UV Photo-oxidation Research Articles

Measurement of dissolved total nitrogen in wastewater by UV photooxidation with peroxodisulphate

A simple, rapid procedure using mild conditions has been developed for total nitrogen determination in water samples (10–700 mg N l −1). Reduced forms of nitrogen are oxidised to nitrate by peroxodisulphate/far-UV photooxidation. The nitrate concentration is measured with UV spectrophotometry.

UV treatability test for chemical and petrochemical wastewater

There is a tendency to design biological units for chemical or petrochemical wastewater treatment. Some of these treatment plants are even sometimes used for the degradation of any external industrial sewage transported for the purpose. In this case, the decision to accept or refuse the waste must be rapid and sure. The aim of this paper is to propose a new treatability test based on a direct far UV photooxidation of the sample, coupled with a UV spectrophotometric survey of the waste quality. The test has been applied on different samples from chemical and petrochemical industries and the results have been compared to those obtained with more classical tests, as for example, biodegradation tests using either air or pure oxygen. For most of the samples, quite good correlation has been observed between the photooxidation test and biodegradation. The UV treatability test is currently used for checking up on petrochemical wastewater and chemical sewage.

Speciation of arsenic in mussels by the coupled system liquid chromatography—UV irradiation—hydride generation-inductively coupled plasma mass spectrometry

A method has been developed for the determination of seven arsenic species in mussel tissues by liquid chromatography—hydride generation—UV photo-oxidation and detection by inductively coupled plasma mass spectrometry. In order to determine the different species, two ion-exchange columns (anionic and cationic) were used with phosphate and nitric acid/ammonium nitrate as mobile phases, respectively. The optimisation of the conditions for separation, photo-oxidation and hydride generation is described. For each of these species, the limits of detection and repeatability are reported with the entire system coupling. This system was applied to the analysis of certified reference material (CRM 278) and mussels collected from Barcelona harbour. Extractions were achieved in methanol/water (1:1) using low-power focused microwaves as leaching process. As expected, arsenobetaine was the main compound extracted from both materials; the typical concentrations found were between 1 and 7 mg kg −1. Other organoarsenical compounds, probably arsenosugars, were extracted in a concentration range of 0.3–1.5 mg kg −1 in both cases. Amounts of dimethylarsinate (DMA) were found to be significant in the CRM 278, but very low in mussels from Barcelona harbour. The low limits of detection of the coupled system allow us to quantify low contents of other species (As(V), arsenocholine and monomethylarsonate (MMA)).

パイロットスケール紫外線反応装置によるトリクロロエチレンガスの分解処理

A pilot scale UV photooxidation system which involves a complete mixing flow type UV reactor connected in series with a multiple stage type UV reactor and a gas absorption tower filled with crashed marble has been fabricated to investigate a treatment for the trichloroethylene (TCE) gas extracted from contaminated soil. The photooxidation reaction rate in the complete mixing flow type reactor was increased with increasing the photo intensity in the reactor and was correlated with the laboratory scale experimental result. At the outlet of the multiple stage type reactor the TCE was decomposed less than 1 ppm, when the TCE concentrations at the inlet of the complete mixing flow type reactor were more than 100 ppm. The photooxidation products which exhibited acidity were found to be more effectively eliminated by the pilot scale absorption tower than by the laboratory scale tower.

UV treatability test for chemical and petrochemical wastewater

There is a tendency to design biological units for chemical or petrochemical wastewater treatment. Some of these treatment plants are even sometimes used for the degradation of any external industrial sewage transported for the purpose. In this case, the decision to accept or refuse the waste must be rapid and sure. The aim of this paper is to propose a new treatability test based on a direct far UV photooxidation of the sample, coupled with a UV spectrophotometric survey of the waste quality. The test has been applied on different samples from chemical and petrochemical industries and the results have been compared to those obtained with more classical tests, as for example, biodegradation tests using either air or pure oxygen. For most of the samples, quite good correlation has been observed between the photooxidation test and biodegradation. The UV treatability test is currently used for checking up on petrochemical wastewater and chemical sewage.

Preparation of Self-Assembled Monolayer (SAM) Modified Silver Substrates for Surface Enhanced Raman Scattering (SERS)

Abstract Self-assembled thiolate and sulfinate monolayers on smooth silver substrates were successfully characterized with SERS by applying for a selective etchant. The enhancement effect (EF) observed was comparable with those achieved by other techniques. The reusability of the resulted substrate was provided by UV photooxidation of the monolayer in air.

