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PubMed2000

Production of tomato flavor volatiles from a crude enzyme preparation using a hollow-fiber reactor.

In recent years there has been an increase in the interest in the production of compounds by isolation from natural sources or through processes that can be deemed "natural". This is of particular interest in the food and beverage industry for flavors and aromas. Hexanal, organoleptically known to possess "green character", is of considerable commercial interest. The objective of this study was to determine if the enzyme template known to be responsible for the synthesis of hexanal from linoleic acid (18:2) in tomato fruits could be harnessed using a hollow-fiber reactor. A hollow-fiber reactor system was set up and consisted of a XAMPLER ultrafiltration module coupled to a reservoir. The enzyme template was extracted from ripe tomato fruits and processed through an ultrafiltration unit (NMWC of 100 kDa) to produce a retentate enriched in soluble and membrane-associated lipoxygenase (LOX) and hydroperoxide lyase (HPL). This extract was recirculated through the lumen of the hollow-fiber ultrafiltration unit with the addition of substrate in the form of linoleic acid, with buffer addition to the reaction flask to maintain a constant retentate volume. Product formation was measured in the permeate using solid phase microextraction (SPME) developed for this system. At exogenous substrate concentrations of 16 mM and a transmembrane pressure of 70 kPa, hexanal production rates are in the order of 5.1 microg/min. Addition of Triton X-100 resulted in membrane fouling and reduced flux. The reactor system has been run for periods of up to 1 week and has been shown to be stable over this period.

Aldehyde-Lyases↗

PubMed1998

Comparison of two sample preparation techniques for sniffing experiments with broccoli (Brassica oleracea var. italica Plenck).

The suitability of the headspace solid phase microextraction (HSSPME) for gas chromatography-olfactometry (GC-O) with aroma extract dilution analysis in comparison to the dynamic head space sampling on a Tenax trap was tested exemplarily by the aroma volatiles of fresh broccoli. A high number of odour sensations in qualitative olfactometry was registered with both sample preparation techniques. The key aroma compounds of the fresh broccoli material are represented by high flavour dilution factors with dynamic head space sampling and headspace SPME. The SPME method has found to be a convenient and fast technique suitable especially for qualitative GC-O. The adsorption selectivity of the fiber and the substance discrimination have to be taken into account for quantitative use like aroma extract dilution analysis.

Brassica↗

PubMed2002

Comparison of long-chain alcohols and other volatile compounds emitted from food-borne and related Gram positive and Gram negative bacteria.

Numerous reports have been published on the antimicrobial activity of synthetic volatile long chain alcohols, such as 1-decanol and 1-dodecanol, against bacteria and fungi. The objective of the present study was to survey microorganisms for emission patterns of naturally occurring long chain alcohols and other volatile components to determine if these compounds are associated with certain groups of bacteria. Cultures were grown in trypticase soy broth overnight and volatile compounds were trapped on a porous polymer and identified by mass spectrometry. Subsequently, volatile compounds were collected from 26 strains of food associated bacteria using solid-phase microextraction and analyzed by gas chromatography. Alcohols comprising 1-octanol, 1-decanol, and 1-dodecanol occurred as products from enteric Gram negative bacteria, which included Citrobacter, Enterobacter, Klebsiella, Salmonella, and Shigella. However, the long chain alcohols were not detected as products from the nonenteric Gram negative species studied which included Acinetobacter, Pseudomonas, and Shewanella. Among Gram positive bacteria, including Bacillus, Enterococcus, Lactococcus, Leuconostoc, Listeria, Staphylococcus, and Streptococcus, the only long chain alcohol detected was 1-decanol and, if present, it occurred in relatively small amounts. Other classes of compounds emitted by bacteria included methylketones and sulfides. The methylketones were found as products from Gram positive and Gram negative bacteria, whereas the sulfides were closely associated with Gram positive bacteria. In summary, the emission patterns of volatile compounds from bacteria showed many trends including the association of long chain alcohols with enteric Gram negative bacteria. The results provide a basis for future in vivo studies to determine if volatile compounds such as natural long chain alcohols function in the ecology of food-borne Gram negative bacterial pathogens.

Alcohols↗

PubMed2004

Application of HS-SPME and GC-MS to characterization of volatile compounds emitted from Osmanthus flowers.

