Improved determination of gaseous divalent mercury in ambient air using KCl coated denuders

An improved method for the determination of gaseous divalent mercury (GDM) in ambient air using KCl coated denuders has been developed and tested. GDM collected in the KCl coated denuders can be quantitatively desorbed at 450?°C in 10 min. After being complete thermally reduced to Hg⁰ at 900?°C, all mercury released from the denuder is pre-concentrated on the analytical Au trap, and detected by cold vapor atomic fluorescence spectrometry (CVAFS). The absolute detection limit of the method is less than 3 pg. Preliminary data of GDM concentration in ambient air from different sampling stations show that GDM concentrations in the urban air of Göteborg are much higher than in rural air (Rörvik and Sasetta), which indicates the anthropogenic origin of GDM.     

Sampling and determination of gas phase divalent mercury in the air using a KCl coated denuder

KCl coated denuders were employed for the measurement of divalent mercury (Hg²⁺) species in the air. Laboratory tests show that gaseous Hg²⁺ can be collected by the denuder with an average efficiency of 98% and elemental Hg will pass through it freely. Hg²⁺ trapped in the denuder can be quantitatively extracted by 1 mol/L HCl and analyzed by the method of SnCl₂ reduction-CVAFS determination. Hg²⁺ concentrations of 0.04–0.15 ng m^–3 corresponding to about 2–9% of the total gaseous mercury in the ambient air were determined at several sampling locations.     

Sampling and determination of gas phase divalent mercury in the air using a KCl coated denuder

KCl coated denuders were employed for the measurement of divalent mercury (Hg²⁺) species in the air. Laboratory tests show that gaseous Hg²⁺ can be collected by the denuder with an average efficiency of 98% and elemental Hg will pass through it freely. Hg²⁺ trapped in the denuder can be quantitatively extracted by 1 mol/L HCl and analyzed by the method of SnCl₂ reduction-CVAFS determination. Hg²⁺ concentrations of 0.04–0.15 ng m^–3 corresponding to about 2–9% of the total gaseous mercury in the ambient air were determined at several sampling locations. Received: 24 September 1996 / Revised: 14 January 1997 / Accepted: 18 January 1997     

Direct thermal desorption of semivolatile organic compounds from diffusion denuders and gas chromatographic analysis for trace concentration measurement

A novel method for collection and analysis of vapor-phase semivolatile organic compounds (SOCs) in ambient air is presented. The method utilizes thermal desorption of SOCs trapped in diffusion denuders coupled with cryogenic preconcentration on Tenax-TA and analysis by high resolution gas chromatography (GC)-electron-capture detection (ECD). The sampling and analysis methods employ custom-fabricated multicapillary diffusion denuders, a hot gas spike (HGS) apparatus to load known quantities of thermally stable standards into diffusion denuders prior to sample collection, a custom-fabricated oven to thermally desorb SOCs from the diffusion denuder, and a programmable temperature vaporization (PTV) inlet containing a liner packed with Tenax-TA for effective preconcentration of the analytes and water management. High flow rates into the PTV inlet of 750mLmin(-1)during thermal desorption are ca. a factor of ten greater than typically used. To improve resolution and retention time stability, the thermal desorption and PTV inlet programming procedure includes three steps to prevent water from entering the analytic column while effectively transferring the analytes into the GC system. The instrumentation and procedures provide virtually complete and consistent transfer of analytes collected from ambient air into the GC evidenced by recovery of seven replicates of four internal standards of 90.7+/-4.0-120+/-23% (mean+/-95% confidence interval, CI). Retention time based compound identification is facilitated by low retention time variability with an average 95% CI of 0.024min for sixteen replicates of eight standards. Procedure details and performance metrics as well as ambient sampling results are presented.     

Use Of Diffusion Controlled Preconcentration Systems With Chemically Immobilized Coatings For The Determination Of Atmospheric Nitric Acid

Abstract

A new coating procedure for different diffusion controlled preconcentration methods (tubular denuder, annular denuder, diffusion screen) is described for the determination of nitric acid in air. In this study, a silanization reaction is applied to obtain a chemically fixed coating with an end placed functional NH₂-group, which can be used as a sink to collect acidic compounds from air. This coating must be carried out only once and can be used for a long time. The denuders, coated with this procedures, were compared with conventionally coated NaF denuders.     