Organic nitrogen in precipitation at the mid-Atlantic U.S. Coast—methods evaluation and preliminary measurements

Recent studies have documented the importance of inorganic nitrogen deposited from the atmosphere to coastal waters. However, due to the limited number of field measurements and concerns about the reliability of measurement techniques, the aeolian flux of organic N is very uncertain. In this study we evaluate commonly employed collection and analytical techniques for dissolved organic nitrogen (DON) in precipitation, and provide preliminary estimates of organic-N wet fluxes at the mid-Atlantic U.S. Coast (Lewes, DE). Precipitation was sampled on a daily basis using an automated wet-only collector. Compared with UV photo-oxidation, persulfate wet chemical oxidation was more efficient at converting organic-N compounds to NO - 3. Side-by-side comparisons of white polyethylene buckets (typically employed in “acid rain” studies) with stainless steel buckets suggest that DON is lost in varying amounts to the plastic surfaces. Stability tests reveal that organic-N in precipitation can be quite labile under field conditions, with significant losses observed within a few hours in some samples. Based on analysis of 37 events collected from October 1993 through December 1994, the volume-weighted average concentration of DON in precipitation at the mid-Atlantic coast is ≥9.1 μmol ℓ -1. On an annual basis, organic-N comprises at least 20% of the total dissolved nitrogen in precipitation; on an event basis, it comprises as much as 64%. From the perspective of coastal ecosystem eutrophication, the atmospheric loading of DON would appear to represent an important exogenous source of N to local coastal waters such as the Delaware and Chesapeake Bays.

Ozonolysis Is the Primary Cause of UV Photooxidation of Alkanethiolate Monolayers at Low Irradiance

Ozonolysis Is the Primary Cause of UV Photooxidation of Alkanethiolate Monolayers at Low Irradiance

Speciation determination of arsenic in urine by high-performance liquid chromatography-hydride generation atomic absorption spectrometry with on-line ultraviolet photooxidation.

A coupled system for arsenic speciation determination based on high-performance liquid chromatography (HPLC), on-line UV photooxidation and continuous-flow hydride generation atomic absorption spectrometry (HGAAS) was built from commercially available modules with minor modifications to the electronic interface, the software and the gas-liquid separator. The best results were obtained with strong anion-exchange columns, Hamilton PRP X-100 and Supelcosil SAX 1, and gradient elution with phosphate buffers containing KH2PO4-K2HPO4. The on-line UV photooxidation with alkaline peroxodisulfate, 4% m/v K2S2O8-1 mol l-1 NaOH, in a PTFE knotted reactor for 93 s ensures the transformation of inorganic AsIII, monomethylarsonate, dimethylarsinate, arsenobetaine, arsenocholine, trimethylarsine oxide and tetramethylarsonium ion to arsenate. About 32-36 HPLC-UV-HGAAS runs could be performed within 8 h, with limits of detection between 2 and 6 micrograms l-1 As, depending on the species. The method was applied to the analysis of spot urine samples and certified urine reference materials (CRMs). Upon storage at 4 degrees C, reconstituted CRMs are stable for at least 2 weeks with respect to both their total arsenic content and the individual species distribution.

Temporal variability in dissolved phosphorus concentrations in the subtropical North Pacific Ocean

Dissolved phosphorus pool measurements were made on approximately monthly intervals during the period October 1988-November 1994 at an oligotrophic, deep-ocean station near Hawaii (Station ALOHA; 22 °45′N, 158 °W). Data include depth profiles (0–200 m) of soluble reactive phosphorus (SRP), measured by two independent techniques (a high-sensitivity, magnesium-induced coprecipitation (MAGIC) method, and standard autoanalysis procedure), and total dissolved phosphorus (TDP) based on UV photo-oxidation treatment followed by automated SRP analysis. Considerable variability in SRP was observed both with depth and with time over the 6-yr period. Upper water column (0–100 m) SRP concentrations varied in time from > 150 to 60 nM, respectively. Throughout the entire 6-yr observation period, the upper water column (0–100 m) inventory of SRP displayed a systematic decrease from ∼ 10 to ∼ 5 mmol m−2 P, a result that is consistent with the hypothesized role of N2 fixation and P control of new and export production at Station ALOHA. Three independent, but not mutually exclusive, models are presented to explain these time-varying SRP concentrations: (1) convective mixing; (2) atmospheric deposition; and (3) upward P flux. The upward P flux model including both passive (upward particle flux) and active (biological transport) processes, is the most consistent model for the available data set.

Pattern Formation Using Metal Silver Staining on Cellulosic Substrate by Patterned Ultraviolet Light Irradiation.

