Effect of temperature on retention of alkali and alkaline-earth metal ions on some aminocarboxylic acid functionalised silica based ion exchangers

Retention behavior of carbohydrates on metal loaded chelating stationary phase under conditions of hydrophilic interaction liquid chromatography

The chromatographic retention of carbohydrates on chelating stationary phase loaded with different metal ions was studied under conditions of hydrophilic interaction chromatography (HILIC). The chelating stationary phases represented silica microparticles with immobilized 2-hydroxyethyliminodiacetic acid (HEIDA) groups in loose form and saturated with Ca2+, Pb2+, and La3+form. The role of loaded metal ion, the acetonitrile and methanol content in the mobile phase, buffer pH and column temperature on the retention of l-(+)-arabinose, d-(+)-maltose, l-(+)-rhamnose, d-(+)-lactose, d-(+)-xylose, glucose, fructose, sucrose, mannose, maltotriose and d-(+) raffinose was studied. The investigation was mainly focused on possible contribution of the complexation in the stationary phase on retention of carbohydrates as well as on effect of the presence metal ion in HEIDA-silica on resulting HILIC behavior of. It is shown that adsorbents with immobilized metal complexes have a good potential for the separation of organic ligands under HILIC mode.

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.

Ion chromatographic investigation of the ion-exchange properties of microdisperse sintered nanodiamonds

The possibility of using sintered diamonds as a stationary phase in ion chromatography has been evaluated. Bare sintered synthetic nanodiamonds demonstrated the properties of a weak cation-exchanger. The observed ion-exchange selectivity is similar to carboxylic type cation-exchangers. The regularities of retention of alkali, alkaline-earth and transition metal ions on a column packed with sintered nanodiamonds in dilute nitric acid were studied and the occurrence of chelating properties was noted. For the first time chromatographic separations of model mixtures of cations on diamonds have been obtained.

Effect of temperature on the retention of amino acids and carbohydrates in high-performance anion-exchange chromatography

Effect of temperature on the retention of amino acids and carbohydrates in high-performance anion-exchange chromatography (HPAEC) was investigated. Amino acids retention exhibited both exothermic and endothermic behavior. Significant selectivity variations of some weakly retained amino acids were achieved through changing temperature. However, temperature was almost ineffective at changing the selectivity of strongly retained amino acids. Sugars retention exhibited only exothermic behavior. However, individual carbohydrates showed different relative changes in retention time with increased temperature. There is the general regularity, which is the variation of retention time increases as the sequence of monosaccharide, disaccharide, trisaccharide and tetrasaccharide when the column temperature is increased. Selectivity changes of carbohydrates, including elution order reversal, were also achieved by varying temperature. Temperature was effective at changing the selectivity of between amino acids and carbohydrates. In achieving optimal separation of amino acids and carbohydrates, temperature is a valuable tool.

Fast ion chromatography of inorganic anions and cations on a lysine bonded porous silica monolith

A 0.46 cm x 10.0 cm silica monolith column was modified through the in situ covalent attachment of lysine (2,6-diaminohexanoic acid) groups. Due to the zwitterionic nature of the resultant stationary phase, the modified monolithic column contained both cation and anion exchange capacity. In the case of cation exchange, the capacity was found to be relatively low at between 5 and 6.5 micromoles Me2+ per column. However, as expected, the lysine monolith exhibited a higher anion exchange capacity at 12-13 micromoles A- per column (at pH 3.0), which was found to be dependent upon column pH, due to the dissociation of the weak acid carboxylic acid groups. High-performance separations of transition metal cations and inorganic anions were achieved using the modified monolith, with the effects of eluent concentration, pH and flow rate evaluated. Using elevated flow rates of up to 5 mL/min the separation of nitrite, bromate, bromide, nitrate, iodide and thiocyanate was possible in approximately 100 s with peak efficiencies of between 50 and 100,000 N/m and retention time %RSD of under 0.3%.

Use of temperature programming to improve resolution of inorganic anions, haloacetic acids and oxyhalides in drinking water by suppressed ion chromatography

Temperature programming was used to improve selectivity in the suppressed ion chromatographic (IC) separation of inorganic anions, haloacetic acids and oxyhalides in drinking water samples when using NaOH gradient elution. The programme exploited varying responses of these anions to changes in temperature. Heats of adsorption (deltaH, kJ/mol) for 17 anionic species were calculated from van't Hoff plots. For haloacetic acids, both the degree of substitution and log P (log of n-octanol-waterpartition coefficient) values correlated well with the magnitude of the temperature effect, with monochloro- and monobromoacetic acids showing the largest effect (deltaH= -10.4 to -10.7 kJ/mol), dichloro- and dibromoacetic acids showing a reduced effect (deltaH= -6.8 to -8.4 kJ/mol) and trichloro-, bromodichloro- and chlorodibromoacetic acids showing the least effect (deltaH= -4.7 to -2.4 kJ/mol). The effect of temperature on oxyhalides ranged from deltaH= 8.4 kJ/mol for perchlorate to deltaH= -9.1 kJ/mol for iodate. The effectiveness of two commercial column ovens was investigated for the application of temperature gradients during chromatographic runs, with the best system applied to improve the resolution of closely retained species at the start, middle and end of the separation obtained using a previously optimised hydroxide gradient, in a real drinking water sample matrix. Retention time reproducibility of the final method ranged from 0.62 to 3.18% RSD (n = 30) showing temperature programming is indeed a practically important parameter to manipulate resolution.

