Phil Jones

High-performance chelation ion chromatography. A new dimension in the separation and determination of trace metals

A review of so-called high-performance chelation ion chromatography (HPCIC) is presented. The principles of this separation technique are based on exploitation of the chelation effect of stationary phases in the presence of comparatively reduced electrostatic ion-exchange interactions. The common ways to suppress ion-exchange, including increasing the ionic strength and pH of the eluent and the column temperature, are discussed. Unlike the majority of low-efficiency chelation exchangers that are used as preconcentration columns for batch separations, HPCIC can be used for high-efficiency analytical separations of trace metals. The range of applications of chelating exchangers used for the separation and determination of alkaline-earth and transition metal ions by HPCIC as well as their types and properties are considered. The main features of HPCIC are the much greater flexibility in selectivity control compared to ion-exchange and the relative insensitivity to high ionic strengths. These properties make it a more preferable technique for the trace analysis of complex samples, such as seawater, saturated brines, etc.

Isocratic separation of lanthanides and yttrium by high-performance chelation ion chromatography on iminodiacetic acid bonded to silica

Abstract The variation of chromatographic retention of lanthanide ions and yttrium on a column packed with iminodiacetic acid bonded to silica was studied. The influence of nitric acid concentration, ionic strength of the eluent and temperature as well as complexing agents (diglycolic, maleic acid) was investigated. It was shown that with nitric acid as eluent in the presence of 0.5 M–1.0 M potassium nitrate the retention of the lanthanides under increased temperature is defined mainly by the stability of the corresponding surface complexes with iminodiacetic acid functional groups. The combination of increased ionic strength of the eluent (0.5 M potassium nitrate) with increased temperature of the chromatographic column (65°C) allowed, under optimal concentration of nitric acid (1.6·10−2 M), the isocratic separation of 14 lanthanide ions and yttrium in 65 min.

Capillary electrophoresis determination of methylmercury in fish and crab meat after extraction as the dithizone sulphonate complex

Abstract Dithizone sulphonate (DzS) is used in place of cysteine to separate methylmercury in the final stage of a simplified Westoo extraction procedure. The intensely absorbing methylmercury DzS complex is then separated by CE using a coated capillary and determined by direct absorption measurement at 480 nm. Good quantitative performance is demonstrated by spiking experiments and analysis of DORM-1 certified reference material. Values found ranged from 218 μg kg −1 for a tuna fish to 2.8 μg kg −1 for a crab sample. The very stable baseline and lack of interfering peaks meant that a low detection limit of 2 μg kg −1 could be achieved for a 10 g sample.

Determination of natural uranium and thorium in environmental samples by ETV-ICP-MS after matrix removal by on-line solid phase extraction

An on-line solid phase extraction method has been developed for the determination of 238 U and 232 Th biological certified reference material using inductively coupled plasma mass spectrometry (ICP-MS). Absolute detection limits were 2.7 pg and 3.1 pg for the determination of 238 U and 232 Th respectively, both being blank limited. The result for the determination of 238 U in NASS-4 Open Ocean Sea Water was 2.13±0.28 ng ml –1 compared with a certified value of 2.68±0.12 ng ml –1 . The results for the determination of 238 U in SLRS-3 River Water was 0.043±0.002 ng ml –1 compared with an indicative value of 0.045 ng ml –1 . Results for the determination of 238 U and 232 Th in NIST 1575 Pine Needles were 14.6±3.4 ng g –1 and 28.3±4.5 ng g –1 respectively compared with certified values of 20±4 ng g –1 and 37±3 ng g –1 , using a dry and wet ashing sample preparation method. Results for the determination of 238 U and 232 Th in NIST 1566a oyster tissue were 121±21 ng g –1 and 29±8 ng g –1 for 238 U and 232 Th compared to certified and indicative values of 132±12 ng g –1 and 40 ng g –1 , using the same method. When a lithium metaborate fusion method was used, results for 238 U and 232 Th were 23.3±2.0 ng g –1 and 36.2±5.6 ng g –1 respectively in NIST 1575 Pine Needles. The application of electrothermal vaporisation ICP-MS (ETV-ICP-MS) to NASS-4 Open Ocean Sea Water gave 2.81±0.54 ng ml –1 and SLRS-3 River Water 0.045±0.004 ng ml –1 for 238 U. When the fused NIST 1575 samples were analysed using ETV-ICP-MS, results for 238 U and 232 Th were 19.5±1.7 ng g –1 and 38.8±2.2 ng g –1 respectively. Absolute detection limits for ETV-ICP-MS were 30 fg and 9 fg for 238 U and 232 Th respectively, both being blank limited.

