M. Riaz

Simultaneous determination of nitrite and nitrate by normal phase ion-pair liquid chromatography

Normal phase ion-pair high performance liquid chromatography has been used for simultaneous separation of nitrite and nitrate using tetraethylammonium (TEA)(+) as ion-pairing reagent. The concentration effect of (TEA)(+), buffer salt and pH of the eluent on separation is investigated. The UV detector response at various wavelengths has been optimized. The performance of the proposed method is compared with ion chromatography for quantification of the anions in potable water, wastewater and in food samples, such as spinach and lettuce.

Determination of cations and anions in environmental samples by HPLC: review.

Abstract Inorganic ionic pollutants are of great environmental concern due to their health related impact. Around 16 inorganic contaminants are to be monitored regarding the primary drinking water regulation set by US, EPA. The permissible limits or guideline values are generally in the range of submicro gram or even less. Moreover, the analytes of concern are present at tracer concentration in the bulk matrices. Of particular concern are non-metallic ions that are difficult to monitor accurately and precisely in the presence of bulk unwanted ions. HPLC has played an important role in analyzing ionic pollutants, in particular, speciation of elements. In this review, some fundamentals of high performance liquid chromatography and, in particular, ion chromatography and ion pair chromatography have been described in some detail. The use of ion chromatography in combination with different types of mass spectrometric techniques has also been outlined. The LC-MS detection limits range from submicrogram to picogram and most of these techniques met the primary drinking water regulation requirement.

Determination of UV active inorganic anions in potable and high salinity water by ion pair reversed phase liquid chromatography.

Reversed phase column was dynamically modified into anion exchange column using various types of tetraalkylammonium salts as ion pair reagents (IPRs) for the separation and quantification of toxic anions such as nitrite, bromate, bromide and nitrate in potable and high salinity water. Various chromatographic parameters such as types and concentration of IPRs, concentration of organic modifier, phosphate buffer and mobile phase pH were optimized for the base-line separation of anions. The lowest detection limits (LDLs) were 0.2 for nitrate and nitrite, 0.6 µg ml(-1)for bromate and bromide respectively for potable water samples. NaCl and Na₂SO₄ were incorporated in the mobile phase for the analysis of high salinity water samples to minimize matrix interferences. This has resulted in change in elution order of anions, better tolerance of matrix anions such as chloride and sulphate. The developed method was successfully utilized for analysis of anions in potable, high salinity and sea water samples.

Evaluation and performance comparison of bare powdered graphite and coated columns for gas chromatographic separation of halocarbons and halobenzenes

ABSTRACT Powdered graphite has been explored as column material for adsorption gas chromatography (GC). Surface of graphite has been coated with polyethylene glycol (PEG-6000) for improved separation of halobenzenes. The qualitative performance comparison of bare and coated graphite columns has been carried out with commercial packed and capillary columns regarding various chromatographic kinetic parameters. The reported graphite column can effectively separate three commonly known halocarbons and halobenzenes. Coating of graphite has increased the sensitivity of the halobenzenes due to improvement in peaks symmetry. The RSD values of measured number of theoretical plates for 1,2,4-trichlorobenzene for bare and coated graphite and on commercial PEG-20M are 2.5, 1.4 and 1.3, respectively.

Influence of the Lipophilicity of an Ion‐Pairing Reagent on Metal Ion Separation using Ion‐Pair HPLC

Abstract Tetraalkyl ammonium salts (TAAS) of a wide range of lipophilicities are used as ion‐pairing reagents for simultaneous separation of proposed anionic metal complexes [M (H2PO4) 3]− of U(VI), Fe(III), and neutral Cu(II) using reversed‐phase ion pairing high performance liquid chromatography (RPIP‐HPLC). Tetramethylammonium bromide, tetraethyl ammonium chloride, and tetrapropyl ammonium bromide, due to their low hydrophobicities, are unable to separate U(VI) and Fe(III). Tetrabutyl ammonium perchlorate has separated the three metal ions. Tetrahexyl ammonium bromide, tetraheptyl ammonium bromide, and tetraoctyl ammonium bromide have enhanced resolution for the metal ions, but analysis time was prolonged due to the strong retention of nitrate ion. Also, equilibration time with the stationary phase increases with the increase in carbon atoms in the IPR. The potential of varied carbon containing IPRs has been compared for the analysis of U(VI) in simulated standards. The detection limit and RSD for Cu, Fe, and U are 2, 0.5, and 2 ppm and 4, 5, and 3.3%, respectively.

STRATEGIES FOR THE OPTIMUM SEPARATION OF GAMMA RADIOLYTIC DEGRADATION PRODUCTS OF METHOXYCHLOR USING RP-HPLC

Different types of reversed phase (RP) columns have been incorporated for the separation of gamma radiolytic degradation products (DPs) of methoxychlor. The effect of carbon chain length, carbon content, surface area, pore size, pore volume, and column dimensions of RP columns on DPs separation has also been investigated. The separation of DPs has been optimized employing methanol-water mobile phase and UV-DAD. In methanol media two major and five minor DPs were detected in gamma irradiated MXC by RP-HPLC. The peaks eluting before the parent peak on reversed phase column are expected to be relatively polar compounds while peaks after MXC are assumed to be non-polar in nature corresponding to general RP behavior. From HPLC analysis it is inferred that at gamma radiation dose of 5 kGy ≥95% MXC has been degraded for a dose rate of 200 Gyh−1. The chemical radiation yield (G-value) along with effect of MXC concentration on degradation has also been explored. The physico-chemical parameters of RP columns have been compared under the optimum separation conditions. It may be concluded that HPLC is an excellent tool to investigate radiolytic degradation of persistent organic pollutants.

Demasking role of various complexans in the determination of uranium in torbernite ore using ion-pair HPLC

Abstract Various masking agents such as ethylenediamine tetra‐acetic acid (EDTA), diethylenetriamine penta‐acetic acid (DTPA), ethyleneglycol‐2‐(amino‐ethyl) tetra‐acetic‐acid (EGTA), ascorbic acid, fluoride, tartrate, citrate, oxalate, thiourea, triethanolamine (TEA), and ethylenediamine (EDA) have been used in the sample processing to eliminate the iron interference in the determination of uranium U (VI) by ion‐pair high performance liquid chromatography (IP‐HPLC). Among the investigated masking agents, oxalate, thiourea, TEA, EDA interfere. However, EDTA and DTPA, are effective to mask iron without affecting U (VI) quantification, while citrate slightly reduces the response. The lowest detection limits for the reported method in standard solution is 2 ppm. The developed method has been applied to analyze U (VI) in simulated standards and IAEA SRM, such as Torbernite ore containing iron. The relative standard deviation (RSD) for uranium determination in Torbernite ore (n=5) is ∼2%.