离子的离子色谱法测定

选用柱容量较高、亲水性较强的阴离子分析柱IonPac AS18,以30mmol／L KOH为淋洗液,等度淋洗分析了高浓度柠檬酸中的痕量无机阴离子。选用柱容量较高的阳离子分析柱IonPac CS12A,以H2SO4作淋洗液分析了柠檬酸试剂中的痕量阳离子。在所选色谱条件下,无需样品前处理,直接进样,电导检测,高浓度柠檬酸不影响痕量阴离子或阳离子的测定。方法具有良好的线性(r=0．9941～1．000),样品中所测离子峰面积的相对标准偏差(RSD)均在9．0％以下(n=7),回收率在82．7％～110％之间,检出限低于3．7μg/L。     

Ion-chromatographic separation of metal cations in the presence of a-hydroxyisobutyric acid

Separations of metal cations on a column packed with the strongly acidic cation exchanger Separon SGX CX were investigated in the presence of -hydroxyisobutyric acid (HIBA) in the mobile phase. A retention model based on the general theory of side equilibria was elaborated and relations describing dependences of capacity factors of analytes on the compositon of the mobile phase were derived. Effects of HIBA concentration and pH of the mobile phase on the analyte retention were studied in detail. Stability constants of divalent metal cations (Cd²⁺, Co²⁺, Mn²⁺, Ni²⁺ and Zn²⁺) with HIBA were calculated from the experimental dependences of the reciprocal values of capacity factors on the ligand concentration.     

High capacity organic monoliths for the simultaneous application to biopolymer chromatography and the separation of small molecules

A method for controlling the mesoporous structure of monolithic organic copolymers is presented by systematic variation in polymerisation time, employing poly(p-methylstyrene-co-1,2-(p-vinylphenyl)ethane) (MS/BVPE) as a representative styrene system. Decreasing the time of polymerisation introduces a considerable fraction of mesopores (up to 20% of the total pore volume), while keeping the support permeability reasonable high (～1.3 × 10^?14 m²). Monolith structures, prepared in such a manner, enable efficient (typically around 70,000 plates/m) and fast separation of low-molecular-weight compounds, whereas their performance towards biopolymers is comparable to column supports, fabricated according to typically used protocols (polymerisation time >12 h and thus monomer conversion >98%). The polymerisation time is hence a valuable tool to tailor the fraction of support flow-channels, macropores as well as mesopores, which is shown dramatically to influence the chromatographic separation characteristics of the respective column. This way, the preferred applicability of organic (styrene) monolithic copolymers can be extended to the separation of small molecules beyond biopolymer chromatography.     

Simultaneous determination of inorganic cations by capillary ion chromatography with a non-suppressed contactless conductivity detector

A non-suppressed capillary ion chromatographic method with a laboratory-made packed cation-exchange column (100 mm × 0.32 mm i.d.) was developed for the separation and simultaneous determination of five common inorganic cations (sodium, ammonium, potassium, magnesium and calcium). Cation exchangers were prepared by the reaction of the hydroxyl group on the surface of diol-group bonded silica gel with 1,3-propanesultone in methanol. Simultaneous separation of these five common inorganic cations were achieved within 17 min using 1 mM methanesulfonic acid and 0.1 mM 15-crown-5 ether in methanol-water (8:2, v/v) as the eluent. The effects of organic solvents and crown ethers in the eluent on the retention of analytes were investigated. The limits of detection (S/N = 3) of the cations were in the range of 18-124 μg/l, the linear correlation coefficients were 0.9991-0.9998, and the RSD values of retention time and peak height were all smaller than 2.1%. The present analytical method was successfully applied to the rapid and direct determination of inorganic cations in samples of river water and commercial drinks, with satisfactory results.     

毛细管离子色谱法测定酒和饮料中阳离子

建立了毛细管离子色谱测定酒、饮料等样品中阳离子的分析方法。使用毛细管离子色谱柱IonPac CS12A(250 mm×0.4 mm, 8 μm),以甲基磺酸淋洗液发生器(EGC-MSA)产生18 mmol/L的甲基磺酸为流动相,进样量0.4 μL,在流速0.01 mL/min的条件下,采用自循环抑制电导检测的方法对啤酒、葡萄酒、白酒、果汁及奶茶等样品中的阳离子含量进行检测。结果表明,毛细管离子色谱法能满足阳离子含量的测定要求,系统稳定不易堵,在灵敏度方面优于常规离子色谱系统。该方法能够快速、准确地测定酒、饮料等样品中的5种阳离子(钠、铵、钾、镁和钙),回归方程的相关系数在0.9997以上,实际样品的加标回收率为95.2%～103.3%。该方法具有灵敏度高,操作简单,环境友好的特点。     

