Development and field evaluation of a new diffusive sampler for Hydrogen Sulphide in the ambient air

A diffusive sampler for the determination of hydrogen sulphide (H₂S) based on collection on a paper filter coated with silver nitrate followed by optical densitometric determination of the metal sulphide was developed. Laboratory tests were conducted in controlled atmosphere to evaluate linearity, uptake rate, face velocity effects, sample stability, influence of relative humidity and of interferents, precision and accuracy. The measured uptake rate for H₂S was determined in experiments involving sampling at different concentration levels in comparison to a wet standard colorimetric technique. The precision of the measurements for co-located passive samplers was lower than 15%. The accuracy of the data collected is within 20% of the actual value measured by the wet method. The sampler is capable of reliable measurements of H₂S at common levels of a polluted atmosphere in urban settings yielding average concentration levels over one month and beyond. Diffusive sampling can be adopted to analyse in detail the temporal and spatial trends of H₂S concentration in ambient air and in specific historic buildings or in museums. Figure At the end of sampling cap #2 is removed and optical density is measured     

Development of a Passive Sampler for Long-Term Measurements of Formaldehyde and Total Oxidants in Air

A diffusive sampling device is described that is capable of reliable measurements of formaldehyde and total oxidants (Ox = ozone + nitrogen dioxide) at sub-ppbv concentration levels in ambient air. These species are collected on silica gel particles coated with 1-methyl-1-(2,4-dinitrophenyl)hydrazine (MDNPH) and phosphoric acid. The formaldehyde hydrazone (HCHO-MDNPh) and the N-methyl-2,4-dinitroaniline (MDNA) formed are extracted with acetonitrile and determined by HPLC with UV detection at 365ánm. The measured sampling rate for HCHO, 15.0 mLmin^-1, agrees well with the theoretical value of 16.0, whilst an experimental sampling rate of 10.7 mLmin^-1 (25% lower than the calculated one) is observed for Ox. The sampling rates seem to be independent of the sampling duration up to one month. The precision of the measurements for co-located passive samplers averaged is 7.3% for HCHO and 7.2% for Ox in urban air.     

Evaluation of a diffusive sampling method for the determination of atmospheric ammonia

A diffusive sampling method is presented for the determination of atmospheric levels of ammonia based on the collection of ammonia at the phosphoric acid coated bottom of small glass vials and subsequent flow injection analysis of the trapped ammonium. In order to avoid effects of varying wind velocities on the sampling rate, the tube-type samplers are covered with a hydrophobic microporous membrane. The experimentally obtained uptake rate of the diffusive samplers (i.e. 7.8 ml min^–1) is in excellent agreement with the theory. The analytical characteristics of the method with respect to sensitivity, selectivity, dynamic range, precision and practicability are evaluated in detail. As the detectability of the proposed method is related to both the mass collected during exposure and the mass sensitivity of the detection step, the role of microanalytical procedures in general, and significance of meticulous control of contamination in particular are discussed. Under optimum conditions the gas-phase detection limit achievable (in terms of time independent exposure dose value) is about 2.3×10³ g m^–3 s^–1, which permits measurements at low g m^–3-levels with a time resolution of a few hours. Application of the method to indoor and outdoor measurements proved its suitability for routine purposes.Dedicated to Professor Dr. Dieter Klockow on the occasion of his 60th birthday     

N-bromosuccinimide-fluorescein based sensitive flow-injection chemiluminescence determination of phenformin.

A novel and highly sensitive method for the determination of phenformin over the range of 6 x 10(-9) - 1 x 10(-5) g ml(-1) in pharmaceutical formulations with flow-injection chemiluminescence (CL) detection is proposed. The method is based on the CL produced during the oxidation of N-bromosuccinimide (NBS) in an alkaline medium in the presence of fluorescein as an effective energy transfer agent. The use of cetyltrimethylammonium bromide (CTAB) as a sensitizer enhances the signal magnitude by about 100 times. The detection limit is 2 x 10(-9) g ml(-1) (3sigma) with a relative standard deviation of 2.3% (n = 11) at 1 x 10(-7) g ml(-1) phenformin. Ninety samples can be determined per hour. The method was evaluated by carrying out a recovery study and by the analysis of commercial formulations. The obtained results compared well with those by an official method, and demonstrated good accuracy and precision. The possible CL mechanism of the proposed system was also briefly analyzed.     

