Determination of Some Organochlorine Compounds in the Atmosphere

Abstract

Since plastics are suspected to adsorb orthophosphate, disposable-tip pipettes have been checked to determine their ability to be used in orthophosphate calibration. No adsorption has been detected through an experiment of standard preparation with and without changing the pipette tip. That is, the pipettes appear to be convenient for orthophosphate calibration.     

Utilization of cyanobacteria in photobioreactors for orthophosphate removal from water

The effectiveness of photosynthetic free-living and polyurethane foam (PU) immobilized Anabaena variabilis cells for, removal of orthophosphate (P) from water in batch cultures and in a photobioreactor was studied. Immobilization in PU foams was found to have a positive effect on P uptake by cyanobacteria in batch cultures. The efficiency of P uptake by immobilized cells was higher than by free-living cells. A laboratory scale photobioreactor was constructed for removal of P from water by the immobilized cyanobacteria. The photobioreactor was designed so that the growth medium (water) from a reservoir was pumped through a photobioreactor column with immobilized cyanobacteria and back to the reservoir. This created a closed system in which it was possible to measure P uptake. No leakage of cells into the photobioreactor medium reservoir was observed during the operation. The immobilized cells incorporated into a photobioreactor column removed P continuously for about 15 d. No measurable uptake was demonstrated after this period. Orthophosphate uptake efficiency of 88–92% was achieved by the photobioreactor.     

Flow-through solid-phase based optical sensor for the multisyringe flow injection trace determination of orthophosphate in waters with chemiluminescence detection

In this work, a novel flow-through solid-phase based chemiluminescence (CL) optical sensor is described for the trace determination of orthophosphate in waters exploiting the multisyringe flow injection analysis (MSFIA) concept with multicommutation. The proposed time-based injection flow system relies upon the in-line derivatisation of the analyte with ammonium molybdate in the presence of vanadate, and the transient immobilisation of the resulting heteropolyacid in a N-vinylpyrrolidone/divinylbenzene copolymer packed spiral shape flow-through cell located in front of the window of a photomultiplier tube. The simultaneous injection of well-defined slugs of luminol in alkaline medium and methanol solution towards the packed reactor is afterwards performed by proper switching of the solenoid valves. Then, the light emission from the luminol oxidation by the oxidant species retained onto the sorbent material is readily detected. At the same time, the generated molybdenum-blue compound is eluted by the minute amount of injected methanol, rendering the system prepared for a new measuring cycle. Therefore, the devised sensor enables the integration of the solid-phase CL reaction with elution and detection of the emitted light without the typical drawbacks of the molybdenum-blue based spectrophotometric procedures regarding the excess of molybdate anion, which causes high background signals due to its self-reduction. The noteworthy features of the developed CL-MSFIA system are the feasibility to accommodate reactions with different pH requirements and the ability to determine trace levels of orthophosphate in high silicate content samples (Si/P ratios up to 500). Under the optimised conditions, a dynamic linear range from 5 to 50 μg P l⁻¹ for a 1.8 ml sample, repeatability better than 3.0% and a quantification limit of 4 μg P l⁻¹ were attained. The flowing stream system handles 11 analysis h⁻¹ and has been successfully applied to the determination of trace levels of orthophosphate in environmental samples such as mineral, ground, tap and pond waters as well as samples from a water-steam cycle of an incineration plant. The t-test comparison of the means for the developed optical sensor and the molybdenum-blue spectrophotometric APHA/AWWA/WPCF reference method revealed that there is no evidence of significant differences between the obtained results at the 95% confidence level.     

A multisyringe flow-through sequential extraction system for on-line monitoring of orthophosphate in soils and sediments