Headspace solid-phase microextraction (HS-SPME) combined with gas chromatography-mass spectrometry (GC-MS) was developed for characterization of volatile compounds emitted from two varieties Osmanthus flowers of O. fragrans var. latifolius and O. fragrans var. thunbergii. The SPME parameters were studied, the optimum conditions of a 65 microm carbowax/divinylbenzene (CW/DVB), extraction temperature of 22 degrees C and extraction time of 10 min were obtained and applied to extraction of the volatile emissions. Fourteen compounds released from both varieties of Osmanthus flowers were separated and identified by GC-MS, which mainly included alpha-linalool, beta-linalool, trans-linalool oxide, cis-linalool oxide, alpha-lonone, beta-lonone, capraldehyde and decalactone. By comparing their peak areas, we found that the sums of the fourteen compounds from the two Osmanthus flowers were very close, while the relative contents of individual volatile compounds in the two emissions were very different. The relative content of alpha-linalool and beta-linalool in O. fragrans var. latifolius were 39.46% and 0.51%, while in O. fragrans var. thunbergii were 9.53% and 27.71%. Due to their different relative contents, the two varieties of flower have different fragrances.

Aldehydes↗

PubMedDate not supplied

Headspace solid phase micro extraction GC-ECD determination of volatile organic chlorinated hydrocarbons in soils.

Soil samples were suspended in a suitable aqueous solvent and a solid phase microextraction (SPME) fibre was used to sample the headspace (HS) for five volatile chlorinated compounds (VOX). Their determination was made by GC-ECD technique in the splitless mode. Preliminary studies on the effects of methanol and of the sand/clay ratio on the fibre extraction were made. Four experimental factors, namely, extraction time, extraction temperature, pH and NaCl%, able to affect distribution of the analytes among the four different phases, were varied in suitable ranges. A multivariate approach applied to the face centred cube (FCC) experimental design, was used to try to optimise the overall sample response. The suitable set of factors found for the determination of chloroform, 1,2-dichloroethane, trichloroethylene, 1,1 ,2-trichloroethane, 1,1,2,2-tetrachloroethane, was a compromise among the relevant optimal factor sets of the single analytes. Detection limits of 0.003 ng, 0.022 ng, 0.001 ng, 0.015 ng and 0.002 ng were found respectively for the five cited analytes. The method was successfully used to determine the analyte contents in two real soils sampled in an industrial area.

Chromatography, Gas↗

PubMedDate not supplied

SPME sampling of BTEX before GC/MS analysis: examples of outdoor and indoor air quality measurements in public and private sites.

This article presents the results of an exploratory application of the Solid Phase MicroExtraction (SPME) technique to the analysis of BTEX (benzene, toluene, ethylbenzene and xylenes) at the microg/m3 level in outdoor and indoor air. The salient features of the method validation are reported. As shown by the various examples of field sampling described, SPME technique appears as a method of choice for fast qualitative analysis and quantitative determination of Volatile Organic Compounds (VOC). The small dimensions of the SPME sampling system and the short sampling time let envisage its utilisation for the rapid diagnostic of outdoor and indoor air quality.

Air Pollutants↗

PubMed2004

Identification and biosynthesis of an aggregation pheromone of the storage mite Chortoglyphus arcuatus.

In an effort to identify new pheromones from mites, the headspace of undisturbed colonies of the storage mite Chortoglyphus arcuatus was analyzed by GC-MS by use of a closed-loop stripping apparatus (CLSA) or solid-phase microextraction (SPME). The major compound emitted from the mites is (4R,6R,8R)-4,6,8-trimethyldecan-2-one (4R,6R,8R-8). The structure was elucidated by analysis of the mass spectrum, synthesis of authentic samples, and gas chromatography on a chiral phase. Bioassays show that this compound, for which we propose the trivial name chortolure, is an aggregation pheromone for both sexes of this species. Several related compounds are released in smaller amounts by the mites. The alarm pheromones of these mites, neral and geranial, can only be found in total extracts of the mites, in which 8 occurs only in minute amounts. The method of sampling is therefore crucial for pheromone identification. Feeding experiments with deuterated propionate showed that chortolure is a polyketide, formed by successive addition of four propionate units to an acetate starter.

Acaridae↗

PubMedDate not supplied

High sensitivity identification of proteins by electrospray ionization tandem mass spectrometry: initial comparison between an ion trap mass spectrometer and a triple quadrupole mass spectrometer.

