Adsorption studies of dodecylamine at the quartz interface using an electrode-separated piezoelectric sensor

The adsorption process of dodecylammonium chloride (DAC) from aqueous solutions onto a quartz crystal interface was investigated in situ using an electrode-separated piezoelectric sensor (ESPS). Increasing amounts of DAC adsorbed onto a quartz crystal surface resulted in linearly decreasing oscillating frequencies of the ESPS. The adsorption density can be monitored by the frequency decrease. The adsorption density obtained by calculation using the Sauerbrey equation in the ESPS method is greater than that in solution depletion method. A calibration coefficient is added into the Sauerbrey equation to correct the influence of surface roughness of the quartz crystal on the adsorption density. The influence of solution properties on the adsorption density measurement was discussed. A dependence of the adsorption density on pH was reported. Received: 17 April 1997 / Revised: 1 December 1997 / Accepted: 7 December 1997     

Adsorption studies of dodecylamine at the quartz interface using an electrode-separated piezoelectric sensor

The adsorption process of dodecylammonium chloride (DAC) from aqueous solutions onto a quartz crystal interface was investigated in situ using an electrode-separated piezoelectric sensor (ESPS). Increasing amounts of DAC adsorbed onto a quartz crystal surface resulted in linearly decreasing oscillating frequencies of the ESPS. The adsorption density can be monitored by the frequency decrease. The adsorption density obtained by calculation using the Sauerbrey equation in the ESPS method is greater than that in solution depletion method. A calibration coefficient is added into the Sauerbrey equation to correct the influence of surface roughness of the quartz crystal on the adsorption density. The influence of solution properties on the adsorption density measurement was discussed. A dependence of the adsorption density on pH was reported. Received: 17 April 1997 / Revised: 1 December 1997 / Accepted: 7 December 1997     

Development of a calibration instrument for the dynamic generation of organic vapors

A computer controlled automatic calibration apparatus for the dynamic generation of organic vapors was developed. A calibration loop was filled by diffusion with organic compounds and diluted using nitrogen as a carrier gas. The compound holder pipe was thermostated at 40°?C. Fittings were made of PTFE and the valves were constructed of stainless steel. Moisture interferences were reduced using a Nafion membrane filter. The vapor generator was validated by a gas chromatographic method. The measured and calculated values were compared and good correlation (r = 0.9903) was found.     

A flow analysis system with an amperometric detector for the determination of hydrogen sulphide in waters

 A flow analysis system with an amperometric H₂S detector and a gas extraction unit as well as an integrated coulometric calibration unit is described, which allows an on-line determination of hydrogen sulphide in aquatic samples. By variation of different parameters (e.g. flow rate, gas injection volume, pH of solution) a wide dynamic working range of concentrations from 1 μmol/l H₂S to 750 μmol/l is accessible. The sampling rate is about 36 samples h⁻¹ using an average flow rate of 1.78 ml/min and a gas injection volume of 28 μl. The measuring system is designed as a portable device. In combination with the polyethylene-tube of a PTFE-underwater pump field-measurements on board are possible. Received: 16 February 1995/Revised: 5 April 1995/Accepted: 11 April 1995 Acknowledgements. This work was supported by the Bundesminister für Forschung und Technologie under the project “DYSMON II” (03F0123D) and by the Fonds der Chemischen Industrie zur F?rderung von Chemie und Biologischer Chemie. Correspondence to: P. Jeroschewski     

Distillation preconcentration and clean-up of aqueous samples for direct aqueous injection-gas chromatographic determination of volatile polar organic pollutants

The applicability of distillation to concentrate and clean up heavily loaded aqueous samples for the analysis of volatile polar organic compounds by means of direct aqueous injection-gas chromatography was studied. Recoveries for acetone, acetonitrile, acrolein, acrylonitrile, butanone, 1,4-dioxane, ethyl acetate, and 3-pentanone were in the range of 60.6 to 73.4% with relative standard deviations of 3.6 to 5.5%. The corresponding enrichment factors were in the order of 200. The recovery did not depend on the concentration in the studied range of 0.70 to 89 μg/kg. The detection limits with the mass selective detector operating in the selected ion monitoring mode were in the order of 0.1 μg/kg. The method was successfully applied to treated waste water from a pharmaceutical factory. The content of the above analytes in the real sample ranged from below 0.1 to ca. 83 μg/kg. Received: 16 December 1996 / Revised: 9 April 1997 / Accepted: 16 April 1997     

