A problem in the spectrophotometric determination of dissolved total phosphorus in brackish anoxic waters

When dissolved total phosphorus in anoxic brackish waters was determined spectrophotometrically by the heteropoly molybdenum blue method after oxidation with potassium peroxodisulfate, negative dissolved organic phosphorus contents were obtained from the differences between the total phosphorus and inorganic phosphorus contents. A major cause of this inconsistency is coprecipitation of phosphate with the colloidal hydrated iron(III) oxide produced fro miron in these waters, or the formation of iron(III) phosphate during the oxidation process. The problem can be avoided by oxidation with nitric and perchloric acids.     

Rapid determination of dissolved organic phosphorus in soil leachates and runoff waters by flow injection analysis with on-line photo-oxidation

A rapid method suitable for the determination of dissolved organic phosphorus (DOP) in soil leachates and runoff waters is presented. The flow injection (FI) manifold contains an in-line PTFE reaction coil wrapped around a low power UV lamp and is based on the spectrophotometric determination of dissolved reactive phosphorus (DRP) and mineralised DOP at 690 nm after reduction of phosphomolybdate to molybdenum blue with tin(II) chloride. The linear range was 0-1.5 mg 1(-1) PO(4)-P, with a detection limit (3 s) of 7 mug 1(-1) and a sample throughput of 40 h(-1). Tolerance to potential matrix interferences in soil pore waters, particularly Al(III), Si(IV), Fe(II) and Fe(III), was achieved using a combination of on-line sample pre-treatment by a strong acid ion exchange column, low photoreactor pH and acid induced control of the kinetics of the molybdenum blue reaction. The results obtained with this manifold were in good agreement with those obtained by a batch spectrophotometric reference method.     

HPLC-SEC: a new approach to characterise complex wastewater effluents

This work investigates the use of HPLC-SEC to characterise dissolved organic matter (DOM) of complex wastewater effluents. A silica-based column, sodium acetate eluent and multiple detections were employed: UV-254 absorbance for humictype, and tryptophan-like (Ex/Em = 270/355) and tyrosine-like (Ex/Em = 270/310) fluorescence for protein type compounds. Effects of eluent pH, eluent ionic strength and injection volume on separation efficiency were tested. Humic-type and protein-type fractions were clearly differentiated and eluted within and out of calibration range. Eluent ionic strength had the greatest influence on global resolution; the lowest eluent concentration of 0.01 M produced the best separation for all wastewater effluents tested at any detection. UV-254 absorbance was higher at neutral and basic eluent pH while tryptophan-like fluorescence depended on the sample composition rather than on the eluent pH or ionic strength. Tyrosine-like fluorescence decreased significantly with the increase of eluent ionic strength. Accurate molecular weight measurements could not be done, the separation being influenced by secondary interactions, but could be approximated using separate calibrations with sodium salts of polystyrene-sulfonates and protein standards. The results show that this method is suitable for determining DOM in wastewater at low eluent concentrations (up to 0.03 M), at neutral or slightly basic pH.     

Determination of dissolved organic phosphorus in soil solutions by an improved automated photo-oxidation procedure

An improved automated photo-oxidation procedure to determine dissolved organic phosphorus in soil solutions is described. Organically combined phosphorus is converted quantitatively to orthophosphate under UV radiation and an excess of dissolved oxygen. The orthophosphate is determined spectrophotometrically using the Murphy and Riley procedure, modified by increasing the concentration of ascorbic acid. Fluoride was added to the system to overcome potential interference when working with soil solution. The limit of detection was 0.64 mug/l. PO(4)(-3) -P and calibration was linear over the range studied (5-1000 mug/l. PO(4)(-3) -P).     

Preparative electroelution of specific protein antigens from MicoplasmaPneumoniae: use in an enazyme-linked immunosorbent assay (Ellisa)

A rapid, simple and preparative method is described for the recovery of the seven highest molecular weight proteins (HMWP) from Mycoplasma pneumoniae membrane. The yield of proteins obtained was approximately 90%. The method involved the separation of M. pneumoniae proteins by socium dodecyl sulphate polycrylamide gel electrophoresis (SDS-PAGE), followed by electroelution of HMWP.These eluted antigens were used in an ELISA to measure IgG antibodies in sera 9 blood donors and 9 patients with M. pneumoniae infection.The specificity fo M. pneumoniae HMWP was examined by competition ELISA and immunoblotting with different mycoplasma species encountered in teh respiratory tract.     