Recently, we have shown that a solid-phase-microextraction/capillary electrophoresis device coupled to an electrospray ionization triple quadrupole mass spectrometer through a microelectrospray interface represents a powerful analytical system for the rapid, conclusive and sensitive identification of proteins separated by gel electrophoresis. Here we report on the successful coupling of the same device to an electrospray ionization ion trap mass spectrometer and on the comparative evaluation of the performance of the triple quadrupole and ion-trap-based systems. In the ion trap mass spectrometer-based system, using a tryptic digest of a calibrated bovine serum albumin sample, we achieved limits of detection in the single mass spectrometry (MS) and tandem MS mode, respectively, of 400 amol (if 20 microL of solution at a concentration of 20 amol/microL was applied). The system was also successfully used to identify six yeast proteins isolated from a single analytical two-dimensional polyacrylamide gel. For the detection of unfragmented peptide ions both systems showed comparable sensitivity, whereas the ion-trap-based system showed superior performance with fragment ion spectra.

Amino Acid Sequence↗

PubMed2002

Topical formulation studies with DEET (N,N-diethyl-3-methylbenzamide) and cyclodextrins.

The purpose of this study was to investigate the utility of cyclodextrins as a safer alternative to the commonly used cosolvent ethanol in topical N,N-diethyl-3-methylbenzamide (DEET) formulations. Ethanol is a known penetration enhancer and would ideally not be used in a formulation containing DEET, a compound known for its potential toxicity. DEET formulations were prepared containing up to 20% w/w gamma-cyclodextrin (GCD) or 30% w/w hydroxypropyl-beta-cyclodextrin (HPBCD). These formulations were evaluated by determining the release rate of DEET from its vehicle through a synthetic membrane into a receiver medium with a high affinity for DEET using a fully automated Franz-diffusion cell system. DEET release was measured by ultraviolet spectrophotometry at 260 nm. Both the traditional Higuchi release model and an alternate repeated measures analysis of variance with nested factors were used to analyze the data. The influence of the cyclodextrins on the volatility of DEET was determined by solid-phase microextraction. Morphological characterization of the formulations was performed by light microscopy. Physical stability of the formulations was evaluated by rheology in an accelerated study performed at 50 degrees C for 28 days. The cyclodextrins caused a decrease in the release of DEET from its vehicle compared with an ethanol-containing formulation. This effect became more pronounced as the amount of cyclodextrin in the formulation was increased. The addition of the cyclodextrins resulted in a cream-like product compared with the ethanol formulation, which was a lotion. The DEET formulations had the following rank order of volatility: ethanol < DEET = GCD < HPBCD. Examination of the formulations by light microscopy indicated that the CD-based formulations produced a smaller and more homogeneous droplet size distribution than the ethanol-based formulations. The accelerated physical stability study indicated that cyclodextrin-based formulations are both technically and commercially feasible. Cyclodextrins are a promising alternative to ethanol in DEET-containing formulations. The reduced release rate of DEET from these formulations suggests that the toxic potential of DEET may be decreased in these products, while its repellency and stability are maintained.

Administration, Topical↗

PubMed2026

Multi-omics characterization of flavor profile differences in the Longissimus thoracis between Angus and Hereford cattle.

BACKGROUND: Angus and Hereford cattle are premier breeds widely used in genetic improvement and crossbreeding programs to enhance meat quality, yet the flavor differences between them remain poorly understood. RESULTS: In this study, we performed an integrated analysis using headspace solid-phase microextraction coupled with gas chromatography-mass spectrometry (HS-SPME-GC-MS)-based volatile metabolomics, lipidomics, and untargeted metabolomics to characterize the flavor profiles of the Longissimus thoracis (LT) muscle from both breeds and to identify potential precursor substances underlying flavor formation. In total, we identified 76 differential volatile organic compounds (VOCs) among the 493 candidate VOCs. By combing relative odor activity value (ROAV) and sensory attribute annotation, 2,3-butanedione which may contribute to the creamy aroma was revealed as the core differential VOC between the two breeds. This finding was robustly validated across SHAP (Shapley additive explanations) analysis, KEGG (Kyoto Encyclopedia of Genes and Genomes) pathway enrichment, and flavor annotation. Lipidomic analysis revealed 689 differential lipids primarily belonging to classes such as phosphatidylcholine, triglycerides, and phosphatidylethanolamine. Correlation analysis further linked these lipid profiles to flavor, showing that fatty acids (FAs) including FA(19:0), FA(18:2 + O), FA(14:1), FA(16:1), and FA(14:0) were significantly correlated with 2,3-butanedione. Notably, the unsaturated fatty acids (UFAs) in the Longissimus thoracis (LT) of Hereford cattle exhibited higher double bond content compared to Angus cattle, suggesting a greater potential for rich flavor development. Untargeted metabolomics revealed that nine of the 9474 metabolites were significantly correlated with both 2,3-butanedione and FAs, including norepinephrine, l-beta-aspartyl-l-leucine, and artemetin. CONCLUSIONS: Overall, our research has identified differential flavor compounds and potential precursor substances between Angus cattle and Hereford cattle, providing targeted guidance for breed improvement. © 2026 Society of Chemical Industry.

