Evaluation of denuder sampling for a mixture of three common gaseous diisocyanates

A denuder sampler has been evaluated for a mixture of three gaseous diisocyanates, i.e. toluene diisocyanate (TDI), hexamethylene diisocyanate (HDI) and isophorone diisocyanate (IPDI). Sampling was performed at a total concentration of diisocyanates close to the Swedish occupational exposure limit (OEL), which is 10 ppbv (69-92 microg m(-3)), for a 5-min period. The denuder tube was coated with a chemosorptive stationary phase consisting of SE-30 (polydimethylsiloxane) and the derivatising reagent dibutylamine (DBA). It was shown that the denuder has a collection efficiency for HDI and IPDI comparable to that of an impinger method, while sampling of TDI resulted in an 8% lower concentration. Both short-term (15 min) and long-term (8 h) sampling periods were shown to yield reproducible results. For 8-h measurements, a sampling flow rate of 5 mL min(-1) was shown to be suitable for the investigated concentration range, i.e. 10-100 ppbv (69-921 microg m(-3)). A flow rate of 25 mL min(-1) or higher resulted in breakthrough after 8 h due to chromatography of the compounds in the adsorbent. The limit of detection (LOD) for the air sampling method is nearly 500 times lower than the OEL. The denuder tubes can be prepared at least 10 days prior to sampling without degradation of performance. Furthermore, they can be stored up to 6 days in a freezer after sampling without significant loss of analytes.     

Comparison of denuder and impinger sampling for determination of gaseous toluene diisocyanate (TDI)

An air-sampling method employing denuders coated inside with a chemisorptive stationary phase has been evaluated for analysis of the hazardous gaseous 2,4 and 2,6 isomers of toluene diisocyanate (TDI). The denuder stationary phase consisted of polydimethylsiloxane (SE-30) to which dibutylamine (DBA) was added as a reagent for derivatization of TDI. The accuracy and precision of sampling by means of denuders were shown to differ only slightly from those of the established impinger method. The denuder method was, however, also shown to be suitable for long-term measurements (up to 8 h). The limit of determination (LOD) of the method, including LC-APCI-MS-MS analysis, was found to be 1.9 microg m(-3) and 1.2 microg m(-3) for 2,4- and 2,6-TDI, respectively, for short-term measurements (15 min). Significant lower LOD was obtained for long-term measurements. This is well below the Occupational Safety and Health Administration (OSHA) 8-h TWA (time-weighted average) exposure limit, which is 40 microg m(-3) for the sum of the TDI isomers. The denuder method was also found to be robust and easy to handle. The samplers can be prepared several days before sampling with no loss in performance. The contents of denuders should, on the other hand, be extracted immediately after sampling to prevent degradation of the isocyanate derivatives formed.     

New organosols of ZnS and HgS in N,N-dimethylformamide and dimethyl sulfoxide. Use in the preparation of semiconductive polymer-metal sulfide composite films

Organosols of ZnS and HgS in N,N-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) were prepared by reaction of Zn and Hg salts with H₂S. ZnS in the DMF organosol has a particle size of about 300 Å, determined by an argon laser scattering technique. The form of HgS in the organosols varies with temperature, concentration of HgS, and type of solvent;-HgS in a DMF organosol is converted into-HgS at –30 °C or above. Poly(acrylonitrile)-ZnS or -HgS composite films prepared from organosols are semiconductive, and the electrical conductivity of the film increases by a factor of 10²–10³ on exposure to moisture or alcohol vapour. Poly(acrylonitrile)--HgS composite films, prepared from heated-HgS, show electrical conductivity of a range of 10^–1–10^–2 S cm^–1 and a large electron mobility.     

Application of the denuder technique in filter sampling of airborne chromates at ground level concentrations