Retention,enantioselectivity and enantiomeric elution order of propranolol and its ester derivatives on an alpha1-acid glycoprotein-bonded column

Summary The retention, enantionselectivity and enantiomeric elution order of racemic propranolol (PP) and its ester derivatives (O-acetyl,-propionyl,-butyrul and-valeryl PP) on an ₁-acid glycoprotein (AGP)-bonded column have been investigated by changing eluent composition (eluent pH, buffer concentration, type and content of organic modifier). The retention of these cationic solutes, PP and its ester derivatives, was influenced by eluent pH, ionic strength and organic modifier content. The enantioselectivity was dependent on eluent pH and type of organic modifier. Reversal of the enantiomeric elution order of ester derivatives of PP (O-propionyl-butyryl) and-valeryl PP) occurred around eluent pH 6–7. These results suggst that chiral recognition or binding properties may be altered by the change in eluent composition, espeically eluent pH and type of organic modifier.     

Determination of total dissolved inorganic carbon in freshwaters by reagent-free ion chromatography

Studies of inorganic carbon cycle in natural waters provide important information on the biological productivity and buffer capacity. Determination of total inorganic carbon, alkalinity and dissolved carbon dioxide gives an indication of the balance between photosynthesis and respiration by biota, both within the water column and sediments, and carbon dioxide transfers from the water column to the atmosphere. There are few methods to measure and distinguish the different forms of inorganic carbon, but all require a measure or an indirect quantification of total inorganic carbon. A direct measurement of TIC in water is made possible by the introduction of electrolytic generated hydroxide eluent in ion chromatography which allows to detect a chromatographic peak for carbonate. The advantage of this method is that all the inorganic forms of carbon are converted in carbonate at eluent pH and can be detected as a single peak by conductivity detection. Repeatability of carbonate peak was evaluated at different levels from 0.02 to 6 mequiv.l(-1) both in high purity water and in real samples and ranged from 1 to 9%. The calibration curve was not linear and has to be fitted by a quadratic curve. Limit of detection was estimated to be 0.02 mequiv.l(-1). Accuracy has been estimated by comparing ion chromatography method with total inorganic carbon calculated from alkalinity and pH. The correlation between the two methods was good (R(2)=0.978, n=141). The IC method has been applied to different typologies of surface waters (alpine and subalpine lakes and rivers) characterised by different chemical characteristics (alkalinity from 0.05 to 2 mequiv.l(-1) and pH from 6.7 to 8.5) and low total organic carbon concentrations. This analytical method allowed to describe the distribution of TIC along the water column of two Italian deep lakes.     

Gel Permeation Chromatography of Polyelectrolytes

Abstract

The mechanisms are discussed which control the GPC elution of ionic solutes, both the polyelectrolytes and the low molecular salts. The processes involved are quite general and valid in organic and in aqueous solvents. The conclusion is that gel permeation chromatography is a powerfull method to characterize poly-electrolytes; and it is shown that the correct data on molecular weight distribution can be obtained when the ionic content in the eluent is larger than 5.10^?2 M and when the concentration injected is lower than the critical overlapping concentration. The interpretation of chromatograms can be performed using the universal calibration and a viscosimetric detector.     

On-line extraction of metal ions using liquid-liquid segmentation and a membrane type phase separator for fluorescence detection

Summary A liquid segmented post-column reaction system has been used to extract metal ions from an aqueous eluent into an organic solvent for fluorescence detection. The metals Zr(IV), Ga(III), Sc(III), Y(III), In(III), Al(III), La(III), Zn(II), Cd(II), Ca(II) and Mg(II) have been isocratically separated on a C₁₈ column by virtue of the secondary chemical equilibrium established by an eluent containing n-octanesulfonate, tartaric acid, and hydroxyisobutyric acid. The chelating reagent 8-hydroxyquinoline dissolved in methylisobutyl ketone (MIBK) was used to extract the metals and a membrane type phase separator was effective at separating the phases and directing the organic stream to the detector. The response for this detection approach was linear for metal ion concentrations spanning the range of the detector, and detection limits for most metals were low parts-per-billion (ppb). Band broadening for the extraction system was examined and compared to a direct post-column reaction using oxine dissolved in acetone.     