A fully automated flow-through microcolumn fractionation system with on-line post-extraction derivatization is proposed for monitoring of orthophosphate in solid samples of environmental relevance. The system integrates dynamic sequential extraction using 1.0 mol l⁻¹ NH₄Cl, 0.1 mol l⁻¹ NaOH and 0.5 mol l⁻¹ HCl as extractants according to the Hieltjes-Lijklema (HL) scheme for fractionation of phosphorus associated with different geological phases, and on-line processing of the extracts via the Molybdenum Blue (MB) reaction by exploiting multisyringe flow injection as the interface between the solid containing microcolumn and the flow-through detector. The proposed flow assembly, capitalizing on the features of the multicommutation concept, implies several advantages as compared to fractionation analysis in the batch mode in terms of saving of extractants and MB reagents, shortening of the operational times from days to hours, highly temporal resolution of the leaching process and the capability for immediate decision for stopping or proceeding with the ongoing extraction. Very importantly, accurate determination of the various orthophosphate pools is ensured by minimization of the hydrolysis of extracted organic phosphorus and condensed inorganic phosphates within the time frame of the assay. The potential of the novel system for accommodation of the harmonized protocol from the Standards, Measurement and Testing (SMT) Program of the Commission of the European Communities for inorganic phosphorus fractionation was also addressed. Under the optimized conditions, the lowest detectable concentration at the 3σ level was ≤0.02 mg P l⁻¹ for both the HL and SMT schemes regardless of the extracting media. The repeatability of the MB assay was better than 2.5% and the dynamic linear range extended up to 7.0 mg P l⁻¹ in NH₄Cl and NaOH media and 15 mg P l⁻¹ whenever HCl is utilized as extractant for both the HL and SMT protocols.     

Kinetic spectrophotometric determination of submicromolar orthophosphate by molybdate reduction

A kinetic spectrophotometric procedure was developed for determination of submicromolar orthophosphate based on the reaction in which orthophosphate serves as a catalyst in the reduction of molybdenum, and the initial rate of molybdenum-blue formation (λ_max = 780 nm) is proportional to the concentration of orthophosphate in the samples. The detection limit (3 × standard deviation of blank, n = 8) was 6 nM and the linear calibration ranged from 10 to 100 nM (r² = 0.997). The precisions of this method were 3.3% at 10 nM and 5.4% at 50 nM (n = 8), respectively. Similar to other molybdate based methods, silica and arsenate in the samples can interfere with phosphate determination. The responses of silicate and arsenate were about 25% and 7% of that of orthophosphate, respectively, and their interferences were enhanced in the presence of phosphate in the samples due to the synergistic effect of phosphate with arsenate or silicate on the molybdate reagent.     

Multi-pumping flow system for the determination of dissolved orthophosphate and dissolved organic phosphorus in wastewater samples

A multi-pumping flow system (MPFS) for the spectrophotometric determination of dissolved orthophosphate and dissolved organic phosphorus in wastewater samples is proposed. The determination of orthophosphate is based on the vanadomolybdate method. In-line ultraviolet photo-oxidation is employed to mineralise organic phosphorus to orthophosphate prior to detection. A solenoid valve allows the deviation of the flow towards the UV-lamp to carry out the determination of organic phosphorus.Calibration was found to be linear up to 20 mg P L⁻¹, with a detection limit (3s_b/S) of 0.08 mg P L⁻¹, an injection throughput of 75 injections h⁻¹ and a repeatability (R.S.D.) of 0.6% for the direct determination of orthophosphate. On the other hand, calibration graphs were linear up to 40 mg P L⁻¹, with a detection limit (3s_b/S) of 0.5 mg P L⁻¹, an injection throughput of 11 injections h⁻¹ and a repeatability (R.S.D.) inferior to 2.3% for the procedures involving UV photo-oxidation.     

Determination of orthophosphates using a macro segmented flow analyzer (MSFA) based on colorimetric detection

Fabrication of a macro segmented flow analysis (MSFA) system based on reconfiguration of the manifold by adjustment of the sample/reagent ratio, has been found to produce a sensitive method for orthophosphate analysis based on colorimetric detection at 880 nm. Optimization of sample tube length, reaction temperature and molybdate concentration in the carrier solutions has been carried out. The larger sample tube internal diameter led to the combined advantages of better sensitivities, wider working range and higher sample throughput over most existing methods. Using the optimized conditions of 50.0 cm sample tube length (1.6 mm i.d.), 37.0 °C reaction temperature and 0.0113 M molybdate concentration in the carrier solution, the calibration model for orthophosphate standard solutions was found to be linear (y = 0.04895x + 0.003561; correlation coefficient, r²=0.9970) over the working range 0.01-2.00 mg l⁻¹ orthophosphate. The volume of the sample injected was 1.396 ml at a flow rate of 6.0 ml min⁻¹. The sample throughput of this MSFA method was 40 samples per an hour, with a detection limit of 4.0 μg l⁻¹, and %R.S.D.’s below 5%. The MSFA method was successfully applied to analysis of water and wastewater samples.     

