Analysis of p-chlorobenzoic acid in water by liquid chromatography-tandem mass spectrometry

para-Chlorobenzoic acid (p-CBA) is typically used as a probe compound to indirectly quantify hydroxyl radicals formed during advanced oxidation processes used in drinking water and wastewater treatment. A method has been developed for the sensitive analysis of p-CBA in water using liquid chromatography-tandem mass spectrometry (LC-MS/MS). A reporting limit in water of 100 ng/L was determined for the method, which is 40-fold lower than the 4.0 microg/L reporting limit of the widely used liquid chromatography with UV detection (LC-UV) method. The method was found to be robust in difficult matrices such as wastewater and highly selective, unlike LC-UV which relies on non-specific detection at 234 nm. The detection of p-CBA below 1 microg/L during bench-scale ozonation of wastewater after hydrogen peroxide addition was demonstrated. Duplicate samples were analyzed by LC-MS/MS and LC-UV and results were found to be comparable at concentrations quantifiable by both methods.     

Development of novel reagent for Hantzsch reaction for the determination of formaldehyde by spectrophotometry and fluorometry.

A novel reagent, acetoacetanilide (AAA), was introduced to the determination of formaldehyde based on Hantzsch reaction. A simple and highly sensitive fluorometric method was achieved by using AAA. The main advantages in the use of this reagent are: the reaction is carried out at room temperature without any heating system, the cyclization product based on Hantzsch reaction is soluble in water, and the product can be detected by spectrophotometry and fluorometry. The maximum absorption wavelength of the product occurs at 368 nm, and the maximum excitation and emission wavelengths are found at 370 and 470 nm, respectively. Several important experimental variables of the procedures were examined; particularly, the reaction temperature, reaction time, concentrations of reagents, and pH of the reagent solution were optimized for improving the detecting sensitivity. The calibration graph was linear in the range of 1 x 10(-7) - 1 x 10(-6) M or much higher concentrations. The limit of detection (LOD), based on three times of the standard deviation of the reagent blank, was 2.0 x 10(-8) M. The proposed method was applied to the determination of formaldehyde in environmental water samples. Many foreign species commonly existing in water samples did not interfere with the determination of formaldehyde in the proposed method.     

Quantitative Analysis of Formaldehyde Using UV‐VIS Spectrophotometer Pattern Recognition and Artificial Neural Networks

Abstract

This study is focused on the quantitative analysis of formaldehyde in aqueous solution using a Fluoral‐P reagent and describes the characterization of the reaction, including the effect of reagent concentrations, pH, response time, dynamic range, reproducibility, photostability, and selectivity by using an ultraviolet‐visible (UV‐VIS) spectrophotometer. The relative standard deviation value was 1.79 to 2.12%. The dynamic range of the complex gives a linear stimulation of 0.00 to 3.60 ppm for the concentration of formaldehyde. The reproducibility of this study is high, with 1.79 and 2.12% for 20 and 40 ppm of formaldehyde, respectively. The interference from acetaldehyde (formaldehyde: acetaldehyde=1:100) was lower than 2.10%. In addition, the application of artificial neural networks to quantitative analysis for formaldehyde has also been done in this study to optimize the dynamic range of formaldehyde involved in the formation of Fluoral‐P–formaldehyde complex. A three‐layer feed‐forward network and the back propagation algorithm‐operated training process were used in this study. For quantitative analysis of formaldehyde, artificial neural networks, networking with 23 hidden neurons and 40,000 cycle numbers with 0.001% learning rate, produce the best training results, with sum‐squared error value 0.5847.     

Determination of metal complexes of ethylenediaminetetraacetate in the presence of organic matter by high-performance liquid chromatography

A high-performance liquid chromatography method is described here for the determination of the Cd(II), Co(II), Cu(II), Pb(II), and Zn(II) complexes of ethylenediaminetetraacetate (EDTA) in municipal wastewaters and surface waters. The method involves separation by ion-exchange chromatography on a reversed-phase C18 column coated with ion-pair reagent, followed by post-column conversion to FeEDTA and subsequent detection by UV absorbance. Although Co(II) and Cu(II) coelute, they can be quantified by analyzing absorbance by CuEDTA2- prior to post-column conversion. The method detection limit of 6-8 x 10(-8) M (5-7 ng) is an order of magnitude improvement over previous UV absorbance post-column reaction methods. The technique can be used in the presence of organic matter encountered in matrices such as untreated wastewater without pre-concentration or sample cleanup.     