Detection of hydrogen peroxide in rainwater based on Mg-Al-carbonate layered double hydroxides-catalyzed luminol chemiluminescence

Using a green catalyst of luminol chemiluminescence (CL), Mg-Al-carbonate layered double hydroxides (denoted as Mg-Al-CO(3) LDHs), a novel, sensitive and rapid CL method was developed for the determination of hydrogen peroxide (H(2)O(2)). The corresponding linear regression equation was established in the range of 0.05-10 μM for H(2)O(2). The detection limit (S/N = 3) is 0.02 μM and the relative standard deviation (RSD) for nine repeated measurements of 1.0 μM H(2)O(2) was 2.9%. This proposed method has been successfully applied to detect H(2)O(2) in rainwater samples with good accuracy and precision. The novel methodology is expected to provide a general protocol for the determination of H(2)O(2) as well as for numerous other oxidase-based reactions giving H(2)O(2) as a product (e.g., glucose).     

Chemiluminescence determination of sulfite in sugar and sulfur dioxide in air using Tris(2,2'-bipyridyl)ruthenium(II)-permanganate system

A chemiluminescence (CL) detection for the determination of sulfite using the reaction of Ru(bipy)(3)(2+) (bipy=2,2'-bipyridyl) -SO(3)(2-)-KMnO(4) is described. The concentration of sulfite is proportional to the CL intensity from 5.0x10(-8) to 1.25x10(-4) mol l(-1). The limit of detection is 2.5x10(-8) mol l(-1) and the relative standard deviation is 4.9% for the 2x10(-5) mol l(-1) sulfite solution in six repeated measurements. This method has been successfully applied to the determination of sulfite in sugar and sulfur dioxide in air by using triethanolamine (TEA) as the absorbent material.     

不同基体改进剂对石墨炉原子吸收法测定土壤和沉积物中铊的影响

应用Pd(NO3)2-抗坏血酸(Vc)基体改进剂,建立了石墨炉原子吸收法(GFAA法)测定土壤和沉积物样品中铊。针对土壤和沉积物复杂基体,GFAA法测定铊元素主要受到氯离子的干扰,文中研究了常见基体改进剂(包括NH4NO3,(NH4)2SO4,La(NO3)3,Mg(NO3)2,Vc,Pd(NO3)2,Pd(NO3)2-Vc)对氯离子的抑制效果。通过研究不同基体改进剂测定含氯铊标准溶液的吸收曲线,探讨出基体改进剂测定铊的作用机理。以土壤或沉积物标准物质为研究对象,优化了应用Pd(NO3)2-Vc测定铊的灰化温度、基改剂浓度以及原子化温度。在最佳实验条件下,通过比较有无基体改进剂条件下,采用GFAA法测定不同土壤和沉积物中铊的精密度和准确度,实验结果表明,应用Pd(NO3)2-VC基体改进剂,测定土壤和沉积物标准物质中铊的测定结果都在标准值范围之内,6次平行测定的相对标准偏差范围为2.8%~8.4%,用于测定实际土壤和沉积物样品加标回收率为128.0%和92.9%。     

A New Ultramicrosensor for Nitric Oxide Based on Electropolymerized Film of Nickel Salen

Abstract

A new amperometric ultramicrosensor for the determination of nitric oxide (NO) is described. The ultramicrosensor, which is based on an electropolymerized film of ethylenebis(salicylideneiminate) nickel [Ni(salen)] and Nafion, shows a low detection limit, high selectivity and sensitivity to NO determination. The oxidation current (measured by a differential pulse amperometric method) is linear with NO concentration ranging from 1.0x10^?8 to 4.0x10^?6 mol/L with a calculated detection limit, at a signal to noise ratio of three, equal to 5.0x10^?9 mol/L. Some endogenous electroactive substances in biological tissues, such as dopamine, 5-HT and nitrite do not interfere with NO determination at the concentrations higher than those in biological systems. The ultramicrosensor could be employed for in vivo measurements of NO. The mechanism of the response of the ultramicrosensor to NO is also studied.     

Flow injection electrogenerated chemiluminescence determination of vanadium and its application to environmental water sample

A selective flow injection electrogenerated chemiluminescence(CL) method for the determination of vanadium is described in this paper. It was based on the chemiluminescence reaction of luminol with vanadium(II), which was on-line electrogenerated from vanadate using a flow-through carbon electrolytic cell. Under the optimal conditions, the CL intensity was linear to the concentration of vanadium in the range of 5.0x10(-10)-1.0x10(-7) gml(-1) with a detection limit of 2x10(-10) gml(-1) vanadium. The relative standard deviation was 4% for 5.0x10(-8) gml(-1) vanadium in 11 repeated measurements. The method has been successfully applied to the determination of vanadium in environmental water samples.     