2,3‐butanedione↗

PubMed2004

Comprehensive multidimensional GC for the characterization of roasted coffee beans.

The present investigation is based on the separation of one of the most complex food matrices: the roasted coffee bean volatile fraction. Analysis of the two main species of coffee (Arabica/Robusta) was achieved through an effective and simple sampling procedure, headspace solid-phase microextraction (SPME), and the unprecedented resolving power of comprehensive gas chromatography (GC x GC). The combination of these two techniques proved to be a powerful tool for the extraction and separation of coffee volatiles. In fact, thousands of compounds that play various roles in the constitution of coffee aroma profile were resolved in the 2-D contour plot, each occupying a specific position pinpointed by two retention time coordinates. The potential use of this method for the assessment of coffee quality and the detection of commercial fraud is discussed. The potential of GC x GC for identification and classification of unknowns was also demonstrated, as the formation of characteristic patterns for structurally related compounds was observed in the bidimensional chromatogram. Moreover, reproducibility results were supported by the use of an autosampler for SPME applications that allowed any inaccuracy arising from manual handling to be avoided.

Journal Article↗

PubMed2006

Analysis of amides in the air by sampling with SPME and detection by GC-FID.

This paper proposes a solid-phase microextraction (SPME) method for the passive sampling and determination of N,N-dimethylacetamide (DMA) and N,N-dimethylformamide (DMF) in air by capillary GC with flame ionization detection. The optimized conditions for SPME method were grab sampling, polydimethylsiloxane/divinylbenzene fiber, extraction for 90 min at 25 +/- 2 degrees C, desorption for 3 min at 220 degrees C, and relative humidity 45 +/- 2%. Under these conditions, the method presented good linearity (R = 0.996), repeatability (%RSD 2.79 and 9.85 for DMF and DMA, respectively), and detection limit (0.021 and 0.024 mg/m3 for DMF and DMA, respectively).

Journal Article↗

PubMed2003

Evaluation of an enzyme immunoassay for the detection of the insect growth regulator fenoxycarb in environmental and biological samples.

A competitive enzyme-linked immunosorbent assay (ELISA) for fenoxycarb was adapted for quantitative detection of this insect growth regulator in various environmental, agricultural, food and biological matrices. Environmental samples were taken from soil and surface waters in Hungary. The ELISA enabled fenoxycarb detection in surface waters in the 1.1-125 ng ml(-1) concentration range without sample cleanup. In contrast, soil produced a strong matrix effect due to humic acids and other soil components. Several fruit homogenates and commercial fruit juices (eg apple, pear, grape) were analyzed by the ELISA. The assay was found to be suitable for analysis of fenoxycarb in fruit juices diluted 1:40. Biological samples included insect, fish and bovine tissues. The ELISA was applied to detect fenoxycarb in various biological matrices from larvae of the silkworm, Bombyx mori L. The assay proved useful for the analysis of haemolymph diluted 1:10 or at higher dilutions. Fat body and whole body homogenates, however, caused severe matrix effects. Fenoxycarb was detected in liver homogenates (diluted 1:40) from fish treated with various doses of fenoxycarb, and the concentrations determined correlated with the applied doses. The method was used to analyze spiked bovine urine samples diluted 1:10 or at greater dilutions. Fenoxycarb content determined by the ELISA in water and fruit juice samples was validated using GC-MS with solid-phase microextraction (SPME) sample preparation. The results of these studies demonstrated both the value and limitations of the assay when used for monitoring fenoxycarb in environmental, food and biological samples.

Animals↗

PubMed2004

Simultaneous determination of t,t-muconic, S-phenylmercapturic and S-benzylmercapturic acids in urine by a rapid and sensitive liquid chromatography/electrospray tandem mass spectrometry method.