Chromatographic and luminescence properties of a 7-aminocoumarin derivative with peroxyoxalate chemiexcitation

A new derivatizing reagent for amines, luminarine 1, is described, and tested as its pentylamine derivative. Chromatographic separation in both normal- and reversed-phase systems was achieved. With fluorescence detection, the limit of detection was in the subpicomole range. With the optimization procedure for chemiluminescence detection, the limit of detection was 1 fmol in the normal-phase system (using bis (2,4-dinitrophenyl) oxalate and hydrogen peroxide), and 6 fmol in the reversed-phase system (using bis (2,4,6-trichlorophenyl) oxalate and hydrogen peroxide ), but the coefficient of variation was lower for the latter system (3.4% vs. 5.8%).     

Characterization of a titanium(IV)–porphyrin complex as a highly sensitive and selective reagent for the determination of hydrogen peroxide: a computational chemistry approach and a critical review

The Ti–TPyP reagent, i.e. an acidic aqueous solution of the oxo[5,10,15,20-tetra(4-pyridyl)porphyrinato] titanium(IV) complex, TiO(tpyp), was developed as a highly sensitive and selective spectrophotometric reagent for determination of traces of hydrogen peroxide. Using this reagent, determination of hydrogen peroxide was performed by flow-injection analysis with a detection limit of 0.5 pmol per test. The method was actually applied to determination of several constituents of foods, human blood, and urine mediated by appropriate oxidase enzymes. The reaction specificity of the TiO(tpyp) complex for hydrogen peroxide was clarified from the viewpoint of the reaction mechanisms and molecular orbitals based on ab initio calculations. The results provided a well-grounded argument for determination of hydrogen peroxide using the Ti–TPyP reagent experimentally. This review deals with characterization of the high sensitivity and reaction specificity of the Ti–TPyP reagent for determination of hydrogen peroxide, to prove its reliability in analytical applications. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Determination of artemisinin in human serum by high-performance liquid chromatography with on-line UV irradiation and peroxyoxalate chemiluminescence detection

Artemisinin is an antimalarial drug containing an internal endoperoxide linkage in its structure. A simple, selective and sensitive high-performance liquid chromatography (HPLC)-peroxyoxalate chemiluminescence (PO-CL) method for the determination of artemisinin was developed. This method is based on the fact that endoperoxide in artemisinin structure can be converted to hydrogen peroxide (H(2)O(2)) under ultraviolet (UV) irradiation and the generated hydrogen peroxide can be measured using PO-CL detection. The HPLC-PO-CL system was optimized on a mobile phase, post column chemiluminescence reagent, UV source and irradiation time. In addition, the system was combined with simple liquid-liquid extraction using n-hexane that allowed selective and sensitive determination of artemisinin in serum. The limit of detection using 0.5 mL of blood was 0.062 micromol/L (17.5 ng/mL) at a signal-to-noise ratio of 3. Calibration curve obtained for artemisinin in human serum 4-80 micromol/L (1.1-22.6 microg/mL) showed a good linearity (r = 0.999).     

Reaction specificity of a titanium(IV)-porphyrin complex to hydrogen peroxide in view of an Ab initio study.

A Ti-TPyP reagent, i.e. an acidic aqueous solution of oxo[5,10,15,20-tetra(4-pyridyl)porphyrinato]titanium(IV) complex, TiO(tpyp), was previously developed as a highly sensitive and specific reagent for determining hydrogen peroxide. In the present work, the reaction specificity of the TiO(tpyp) complex to hydrogen peroxide was clarified based on ab initio calculations. The results provide a well-grounded argument for determining hydrogen peroxide using the Ti-TPyP reagent experimentally.     