Single-column method of chelation ion chromatography for the analysis of trace metals in complex samples

A single-column chelation ion chromatographic system for the preconcentration and separation of trace transition metals is described. The system includes standard chromatographic equipment with a post-column reagent system based on the reaction with 4-(2-pyridylazo)resorcinol followed by photometric detection at 495 nm. Iminodiacetic acid bonded to 5 μm silica (Diasorb IDA) was used as a chelating stationary phase. The strong complexing ability in combination with good kinetics of complexation and ion-exchange selectivity of iminodiacetic functional groups allow both preconcentration of Mn, Co, Cd, Zn, Ni and Cu from waters of high salinity and efficient separation with the same column. The retention characteristics of alkaline-earth and transition metal ions on Diasorb IDA silica (250×4 mm I.D.) column was investigated for a variety of eluents including nitric acid, maleic, malonic, citric, dipicolinic, picolinic, tartaric and oxalic acids. The influence of ionic strength on retention of metal ions involving high nitrate and chloride concentrations was also evaluated. The baseline separation of preconcentrated metals was achieved using a three-step gradient elution scheme which involved first, flushing of the column loaded with the sample with 0.5 M KCl−0.5mMHNO3 for 10 min, followed by 80 mM tartaric acid for 20 min and finally 10 mM picolinic acid for 20 min.

Analysis of oilfield produced waters and production chemicals by electrospray ionisation multi-stage mass spectrometry (ESI-MSn).

Large quantities of diverse polar organic chemicals are routinely discharged from oil production platforms in so-called produced waters. The environmental fate of many of these is unknown since few methods exist for their characterisation. Preliminary investigations into the use of multistage electrospray ionisation ion trap mass spectrometry (ESI-MSn) show its potential for the identification and quantification of compounds in specialty oilfield chemicals (corrosion inhibitors, scale inhibitors, biocides and demulsifiers) and produced waters. Multiple stage mass spectrometry (MSn) with both positive and negative ion detection allows high specificity detection and characterisation of a wide range of polar and charged molecules. For example, linear alkylbenzenesulfonates (LAS), alkyldimethylbenzylammonium compounds, 2-alkyl-1-ethylamine-2-imidazolines, 2-alkyl-1-[N-ethylalkylamide]-2-imidazolines and a di-[alkyldimethylammonium-ethyl]ether were all identified and characterised in commercial formulations and/or North Sea oilfield produced waters. The technique should allow the marine environmental effects and fates of some of these polar compounds to be studied.

Method comparison for the determination of labile aluminium species in natural waters

Abstract An inter-laboratory comparison project to evaluate the portability of a standard method for the determination of aluminium species in waters and to investigate the probability of producing reference waters for aluminium speciation analysis is described. High-density polyethylene containers were found to be appropriate for the storage of water samples, intended for speciation analysis, after leaching with 10% (v/v) nitric acid for 48 h. A quality control programme for total aluminium in water samples was completed by all participating laboratories, showing the value of such a parallel programme, especially for aluminium with its inherent problems with contamination. Water samples (lake and tap) proved to be stable for up to 30 days, after which increasing pH caused aluminium hydroxy species to precipitate. A defined Driscoll-Pyrocatechol Violet fractionation method was found to be robust enough to be fully portable, the participating laboratories achieving relative standard deviations of 15% for the toxic “labile monomeric” aluminium fraction in the more stable water samples.

Determination of trace amounts of aluminium by ion chromatography with fluorescence detection

A method is described for the determination of aluminium by high-performance ion chromatography followed by post-column derivatisation with 8-hydroxyquinoline-5-sulphonate and fluorescence detection at 512 nm (excitation at 360 nm). A short (50 mm) low-capacity cation-exchange resin column was used as the analytical column and 0.1 M K2SO4, adjusted to pH 3.0, as the eluent. The calibration graph was linear from 5 to 10 000 µg l–1 of aluminium with a detection limit (3σ) of 1 µg l–1. Typical relative standard deviations were 3.4% at the 250 µg l–1 level. No interference was observed from other commonly occurring metals and aluminium was successfully determined in a certified reference material (Monel Alloy) and in tap water.

Development of a capillary electrophoretic method for the separation and determination of trace inorganic and organomercury species utilizing the formation of highly absorbing water soluble dithizone sulphonate complexes

Abstract This paper details results which show that rapid, good quality separations can be achieved for inorganic and organomercury species as their dithizone sulphonate complexes, using coated capillary columns. The complexes were pre-formed before injection and detection was by direct measurement of the absorbance of the complexes. Good linear calibration curves were obtained for all the mercury species studied and the exceptionally low background noise and straight base lines meant that detection limits in the low μg l−1 range could be obtained.

Determination of total mercury in environmental and biological samples by flow injection cold vapour atomic absorption spectrometry

Abstract A simple and accurate method has been developed for the determination of total mercury in environmental and biological samples. The method utilises an off-line microwave digestion stage followed by analysis using a flow injection system with detection by cold vapour atomic absorption spectrometry. The method has been validated using two certified reference materials (DORM-1 dogfish and MESS-2 estuarine sediment) and the results agreed well with the certified values. A detection limit of 0.2 ng g −1 Hg was obtained and no significant interference was observed. The method was finally applied to the determination of mercury in river sediments and canned tuna fish, and gave results in the range 0.1–3.0 mg kg −1 .