Quantitative analysis of perfumes in talcum powder by using headspace sorptive extraction

Quantitative analysis of perfume dosage in talcum powder has been a challenge due to interference of the matrix and has so far not been widely reported. In this study, headspace sorptive extraction (HSSE) was validated as a solventless sample preparation method for the extraction and enrichment of perfume raw materials from talcum powder. Sample enrichment is performed on a thick film of poly(dimethylsiloxane) (PDMS) coated onto a magnetic stir bar incorporated in a glass jacket. Sampling is done by placing the PDMS stir bar in the headspace vial by using a holder. The stir bar is then thermally desorbed online with capillary gas chromatography-mass spectrometry. The HSSE method is based on the same principles as headspace solid-phase microextraction (HS-SPME). Nevertheless, a relatively larger amount of extracting phase is coated on the stir bar as compared to SPME. Sample amount and extraction time were optimized in this study. The method has shown good repeatability (with relative standard deviation no higher than 12.5%) and excellent linearity with correlation coefficients above 0.99 for all analytes. The method was also successfully applied in the quantitative analysis of talcum powder spiked with perfume at different dosages.     

Determination of partition coefficients by automatic equilibrium headspace gas chromatography by vapor phase calibration

Summary Equilibrium headspace gas chromatography has been applied to the determination of the partition coefficients of volatile compounds in water-air systems. Only techniques that are suited to a fully automatic headspace procedure using the pneumatic headspace sampling-technique have been considered. Particularly simple is the technique of vapor phase calibration —VPC where an external vapor standard is used to calibrate the concentration of the volatile analyte in the headspace, while the concentration in the sample is found from the difference in the total amount in the vial. This technique is described in detail for 2-butanone in water. Finally, the water-air partition coefficients of several selected volatile compounds at different temperatures are listed together with their temperature functions.Dedicated to Professor Leslie S. Ettre on the occasion of his 70th birthday.     

Application of the headspace analysis to systems with unknown partition coefficients

Summary Possibilities for the quantitative determination of volatile constituents in solutions by headspace analysis are investigated in cases where the partition coefficients (K) depend on the composition of the object under study. The timeconsuming work of revealing and taking into account the effect of the analytes and the other present constituents on the magnitude of K can be eliminated if simultaneously with determining the analyte content in the equilibrium gas one also measures the partition coefficients characteristic for the solution under study. These quantities can be obtained by repeated analysis of the equilibrium gas after partial removal of the volatile solution constituents. At small K (0.1 to 10) the required change of analyte concentration in the solution can be attained by single replacement of the equilibrium gas by pure gas, and at large K, by passing a known volume of pure gas through the solution under study under equilibrium conditions. The paper establishes the range of applicability of each version, provides the necessary equations and presents the results of an experimental check in the case of determining alcohol admixtures in water solutions.     

Determination of beer aroma compounds using headspace solid-phase microcolumn extraction

A rapid sampling technique for the analysis of beer aroma compounds is described. The headspace (10 ml) is passed through the microcolumn filled with 5 mg of Tenax TA and thermally desorbed in a modified GC inlet (modification is described). Eight compounds (from acetaldehyde to 2-phenylethanol) in four beer samples were analyzed. The correlation coefficients (r²), repeatability (RSD) and limits of detection (LOD) were 0.9973-0.9994, 2.1-6.9% and 0.00002-0.13 mg/l, respectively. The methodology can be useful for routine beer sample analysis.     

Monitoring and fast detection of mycotoxin-producing fungi based on headspace solid-phase microextraction and headspace sorptive extraction of the volatile metabolites

Solid phase microextraction in combination with capillary GC-MS was used as monitoring technique for the collection and detection of the fungal volatile metabolite (+)-aristolochene by sporulated surface cultures of Penicillium roqueforti. A comparison was made between different toxigenic and nontoxigenic strains of P. roqueforti. Different growth conditions and media, such as malt extract agar, potato dextrose agar and sabouraud dextrose agar were compared. Whereas toxigenic strains produced large amounts of (+)-aristolochene, beta-elemene, valencene and germacrene A, nontoxigenic P. roqueforti strains showed a remarkably different headspace profile, in which ethyl-2-hexenoate, E-beta-caryophyllene, aromadendrene and beta-patchoulene were the predominant volatiles, apart from other sesquiterpene hydrocarbons present at lower concentrations. Stir bar sorptive extraction, was also applied in the headspace sampling mode, i.e. headspace sorptive extraction (HSSE) for the enrichment of fungal volatiles from sporulated surface cultures to differentiate between toxigenic and nontoxigenic fungi. Hence, it can be concluded that headspace analysis of volatile fungal metabolites by SPME and HSSE in combination with capillary GC-MS is a suitable monitoring technique for the fast detection of mycotoxin producing fungi.     