Flow injection chemiluminescence determination of hydrazine by oxidation with chlorinated isocyanurates

A rapid and sensitive flow injection chemiluminescence (CL) method is described for the determination of hydrazine based on the CL generated during its reaction with either sodium dichloroisocyanurate (SDCC) or trichloroisocyanuric acid (TCCA) in alkaline medium. The emission intensity is greatly enhanced if dichlorofluorescein (DCF) as sensitizer is present in the reaction medium. The presence of citrate prevents the precipitation of some cations in the reaction medium and also causes an enhancement in emission intensity. The effect of analytical and flow injection variables on these CL systems and determination of hydrazine are discussed. The optimum parameters for the determination of hydrazine were studied and were found to be the following: SDCC and TCCA both 1x10(-3) M; NaOH, 2x10(-1) M; DCF, 5x10(-6) M; citrate, 1x10(-3) M and flow rate, 3.8 ml min(-1). The optimized method yielded 3sigma detection limits of 2x10(-7) and 3x10(-7) M for hydrazine with SDCC and TCCA oxidants, respectively. The method is simple, fast, sensitive, and precise and was applied to the determination of hydrazine in water samples.     

A high precision spectrophotometric method for on-line shipboard seawater pH measurements: the automated marine pH sensor (AMpS)

Measurement strategies for understanding the oceanic CO(2) (carbon dioxide) system are moving towards in situ and ship of opportunity sampling techniques. Automated instrumentation with high accuracy and sampling frequencies will enable a greater understanding of the fluxes of marine carbon and lead to a more reliable constrain on the calculated uptake of anthropogenic CO(2) by the oceans. This paper describes the automated marine pH sensor (AMpS); new instrumentation and methodology for the determination of seawater pH using dual spectrophotometric measurements of sulfonephthalein indicator in a semi-continuous seawater stream. The pH values measured during a recent study in the Weddell Sea are used to illustrate the excellent properties of the AMpS. The method has an on-line precision of better than 0.001 pH units and an estimated accuracy of better than 0.004 pH units. The instrument is compact, portable and has a measurement frequency of 20 samples per hour. The instrument is ideally suitable for operation on ships of opportunity.     

Sensitive assay for catecholamines in pharmaceutical samples and blood plasma using flow injection chemiluminescence analysis.

A rapid and sensitive chemiluminescence (CL) method using flow injection analysis was described for the determination of three catecholamines: dopamine, adrenaline and dobutamine, based on their greatly enhancing effects on the CL reaction of luminol-potassium periodate in basic solutions. Under the optimized conditions, the calibration graphs relating the increase of CL intensity to the concentration of the analytes were linear. The present method allows for the determination of dopamine, adrenaline, and dobutamine over the range of 1.0 x 10(-10) - 1.0 x 10(-7) g/ml. The relative standard deviations for measurements (n=11) of dopamine, adrenaline and dobutamine were 2.9, 2.3 and 1.8% when the concentrations of three catecholamines were at 1.0 x 10(-9) g/ml, respectively. The detection limits of the method were 2.0 x 10(-11) g/ml dopamine, 1.0 x 10(-11) g/ml adrenaline and 4.0 x 10(-11) g/ml dobutamine. The method was successfully applied to the determination of three catecholamines in pharmaceutical samples and blood plasma.     

Flow-injection determination of trace amounts of dopamine by chemiluminescence detection

A flow-injection analysis (FIA) for the determination of dopamine has been developed. The method is based on the inhibition effect of dopamine on the iron(II)-induced chemiluminescence (CL) of 10,10'-dimethyl-9,9'-biacridinium dinitrate (lucigenin). The presence of a non-ionic surfactant, polyoxyethylene (23) lauryl ether (Brij 35), caused an increase in the inhibition effect. The present method allows the determination of dopamine over the range 1x10(-8)-2x10(-7) mol dm(-3). The relative standard deviation was 0.7% for eight determinations of 6x10(-8) mol dm(-3) dopamine. The detection limit (S/N=3) was 2x10(-9) mol dm(-3) with the sampling rate of 40 samples h(-1). The effect of other catecholamines and compounds of similar structure on the lucigenin CL reaction was studied: quinone, hydroquinone, norepinephrine, pyrocatechol and l-dopa suppressed the CL intensity.     