Transformation and source of nutrients in the Changjiang Estuary

The concentrations of phosphate(PO43-),ammonium,nitrite,nitrate,silicate,dissolved organic nitrogen(DON),dissolved organic phosphorus(DOP),particulate phosphorus(PP)and particulate nitrogen(PN)along the salinity gradient were measured in the Changjiang Estuary in April 2007.The behavior of nutrient species along the continuum from the freshwater to the coastal zone is discussed.In the mixing zone between the riverine and marine waters,nitrate and phosphate behave non-conservatively,while silicate behaves conservatively.Nutrient import was quantified from the river load.Nutrient export to the sea was quantified from river discharge and from the salinity-nutrient gradient in the outer estuary.Using these data,a nitrogen and phosphorus budget was made.The internal estuarine fluxes played an important role in the nutrient estuarine fluxes,which accounted for approximately 41%of the nitrogen flux and 45%of the phosphorus flux.The mixing experiments in the laboratory generally reproduced well the inorganic process affecting nutrient dynamics in the Changjiang Estuary,indicating that the primary P and N transformation processes were phosphate and nitrate desorption along the salinity gradient.     

Abraham model correlations for describing the solubilising character of 3-Methoxy-1-butanol and 1-tert-Butoxy-2-propanol solvents

Experimental solubilities are measured for 18 crystalline organic nonelectrolyte solutes dissolved in 3-methoxy-1-butanol and for 23 crystalline organic nonelectrolyte solutes dissolved in 1-tert-butoxy-2-propanol. The measured experimental data, combined with published literature data, are used to determine Abraham model correlations for the two alkoxyalcohol solvents. The derived Abraham model correlations back-calculated the observed solubilities to within 0.12 log units.     

Comparative study for differentiation of aquatic humic-type organic constituents by capillary zone electrophoresis using polyvinyl alcohol-coated capillary

Capillary zone electrophoresis (CZE) with UV detection (254 nm) was applied to characterize aquatic dissolved humic matter (DHM) from different environmental sources (lake, river and sea waters, in all 15 different samples). A series of separation examples of DHMs using a polyvinyl alcohol (PVA)-coated silica open tubular capillary were carried out in a phosphate buffer (40 mM) as a background electrolyte at neutral acidity (pH 6.8). The separative power of electropherograms was reasonable and the reproducibility was above the mark. Each electropherogram was characteristic of the corresponding humic sample. Special functional fulvic and humic acids or their overall mixtures separated with XAD, DAX and DEAE sorbing solids as well as the original dissolved organic matter (DOM) were nicely differentiated according to their environmental sources. The PVA coating of open tubular silica capillaries seems to be very potential in electrophoretic characterization and separation of different humic solutes at neutral acidities with low sample concentrations thus permitting a workable technique, in a growing series of CZE studies, for better compared results from different studies.     

Determination of dissolved manganese in natural waters by differential pulse cathodic stripping voltammetry

A procedure based on differential pulse cathodic stripping voltammetry on the graphite electrode is described for the determination of dissolved manganese in natural waters buffered at pH about 6.5 with acetate solution. In order to avoid interference of iron(II) the addition of fluoride is used. The limit of detection is 3 g/l for a deposition time of 6 min. Acidification and UV-irradiation are recommended for samples containing dissolved organic matter. Results of manganese determination in table mineral waters are reported and the possibility of manganese speciation is discussed.     

Application of retention modelling to the simulation of separation of organic anions in suppressed ion chromatography

The ion-exchange separation of organic anions of varying molecular mass has been demonstrated using ion chromatography with isocratic, gradient and multi-step eluent profiles on commercially available columns with UV detection. A retention model derived previously for inorganic ions and based solely on electrostatic interactions between the analytes and the stationary phase was applied. This model was found to accurately describe the observed elution of all the anions under isocratic, gradient and multi-step eluent conditions. Hydrophobic interactions, although likely to be present to varying degrees, did not limit the applicability of the ion-exchange retention model. Various instrumental configurations were investigated to overcome problems associated with the use of organic modifiers in the eluent which caused compatibility issues with the electrolytically derived, and subsequently suppressed, eluent. The preferred configuration allowed the organic modifier stream to bypass the eluent generator, followed by subsequent mixing before entering the injection valve and column. Accurate elution prediction was achieved even when using 5-step eluent profiles with errors in retention time generally being less than 1% relative standard deviation (RSD) and all being less than 5% RSD. Peak widths for linear gradient separations were also modelled and showed good agreement with experimentally determined values.     