We describe a rapid and sensitive high-performance liquid chromatography/electrospray tandem mass spectrometry (HPLC/ESI-MS/MS) method for simultaneous determination of the most relevant metabolites of benzene and toluene, t,t-muconic acid (t,t-MA), S-phenylmercapturic acid (S-PMA), and S-benzylmercapturic acid (S-BMA). Urine samples were purified before analysis by solid-phase microextraction (SPE) on SAX cartridges with 50 mg sorbent mass. The developed method fulfils all the standard requirements of precision and accuracy. Calibration curves were linear within the concentration range of the standards (0-80 microg/L(urine) for t,t-MA, and 0-25 microg/L(urine) for S-PMA and S-BMA), and had correlation coefficients > or =0.997. Limits of detection were 6.0 microg/L for t,t-MA, 0.3 microg/L for S-PMA, and 0.4 microg/L for S-BMA. The method was used to determine t,t-MA, S-PMA and S-BMA levels in urine of 31 gasoline-station workers, with personal monitoring data obtained from radial symmetry passive diffusive samplers. In the context of mean work-shift exposures of 75.9 microg/m(3) (range 9.4-220.2) for benzene and 331.9 microg/m(3) (78.2-932.1) for toluene, metabolite concentrations in end-of-shift urine samples ranged from 23.5-275.3 microg/g(creatinine) for t,t-MA, non-detectable to 0.9 microg/g(creatinine) for S-PMA, and 3.8-74.8 microg/g(creatinine) for S-BMA. No significant correlation was found between the environmental concentrations and urinary metabolites (p > 0.05 for all cases); the ratios of benzene metabolites could be influenced by exposure levels and co-exposure to xylenes and toluene. The high throughput of this procedure should facilitate exploration of the metabolic effects of benzene-related co-exposure to toluene and alkylbenzenes in large populations of subjects exposed to gasoline.

Acetylcysteine↗

PubMed2006

The scent of urine spots of male mice, Mus musculus: Changes in chemical composition over time.

A dominant male mouse scent-marks his territory very frequently by emitting small urinary spots. The urine spots release in the air a variety of odorants that transmit different information to other mice, especially those concerning the time of deposition. To investigate this effect, small spots of urine of a dominant male mouse were left to freely release the odorants in the air for time intervals ranging from 0 min to 24 h prior to sampling. Thereupon, the odorants remaining in the spot were sampled at diffusion equilibrium (45 degrees C) in a small vial by means of headspace solid-phase microextraction followed by gas chromatography coupled to flame ionisation detection and mass spectrometry. Thirteen odorants were consistently found. Nine odorants were identified and four were matched. The rate of release of each odorant was characteristic and was described using principal component analysis. A first principal component was based on nine early odorants that showed a decreasing release over time. The odorants were 2,4-dehydro-exo-brevicomin, an unknown with 78% matching to 4-acetonilcycloheptanone, linalool, 2,4-dimethyl-phenol, 4-ethylphenol, indole, 2-butyl-1-octanol, an unknown with 83% matching to 2-ethyl-1-decanol, and 2,4-bis-(1,1-dimethylethyl)phenol. A second principal component, based on two unknowns with 73% matching to yohimban-17-one and 71% matching to the 2-methyl-3-hydroxy-2,4,4-trimethyl ester of propanoic acid, had an irregular release after deposition. A third principal component of late odorants, based on 2-sec-butyl-4,5-dihydrothiazole and 6,10-dimethyl-5,9-undecaden-2-one, had a peak of release at about 22 min. In conclusion, the release of the odorants in the headspace of a urine spot may code and transmit information on the deposition time.

Animals↗

PubMed2003

Application of tandem mass spectrometry combined with gas chromatography and headspace solid-phase dynamic extraction for the determination of drugs of abuse in hair samples.

A new method combination, headspace solid-phase dynamic extraction coupled with gas chromatography/tandem mass spectrometry (HS-SPDE/GC/MS/MS), is introduced to determine drugs of abuse in hair samples. This highly automated procedure utilizes SPDE for pre-concentration and on-coating derivatization as well as GC and triple quadrupole MS/MS for selective and sensitive detection. All these steps, apart from washing and cutting of the hair samples, are performed without manual intervention on a robot-like autosampler.SPDE is a solventless extraction technique related to solid-phase microextraction (SPME). The analytes are absorbed from the sample headspace directly into a hollow needle with an internal coating of polydimethylsiloxane by repeated aspirate/dispense cycles.The HS-SPDE/GC/MS/MS procedure was applied to the analysis of methadone, the trimethylsilyl derivatives of cannabinoids and the trifluoroacetyl derivatives of amphetamines and designer drugs. The method was shown to be sensitive with detection limits between 6 and 52 pg/mg hair matrix and precision between 0.4 and 7.8% by the use of an internal standard technique. Linearity was obtained from 0.1-20 ng/mg with coefficients of correlation between 0.995 and 0.999. Compared with conventional methods of hair analysis, HS-SPDE/GC/MS/MS is easier to use, substantially faster, with the degree of sensitivity and reproducibility demanded in clinical and forensic toxicology. The main advantage of the SPDE technique in relation to SPME is the robustness of the capillary.