Highly sensitive and selective catalytic determination of formaldehyde and acetaldehyde

A highly sensitive, simple and selective kinetic method was developed for the determination of ultra-trace levels of formaldehyde and acetaldehyde based on their catalytic effect on the oxidation of N,N-diethyl-p-phenylenediamine (DPD) with hydrogen peroxide. The reaction was monitored spectrophotometrically by tracing the formation of the red-colored oxidized product of DPD at 510nm, within 30s of mixing the reagents. The optimum reaction conditions were: 20mmolL(-1) DPD, 250mmolL(-1) H(2)O(2), 150mmolL(-1) phosphate, 150mmolL(-1) citrate and pH 6.60+/-0.05 at 25 degrees C. Following the recommended procedure, formaldehyde and acetaldehyde could be determined with linear calibration graphs up to 0.50 and 1.4microg mL(-1) and detection limits, based on the 3S(b)-criterion, of 0.015 and 0.035microg mL(-1), respectively. In addition, analytical data for other 10 aldehydes were also presented. The high sensitivity and selectivity of the proposed method allowed its successful application to rain water, mainstream smoke (MSS) and disposed tips of smoked cigarettes (DTSC). A sample aliquot was directly analyzed for its total water-soluble aldehyde content. A second sample aliquot was heated at 80 degrees C for 10min to expel acetaldehyde and the aliquot was analyzed for its content of other water-soluble aldehydes (expressed as formaldehyde equivalent), and acetaldehyde was determined by difference. The analytical results were in excellent agreements with those obtained following the standard HPLC method based on pre-column derivatization with 2,4-dinitrophenylhydrazine. Moreover, published catalytic-spectrophotometric methods for the determination of aldehydes were reviewed.     

Trace determination of beta-lactam antibiotics in surface water and urban wastewater using liquid chromatography combined with electrospray tandem mass spectrometry

A sensitive and reliable method using liquid chromatography-electrospray tandem mass spectrometry has been developed and validated for the trace determination of beta-lactam antibiotics in natural and wastewater matrices. Water samples were enriched by solid-phase extraction. The analytes included amoxicillin (AMOX), ampicillin (AMP), oxacillin (OXA), cloxacillin (CLOX) and cephapirin (CEP). Average recoveries of beta-lactams (BLs) in fortified samples were generally above 75% (except amoxicillin) with the standard deviations lower than 10% in water matrices. Amoxicillin was not quantified due to poor recovery (less than 40%) in the investigated water matrices. Matrix effects were found to be minimal when measuring these compounds in water matrices. The accuracy, within- and between-run precision of the assay fell within acceptable ranges of 15% absolute. The method detection limit (MDL) was estimated to range between 8 and 10 ng/L in surface water, 13 and 18 ng/L in the influent and 8 and 15 ng/L in the effluent from a wastewater treatment plant. A large number of actual water samples were analyzed using this method in order to evaluate the occurrence of the beta-lactams in a river and a wastewater treatment plant in northern Colorado. Most of the samples were negative for all analytes. These compounds were found at 15-17 ng/L in the three influent samples and at 9-11 ng/L in three surface water samples out of a total of 200 samples. This indicates that contamination by beta-lactam antibiotics is of minor importance to the small mixed-watershed.     

Skeletal rearrangements on chemical ionization of dibenzyl ether and derivatives

Protonated molecular ions of dibenzyl ether, formed by chemical ionization using hydrogen and isobutane as reagent gases, undergo skeletal rearrangements to lose water and formaldehyde, both in the ion source and the flight path. The rearrangements have been elucidated by deuterium labelling and chemical substitution. The water lost contains the reagent proton and an aromatic hydrogen atom, and the aromatic hydrogen atoms have been shown to be mobile prior to the reaction. It is proposed that the skeletal rearrangement for water loss is initiated by protonation on the ether oxygen atom, followed by benzyl migration. The formaldehyde lost contains benzylic hydrogen atoms exclusively, and it is proposed that the skeletal rearrangement is preceded by hydrogen rearrangement of an oxygen protonated molecular ion to a ring protonated molecular ion. Daughter ion structures are supported by comparisons of their collision induced dissociation spectra with those of isomeric ions prepared by alternative routes.     