Trace analysis of airborne haloacetates

Haloacetates in various environmental compartments can be determined by gas chromatography-negative-ion chemical-ionization mass spectrometry after derivatization with 1-pentafluorophenyl diazoethane. Detection limits in absolute amounts per injection are between 0.01 fg (chlorodifluoroacetate) and 80 fg (monofluoroacetate). Sampling of haloacetates in urban air was performed by means of cylindrical denuders coated with alkalized glycerol. The haloacetates detected are trifluoro-, monochloro-, dichloro-, trichloro-, monobromo-, and dibromoacetate. The concentrations in ambient air fluctuate strongly, e.g. between 20 and 3000 pg/m³ for TFA. Haloacetates are also found in river waters and tree foliage. A major problem is interference from contamination with trifluoro- and trichloroacetate.     

Critical evaluation of adsorption-based sampling of vaporized metal species in flue gases

Diffusion-controlled sampling techniques, i.e. diffusion screens and diffusion tubes (= denuders), can be used in the collection of several vaporized heavy metal species in clean gases (pure N₂ atmosphere) at elevated temperatures. Collection efficiencies obtained for Hg, HgCl₂, Cd, CdCl₂ and ZnCl₂ were over 90% using adsorption on Au-coated diffusion screens and Ag-coated denuders. However, the collection efficiencies for Zn and PbCl₂ were significantly lower. In field measurements performed at a hazardous waste incineration plant and in a power plant equipped with a circulating fluidized-bed boiler, collection efficiencies seemed to vary noticeably depending on the sampling conditions and metal species to be sampled. Best collection efficiencies were obtained for mercury with both Ag coated denuders and Au coated screens whereas cadmium showed significantly poorer results in field measurements than in the laboratory. Sampling of zinc and lead species seemed to be problematic in all cases. Of the two sampling techniques, the denuder technique is more recommendable than the screen technique for sampling in relatively clean gases. However, neither of these techniques should be used in flue gases without further understanding of the collection mechanisms. Received: 6 November 1996 / Revised: 3 July 1996 / Accepted: 14 July 1996     

The determination of total gaseous mercury in air at background levels

A method is described for the determination of the total gaseous mercury in air at concentrations ranging from ca. 0.1 ng m^-3 to 1μg m^-3. The method is based on the collection of mercury species on gold-coated quartz wool followed by detection with an atomic absorption detector. The collection efficiencies for mercury, dimethylmercury, methyl-mercury(II) chloride, and mercury(II) chloride are nearly quantitative at flow rates up to 10 1 min^-1 and at temperatures up to 50°C. The absolute detection limit of the method is 20 pg of mercury. Under field conditions the precision of the analytical procedure was 14.5% (n=5) for 400-l samples of air and a mercury concentration of 1.5 ng m^-3. Measurements of the mercury distribution in the atmosphere show an ambient background level in clean air masses of 1.0–4.0 ng m^-3.     

涂布2,4-二硝基苯肼的环形溶蚀器/滤膜系统和高效液相色谱法检测大气中二羰基化合物

建立了环形溶蚀器/滤膜系统(Annular denuder/filter pack system)和2,4-二硝基苯肼(DNPH)-高效液相色谱法(HPLC)采集和检测大气中气相和颗粒相二羰基化合物的方法。DNPH作为吸附剂分别涂布在环形溶蚀器的内壁和3层滤膜上,当大气样品经过环形溶蚀器时,含有气相二羰基化合物的气体吸附到环形溶蚀管内壁上与DN-PH发生反应,而颗粒相部分穿过环形溶蚀管,采集到滤膜上。样品经乙腈洗脱、浓缩后,采用HPLC进行分析。根据不同的采样流速、采样时间和DNPH的涂布量采集到的二羰基化合物的浓度,确定的最佳采样条件为:采样流速4 L/min,采样时间4~5 h,DNPH浓度0.47 g/L。使用Tedlar bag验证环形溶蚀器乙二醛和甲基乙二醛的采集效率(分别为82%和85%)。利用此方法对实际大气中的二羰基化合物进行了检测。     