Gas Chromatography-Mass Spectrometry↗

PubMed1999

Bioavailability, biodegradation, and acclimation of Tetrahymena pyriformis to 1-octanol.

Previous work has indicated that the ubiquitous freshwater ciliate Tetrahymena pyriformis acclimates to the presence of hydrophobic chemicals acting by nonpolar narcosis. Four explanations have been identified to explain this apparent acclimation: (1) genetic adaptation occurs resulting in a resistant population, (2) T. pyriformis quickly biodegrades hydrophobic chemicals resulting in a perceived acclimation response, (3) hydrophobic chemicals are not bioavailable, and (4) T. pyriformis contain an endogenous biochemical adaptation system which can quickly cause cellular changes resulting in acclimation. Results of biodegradation experiments indicated that the total extractable 1-octanol did not change over the duration of the experiments. Bioavailability experiments were performed using the solid-phase microextraction technique. Although there is a decrease in freely available concentrations of 1-octanol over a 2.5 log unit range of Tetrahymena population density, the freely available concentration is constant for the population densities used for population growth experiments. Genetic change is highly unlikely since acclimation occurs in less than the time required for one population division. It is hypothesized that the acclimation response seen in Tetrahymena results from partitioning of the chemical into the membrane followed by active changes in the membrane structure to restore homeostasis.

1-Octanol↗

PubMed2001

Determination and theoretical aspects of the equilibrium between dissolved organic matter and hydrophobic organic micropollutants in water (Kdoc).

Literature on the equilibrium constant for distribution between dissolved organic carbon (DOC) (Kdoc) data of strongly hydrophobic organic contaminants were collected and critically analyzed. About 900 Kdoc entries for experimental values were retrieved and tabulated, including those factors that can influence them. In addition, quantitative structure-activity relationship (QSAR) prediction equations were retrieved and tabulated. Whether a partition or association process between the contaminant and DOC takes place could not be fully established, but indications toward an association process are strong in several cases. Equilibrium between a contaminant and DOC in solution was shown to be achieved within a minute. When the equilibrium shifts in time, this was caused by either a physical or chemical change of the DOC, affecting the lighter fractions most. Adsorption isotherms turned out to be linear in the contaminant concentration for the relevant DOC concentration up to 100 mg of C/L. Eighteen experimental methods have been developed for the determination of the pertinent distribution constant. Experimental Kdoc values revealed the expected high correlation with partition coefficients over n-octanol and water (Kow) for all experimental methods, except for the HPLC and apparent solubility (AS) method. Only fluorescence quenching (FQ) and solid-phase microextraction (SPME) methods could quantify fast equilibration. Only 21% of the experimental values had a 95% confidence interval, which was statistically significantly different from zero. Variation in Kdoc values was shown to be high, caused mainly by the large variation of DOC in water samples. Even DOC from one sample gave different equilibrium constants for different DOC fractions. Measured Kdoc values should, therefore, be regarded as average values. Kdoc was shown to increase on increasing molecular mass, indicating that the molecular mass distribution is a proper normalization function for the average Kdoc at the current state of knowledge. The weakly bound fraction could easily be desorbed when other adsorbing media, such as a SepPak column or living organism, are present. The amount that moves from the DOC to the other medium will depend, among other reasons, on the size of the labile DOC fraction and the equilibrium constant of the other medium. Variation of Kdoc with temperature turned out to be small, probably caused by a small enthalpy of transfer from water to DOC. Ionic strength turned out to be more important, leading to changes of a factor of 2-5. The direction of this effect depends on the type of ion. With respect to QSAR relationships between Kdoc and macroscopic or molecular descriptors, it was concluded that only a small number of equations are available in the literature, for apolar compounds only, and with poor statistics and predictive power. Therefore, a first requirement is the improvement of the availability and quality of experimental data. Along with this, theoretical (mechanistic) models for the relationship between DOC plus contaminant descriptors on the one side and Kdoc on the other should be further developed. Correlations between Kdoc and Kow and those between the soil-water partition constant (Koc) and Kow were significantly different only in the case of natural aquatic DOC, pointing at substantial differences between these two types of organic material and at a high correspondence for other types of commercial and natural DOC.

Environmental Monitoring↗