Determination of fluoxetine in plasma by gas chromatography-mass spectrometry using stir bar sorptive extraction

This article presents a method employing stir bar sorptive extraction (SBSE) with in situ derivatization, in combination with either thermal or liquid desorption on-line coupled to gas chromatography-mass spectrometry for the analysis of fluoxetine in plasma samples. Ethyl chloroformate was employed as derivatizing agent producing symmetrical peaks. Parameters such as solvent polarity, time for analyte desorption, and extraction time, were evaluated. During the validation process, the developed method presented specificity, linearity (R² > 0.99), precision (R.S.D. < 15%), and limits of quantification (LOQ) of 30 and 1.37 pg mL⁻¹, when liquid and thermal desorption were employed, respectively. This simple and highly sensitive method showed to be adequate for the measurement of fluoxetine in typical and trace concentration levels.     

Determination of gas-liquid partition coefficients by gas chromatography

This review covers theoretical principles and experimental procedures for the determination of gas-liquid partition coefficients, KL, by gas chromatography. In order to precisely define the relationship between KL, retention time and experimental parameters, the retention theory, both for ideal and for imperfect gas phase, is expounded. The most important sources of systematic error, as peak asymmetry, mixed retention mechanisms, column hold-up time and stationary phase mass determination, are discussed. Although the review is focussed on packed columns, comparison to capillary columns is discussed in those aspects in which these last show advantages.     

Non-destructive method to determine halophenols and haloanisoles in cork stoppers by headspace sorptive extraction

The new solvent-free technique called headspace sorptive extraction (HSSE) was used to determine 2,4,6-trichlorophenol, 2,3,4,6-tetrachlorophenol, 2,4,6-trichloroanisole, 2,3,4,6-tetrachloroanisole, 2,4,6-tribromoanisole, pentachloroanisole in cork stoppers, without grinding them, as these may be responsible for the cork taint off-flavour in wine. The best HSSE sorption kinetics for the target analytes were obtained after submitting the spiked corks to 100 degrees C for 1h, followed by a 30 min stabilization time at room temperature. The stir bar was desorbed in a thermal desorption system coupled to a gas chromatograph-mass spectrometer. The method proposed showed good linearity over the concentration range tested, 1-70 ngg(-1), and correlation coefficients ranged from 0.90 to 0.99 for all the analytes. The reproducibility and repeatability of the method were estimated between 4.91 and 12.67%. The effect of the different cork matrixes on the extraction recovery of the target compounds was studied, with the natural corks showing the higher recovery percentage in relation to agglomerate ones.     

Determination of liquid-liquid partition coefficients by separation methods

By essence, all kinds of chromatographic methods use the partitioning of solutes between a stationary and a mobile phase to separate them. Not surprisingly, separation methods are useful to determine accurately the liquid-liquid distribution constants, commonly called partition coefficient. After briefly recalling the thermodynamics of the partitioning of solutes between two liquid phases, the review lists the different methods of measurement in which chromatography is involved. The shake-flask method is described. The ease of the HPLC method is pointed out with its drawback: the correlation is very sensitive to congeneric effect. Microemulsion electrokinetic capillary electrophoresis has become a fast and reliable method commonly used in industry. Counter-current chromatography (CCC) is a liquid chromatography method that uses a liquid stationary phase. Since the CCC solute retention volumes are only depending on their partition coefficients, it is the method of choice for partition coefficient determination with any liquid system. It is shown that Ko/w, the octanol-water partition coefficients, are obtained by CCC within the -1 < log Ko/w < 4 range, without any correlation or standardization using octanol as the stationary phase. Examples of applications of the knowledge of liquid-liquid partition coefficient in the vast world of solvent extraction and hydrophobicity estimation are presented.     

Rapid headspace gas chromatographic method for the determination of liquid/gas partition coefficients

A rapid, efficient and low-cost headspace technique useful for the determination of liquid/gas partition coefficients of gases and volatile substances of low and intermediate solubility is described. The equilibration step is carried out at constant pressure using glass syringes, with a ratio of liquid/gas phase volumes of ca. 1:3; after 30 min at the desired temperature, the headspace is recovered by transfer into another syringe and analyzed by gas chromatography. A study of the partition coefficients in water at 37 degrees C of 27 volatile compounds demonstrated that the method is fully applicable for all gases, with exception of those with a partition coefficient higher than 300.     