Distillation preconcentration and clean-up of aqueous samples for direct aqueous injection-gas chromatographic determination of volatile polar organic pollutants

The applicability of distillation to concentrate and clean up heavily loaded aqueous samples for the analysis of volatile polar organic compounds by means of direct aqueous injection-gas chromatography was studied. Recoveries for acetone, acetonitrile, acrolein, acrylonitrile, butanone, 1,4-dioxane, ethyl acetate, and 3-pentanone were in the range of 60.6 to 73.4% with relative standard deviations of 3.6 to 5.5%. The corresponding enrichment factors were in the order of 200. The recovery did not depend on the concentration in the studied range of 0.70 to 89 μg/kg. The detection limits with the mass selective detector operating in the selected ion monitoring mode were in the order of 0.1 μg/kg. The method was successfully applied to treated waste water from a pharmaceutical factory. The content of the above analytes in the real sample ranged from below 0.1 to ca. 83 μg/kg. Received: 16 December 1996 / Revised: 9 April 1997 / Accepted: 16 April 1997     

Development of porous and dispersed CRM

Porous and finely dispersed certified reference materials (CRM) were certified using the gas adsorption method. The special certification procedure for IUPAC isotherm classification types I, II, and IV is presented for meso- and macroporous materials with special emphasis on specific surface area, specific pore volume and pore width according to standards DIN 66 131, 66 134, and 66 135. Four CRMs (SiO₂, α-Al₂O₃, two transition aluminas) with a macro- and mesopore range are presented. Certification was made on the basis of BCR guidelines in connection with interlaboratory tests (altogether 38 participating laboratories, 44 various gas adsorption apparatus). Received: 25 April 1997 / Revised: 22 August 1997 / Accepted: 28 August 1997     

Enantioseparation of four-membered rings by gas chromatography; an overview

The separation of enantiomers by gas chromatography on a chiral stationary phase is stored and conveniently retrieved in the molecular database Chirbase/GC. According to the present information content (version 3/96), a great variety of analytes has been published in several hundred journals. A selected review is given on 364 enantiomer separations of 102 different molecules containing at least one four-membered saturated carbocyclic ring. Factors determining the degree of enantioseparation are outlined and analyzed. Received: 16 November 1996 / Revised: 17 April 1997 / Accepted: 30 April 1997     

Enantioseparation of four-membered rings by gas chromatography; an overview

The separation of enantiomers by gas chromatography on a chiral stationary phase is stored and conveniently retrieved in the molecular database Chirbase/GC. According to the present information content (version 3/96), a great variety of analytes has been published in several hundred journals. A selected review is given on 364 enantiomer separations of 102 different molecules containing at least one four-membered saturated carbocyclic ring. Factors determining the degree of enantioseparation are outlined and analyzed. Received: 16 November 1996 / Revised: 17 April 1997 / Accepted: 30 April 1997     

Water solubility and octanol/water-partitioning of hydrophobic chlorinated organic substances determined by using SPME/GC

The critical step in the determination of water solubilitiy (S _w) and octanol-water partition coefficient (K _ow) of hydrophobic organic chemicals by using the generator-column technique and the slow-stirring procedure, respectively, is the exact quantification of the low water-phase concentrations of the substances under investigation. We have tested the applicability of solid-phase microextraction (SPME) and gas chromatography with seven chlorinated organic compounds. The substances cover a S _w range from 500 mg/L to 7 ng/L and a log K _ow range from 3 to 8. The results show that SPME can be a valuable alternative to common preconcentration techniques in the quantification of hydrophobic organics in pure and octanol-saturated water. The apparent SPME distribution constants K _SPME (obtained with the 100 μm-PDMS fiber for analyte’s partitioning between fiber coating and aqueous sample) do not correlate directly with octanol/water partition coefficients and thus cannot be recommended as a surrogate parameter for K _ow. Received: 15 January 1997 / Revised: 2 May 1997 / Accepted: 8 May 1997     

Application of single-drop microextraction to the determination of dialkyl phthalate esters in food simulants

A fast and simple method, using static single-drop microextraction (SDME), has been developed to facilitate the identification and quantification of seven dialkyl phthalate esters in the three aqueous food simulants. The simulants were: A, distilled water; B, 3% (w/v) acetic acid/water; and C, 15% (v/v) ethanol/water. The extraction is performed by simply suspending a drop of organic solvent in the aqueous sample using a conventional gas chromatography (GC) microsyringe. Following extraction, the organic phase is withdrawn into the syringe and analyzed by gas chromatography and flame ionization detection (FID). The optimized method yields a linear calibration curve over three orders of magnitude for all the simulants, and method detection limits (MDLs) allowing detection of all the studied compounds at concentrations below migration limits established by the European Union. The accuracy of the SDME method was tested and compared to that of solid-phase microextraction (SPME) by recovery experiments using spiked samples, with results ranging from 85 to 115% in most cases.     