The use of the denuder technique for the preserving sampling of chromium(VI) in airborne dust at ground level (immission) concentrations was investigated. A simple denuder with activated charcoal retained by a steelwire-net cylinder was constructed. The sorption abilities of the denuder towards sulfur dioxide, which is responsible for the reduction of sampled Cr(VI) on the filter surface, were examined under various conditions. The measurements provide evidence for a laminar flow inside the denuder. At a flow rate of 100 L/h and a temperature of 27 °C the theoretical sorption value of 99.6% is reached within an experimental error of ±0.1%. A relative humidity of 19–91.5% has no influence on the sorption. In order to check if an experimental sorption value of 99.5% is sufficient to stabilize Cr(VI) on the filter surface, sampling was simulated by sucking SO₂-loaded air through Teflon filters loaded with Cr(VI) containing aerosol particles with diameters of about 0.3 m. Aerosols of two different compositions were generated by a sprayer in combination with a diffusion dryer. The particle size distributions were determined from scanning electron microscopic pictures. Chromium(VI) was eluted from the filters with an alkaline buffer and extracted from the filter eluates with a solution of a liquid anion exchanger. Chromium was determined with graphite furnace atomic absorption spectrometry. The Cr(VI) losses are between 57 and 16% depending on the composition of the aerosol particles and the sampling time. Realistic conditions were chosen regarding the initial Cr(VI) on the filters and the amount of sulfur dioxide which passed through the denuder.Dedicated to Professor Dr. Dieter Klockow on the occasion of his 60th birthday     

The improved synthesis and crystal structure of 20-thiocrown-4

An improved synthesis of 20-thiocrown-4 is reported, which exploits the Kellogg method of cesium carbonate in DMF mediated macrocyclization of precondensed synthones which converge at the cycloicosane structure. The crystal structure of 20-thiocrown-4 reveals a rectangular conformation for the free ligand. Each sulfur is in onegauche and oneanti torsion angle. Four carbon positions make up the corners. There are two short sides comprised of –C–C– torsion angle sequencesg ^–ag^– and two long sides (aaa, g ^–ag⁺). The S–C and C–C bond distances average 1.816(2) and 1.523(3) , respectively. Supplementary data relating to this article are deposited with the British Library as Supplementary Publication No. SUP 82147 (9 pages)     

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.     

Time-based on-line preconcentration cold vapour generation procedure for ultra-trace mercury determination with inductively coupled plasma atomic emission spectrometry

A time-based sequential dispensing on-line column preconcentration procedure for mercury determination at trace levels by cold vapour generation inductively coupled plasma atomic emission spectrometry (CV-ICP-AES), by means of a unified module of a preconcentration column and a gas–liquid separator (PCGLS) is described. The complex of mercury formed on-line with ammonium pyrrolidine dithiocarbamate (APDC) is retained on the surface of the hydrophobic poly(tetrafluoroethylene) (PTFE) turnings, which are packed into the lower compartment of the PCGLS. Subsequently, mercury vapour is generated directly on the PTFE turnings by reductant SnCl₂ and separated from the liquid mixture via the PCGLS by argon purge gas. The outlet of the PCGLS is connected directly to the torch adapter of the plasma without the normal spray chamber and nebulizer. With 60-s preconcentration time and 12.0 mL min^–1 sample flow rate, the sampling frequency is 30 h^–1. The calibration curve is linear over the concentration range 0.02–5.0 g L^–1, the detection limit (c_L) is 0.01 g L^–1 and the relative standard deviation (s_r) is 3.1% at the 1.0 g L^–1 level. The proposed method was evaluated by analysis of BCR CRM 278 (Mytilus Edulis) reference material and applied to the determination of total mercury in digested urine, blood and hair samples.     

Concept and validation of a novel approach for producing large batches of reference material of ambient aerosols on filters

A novel method for preparing reference material of aerosol particulate matter (PM) on filters was developed by using the concept of very high volume, multiport sampling, and this was subsequently applied to produce more than 300 well-characterised units. The dedicated sampler built for this purpose features a 0.94-m-diameter, vacuum-tight main chamber with a total of 349 monitor ports, each holding a 37-mm-diameter, cellulose acetate–nitrate ester (CA) membrane filter with a nominal pore size of 0.8 m. At a pressure difference of about 130 hPa across the filter cassettes, the total initial air flow rate was 350 m³ h^–1 (1.0 m³ h^–1 per filter). Investigations into the variability of filter parameters showed that the flow resistance of CA filters is mostly determined by and proportional to their blank mass, with a mean uncertainty of about 5%. Total suspended particulate matter (TSP) was sampled for a total of 50 h using 349 selected filters with a relatively narrow spread in blank mass. The mean TSP mass per filter thus produced was 3.35 mg. Corrected for small differences in blank mass of the filters, the normalised aerosol masses per filter of 96% of the samples exhibited normal distributions with standard deviations of only 2.1 and 3.4%, depending on details of the normalisation procedure. Within the limits of the technique, a variation of aerosol mass with radial distance from the centre of the sampler is not clearly evident. The results provide evidence that the multiport approach allows large batches of particulate matter on filters to be produced in a reliable manner.     