Novel ion chromatographic stationary phases for the analysis of complex matrices

Ion chromatography (IC) has a proven track record in the determination of inorganic and organic anions and cations in complex matrices. Recently, application of IC to the separation and determination of bio-molecules such as amino acids, carbohydrates, nucleotides, proteins and peptides has also received much attention. The key to the determination of all of the above species in the most analytically challenging complex matrices is the ability to manipulate selectivity through control of stationary phase chemistry, mobile phase chemistry and the choice of detection method. This Tutorial Review summarises some of the most significant recent advances made in IC stationary phase technology. In particular, the review details stationary phases specifically designed for ion analysis in complex sample matrices, and considers in which direction future stationary phase development might proceed.

Ionic strength, pH and temperature effects upon selectivity for transition and heavy metal ions when using chelation ion chromatography with an iminodiacetic acid bonded silica gel column and simple inorganic eluents

An investigation into the selectivity of an iminodiacetic acid (IDA) modified silica gel column for transition and heavy metal ions using non-chelating inorganic eluents has been carried out. A number of eluent parameters were investigated to determine the exact retention mechanism taking place and to control selectivity. The parameters studied were eluent ionic strength and the nature of the inorganic salt used, eluent pH and eluent temperature. The results obtained showed how despite certain metal ions exhibiting similar stability constants with the bonded IDA groups, careful control of each of the above parameters, in particular eluent chloride ion concentration and eluent temperature, could result in large changes in selectivity. Optimal conditions for the isocratic and gradient separation of Mg(II), Ca(II), Mn(II), Cd(II), Co(II), Zn(II) and Pb(II) were determined. An isocratic method using a 0.035 M KCl, 0.065 M KNO3 (pH 2.5) eluent was successfully applied to the determination of Mn(II), Cd(II), Co(II) and Zn(II) at concentrations between 20 and 121 microg/l in a freshwater certified reference material (NIST 1640).

Ion chromatography on chelating stationary phases: separation of alkali metals

Analytical 250x4.6 mm I.D. columns packed with iminodiacetic acid (IDA) derivatised silica were used to separate alkali metal ions and the ammonium ion in combination with non-suppressed conductivity detection. The addition of 2.5-10 mmol/l of the macrocyclic crown ether 18-crown-6 to the nitric acid eluent resulted in a change in the elution order and a significant improvement in the resolution between potassium and ammonium because of selective complexation of potassium. However, the admixture of 15-crown-5 did not improve the resolution of lithium and sodium, although 15-crown-5 is a selective complexing agent for sodium. Retention and resolution of lithium, sodium, ammonium, cesium, rubidium and potassium ions increased at lower temperatures down to 1 degree C. The simultaneous separation of alkali and transition metals under isocratic conditions was achieved with an eluent comprising 10 mmol/l 18-crown-6, 1.5 mmol/l dipicolinic acid, and 1.9 mmol/l nitric acid. The chromatographic system enabled the quantitation of alkali metal ions with detection limits in the low ppb range and excellent linearity. Finally, the applicability of the method was approved by quantitation of sodium, ammonium and potassium in different water samples.

Ion-exchange properties of hypercrosslinked polystyrene impregnated with methyl orange

A novel bipolar stationary phase (HCPS-MO) was prepared by impregnation of hypercrosslinked polystyrene (HCPS) with methyl orange (MO; 4-dimethylamino-4'-sulfoazobenzene) and its ion-exchange properties were studied. Simultaneous separation of cations and anions on HCPS-MO is possible, although it behaves preferentially as a cation-exchanger. Unusual selectivity of HCPS-MO for alkali and alkaline-earth metal cations: Na+ < Li+ approximately = K+ < Rb+ < NH4+ < Cs+ and Mg2+ < Sr2+ < Ca2+ < Ba2+ was observed. The effect of temperature on retention of alkali and alkaline-earth metal cations was studied. Separation of Na+, K+, Rb+, NH4+, Cs+, Mg2+ and Ca2+ on HCPS-MO with diluted cerium(III) nitrate solution as an eluent in single run is presented.

Determination of trace alkaline earth metals in brines using chelation ion chromatography with an iminodiacetic acid bonded silica column

The chromatographic behaviour of alkaline earth metals on iminodiacetic acid bonded silica was studied. It was found that the ionic strength of the eluent greatly affected both retention time and selectivity by controlling the extent to which either simple ion exchange or surface complexation was responsible for retention. With a 0.1 M KNO3 eluent, the retention order was Mg(II), Sr(II), Ca(II) and Ba(II), indicating a strong contribution to retention from ion exchange. However, when using a 1.5 M KNO3 eluent, Ba(II) was found to elute first, indicating complexation to be more dominant under these conditions (pH 4.2). The effect of the ionic strength of the sample was also studied and it was found that by matching the eluent cation with that of the sample matrix, efficient separations of alkaline earth metals in 1.0 M NaCl and KCl brines could be obtained without matrix system peaks. Using post-column reaction with o-cresolphthalein complexone, trace levels of Ca(II) and Mg(II) were determined in medicinal NaCl saline solution and laboratory-grade KCl.