Intermethod comparisons of active sampling procedures and analysis of aldehydes at environmental levels

Within the framework of a European interlaboratory exercise, the Vito facility for the generation of controlled atmospheres was used to test the suitability of four sampling techniques for priority aldehydes namely formaldehyde, acrolein, acetaldehyde, and glutaraldehyde at the ranges of 0.5 to 150 microg x m(-3). The samplers are DNPH-containing impingers, DNPH-impregnated cartridges and filters, and 2-HMP coated XAD-2 tubes. The three first DNPH samplers are to be analyzed by HPLC and the latter by GC-MS for the oxazolidine derivatives. The intermethod comparison comprises two to five sets of experiments depending on the compounds of interest. The aim of the exercise was also to assess the chemical interferences caused by ozone, nitrogen dioxide, and ammonia when using different techniques for sampling and analysis. The active DNPH method (with minor modifications such as shorter sampling time, immediate elution after sampling, and/or eventually wetting of samplers) delivered results within the 30% overall relative uncertainty for formaldehyde, acetaldehyde, and acrolein at the upper microg x m(-3) levels. However, the results suggest that the current DNPH methods for aldehydes do not comply with the 30% minimum performance criteria at the sub microg x m(-3) level. Sampling of aldehydes in the presence of ozone and NO2 interferences by using a "scrubber" cartridge appears to be beneficial to the quality of results.     

A novel chemiluminescence technique for quantitative measurement of low concentration human serum albumin.

An efficient and highly sensitive chemiluminescence (CL) technique is proposed in the current study for detection of low levels of human serum albumin (HSA). Chemiluminescence (CL) produced during interaction between fluoresceinyl cypridina luciferin analog (FCLA)-1O2 can be modified with the presence of HSA. The conventional CL technique uses a quenching effect of HSA for its quantitative measurement. We are reporting here that the CL intensity can be enhanced, rather than quenched, by the addition of HSA. The CL signal can be linearly correlated with the HSA concentration over a clinically interesting range of 5 x 10(-9) - 8 x 10(-8) mol L(-1), with a detection limit of 2.5 x 10(-9) mol L(-1). The determination result was consistent with that obtained from conventional methods. One possible mechanism of HSA detection technique using CL enhancement approach is discussed. Intermolecular energy transfer in chemiluminescence systems and changes of microenvironment are likely to be contributors of the CL enhancement with HSA.     

Flow-injection analysis method for the determination of nitrite and nitrate in natural water samples using a chemiluminescence NOx monitor.

A flow-injection analysis method for the determination of nitrite and nitrate in natural water samples has been developed that consists of two systems based on their reduction to NO with hydrazine and/or ascorbic acid, followed by chemiluminescence detection. The procedure of sweeping the generated NO into an NOx monitor, by means of a gas-liquid separating coil consisting of microporous polytetrafluoroethylene (PTFE) tubing, offers practical advantages. The adjustment of the carrier gas-flow rates could yield the same calibration graphs for the two measurement systems, and the accumulation sweeping mode provides a higher sensitivity. Chemiluminescence detection allows a wide linear calibration range of 5 x 10(-8) to 5 x 10(-5) M. The detection limits for nitrate and nitrite, defined as three-times the standard deviation of measurement blanks, are 2 x 10(-8) M and 1 x 10(-8) M, respectively, and the average precision was 3.2% at ambient natural concentration levels. Recovery tests were between 94% and 106% for a variety of natural water samples. The method is relatively free from interferences from the substances normally found in natural water, and only ferric ion has an effect for the nitrite determination.     

Flow-injection chemiluminescence determination of ofloxacin and levofloxacin in pharmaceutical preparations and biological fluids.

A novel, rapid and sensitive analytical method is described for determination of ofloxacin and levofloxacin by enhanced chemiluminescence (CL) with flow-injection sampling. The method is based on the CL reaction of the Ce(IV)-Na2S2O4-ofloxacin/levofloxacin-H2SO2 system. The enhanced CL mechanism was developed and the optimum conditions for CL emission were investigated. The CL intensity was correlated linearly (r = 0.9988) with the concentration of ofloxacin (or levofloxacin) in the range of 1.0 x 10(-8) - 1.0 x 10(-7) g ml(-1) and 1.0 x 10(-7) - 6.0 x 10(-6) g ml(-1). The detection limit (S/N = 3) is 7 x 10(-9) g ml(-1). The relative standard derivation (RSD, n = 11) is 2.0% for ofloxacin at 4 x 10(-7) g ml(-1) and for levofloxacin at 6 x 10(-7) g ml(-1). This method has been successfully applied for the determination of ofloxacin and levofloxacin in pharmaceutical preparations and biological fluids with satisfactory results.     