A simple image formation on cellulosic substrate with using a combination of patterned UV photooxidation reaction on cellulosic substrate and metal silver deposition reaction on the oxidized cellulose substrate has been studied. The color depth of the silver deposit on the substrate increased with increasing the integrated energy of UV irradiation. Assuming that the color depth of the deposit is proportional to the amount of aldehydes formed on the substrate, the photooxidation reaction of hydroxyl group on the cellulose substrate to aldehydes found to apparently follow the first order reaction kinetics.

Influence of Adsorbate Ordering on Rates of UV Photooxidation of Self-Assembled Monolayers

The photooxidation of a range of methyl terminated straight chain alkylthiol (CH3(CH2)n-1SH) self-assembled monolayers (SAMs) on Au has been investigated using X-ray photoelectron spectroscopy (XPS...

Production of dissolved organic carbon in phyloplankton cultures as measured by high-temperature catalytic oxidation and ultraviolet photo-oxidation methods

The production of dissolved organic carbon (DOC) in cultures of the diatoms Chaetoceros gracilis and Phaeodactylum tricornutum, the flagellate Isochrysis galbana, the dinoflagellate Alexandrium tamarense and a natural algal assemblage from the Northwest Arm, Halifax, Nova Scotia, Canada, was followed using a high-temperature catalytic oxidation (HTCO) and a UV photo-oxidation method. Molecular weight fractionation of the DOC was performed for two cultures: C.gracilis and I.galbana. While the DOC in the culture medium increased significantly during log-phase growth for all organisms except the dinoflagellate, this increase was proportional to the increase in cell numbers; the increase in DOC per cell was either small or zero. In all cultures, maximum release took place during stationary and senescent phases, usually after cell numbers had started to decrease. In both C.gracilis and I.galbana, a major portion (>65%) of the organic matter released to the medium during log-phase growth had mol. wts of <10 000 Da. The increase in DOC in the I.galbana culture in stationary and senescent phases was due to the release of high-molecular-weight materials. The differences in extracellular release of DOC between species and between different growth stages in the same species suggest that both the species composition and physiological state of phytoplankton populations must be known before interpretations and predictions based on field data can be made. In order to determine whether the differences in DOC values found by the HTCO and UV oxidation methods are caused by the resistance to UV oxidation of some compounds produced by phytoplankton, rather than by less than optimum efficiency of the UV unit used, standards must be based on naturally occurring compounds, rather than the pure compounds normally used.

Arsenic speciation in serum of uraemic patients based on liquid chromatography with hydride generation atomic absorption spectrometry and on-line UV photo-oxidation digestion

An on-line method was developed for the speciation of arsenic species in human serum, including monomethylarsonic acid (MMA), dimethylarsinic acid (DMA), arsenobetaine (AsB) and arsenocholine (AsC). The method is based on cation-exchange liquid chromatography (LC) separation, UV-photo-oxidation for sample digestion and continuous hydride generation (HG) atomic absorption spectrometry (AAS) for the measurement of arsenic in the LC eluent. By developing the technique of argon segmented flow in the post-column eluent, an substantial improvement in Chromatographic resolution for the separation of these four arsenic species was obtained. The LC separation, photo-oxidation, hydride generation and AAS measurement could be completed on-line within 10 min. The detection limits were 1.0, 1.3, 1.5 and 1.4 μg/l of arsenic for MMA, DMA, AsB and AsC, in serum respectively. The concentration of the 4 species was determined in serum samples of patients with chronic renal insufficiency. Only AsB and DMA were significantly detected by the present method. The main part of arsenic in human serum is AsB. No MMA, AsC and inorganic arsenic were detected in these 6 samples.

Application of the taguchi experimental design to the optimisation of a photo-oxidation procedure for trace metal analysis in freshwater

A UV photo-oxidation device was constructed for the destruction of dissolved organic matter (DOM) in freshwater samples in order to determine traces of zinc, cadmium, lead and copper bound to DOM as inert species, by anodic stripping voltammetry in the differential pulse mode (DPASV). The photodigestor performance was optimised by means of the Taguchi experimental design. Four control factors (or design parameters) at three levels were explored: exposure-time to the UV-irradiation, pH of the sample, hydrogen peroxide concentration and mineral acid added, and assigned to the columns of a L9(34) saturated orthogonal array. A noise factor (nitrilotriacetic acid concentration) at three levels was introduced in the experiment to simulate the uncontrollable amount of DOM in water samples. The experiment was conducted with two replications of each trial and an optimum response insensitive to the variations of DOM concentration was found when samples, acidified at pH 2 with sulphuric acid, were irradiated for 30 min in the presence of 12.3 mmol/L hydrogen peroxide. The proposed procedure is more precise, accurate and fast than the wet digestion method.

