Per Lövkvist

Mass transfer kinetics for analytical enrichment and sample preparation using supported liquid membranes in a flow system with stagnant acceptor liquid

Abstract Supported liquid membranes in a flow system have been utilized for selective sample enrichment, clean up and field sampling, prior to the application of chromatographic and spectrometric analytical methods. For similar objectives, supported liquid membranes may be combined with a number of other analytical systems. The technique has a wide range of applications, especially in the fields of enviromental analysis and bioanalysis. This paper presents the theoretical principles for the technique and the mass transfer kinetic equations relevant to most applications. Guidelines for the optimization of experimental conditions and physical dimensions of the extraction devices are discussed.

Measurement of aliphatic amines in ambient air and rainwater

Abstract Amine concentrations in ambient air and rainwater were measured at several sites in southern Sweden. Air samples were obtained by sampling in dilute H 2 SO 4 and measured by gas membrane enrichment in a liquid flow system followed by gas chromatography. The major amines in both air and rain were trimethylamine and methylamine, but dimethylamine, diethylamine and triethylamine were also detected and individually quantified. The total amine concentration was 0.16 – 2.8 nmol/m 3 in air and 30 – 540 nM in rain.

Determination of aliphatic amines in air by membrane enrichment directly coupled to a gas chromatograph

SummaryA method is described for the determination of shortchain aliphatic amines in ambient air based on impinger sampling in dilute H2SO4, selective enrichment across a PTFE gas membrane and quantification by gas chromatography. The enrichment step is carried out in a flow system directly connected to the chromatograph. The separation is performed on a packed column with nitrogen selective detection. The enrichment per sample volume was in the range 7.3 to 8.2 mL−1 for C1−C6 amines. Detection limits were ca 3–10 nM with enrichment of a 2.9 mL liquid sample. After impinger sampling of 5 m3 air in 10 mL absorption solution, this corresponds, to 0.4–0.8 ng/m3 (ca 0.2–0.5 ppt by volume) in air.

Determination of adsorption isotherms from chromatographic measurements, using the peak maxima method

Abstract Methods for the calculation of a non-linear sorption isotherm from chromatographic data in the presence of significant dispersion effects were compared using chromatographic peaks, generated by a computer from a known Langmuir isotherm. The most accurate and also most easily applied method involves the use of the retention volume at the peak maximum to calculate the slope of the isotherm at the concentration which corresponds to the height of the peak. The so-called method of “elution on a characteristic point” is only accurate when the peak-shaping effects of non-linearity are overwhelming compared with those of dispersion. This condition was not generally met, not even in cases when the diffuse flanks of peaks of various sizes coincided. An equation for non-ideal, non-linear chromatographic peaks developed by other authors under the assumption that the non-linearity effects are small was fitted to the peaks studied. As expected, this is an accurate method for the determination of the isotherm at low concentrations. At higher concentrations, large deviations from the correct isotherm were observed, also when satisfactory fittings were obtained.

Comparison of column packings for trace analysis of free amines by gas-liquid chromatography

Abstract Different packings have been compared with respect to their usefulness for trace analysis of free amines. It was found that 28% Pennwalt 223 with 4% KOH on Gas-Chrom R was the best all-round packing, especially for aqueous samples. The separation efficiency was best on Carbopack B with 4% Carbowax 20M and 0.8% KOH, and the most symmetrical peaks were obtained on Chromosorb 103. The results indicate that the choice of a nitrogen sensitive detector and the addition of ammonia to the sample solution is more important for a successful analysis than the choice of packing

Chromosorb 103 as an adsorbent for sampling of amines in air

Chromosorb 103 was investigated as an adsorbent for the sampling of amines in air. A model system was used in which N-methylmorpholine was sampled from a test atmosphere (concentration 0.25-7 mg/m3). The amine was thermally desorbed and analysed by gas chromatography. This method was compared with sampling by absorption in 0.05 M sulphuric acid. No significant difference was obtained between the two methods, indicating a 100% recovery. Amine concentrations in air could be determined with a relative standard deviation of less than 3%. The presence of moisture in the air was shown to have no influence on the recovery or reproducibility. The breakthrough volume (for a concentration of 0.65 mg/m3 in air with 70% humidity) is approximately 100 1 per gram of adsorbent. Adsorption tubes could be stored for at least 16 days before analysis without significant losses. A practical test demonstrated the applicability of the method.

Description of sample introduction in chromatography as a separate term in the mass-balance equation

Abstract The process of sample introduction into the chromatographic column is described as a separate term in the mass-balance equation. This approach is applied to non-ideal linear equilibrium chromatography, and a general explicit solution is derived for the case where the sample introduction is independent of the concentration within the column. Concentration and flux profiles are presented for a number of input profiles.

Analysis of Amines in the Industrial Environment

Abstract Different methods for gas chromatographic trace analysis of a wide variety of amines are described. Both packed columns and glass capillary columns are used. The advantages of a nitrogen selective detector and a nitrogen-free stationary phase are demonstrated. Special concern is devoted to direct analysis of free amines on packed columns in organic solvents as well as in alkaline aqueous solutions with varying salt concentrations. Determination limits below 0.1 ppm are usually obtained and the precision at the 1 ppm level is generally about 2–3%. A permethylation procedure applicable to aqueous solutions has been developed for polyamines. Air sampling in acidic absorption solutions as well as on a solid adsorbent (Chromosorb 103) combined with thermal desorption is discussed. Applications from various industries and from the building sector are presented.

Calculation of adsorption isotherms from chromatographic peak shapes

Abstract Jonsson, J.A. and Lovkvist, P., 1989. Calculation of adsorption isotherms from chromatographic peak shapes. Chemometrics and Intelligent Laboratory Systems , 5: 303–310. A numeric method is presented for the calculation of a nonlinear sorption isotherm from the shape of a chromatographic peak in the presence of significant dispersion effects (nonideal, nonlinear chromatography). The algorithm involves an initial guess for a reasonable isotherm function, and a reasonable value for D , the diffusion coefficient. This permits the calculation (by numerical solution of the pertinent nonlinear partial differential equation) of a new peak. Using the properties of the original peak and of the calculated peak, new estimates for the isotherm function and for D can be calculated. These calculations are repeated until the discrepancy between consecutive iterations is judged to be insignificant. The procedure was tested with computer-generated peaks and shown to converge to the expected isotherm curve after few iterations even if the initial guesses of isotherm shape and D are relatively coarse. A preliminary application to an experimentally measured chromatographic peak is also presented.