Pressure-induced zircon-type to scheelite-type phase transitions in YbPO4 and LuPO4

The tetragonal orthophosphates, YbPO₄ and LuPO₄, were studied by in situ X-ray diffraction (XRD) at pressures up to 52 and 43 GPa, respectively. A reversible phase transition from the zircon structure-type to the scheelite structure-type was found at ∼22 GPa for YbPO₄ and 19 GPa for LuPO₄. Coinciding with the transition from the zircon structure-type to the scheelite structure-type, there is a ∼10% reduction in volume and a significant increase in the bulk modulus for both compounds.     

Crystal structure of a new phosphate compound, Mg2KNa(PO4)2·14H2O

A new phosphate compound, Mg₂KNa(PO₄)₂·14H₂O, formed in the laboratory by cyanobacteria, has been identified and its crystal structure studied with single-crystal X-ray diffraction and infrared spectroscopy. The crystal is orthorhombic with the space group Pnma and unit-cell parameters a=25.1754(18) Å, b=6.9316(5) Å, c=11.2189(10) Å, V=1957.8(3) Å³. Its structure can be viewed as stacking of three types of layers along the a-axis in a sequence ABCBABCB…, where layer A is composed of Mg1(H₂O)₆ octahedra and Na(H₂O)₆ trigonal prisms, layer B of two crystallographically distinct PO₄³⁻ tetrahedra (designated as P1 and P2), and layer C of Mg2(H₂O)₆ octahedra and highly irregular K-polyhedra formed by five H₂O molecules and one O²⁻ from the P2 tetrahedron. The linkage between layers is principally achieved through hydrogen bonding, except for the K-O5 bond between layers B and C. The structure of Mg₂KNa(PO₄)₂·14H₂O has many features similar to those for the struvite analogs of MgK(PO₄)·6H₂O (Acta Crystallogr. B 35 (1979) 11) or MgNa(PO₄)·7H₂O (Acta Crystallogr. B 38 (1982) 40) and represents the first struvite-type phosphate compound that contains both K and Na as univalent cations.     

Flow injection analysis of ultratrace orthophosphate in seawater with solid-phase enrichment and luminol chemiluminescence detection

Solid-phase extraction technique had been applied to extract molybdophosphoric heteropoly acid (MoP) paired with cetyltrimethylammonium bromide (CTAB) from seawater matrix using C18 sorbent. Chemiluminescence emission could be generated via MoP reaction with alkaline luminol. Based on these, a novel on-line solid-phase extraction method coupled with flow injection (FI) analysis and luminol chemiluminescence detection had been established to determine ultratrace orthophosphate in seawater. The MoP-CTAB compound could be efficiently extracted on an in-line Sep-Pak C18 cartridge, and rapidly eluted by 0.3 mol l⁻¹ sulphuric acid-ethanol solution. Then the compound was reduced by luminol to produce chemiluminescence light, which could be detected using a luminescence analyzer. Experimental parameters were optimized using a univariate experimental design. Using artificial seawater with salinity of 35 as a matrix, the standard curve with a linear range between 0.005 and 0.194 μmol l⁻¹ had been obtained, and the recovery and the detection limit of the proposed method were found to be 92.5% and 0.002 μmol l⁻¹, respectively. The relative standard deviation (R.S.D.), which was determined over eight hour, was 4.66% (n = 7) for the artificial seawater at a concentration of 0.097 μmol l⁻¹ orthophosphate. Si of 200 μmol l⁻¹ would not interfere with the detection of 0.012 μmol l⁻¹ orthophosphate compound. Three typical seawater samples were analyzed using both the proposed method and the magnesium hydroxide-induced coprecipitation (MAGIC) method, and the results of the two methods showed no significant difference using the t test. Compared to the MAGIC method, the proposed method was more sensitive, time saving and easy for on-line analysis.