Platinum concentration in silicone breast implant material and capsular tissue by ICP-MS

Inductively coupled plasma-mass spectrometry (ICP-MS) was used to determine the concentration of platinum (Pt) in silicone breast implant gel (range, 0.26–48.90 g g^–1 Pt; n=15), elastomer (range, 3.05–28.78 g g^–1 Pt; n=7), double lumen (range, 5.79–125.27 g g^–1 Pt; n=7), foam (range, 5.79–8.36 g g^–1 Pt; n=2), and capsular tissue (range, 0.003–0.272 g g^–1 Pt; n=15). The results show that very high levels of Pt are present in the encasing elastomer, double lumen, and foam envelope materials. Silicone breast implants can be a source of significant Pt exposure for individuals with these implants.     

A highly sensitive high-performance liquid chromatographic procedure for the determination of isocyanates in air

Summary A sensitive high-performance liquid chromatographic procedure is described to analyse hexamethylene diisocyanate (HDI), 2,4- and 2,6-toluene diisocyanate (TDI), and 4,4-diphenylmethane diisocyanate (MDI) in air. The isocyanates are trapped on a sorbent coated with 1-(2-methoxyphenyl)piperazine (MPP). The resulting derivatives are separated using a column switching technique using either a diode array UV detector or an electrochemical detector. Working ranges are 1–5000 and 0.05–400 pmol for UV and EC detection, respectively. Virtually no breakthrough occurs if an air volume of up to 1500 l is sampled, and relative detection limits between 0.1 and 1 ng/m³ can be achieved. The procedure can be used to determine HDI and MDI in work place atmospheres and indoor air.Dedicated to Prof Dr. E. Lahmann on the occasion of this 65th birthday     

Development of a competitive liposome-based lateral flow assay for the rapid detection of the allergenic peanut protein Ara h1

A competitive lateral flow assay for detecting the major peanut allergen, Ara h1, has been developed. The detector reagents are Ara h1-tagged liposomes, and the capture reagents are anti-Ara h1 polyclonal antibodies. Two types of rabbit polyclonal antibodies were raised either against the entire Ara h1 molecules (anti-Ara h1 Ab) or against an immunodominant epitope on Ara h1 (anti-peptide Ab). All of them reacted specifically with Ara h1 in Western Blot against crude peanut proteins. Moreover, the anti-Ara h1 Ab was chosen for this assay development because of its highest immunoactivity to Ara h1-tagged liposomes in the lateral flow assay. The calculated limit of detection (LOD) of this assay is 0.45 g mL^–1 of Ara h1 with a dynamic range between 0.1 and 10 g mL^–1 of Ara h1 in buffer. Additionally, the visually determined detection range is from 1 to 10 g mL^–1 of Ara h1 in buffer. Results using this assay can be obtained within 30 min without the need of sophisticated equipment or techniques; therefore, this lateral flow assay has the potential to be a cost-effective, fast, simple, and sensitive method for on-site screening of peanut allergens.     

A novel dynamic approach for automatic microsampling and continuous monitoring of metal ion release from soils exploiting a dedicated flow-through microdialyser

In this paper, a novel concept is presented for automatic microsampling and continuous monitoring of metal ions in soils with minimum disturbance of the sampling site. It involves a hollow-fiber microdialyser that is implanted in the soil body as a miniaturized sensing device. The idea behind microdialysis in this application is to mimic the function of a passive sampler to predict the actual, rather than potential, mobility and bioavailability of metal traces. Although almost quantitative dialysis recoveries were obtained for lead ( 98%) from aqueous model solutions with sufficiently long capillaries (l 30 mm, 200 m i.d.) at perfusion rates of 2.0 L min^–1, the resistance of an inert soil matrix was found to reduce metal uptake by 30%. Preliminary investigation of the potential of the microdialysis analyser for risk assessment of soil pollution, and for metal partitioning studies, were performed by implanting the dedicated probe in a laboratory-made soil column and hyphenating it with electrothermal atomic absorption spectrometry (ETAAS), so that minute, well-defined volumes of clean microdialysates were injected on-line into the graphite furnace. A noteworthy feature of the implanted microdialysis-based device is the capability to follow the kinetics of metal release under simulated natural scenarios or anthropogenic actions. An ancillary flow set-up was arranged in such a way that a continuous flow of leaching solution — mild extractant (10^–2 mol L^–1 CaCl₂), acidic solution (10^–3 mol L^–1 HNO₃), or chelating agent (10^–4 or 10^–2 mol L^–1 EDTA) — was maintained through the soil body, while the concentration trends of inorganic (un-bound) metal species at the soil-liquid interface could be monitored at near real-time. Hence, relevant qualitative and quantitative information about the various mobile fractions is obtained, and metal-soil phase associations can also be elucidated. Finally, stimulus-response schemes adapted from neurochemical applications and pharmacokinetic studies are to be extended to soil research as an alternative means of local monitoring of extraction processes after induction of a chemical change in the outer boundary of the permselective dialysis membrane.     