Suitability of polydimethylsiloxane rods for the headspace sorptive extraction of polybrominated diphenyl ethers from water samples

The suitability of an inexpensive polydimethysiloxane (PDMS) sorbent, produced on an industrial scale, for the extraction of polybrominated diphenyl ethers (PBDEs), from tetra- to hexabrominated congeners, from water samples was assessed. Experiments were carried out using samples spiked with a pentabromo diphenyl ether (pentaBDE) mixture, PDMS rods with a diameter of 2 mm and gas chromatography with micro-electron-capture detection (GC-micro-ECD). Influence of several variables on the efficiency of the enrichment step and the further desorption of the analytes was investigated in detail. The best performance was achieved in the headspace sorptive extraction (HSSE) mode, at 95 degrees C, using 80 mL water samples containing a 30% of sodium chloride. Extractions were performed overnight using disposable PDMS rods with a length of 10 mm (31 microL volume). Analytes were further recovered from the PDMS sorbent using just 1 mL of diethyl ether. This solvent was evaporated and extracts reconstituted with 25 microL of isooctane. Under final working conditions absolute extraction efficiencies from 69 to 93% and enrichment factors higher than 2200 folds were achieved for all species. The proposed method provided acceptable precisions (relative standard deviations values under 12%), correlation coefficients higher than 0.998 and the yield of the HSSE process remained constant for different water samples.     

Determination of pesticides in river water using rotating disk sorptive extraction and gas chromatography-mass spectrometry

The rotating disk sorptive extraction (RDSE) technique was applied to the determination of pesticides in aqueous samples. Pesticides of different polarities were considered in this study: chlorpyrifos, diazinon, fenvalarate, cyhalothrin, cypermethrin, lindane and malathion. The sorptive/desorptive behavior of the pesticides was studied using a rotating disk containing a polydimethylsiloxane (PDMS) phase on one of its surfaces. The analyte polarity was a significant factor in the extraction time; shorter extraction times were required for the more apolar pesticides. The optimum variables for the extraction of all analytes were: extraction time of 3 h, sample volume of 25 mL, rotational velocity of the disk 1250 rpm, desorption time of 30 min using methanol. For pesticides with values of Log K_ow > 4, the extraction time can be reduced to 30 min for a quantitative extraction. Under these conditions, recoveries between 76% and 101% were obtained for the target pesticides, and the repeatability of the methodology, expressed as relative standard deviation, was determined to be between 10% and 20%. Additionally, the limits of detection of the analytes were lower than 3.1 μg L⁻¹. The extraction method developed using the RDSE was compared to a stir bar sorptive extraction (SBSE) under the same conditions. It can be observed that the extraction using the rotating disk offers higher recoveries because of its higher PDMS volume and its higher surface area to volume ratio that allows for improved mass transfer.     

Optimization and validation of headspace sorptive extraction for the analysis of volatile compounds in wine vinegars

Quantification of aroma compounds in wine vinegars is challenging due to the complexity of the matrix and the low concentrations expected. A method for the determination of volatile compounds in wine vinegars employing headspace sorptive extraction-thermal desorption-gas chromatography-mass spectrometry (HSSE-TD-GC-MS) was developed. A central composite design was used to optimize the sampling condition. The proposed method was successfully validated and low detection and quantification limits was obtained. The application of the proposed methodology allows the determination of 53 compounds in different wine vinegars (red, Sherry). Five of them have been detected in wine vinegars for the first time.     

Influence of polydimethylsiloxane outer coating and packing material on analyte recovery in dual-phase headspace sorptive extraction

Dual phase twisters (DP twisters), consisting of a polydimethylsiloxane (PDMS) outer coating and a second complementary (ad)sorbent as inner packing, have recently been shown to extend the applicability of headspace sorptive extraction (HSSE). In comparison to HSSE using PDMS only, the recovery of analytes from the headspace of a solid or liquid matrix is increased by combining the concentration capabilities of two sampling materials operating on different mechanisms (sorption and adsorption). This study compares the performance of DP twisters consisting of different PDMS outer coatings and different packing materials, including Tenax GC, a bisphenol-PDMS copolymer, Carbopack coated with 5% of Carbowax and beta-cyclodextrin, for the analysis of the headspace of roasted Arabica coffee, dried sage leaves and an aqueous test mixture containing compounds with different water solubility, acidity, polarity and volatility as test samples. In general, DP twisters showed a higher concentration capability than the corresponding conventional PDMS twisters for the analytes considered. The highest recoveries were obtained with DP twisters consisting of 0.2mm thick PDMS coating combined with Tenax GC, a bisphenol-PDMS copolymer and Carbopack coated with 5% of Carbowax as inner adsorption phase.     