Stability of self-assembled monolayers on titanium and gold

Methyl- and hydroxyl-terminated phosphonic acid self-assembled monolayers (SAMs) were coated on Ti from aqueous solution. Dodecyl phosphate and dodecyltrichlorosilane SAMs were also coated on Ti using solution-phase deposition. The stability of SAMs on Ti was investigated in Tris-buffered saline (TBS) at 37 degrees C using X-ray photoelectron spectroscopy, contact angle goniometry, and atomic force microscopy. For comparison purposes, a hydroxyl-terminated thiol SAM was coated on Au, and its stability was also investigated under similar conditions. In TBS, a significant proportion of phosphonic acid or phosphate molecules were desorbed from the Ti surface within 1 day, while the trichlorosilane SAM on Ti or thiol SAM on Au was stable for up to 7 days under similar conditions. The stability of hydroxyl-terminated phosphonic acid SAM coated Ti and thiol SAM coated Au was investigated in ambient air and ultraviolet (UV) light. In ambient air, the phosphonic acid SAM on Ti was stable for up to 14 days, while the thiol SAM on Au was not stable for 1 day. Under UV-radiation exposure, the alkyl chains of the phosphonic acid SAM were decomposed, leaving only the phosphonate groups on the Ti surface after 12 h. Under similar conditions, decomposition of alkyl chains of the thiol SAM was observed on the Au surface accompanied by oxidation of thiolates.     

Performance of a 2,4-DNPH coated annular denuder/HPLC system for formaldehyde monitoring in air

Summary The performance of annular denuders coated with 2,4-dinitrophenylhydrazine for collection of atmospheric HCHO has been evaluated by HPLC/UV analysis of samples coming from laboratory tests and field experiments. A number of parameters, such as collection efficiency at varying air humidity, detection limit, operative capacity and temporal self-consistency have been investigated to optimize the denuder behaviour under different weather conditions and to obtain short-term concentration profiles of HCHO. Deviations between measurements made simultaneously by the DNPH denuder method and differential optical absorption spectrometry (DOAS) have been found to average approximately 30% in the 0–5 ppb HCHO concentration range.     

Evaluation and applications of a gaseous mercuric chloride source

In this study, a diffusion-type device for generating gaseous mercuric chloride (HgCl₂) was systematically evaluated and applied to validate the annular denuder method for sampling gaseous HgCl₂ species in a synthetic gas stream. The results show that it takes at least 48 h for the system to reach a steady-state condition after the diffusion cell reaches the temperature set-point and the carrier gas is activated. The primary Hg species from the source was proven to be HgCl₂. In the temperature range from –5.00 to 11.80 °C, the Hg emission rates from the source vary from 1.8 to 14.2 pg min^–1. It is shown that, under the experimental conditions examined, KCl-coated annular quartz denuders designed for ambient reactive gaseous mercury (RGM) collection could quantitatively collect HgCl₂. It is also demonstrated that the impactors used to remove coarse airborne particulate matter could lead to a loss of up to one third of the HgCl₂ in the gas stream.     

戊二醛合成跟踪分析

用气相色谱法对液 液相转移反应萃取法合成戊二醛（ＧＡ）反应进行跟踪分析,采用φ３ｍｍ×４ｍ［ｍ（ＳＥ ３０）∶ｍ（硅烷化１０１白色担体）＝１５∶１００］＋φ３ｍｍ×２ｍ［ｍ（ＰＥＧ ２０Ｍ）∶ｍ（硅烷化１０１白色担体）＝１０∶１００］不锈钢柱,双柱双氢焰程序升温,升温程序为７０℃（４ｍｉｎ）１０℃／ｍｉｎ１４０℃（６ｍｉｎ）。Ｎ２４５ｍＬ／ｍｉｎ,Ｈ２６５ｍＬ／ｍｉｎ,空气３００ｍＬ／ｍｉｎ,汽化温度１８５℃,检测温度１８５℃。所建立的方法能较好地分离环戊烯、溶剂、氧化中间产物、ＧＡ、内标、氧化副产物。     

Determination of volatile mercury compounds in air with the coleman mercury analyzer system

A simple but very selective cold-vapour atomic absorption system is described for the determination of volatile mercury compounds at very low levels in ambient air. Three different absorbers are compared: activated charcoal, silver-coated sea sand and gold-coated sea sand. To eliminate interferences, a two-step desorption unit is used. After thermal desorption, the mercury is measured by using a modified MAS-50 spectrophotometer. The effects of flow rate and desorption temperature are discussed. The detection limit is 0.1 ng. Above 1 ng, the reproducibility is about 1%. Calibration is done by injection of elemental mercury vapour. The method with gold-coated sand absorbers is most satisfactory and is suitable for the analysis of ambient outdoor and indoor air. All likely volatile mercury compounds are absorbed, and a wide range of mercury concentrations can be determined. In routine application, one analysis takes about 3 min.     