Determination of suspended particulates matter of major significance to human health using nuclear techniques in kenya

Energy dispersive X-ray fluorescence (EDXRF) analysis of aerosol samples in Nairobi is presented. Results show that elemental concentrations are of the order of 10^–4 to 10^–6 g/m³ for most elements analyzed. The total suspended particulate (TSP) matter was between 30–80 g/m³ for the entire sampling period between December 1993 to October 1994. Levels of lead (Pb) are below WHO guidelines. However, the obtained bromine (Br) to Pb ratio: 0.3–0.51, shows the origin of Pb to be from vehicular emissions. This ratio was particularly high during the months of April to July 1994 which were also found to be very active in terms of weather parameters.     

Method comparison study on soot-selective techniques

In a long-term field study at two locations with different air pollution levels several soot-selective measurement techniques were compared with a thermochemical method which measures non-extractable carbon (NEC) detecting the evolved CO₂ by means of coulometric titration. The attenuation measurement technique (aethalometer) and the aerosol photoemission method showed good correlations to NEC for concentrations ranging from 1.6g/m³ to 40.8g/m³. The specific mass absorption coefficient of black carbon with respect to NEC varied between 8.4m²/g and 13.7m²/g with respect to the measurement sites, but the value was found to remain constant at each site independent of seasonal or meteorological variations. The ratio of photoelectric signal to NEC varied between 16 fA·(g/m³)^–1 and 33 fA·(g/m³)^–1 depending on the age of the aerosol. The diurnal variations of that ratio showed strong similarities to the traffic patterns. Additionally a slight temperature dependence of this ratio was found for the aged aerosol with a proportionality factor of – 0.35 fA·(K·g/m³)^–1. With the reflectance measurement technique (smoke shade method) reliable NEC determination was not possible for NEC concentrations 5 g/m³.     

Liquid chromatography of phenolic compounds in natural water using on-line trace enrichment

Summary Two packing materials, C18 and PLRP-S, are studied for on-line trace enrichment of phenolic compounds in water. Various precolumns of different internal diameter are also tested and the addition of an ion-pair reagent to increase retention and thus, breakthrough volumes of phenolic compounds, is studied. Best results are obtained when a PLRP-S precolumn is coupled on-line with a C18 analytical column and DAD detector. Addition of TBA considerably increases breakthrough volumes. In contrast, when a C18 precolumn is used, breakthrough volumes are lower and it is impossible to determine TCP and PCP, under the experimental conditions used, because of interference of other nonpolar compounds in the samples. The performance of the system is evaluated with river and tap water and the preconcentration of 10 ml of sample in a PLRP-S precolumn involves a linear range between 1 g 1^–1 and 20 l^–1 and limits of determination between 0.5 g l^–1 and 1 g l^–1 are obtained.     

The lipid composition of the Western Mediterranean aerosol

Summary Marine remote aerosol samples collected in a fixed station situated at 1100 m above sea level in Mallorca Island (Western Mediterranean) have been analyzed for lipids, both neutral and acidic, by capillary gas chromatography (GC) and GC coupled to mass spectrometry. Higher plant and algal compounds are predominant. The former encompass distributions of even numbered C22–C32 n-alkan-1-ols (8–21 ng/m³) and n-aldehydes, C25–C32 odd numbered n-alkanes (3–6 ng/m³), and n-nonacosan-10-ol, -sitosterol (0–0.09 ng/m³), dehydroabietic acid and triterpenols. The latter are constituted by even numbered C14–C18 fatty acids (0.6–30 ng/m³) and cholest-5-en-3-ol (0–0.86 ng/m³). Pyrolytic polycyclic aromatic hydrocarbons are also found (86–410 pg/m³) whereas direct petrogenic inputs are not significant.     