High-performance liquid chromatographic fractionation and characterization of fulvic acid

High-performance immobilized metal ion affinity chromatography (HP-IMAC) was used to fractionate humic substances (HS) based on their affinity for the immobilized copper(II) ion using acidic and glycine eluents. The work was carried out with two naturally occurring aqueous fulvic acids and commercially available Suwannee River fulvic acid. The IMAC-fractionated HS were then characterized by reversed-phase high-performance liquid chromatography (RP-HPLC) and size exclusion chromatography. The results showed that the affinity HS fraction eluted first using an acidic pH=2 eluent exhibited a relatively high hydrophilic character, whereas the fraction eluted later using a glycine eluent exhibited both a higher hydrophobic character and larger molecular size. On the other hand, the HS fraction with no affinity for the immobilized copper had low molecular size. The affinity of the HS fraction for copper(II) increased with increasing molecular weight. Based on the composite results of three different HS, it is evident that strong relationships exist between affinity, molecular weight, and hydrophilic/hydrophobic properties during the HP-IMAC fractionation. The results presented here have significance for understanding the nature of chemical interactions at the molecular level between dissolved organic matter and trace metals. IMAC, coupled with other liquid chromatographic strategies, is a promising tool for chemical fractionation and characterization of HS.     

Subcritical water chromatography: A green approach to high-temperature liquid chromatography

At temperatures and pressures lower than 374 degrees C and 218 atm, subcritical water has widely tunable properties such as dielectric constant, surface tension, viscosity, and dissociation constant achieved by simply adjusting the temperature with a moderate pressure to keep water in the liquid state. At elevated temperatures, water acts like a weak polar organic solvent. Thus, subcritical water has been used as a green eluent to replace hazardous solvents commonly used as organic modifiers in RPLC. Subcritical water chromatography (SBWC) is capable of separating polar, moderately polar, and even some nonpolar analytes. Most of these low molecular weight solutes are stable at elevated temperatures during a chromatographic run. Some new packing materials are also quite stable and robust at mild temperatures ranging from 80 to 150 degrees C. Advantages of SBWC include the elimination of hazardous organic solvents used in traditional RPLC, rapid analysis time, improved selectivity, temperature-dependent separation efficiency, temperature-programmed elution, and compatibility with both gas- and liquid-phase detectors. In this paper, the technical aspects as well as the applications of SBWC are reviewed. Topics addressed in this review include the unique characteristics of subcritical water, analytes separated by SBWC, packing materials tested for SBWC, the application of GC and LC detection techniques in SBWC, SBWC instrumentation development, temperature effects on SBWC separation, and models developed for separation in SBWC.     

Development of Abraham model correlations for describing the transfer of molecular solutes into propanenitrile and butanenitrile from water and from the gas phase

Experimental solubilities were measured for 20 crystalline organic solutes dissolved in propanenitrile and for 13 crystalline organic solutes dissolved in butanenitrile at 298.15 K. Infinite dilution activity coefficient data for solutes dissolved in propanenitrile and butanenitrile have been compiled from the published chemical and engineering literature and converted into gas-to-liquid partition coefficients and water-to-organic solvent partition coefficients through standard thermodynamic relationships. Abraham model correlations were developed for describing solute transfer into both propanenitrile and butanenitrile by combining our measured solubility data with the partition coefficients that we calculated from the published activity coefficient data. The derived Abraham model correlations were found to back-calculate the observed partition coefficients and molar solubility data to within 0.14 log units.     

Determination of dissolved organic nitrogen in natural waters using high-temperature catalytic oxidation

Studies on nitrogen in natural waters have generally focussed on dissolved inorganic nitrogen (DIN), primarily because of relative ease of analysis and the important influence of DIN on water quality. Advances in analytical techniques now permit the systematic study of dissolved organic nitrogen (DON), and this work has shown that DON is quantitatively significant in many waters. This article describes the sampling and analytical protocols required for rapid, precise and reliable determinations of DON, involving high-temperature catalytic oxidation (HTCO), coupled to chemiluminescence detection. This approach simultaneously determines dissolved organic carbon (DOC) and total dissolved nitrogen (TDN), and DON is derived by subtraction of DIN measured by colorimetry. The DON determination is simple to perform, exhibits excellent precision (<1% for C and 1.5% for N) and is applicable to a wide range of natural waters.