RPLC retention of 1,ω-di(alkoxy)-polysulphides

Summary A simple and reliable method for routine measurement of ammonia in ambient air is described. It is based on the collection of ammonia on H₃PO₃-coated annular denuders and its subsequent derivatization withm-toluoyl chloride (MTC) in alkaline acetonitrile. The resultingm-toluamide is determined by reversed phase HPLC with UV detection at 230 nm. The limit of dotection is about 0.3g m^–3 for NH₃ in air samples collected at 151 min^–1 for one hour.     

The accuracy of the vapour-injection calibration method for the determination of mercury by amalgamation/cold-vapour atomic absorption spectrometry

A vapour-injection method is described for the calibration of mercury determinations. Its accuracy depends mainly on the temperature of the mercury-saturated air, which must be lower than the ambient temperature. By preconditioning the syringe, initial irreproducible measurements caused by sorption are avoided. Under optimal conditions, the precision of the injection in the range 1–100 ng of mercury is generally better than 1%.     

Improved HPLC determination of aliphatic amines in air by diffusion and derivatization techniques

Summary Traces of C₁–C₄ aliphatic amines, sampled from ambient air on H₃PO₃-coated annular denuders, are derivatized with m-toluoyl chloride (MTC) in alkaline acetonitrile. The resulting derivatives are determined by reversed phase HPLC with ultraviolet detection at 230 nm. The detection limits of the individual amines are in the 1 to 5 picomole range corresponding to gasphase concentrations lower than 0.1 g m^–3 in air samples collected at 5 Lmin^–1 for one hour.     

Simultaneous measurements of formaldehyde and ozone in air by annular denuder-HPLC techniques

Summary A denuder sampling method combined with HPLC analysis for the simultaneous determination of formaldehyde and ozone in ambient air is described. It is based on the reactions of CH₂O and O₃ with 2,4-dinitrophenylhydrazine (DNPH) and 4-allyl-2-methoxyphenol (eugenol)_respectively, both acting as coatings of two annular denuders connected in series. Formaldehyde released from the ozonolysis of eugenol is quantitatively collected on a third downstream DNPH-coated denuder. The two DNPH denuders are then extracted and analyzed as hydrazone derivative by HPLC with UV absorbance detection.The stoichiometric factor of the eugenol-ozone reaction was found to be 2.0±0.1 moles of O₃ per mole of CH₂O. The limits of detection are 0.8gm^–3 CH₂O and 3gm^–3 O₃ for 100l air sampled, corresponding to 1-h sampling at 1.7l min^–1.     

应用搅拌棒吸附萃取-热脱附-气相色谱-质谱分析烟用香料的化学成分

应用搅拌棒吸附萃取法(SBSE)提取烟用香料的化学成分,并利用热脱附(TD)和色谱-质谱联用(GC-MS)进行分析。对影响萃取效果的因素(萃取时间和氯化钠的加入量)进行了考察,并采用正交试验法对影响热脱附的3个主要因素(脱附温度、脱附时间和冷阱温度)进行了优化,得到了较优的实验条件。对方法的重现性进行了考察,同一样品6次测定所得30个组分的峰面积的相对标准偏差（RSD）平均值小于10%,说明所建立方法的重现性较好。在样品中鉴别出酯类、酮类和醛类等30种不同化学组分,这些物质反映了该香料的香气特点。实验证明SBSE和TD适用于烟用香料的快速分析测定。     

Gas collection efficiency of annular denuders: A spreadsheet-based calculator

Denuders are widely used for atmospheric analysis. Annular denuders are especially well-suited for preconcentration of trace gases compared to simpler single tube designs. While traditionally coated annular denuders have both bounding surfaces that behave as sinks, annular denuders/membrane-based scrubbers with the same basic geometric design and with only one of the annular surfaces functioning as sink (e.g., a membrane tube whose outer surface behaves as a sink disposed within an inert jacket tube) have become common. However, the gas collection efficiency of such devices cannot be expressed as a simple equation with fixed constants and there is no presently available tool to a priori determine the denuder performance or to design denuders with specific removal efficiencies at specific sampling rates. This paper presents a simple to use “spreadsheet calculator” for concentric annular denuders of any dimension based on known solutions to analogous heat transfer problems. The results from the present spreadsheet calculator are compared with results from a commercial computational fluid dynamics package (Fluent™; this takes significant expertise and development effort to run)—the two approaches produce essentially the same results. The present spreadsheet calculator can be used easily and simply without training and will be a useful tool for denuder users and designers.