Analysis of high-purity reagents using automatic on-line column preconcentration-separation and electrothermal atomic absorption spectrometry

Summary A fully automatic flow-injection on-line column preconcentration and separation procedure for electrothermal atomic absorption spectrometry is described for the determination of cadmium and lead in high-purity reagents. A microcolumn with 9 L of solid sorbent, introduction of air prior to elution, and use of methanol as the eluent made it possible to elute the sorbed analyte quantitatively with only 80 L of solvent. The total eluate volume was transferred into the graphite tube which was pre-heated to 80°C using a flow rate of 0.08 mL min^–1 which allowed the solvent to evaporate in part during eluate introduction. The efficiency of the total procedure was 0.63 and 0.65, and the enrichment factor was 62 and 64 for cadmium and lead, respectively, compared with the direct introduction of 30 L of an aqueous solution. The sample throughput was 13 h^–1 for a sample loading time of 60 s and the detection limits (3 ) were 0.7 and 4.5 ng L^–1 for cadmium and lead, respectively. The relative standard deviation of the entire procedure in the optimum working range was typically around 3% (n=6). A number of high purity (suprapure) and analytical grade (pro analysi) reagents were analyzed, and spiking experiments resulted in recoveries of 97–104%.Dedicated to Professor Dr. Wilhelm Fresenius on the occasion of his 80th birthdayOn leave from Jiangsu Institute of Petrochemical Technology, Changzhou, Jiangsu, China     

Use of a stopped-flow technique for investigation and determination of thiourea and its <Emphasis Type="Italic">N</Emphasis>-methyl derivatives as inducers of the iodine–azide reaction

A stopped-flow technique has been used to investigate the behaviour of 2-thiourea, 1-methyl-2-thiourea, 1,3-dimethyl-2-thiourea, and 1,1,3,3-tetramethyl-2-thiourea in the induced iodine–azide reaction. This technique enables the progress of the reaction to be followed by monitoring the decrease in the absorbance of the iodine–starch complex at 595 nm. The effect of the concentration of the reagents on the rate of the reaction was investigated and a kinetic method for determination of the compounds is proposed. 2-Thiourea, 1-methyl-2-thiourea, and 1,3-dimethyl-2-thiourea can be determined in the range 3–75 mol L^–1 and 1,1,3,3-tetramethyl-2-thiourea in the range 2–200 mol L^–1.     

Gas-chromatographic determination of airborne monoethanolamine using reagent-coated adsorbent tubes

A sampling and analytical procedure was developed for the monitoring of airborne monoethanolamine (MEA). The analyte is collected by drawing air through the adsorbent tubes containing XAD-4 resin coated with cyclohexanone as a derivatising reagent. Derivatisation takes place during sampling. After desorption with methanol, the MEA derivative was quantified by gas chromatography using a thermionic specific detector (TSD) in the nitrogen mode. Application of cyclohexanone as a derivatising reagent gives a more stable product and TSD allows subsequent GC analysis in the presence of excess reagent. The structure of the MEA derivative was confirmed by mass spectrometry. The lower limit of detection for MEA was 1 g and the detector response was linear between 5 and 200 g. The working range of the method is 0.5 to 20 mg/m³ in a 10 l air sample. Collected samples were stable for at least 2 weeks at 4°C and room temperature. The efficiency of sampling was evaluated using a Test Atmosphere Generation System.Presented at the Lab-Ex 1990 Conference in Palais de Congres, Montreal, during October 23–24, 1990     

A new polymeric chromogenic reagent for dual-wavelength spectrophotometric determination of iron(III)

By condensing chitosan with 7-(4-formyl-phenylazo)-8-quinolinol-5-sulfonic acid (FPAQS), a new polymeric chromogenic reagent C-FPAQS has been synthesized and its properties investigated. In acidic media (pH 2.7), C-FPAQS reacts with iron(III) to yield an orange complex with a molar absorptivity of 2.8 × 10⁴ lmol^–1 cm^–1 at 420 nm, and in the meantime a negative peak at 524 nm. The apparent molar absorptivity (420–524 nm) obtained by dual-wavelength measurements is 7.9 × 10⁴lmol^–1cm^–1 which is about two times higher than that by single-wavelength measurements at 420 nm Beer's law is obeyed in the range of 0–0.8 g ml^–1 for iron(III). The developed method has been satisfactorily used to determine iron at the 0.03 to 3% (ww) level in a nylon-6 and in a soil sample. Compared to the corresponding low-molecular weight FPAQS and other chromogenic reagents, C-FPAQS has not only good sensitivity but also largely increased acid solubility and improved selectivity for iron, which may be explained by the incorporation of FPAQS into an acid-soluble polymer.