Determination of arsenic speciation by liquid chromatography—hydride generation inductively coupled plasma atomic emission spectrometry with on-line UV photooxidation

The determination is described of the six arsenic species arsenite, arsenate, monomethylarsonate (MMA), dimethylarsinate (DMA), arsenobetaine and arsenocholine by hydride generation inductively coupled plasma atomic emission spectrometry after liquid chromatographic separation and on-line photooxidation. An anion-exchange polymer-based column is used for separation. The details of the photoreactor designed to transform arsenobetaine and arsenocholine into simpler species that can be reduced are presented. The reducing conditions to obtain the arsine from arsenate (as the final product of the photooxidation process) are optimized. The overall assembly is presented and using the optimized operating condition the quality parameters (detection limits, precision and accuracy) for all the arsenic species are reported. These parameters for arsenic, arsenate, MMA and DMA are compared with those obtained without photooxidation. The introduction of a new step on-line in the coupling does not produce any loss of quality of information or a significant increase in analysis time.

A high-temperature catalytic oxidation method for the determination of marine dissolved organic carbon and its comparison with the UV photo-oxidation method

A modified high-temperature catalytic oxidation (HTCO) method for marine dissolved organic carbon (DOC) measurement is described. The method has a high oxidation efficiency and a precision of 1–2%. It is robust and relatively easy to perform, and hence can be used for routine analyses. Components of the system blank are determined by the use of deionized water treated by high-temperature catalysed oxidation, and the results are checked by an experiment using 14C. Extensive comparisons between this method and UV photo-oxidation are presented. The HTCO method consistently yields 5–60% more DOC than the UV method, with most results in the range of 10–40%. No simple explanation has been found for the differences between the two methods, as a result of the complex nature of DOC in seawater.

Photooxidation of thiols in self-assembled monolayers on gold

The authors report here on the UV photooxidation of self-assembled monolayers (SAMs) of alkanethiols in air. Efficient photooxidation to form the alkanesulfonate (RSO[sub 3][sup [minus]]) is observed for a variety of straight chain alkanethiols as well as thiophenols. As the result of such studies, details of the structure and chemical properties of SAMs have been revealed. Methods for the controlled chemical modification of SAMs are of great interest, particularly if there is potential for spatial resolution of the chemical modification, as would be the case for an optically induced modification. In previous work the authors have shown that laser-induced desorption coupled with Fourier transform mass spectrometry (LID-FTMS) is a sensitive molecular probe of alkanethiol SAMs. The LID-FTMS technique has allowed them to directly determine the molecular identity of the photooxidation product in these experiments. 18 refs., 2 figs.

How the nature of dissolved organic matter might affect the analysis of dissolved organic carbon

A discrepancy exists between the low concentrations of dissolved organic carbon (DOC) in seawater measured by ‘standard’ techniques, such as wet-chemical oxidation, UV photo-oxidation, and dry high-temperature combustion, and the relatively high concentrations measured using new catalyzed, high-temperature combustion methods. One of the factors that could help explain this discrepancy is the nature of the DOC being analyzed. Because little is known about the structure of the bulk of DOC, here we will discuss DOC sources, how sources could affect structure, and how structure as well as chemical factors and sampling procedures might affect analysis of DOC. One likely reason for the discrepancy between the standard and new methods is the presence of a fraction of DOC not previously measured by the standard techniques. This ‘new’ DOC could consist of refractory, large, highly cross-linked macromolecular organic material, possibly colloidal in nature. Material that incorporates sulfur or specific organic structures which inhibit wet-chemical oxidation or photo-oxidation could also be present. Other possible materials present that might explain the discrepancy are those that are prone to incomplete oxidation because they form unreactive compounds during standard oxidation procedures.

Photochemistry of some organosulfur pesticides

Studies on two dithiocarbamates showed that they undergo UV photolysis and photo- oxidation and visible light photosensitized oxidation. A variety of products were identified including hydrogen sulfide, sulfur, sulfur dioxide, sulfate ion, carbon disulfide, amines, hydrazines, thioamides and thioureas. Reaction schemes involving radical intermediates, derived from CS, SS and SH bond cleavages, are suggested. Three commercial fungicides, Captan, Captafol and Folpet were also found to undergo UV photolysis and photo-oxidation and visible light photosensitized oxidation. Products were: imides, sulfur, sulfur dioxide; carbon dioxide, hydrogen chloride. Common mechanisms of photochemical change are discussed for these fungicides.