Dynamic chelation ion chromatography of transition and heavy metal ions using a mobile phase containing 4-chlorodipicolinic acid

The chromatographic behaviour of selected transition and heavy metal ions, the lanthanides, uranium and aluminium, on a neutral polystyrene-divinylbenzene (PS-DVB) stationary phase (7 microm Hamilton PRP-1) dynamically modified with 4-chlorodipicolinic acid, was investigated to evaluate retention characteristics. Complicated retention factor against pH plots were found for these metals demonstrating changes in retention order. It was concluded that complexation between the metal ions and the ligand adsorbed on the resin was strongly influenced by the decrease in dynamic loading with increase in pH, coinciding with changes in the metal-to-ligand ratio in the mobile phase. Possible reversed-phase interactions between metal-chlorodipicolinic acid complexes and the hydrophobic PS-DVB stationary phase also could not be ruled out. An eluent of 0.25 mM chlorodipicolinic acid, I M potassium nitrate at pH 2.2 was suitable for the separation of seven transition and heavy metal ions in under 20 min on a 250 x 4.6 mm column (with 50-mm guard column), determined in a certified water sample with good accuracy (R2 > or = 0.994) and reproducibility (RSD 1-4.2%). Pb(II), Cd(II) and Cu(II) were additionally analysed in <10 min in a more complicated certified rice flour matrix, using the same eluent but adjusted to pH 1.5, again with good accuracy (R2 > or = 0.998) and reproducibility (RSD 0.48-1.38%).     

Preparation of a hybrid monolithic stationary phase with allylsulfonate for the rapid and simultaneous separation of cations in capillary ion chromatography

A hybrid monolithic column with sulfonate functionality was successfully prepared for the simultaneous separation of common inorganic cations in ion‐exchange chromatographic mode through a simple and easy single‐step preparation method. The strong cation‐exchange moieties were provided directly from allylsulfonate, which worked as an organic monomer in the single‐step reaction. Inorganic cations (Li⁺, Na⁺, K⁺, NH₄⁺, Cs⁺, Rb⁺, Mg²⁺, Ca²⁺, and Sr²⁺) were separated satisfactorily by using CuSO₄ as the eluent with indirect UV detection. The allysulfonate hybrid monolith showed a better performance in terms of speed and pressure drop than the capillary packed column. The number of theoretical plates achieved was 19 017 plates/m (in the case of NH₄⁺ as the analyte). The relative standard deviations (n = 6) of both retention time and peak height were less than 1.96% for all the analyte cations. The allysulfonate hybrid monolithic column was successfully applied for the rapid and simultaneous separation of inorganic cations in groundwater and the effluent of onsite domestic wastewater treatment system.     

Affinity chromatography with monolithic capillary columns. II. Polymethacrylate monoliths with immobilized lectins for the separation of glycoconjugates by nano-liquid affinity chromatography

Monolithic capillary columns with surface bound lectin affinity ligands were introduced for performing lectin affinity chromatography (LAC) by nano-liquid chromatography (nano-LC). Two kinds of polymethacrylate monoliths were prepared, namely poly(glycidyl methacrylateco-ethylene dimethacrylate) and poly(glycidyl methacrylate-co-ethylene dimethacrylate-co-[2-(methacryloyloxy)ethyl]trimethyl ammonium chloride) to yield neutral and cationic macroporous polymer, respectively. Two lectins including concanavalin (Con A) and wheat germ agglutinin (WGA) were immobilized onto the monolithic capillary columns. The neutral monoliths with immobilized lectins exhibited lower permeability under pressure driven flow than the cationic monoliths indicating that the latter had wider flow-through pores than the former. Both types of monoliths with immobilized lectins exhibited strong affinity toward particular glycoproteins and their oligosaccharide chains (i.e., glycans) having sugar sequences recognizable by the lectin. Due to the strong binding affinity, the monoliths with surface bound lectins allowed the injection of relatively large volume (i.e., several column volumes) of dilute samples of glycoproteins and glycans thus allowing the concentration of the glycoconjugates and their subsequent isolation and detection at low levels (approximately 10(-8) M). To further exploit the lectin monoliths in the isolation of glycoconjugates, two-dimensional separation schemes involving LAC in the first dimension and reversed-phase nano-LC in the second dimension were introduced. The various interrelated methods established in this investigation are expected to play a major role in advancing the sciences of "nano-glycomics".