Determination of iron(II) and total iron in environmental water samples by flow injection analysis with column preconcentration of chelating resin functionalized with N-hydroxyethylethylenediamine ligands and chemiluminescence detection

A flow injection analysis (FIA) technique for the determination of Fe(II) and total-Fe in environmental water samples has been developed with a high sensitivity. The resin used for preconcentration of iron was the macroporous resin, Amberlite XAD-4 functionalized by N-hydroxyethylethylenediamine (HEED) groups. The technique employed was FIA by combination of on-line chelate resin preconcentration and chemiluminescence detection (CL), using brilliant sulfoflavine and hydrogen peroxide reagent solutions. The interference by coexisting Fe(III) could be eliminated by addition of 1×10⁻⁶ mol of deferrioxamine B solution. The detection limits of Fe(II) and total-Fe were 0.80 and 0.36 nmol l⁻¹ for 5.6-ml seawater samples with a concentration of 2 nmol l⁻¹. The relative standard deviations for both samples were less than ±4%. A typical analysis for Fe(II) can be performed in 7.5 min. The technique was ascertained by comparing the analytical value of total-Fe with the certified value of Fe in the reference standard seawater CASS-3.     

An EPR study on wastewater disinfection by peracetic acid,hydrogen peroxide and UV irradiation

EPR spectroscopy was applied to obtain qualitative and quantitative information on the radicals produced in disinfection processes of wastewater for agricultural reuse. The DEPMPO spin trap was employed to detect hydroxyl and carbon-centered short living radicals in two different peracetic acid solutions and a hydrogen peroxide solution used for water disinfection either in the absence or in the presence of UV-C irradiation. Moreover, three different kinds of water (wastewater, demineralized water, distilled water) were analysed in order to assess the contribution of Fenton reactions to the radical production. The spectroscopic results were discussed in relation to the efficiency of the different oxidizing agents and UV irradiation in wastewater disinfection evaluated as Escherichia Coli, Faecal and Total Coliforms inactivation.     

基于巯基化衍生的气相色谱-质谱法测定有机相及水相中氯化氰

氯化氰(ClCN)是常用的化工中间体,也是《禁止化学武器公约》附表颁布的化学毒剂之一.采用传统的比色法或气相色谱法对ClCN进行分析时,稳定性差且检出限高.研究建立了有机相及水相中ClCN的巯基化衍生过程及气相色谱-质谱(GC-MS)的检测方法.经比较后选择1-丁基硫醇作为衍生试剂,有机相中ClCN的衍生条件为衍生温度...     

二氧化硒催化过氧化氢氧化萘丙醛制萘丙酸的研究

萘丙酸((±)-2-(6-甲氧基-2-萘基)-丙酸)的右旋体有解热镇痛特效,国内生产中由萘丙醛氧化成酸系采用多伦试剂,耗费大量硝酸银。我们采用过氧化氢作氧化剂,结果表明,制得的产品纯度高,而且成本低。     

Intermediate free radicals in the oxidation of wastewaters

The cleaning action on wastewater as obtained through oxidation methods has been investigated by means of EPR spectroscopy to achieve qualitative and quantitative information on the radicals produced upon utilising peracetic acid and hydrogen peroxide with and without UV irradiation. The DEPMPO spin trap was employed to detect hydroxyl and carbon-centred short living radicals during water disinfection, either in the absence or in the presence of UV-C irradiation. Moreover, three different kinds of water (wastewater, demineralized water, distilled water) were analysed in order to assess the contribution of Fenton reactions to the radical production. The spectroscopic results are discussed in relation to the efficiency of the different oxidising agents and UV irradiation in wastewater disinfection evaluated as Escherichia coli, faecal and total coliforms inactivation.     