Karl Fischer titration A method for determining the true water content of cereals

A variation of the Karl Fischer titration was developed to measure the water content of cereals such as various grains and flours. The presented method is based on an elevated working temperature. It can even reach the boiling point of the working medium which contains methanol as solvent. The influence of different sample preparations is also discussed. A standardized procedure could be found to achieve highly reproducible and statistically safe results. The proposed titration method can be carried out with titrators of different manufacturers. The method may serve as a reference technique for these products and, by consequence, as calibration method for other more rapid methods, which may then be used in the daily laboratory practice or in industrial production lines. Received: 28 April 1997 / Revised: 17 July 1997 / Accepted: 24 July 1997     

Use of calibration gases in the U.S. acid rain program

The United States Acid Rain Program continuous emission monitors (CEMs) have been successful in producing quality-assured data 95% of the time, and in meeting a relative accuracy standard of less than or equal to 10.0% at over 99% of the CEMs in the program. One key reason for this high accuracy is the required use of high quality calibration gases in certification and quality assurance/quality control (QA/QC) tests. An annual QA audit helps ensure high quality calibration gases. A third party purchases gases from gas vendors. An Environmental Protection Agency (EPA) laboratory analyzes the gases and compares the results with the tag value on the cylinder. The results are posted on an EPA website. This allows purchasers of calibration gases to buy gases from vendors producing the most accurate gases. Over time, we believe it also results in better accuracy from all gas vendors. Because of a change in SO₂ quantification methodology, SO₂ emissions were underreported by approximately 2% between 1989 and 1996. EPA, the National Institute for Standards and Technology and calibration gas vendors collaborated to produce a correction policy and a standard correction form to be used by affected electric utility plants. Calibration gas cylinder tag values were required to be corrected by 1 January, 1997. In the future, it is possible that cleaner, more varied sources will be regulated for greenhouse effect, ozone and toxic emissions control. This will probably require more accurate CEMs, lower calibration gas concentrations, and a broader menu of gas mixtures. Received: 23 December 1999 Accepted: 12 December 2000     

Field method for the micro-quantitative determination of tetracycline in human urine

A simple, fast and sensitive titrimetric method has been developed for the determination of tetracycline hydrochloride in human urine using m-dinitrobenzene as color agent and Dowex 1 × 8 as detection medium. Received: 26 February 1997 / Revised: 23 April 1997 / Accepted: 29. April 1997     

Platinum speciation with hyphenated techniques: high performance liquid chromatography and capillary electrophoresis on-line coupled to an inductively coupled plasma-mass spectrometer – application to aqueous extracts from a platinum treated soil

1. An on-line hyphenation of reversed phase high-performance liquid chromatography (RP-HPLC) with inductively coupled plasma-mass spectrometry (ICP-MS) is applied, using an ultrasonic nebuliser combined with a membrane desolvator as the interface. Thus, organic solvents (e.g. methanol, hexane) or gradients (e.g. methanol/water) as well as aqueous NaHCO₃/NaCl mixtures can be directly used without influence on the plasma. The high resolution power of HPLC enables the separation of Pt-species, whereas ICP-MS is taken for element specific detection with low detection limits. 2. Additionally, a powerful on-line coupling of capillary electrophoresis (CE) and ICP-MS [1, 2] was used for platinum speciation in parallel. With these two methods, independent from each other, first characterisation is achieved about the nature of Pt species formed by interaction with a soil. Aqueous extracts of a clay-like humic soil, treated with a Pt contaminated tunnel dust and Pt model compounds [3] were examined to elucidate transformation processes of Pt-species in a soil. Received: 19 February 1997 / Revised: 15 April 1997 / Accepted: 18 April 1997     

Platinum speciation with hyphenated techniques: high performance liquid chromatography and capillary electrophoresis on-line coupled to an inductively coupled plasma-mass spectrometer – application to aqueous extracts from a platinum treated soil