Determination of benzothiazole in untreated wastewater using polar-phase stir bar sorptive extraction and gas chromatography-mass spectrometry

Stir bar sorptive extraction (SBSE) was applied to extract benzothiazole (BT) from untreated wastewater using a novel polyacrylate (PA)-coated stir bar (PA Twister^®). After extraction, BT was desorbed in a thermal desorption system (TDS) and analysed by GC–MS (gas chromatography–mass spectrometry). The sample contained 30% (w/w) NaCl, the sample temperature was 30 °C and the extraction time was 240 min. Since no filtering or clean-up steps or solvents were necessary SBSE clearly performs better than all previously used extractions techniques for analysing BT in untreated wastewater in terms of easy use, sample throughput and analytical costs. In addition, matrix effects were small. The calibration curve resulting from the standard addition method was linear with a value of the stability index (R²) of 0.999 (n = 3). A good inter-day repeatability of the method was observed with a relative standard deviation (RSD) of 9.8% (n = 6). A low limit of detection (LOD) of 0.256 μg L⁻¹ was achieved using only a small sample volume of 18 mL. Small sample volumes significantly reduce sample transport costs. The concentration of BT in untreated wastewater was determined to be 1.04 μg L⁻¹.     

Measuring gas-liquid partition coefficients of aroma compounds by solid phase microextraction, sampling either headspace or liquid

Hydrophobic compounds are important odorants and nutrients in foods and beverages, as well as environmental contaminants and pharmaceuticals. Factors influencing their partitioning within multi-component systems and/or from the bulk liquid phase to the air are critical for understanding aroma quality and nutrient bioavailability. The equilibrium partitioning of hydrophobic analytes between air and water was analyzed using solid phase microextraction (SPME) in the headspace (HS-SPME) and via direct immersion in the liquid (DI-SPME). The compounds studied serve as models for hydrophobic aroma compounds covering a range of air-water partition coefficients that extends over four orders of magnitude. By varying the total amount of analyte as well as the ratio of vapor to liquid in the closed, static system, the partition coefficient, K(vl), can be determined without the need for an external calibration, eliminating many potential systematic errors. K(vl) determination using DI-SPME in this manner has not been demonstrated before. There was good agreement between results determined by DI-SPME and by HS-SPME over the wide range of partitioning behavior studied. This shows that these two methods are capable of providing accurate, complementary measurements. Precision in K(vl) determination depends strongly on K(vl) magnitude and the ratio of the air and liquid phases.     

Determination of partition coefficients of metals in the Sava River environment

Site specific data and partition coefficients of stable elements in the Sava River environment have been measured. Distribution of metals in periphyton was similar to those found in sediments from the same locations. The concentration ratios of periphyton over sediments for Zn, As, Cd and Pb exceeded one. Thus the content of these metals in periphyton provides more information about anthropogenic pollution than either sediment or water samples collected at the periphyton site. In addition, the enrichment factors of the most abundant metals in the sediment samples have been calculated.     

Determination of octanol/water partition coefficients by flow injection analysis

Determination of octanol/water partition coefficients by batch-extraction methods is currently the only acceptable procedure for application to structure/activity relationships. Work on the development of flow-injection systems to determine these partition coefficients is reported. It is shown that it is not necessary to know the concentration of the analytic in either phase; the partition coefficient should be equal to the differences in the octanol and water peak widths divided. by the system residence time. For a limited number of compounds, this is shown to be valid. Several systems were developed, including a flow-through dialyzer which was 5 times more efficient than the best commercial unit.     

Non-linear modeling of bioconcentration using partition coefficients for narcotic chemicals

Bioconcentration factors (BCFs) have traditionally been used to describe the tendency of chemicals to concentrate in aquatic organisms. A reexamination of the log-log QSAR between the BCF and K OW for non-congener narcotic chemicals is presented on the basis of recommended data for fish. The model is extended to give a simple correlation between BCF and the toxicity of highly, moderately and weakly hydrophilic chemicals. For the first time, in this study an equation for calculating BCF was applied in a QSAR model for predicting the acute toxicity of chemicals to aquatic organisms.