Determination of H2O2 and organic peroxides by high-performance liquid chromatography with post-column UV irradiation, derivatization and fluorescence detection

A method for the determination of hydrogen peroxide and several organic peroxides by high-performance liquid chromatography with post-column UV irradiation, derivatization and fluorescence detection is described. By means of post-column UV irradiation in the presence of water organic peroxides are converted into hydrogen peroxide and organic hydroperoxides, which react rapidly with the post-column derivatization agent p-hydroxyphenylacetic acid (PHPAA) under catalysis of horseradish peroxidase to yield the fluorescent PHPAA dimer that is detected at excitation and emission wavelengths of 285 and 400 nm, respectively. The detection limit for hydrogen peroxide is 14 ng/mL, for organic peroxides between 34 ng/mL and 5 μg/mL. No interference by other compounds was observed when their concentrations were below 10 mg/mL except ethers and phenols. Received: 6 August 1997 / Revised: 11 December 1997 / Accepted: 15 December 1997     

Solid‐phase Extraction Coupled Simple On‐line Derivatization Gas Chromatography – Tandem Mass Spectrometry for the Determination of Benzophenone‐type UV Filters in Aqueous Samples

The rapid determination of three benzophenone‐type UV filters: 2‐hydroxy‐4‐methoxy‐benzophenone (BP‐3), 2,4‐dihydroxybenzophenone (BP‐1) and 2,2′‐dihydroxy‐4‐methoxy‐benzophenone (BP‐8), in aqueous samples is described. The method involved the extraction of an aqueous sample using an Oasis HLB solid‐phase extraction (SPE) cartridge, followed by on‐line derivatization gas chromatography ‐ tandem mass spectrometry (GC‐MS/MS) with a trimethylsilylating (TMS) reagent. This eco‐friendly, injection‐port derivatization method, is sensitive, rapid, and provides reproducible results for these hydroxylated benzophenones in aqueous samples. The limits of quantitation (LOQs) were determined to be 1.0 to 2.5 ng/L for samples in 100 mL of water. The precision for these analytes, as indicated by relative standard deviations (RSDs), proved to be less than 11% for both intra‐ and inter‐day analysis. Accuracy, expressed as the mean extraction yield, was between 80 and 106%. The method was then applied to some environmental water samples, river water and samples of effluents from a wastewater treatment plant (WWTP), having the potential to contain BP‐3 and BP‐1.     

Rapid determination of hydrogen peroxide in whitening patches for teeth using a new portable near-infrared spectrometer

A nondestructive determination method of hydrogen peroxide in whitening patches for teeth was developed by using a new portable near-infrared (NIR) spectrometer. Development of the portable NIR spectrometer was based on microchip technologies with photodiode arrays. By using the portable NIR spectrometer, the new determination method is very rapid; it requires less than 1 s. The conventional method for the determination of hydrogen peroxide, redox titration, requires about 2 h of analysis, including the sample extraction time from a sample matrix. The conventional method also uses hazardous and harmful solvents and, furthermore, its samples cannot be used after titration. To find the peak due to the O–H bond vibration of hydrogen peroxide under the existence of water which shows huge absorption O–H absorption around 1450 nm, the NIR spectra of a hydrogen peroxide aqueous solution were investigated. A clear variation of absorption based on the concentration of the hydrogen peroxide due to the O–H bond vibration was found in the standard deviation plot around 1400 nm. In this study, two kinds of whitening patch products, A and B, were used for samples. A partial least squares (PLS) regression was used for calibration and validation in the 1100 to 1720 nm spectral range. For validation results, the standard error of prediction (SEP) was 0.38% for Patch A and 0.37% for Patch B. This study shows the feasibility of using the portable NIR spectrometer with photodiode arrays for the rapid and safe determination of hydrogen peroxide in whitening patches.     

HPLC Determination of Hepatic Cholesterol 7α-Hydroxylase Activity Using Immobilized Cholesterol Oxidase and Chemiluminescence Detection

Abstract

This paper describes an HPLC method for the determination of cholesterol 7α-hydroxylase activity, at high or low activity levels, that is sensitive and specific for 7α-hydroxycholesterol. The method relies on the generation of hydrogen peroxide by oxidation of 7α-hydroxycholesterol using the enzyme cholesterol oxidase which has been immobilized on porous glass beads. The hydrogen peroxide is subsequently detected by chemiluminescence generated by reaction of peroxide with bis-(2, 4, 6-trichlorophenyl)-oxalate (TCPO), a commonly used chemiluminescence reagent specific for peroxides. In the procedure, sample preparation is limited to extraction of the incubation mixture and injection of the concentrated extract.