1. An on-line hyphenation of reversed phase high-performance liquid chromatography (RP-HPLC) with inductively coupled plasma-mass spectrometry (ICP-MS) is applied, using an ultrasonic nebuliser combined with a membrane desolvator as the interface. Thus, organic solvents (e.g. methanol, hexane) or gradients (e.g. methanol/water) as well as aqueous NaHCO₃/NaCl mixtures can be directly used without influence on the plasma. The high resolution power of HPLC enables the separation of Pt-species, whereas ICP-MS is taken for element specific detection with low detection limits. 2. Additionally, a powerful on-line coupling of capillary electrophoresis (CE) and ICP-MS [1, 2] was used for platinum speciation in parallel. With these two methods, independent from each other, first characterisation is achieved about the nature of Pt species formed by interaction with a soil. Aqueous extracts of a clay-like humic soil, treated with a Pt contaminated tunnel dust and Pt model compounds [3] were examined to elucidate transformation processes of Pt-species in a soil. Received: 19 February 1997 / Revised: 15 April 1997 / Accepted: 18 April 1997     

Long-term permeation properties of poly(1-trimethylsilyl-1-propyne) membranes in hydrocarbon—Vapor environment

Poly(1-trimethylsilyl-1-propyne) (PTMSP), a high free-volume glassy di-substituted polyacetylene, has the highest gas permeabilities of all known polymers. The high gas permeabilities in PTMSP result from its very high excess free volume and connectivity of free volume elements. Permeability coefficients of permanent gases in PTMSP decrease dramatically over time due to loss of excess free volume. The effects of aging on gas permeability and selectivity of PTMSP membranes continuously exposed to a 2 mol % n-butane/98 mol % hydrogen mixture over a period of 47 days are reported. The permeation properties of PTMSP membranes are quite stable when the polymer is continuously exposed to a gas mixture containing a highly sorbing organic vapor such af n-butane. The n-butane/hydrogen selectivity was essentially constant for the 47-day test period at a value of 29, or 88% of the initial value of the as-cast film of 33. Condensable gases such as n-butane may serve as a “filler” in the nonequilibrium free volume of the polymer, thereby preserving the high level of excess free volume. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 1483–1490, 1997     

Determination of copper, lead, cadmium, zinc, and iron in calcium fluoride and other fluoride-containing samples by means of direct solid sampling GF-AAS

Direct solid sampling graphite furnace AAS (SS-GF-AAS) provides an advantageous alternative to the conventional AAS which requires wet digestion of the samples. This method is suitable for trace element determination in calcium fluoride and other fluoride-containing samples. Matrix effects were studied by using calibration standards, certified reference materials with different matrices and by means of three-dimensional calibration. 3D calibration is suitable for selection of calibration samples for more reliable analyses. Cu, Pb, Cd, Zn, and Fe were determined by means of calibration with variation of sample weight using certified reference materials and suitable fluoride-containing calibration samples. Received: 25 July 1997 / Revised: 15 December 1997 / Accepted: 20 December 1997     

Determination of copper, lead, cadmium, zinc, and iron in calcium fluoride and other fluoride-containing samples by means of direct solid sampling GF-AAS

Direct solid sampling graphite furnace AAS (SS-GF-AAS) provides an advantageous alternative to the conventional AAS which requires wet digestion of the samples. This method is suitable for trace element determination in calcium fluoride and other fluoride-containing samples. Matrix effects were studied by using calibration standards, certified reference materials with different matrices and by means of three-dimensional calibration. 3D calibration is suitable for selection of calibration samples for more reliable analyses. Cu, Pb, Cd, Zn, and Fe were determined by means of calibration with variation of sample weight using certified reference materials and suitable fluoride-containing calibration samples. Received: 25 July 1997 / Revised: 15 December 1997 / Accepted: 20 December 1997     

Determination of total dissolved phosphorus in water samples by axial inductively coupled plasma atomic emission spectrometry

A procedure was developed to determine total dissolved phosphorus in groundwater-like samples using axial ICP-AES. Severe and peculiar matrix effects (strongly positive at lower and leveling off at higher matrix concentrations) in the presence of Na and Ca were observed. To reduce these matrix effects, a double approach was utilized consisting of a so-called minimum matrix in combination with an internal standard (Ga in this case). The ‘minimum matrix’ (small amounts of K, Mg and Na) was only added to the standard solution(s) used for the calibration. The detection limit for the whole procedure was 12 μg/L using the P213 nm line. Residual matrix effects were less than 3% (P213 nm line). Received: 21 February 1997 / Revised: 5 June 1997 / Accepted: 6 June 1997