Determination of small amounts of L-ascorbic acid using the chemiluminescence of an iron-chlorophyllin complex.

Chemiluminescence (CL) was immediately observed after an iron-chlorophyllin aqueous solution was added to an acetonitrile/water mixed solution containing hydrogen peroxide. Quenching of the iron-chlorophyllin complex CL was caused by adding L-ascorbic acid. Based on these facts, a determination method involving small amounts of L-ascorbic acid was developed. As a result, this CL system is able to determine L-ascorbic acid over a wide concentration range of 4.0 x 10(-12) to 4.0 x 10(-4) mol L(-1). Also, coexisting substances, such as sugar and vitamins, did not interfere with the determination. Moreover, the participation to the CL was not observed when using other reducing agents, such as hydroxylamine hydrochloride. As an application for practical use, L-ascorbic acid in soft-drink powder was determined. The experimental value was almost the same as the calculated one (5.30 x 10(-5) mol L(-1)).     

Fluorimetric determination of nitrogen oxides in the air by a novel red-region fluorescent reagent

A sensitive fluorimetric method for the determination of nitrogen oxides (NO(x): NO+NO(2)) in air is described. Nitrogen dioxide (nitrogen monoxide was previously converted to nitrogen dioxide in oxide tubes) was aspirated through a fritted glass bubble at a flow rate of 500 ml min(-1) for 120 min and fixed as nitrite, using 0.1 N NaOH as a trapping solution with the empirical absorption efficiency 0.74 and the stoichiometric factor 0.5. The method is based on the fluorescence quenching of a red-region fluorescent reagent, tetra-substituted amino aluminum phthalocyanine (TAAlPc), after being diazotized by nitrite. Under optimal conditions the linear range of the calibration curve for nitrite is 1-40 ng ml(-1) (NO(2) 0.24-9.6 ppb, v/v). The detection limit is 0.34 ng ml(-1) for nitrite (NO(2) 0.08 ppb, v/v) and the relative standard deviation for six replicate measurements of 15 ng ml(-1) nitrite is 3.2%. The method has been applied to the determination of nitrogen oxides in the air with satisfactory results. Typical gaseous co-pollutants such as SO(2), H(2)S and HCHO did not interference the determination.     

Heterogeneous reactions of gaseous HNO3 and NO2 on the clay minerals kaolinite and pyrophyllite

Airborne clay mineral particles have long atmospheric lifetimes due to their relatively small size. To assess their impact on trace atmospheric gases, we investigated heterogeneous reactions on prototype clay minerals. Diffuse reflectance infrared spectroscopy identified surface-adsorbed products formed from the uptake of gaseous nitric acid and nitrogen dioxide on kaolinite and pyrophyllite. For kaolinite, a 1:1 phyllosilicate, HNO3 molecularly adsorbed onto the octahedral aluminum hydroxide and tetrahedral silicon oxide surfaces. Also detected on the aluminum hydroxide surface were irreversibly adsorbed monodentate, bidentate, bridged, and water-coordinated nitrate species as well as surface-adsorbed water. Similar adsorbed products formed during the uptake of NO2 on kaolinite at relative humidity (RH) of 0%, and the reaction was second order with respect to reactive surface sites and 1.5 +/- 0.1 for NO2. Reactive uptake coefficients, calculated using Brunauer, Emmett, and Teller surface areas, increased from (8.0 +/- 0.2) x 10(-8) to (2.3 +/- 0.4) x 10(-7) for NO2 concentrations ranging from 0.56 x 10(13) to 8.8 x 10(13) molecules cm(-3). UV-visible spectroscopy detected gaseous HONO as a product for the reaction of NO2 on wet kaolinite. The uptake of HNO3 on pyrophyllite, a 2:1 phyllosilicate, resulted in stronger signal for nitric acid molecularly adsorbed on the silicon oxide surface compared to kaolinite. Monodentate, bridged, and water-coordinated nitrate species bound to aluminum sites also formed during this reaction indicating that reactive sites on edge facets are important for this system. The uptake of NO2 on pyrophyllite, gammaBET = (7 +/- 1) x 10(-9), was significantly lower than kaolinite because NO2 did not react with the dominant tetrahedral silicon oxide surface. These results highlight general trends regarding the reactivity of tetrahedral silicon oxide and octahedral aluminum hydroxide clay surfaces and indicate that the heterogeneous chemistry of clay aerosols varies with mineralogy and cannot be predicted by elemental analysis.