Supersaturated Salt Solution Research Articles

The enhancement detection method based on the Fabry–Pérot cavity using terahertz frequency-domain spectroscopy

This article demonstrates a simple, efficient, and low-cost gas detection method for gases with absorption peaks in the terahertz range. A modes-adjustable Fabry–Pérot cavity is designed. By adjusting the length of the cavity, the center resonant frequency of the cavity can be coupled to the gas absorption peak. This kind of coupling can greatly enhance gas detection. To detect gas absorption peaks, we choose terahertz frequency domain spectroscopy (THz-FDS), whose frequency resolution can be up to the MHz level. Vapor is selected to verify the coupling phenomenon. The resonant frequency of the cavity is modified to couple to 0.56 THz, the absorption peak of vapor. Experiments are conducted at different humidity levels, the humidity is controlled by the supersaturated salt solution. Results indicate that at a humidity level of 15%, the coupling effect can enhance the detectability of vapor by approximately 167%, and this enhancement effect diminishes as humidity increases. We analyze the effect of different modes on the coupling and find that the high modes can make the coupling easier, but have little effect on the enhancement. Furthermore, the method is used to detect biomolecule-α-tyrosine to ensure it has wide applicability. This method can be used to detect substances with absorption peaks in the THz regime, especially for low-concentration gas.

Intermittent Exothermic and Self-Healing Hydrated Salt Gels for Advanced Thermal Management of Underfloor Radiant Heating System.

Phase change materials (PCMs) have great prospects in thermal management applications because they can store and release latent heat. However, they are not suitable for on-demand heating as they can only release heat once. Herein, this work reports the intermittent exothermic of PCMs based on a supersaturated salt solution, exhibiting fully controlled long-term storage of energy, releasing and suspending heat on demand. Due to the high energy barrier, it is difficult for the supersaturated salt solution to nucleate; thus, it can store energy for a long time. Contact with seeds or other foreign objects can destroy the metastable state of the supersaturated salt solution and promote the formation of crystal nuclei, enabling crystallization and heat release on demand. The release of crystallization heat can be interrupted using scissors dip in water. Additionally, self-healing behavior allows it to be recycled and last longer, due to the presence of Fe3+ , inducing strong dynamic reversible non-covalent crosslinking through metal coordination bonds. Furthermore, the hydrated salts gels are applied for thermal management of underfloor radiant heating system, demonstrating four types of intermittent exotherms sequences amazingly. Further, the intermittent exothermic hydrated salts gels provide a more user-friendly thermal management of underfloor radiant heating systems.

Green biosynthesis of DHA-phospholipids in tailor-made supersaturated DHA aqueous solution and catalytic mechanism study

Docosahexaenoic acid-phospholipids (DHA-PLs) were prepared via lipase-mediated transesterification of DHA donor and phosphatidylcholine (PC) in a purely aqueous solution. Pre-existing carriers would play the role as “artificial interfaces” to adsorb water-insoluble PC and made them disperse in water. DHA donors were concentrated by a pH-responsive method and presented as supersaturated salt solutions. 153 triacylglycerol lipase structures were analyzed and screened in silico. Transesterification was carried out to further evaluate the six lipase candidates. Lipase B from Candida antarctica (CALB) was the best biocatalyst with 34.8% of DHA incorporation and 80.0% of PLs yields (involving 38.1% PC and 41.9% sn-1 lyso-PC). Toxic organic solvents were avoided. Six possible microunits of our aqueous system consisting of three PLs donors (PC, lyso-PC, sn-glycero-3-PC) and two DHA donors (DHA and DHA salts), were simulated by molecular dynamics (MD) to illustrate the enzymatic mechanism based on diffusional channels, competitive bindings, and enzymatic structures.

Fluorescent‐tagged Antiscalants: A New Look at the Scale Inhibition Mechanism and Antiscalant Selection

AbstractSolid deposits onto equipment surfaces represent a serious problem all over the world. Mitigation of this process is provided by chemical inhibitors. However, irrespective of successful antiscalant application, the mechanisms of scale inhibition are still not very clear. Thus, the present review summarizes recent advances in novel fluorescent‐tagged antiscalants (polyacarboxylates, phosphonates) application for scale inhibition mechanisms study. Some paradoxical effects, detected during gypsum and barite scale formation visualization are described and interpreted within the “nanodust” concept. It is demonstrated, that the solid nanoimpurities, naturally occurring in both industrial and deionized water samples, are definitely playing a key role in any crystal nucleation process. Such nanoimpurities are responsible for the bulk heterogeneous nucleation in a supersaturated salt solution. Scale inhibitor molecules block and isolate exactly these “nanodust” nucleation centers and therefore retards crystallization process on the whole. The advantages of fluorescent antiscalants to provide a new look at scale inhibition phenomenon and inhibition mechanisms are discussed. Among these, there is a possibility to distinguish particular scale inhibitors in their blends, and an opportunity to track an antiscalant location along the process of scale formation and deposition. Besides, a need of antiscalants testament procedure unification is considered, and a possible role of fluorescent reagents in such a procedure elaboration is indicated.

Pilot plant tests to demonstrate the functionality of sealing elements made of salt cut bricks

Abstract. The long-term safe containment of high-level radioactive waste in a repository in rock salt is ensured if the geological barriers in conjunction with the geotechnical barriers are permanently impermeable to fluids. As such, an essential factor in underground disposal is to confirm that the interfaces between the biosphere and the lithosphere, i.e., shafts, boreholes, and galleries, created during the excavation of underground cavities can be sufficiently tightly sealed. An essential element of the sealing system required to this end is shaft closure. All shaft closure concepts developed thus far include sealing and supporting elements in repository shafts, but differ in the arrangement of these structural elements and the materials used. The materials currently proposed and planned for the construction of the sealing elements include: clay/bentonite, asphalt/bitumen, crushed salt, and salt/sorel cement. In addition to the materials mentioned above, a research project funded by the German Federal Ministry for Economic Affairs and Energy (Bundesministerium für Wirtschaft und Energie, BMWi) is investigating the possibility of integrating a layer of salt cut bricks several decameters to 100 m thick into the shaft closure system as a sealing element that provides the option of allowing the geological barrier to heal in the long term. Like the surrounding rock mass, the salt cut bricks are made of natural rock salt. According to this plan, the profile of the bricks is designed to minimize joint volume as far as possible by cutting them to match the geometry of the shaft. The joints between the salt cut bricks can either be filled with, for example, a supersaturated salt solution, Magnesium building materials, molten salt, crushed salt, etc., or directly brought into contact by wetting the surface of the salt cut bricks. Once the salt solution has hardened (cooling of the solution, evaporation of the mixing water), only the pore space in the crushed-salt joint sealant filled with salt solution or air, or the joint volume resulting from the mismatch between individual rock salt bricks are susceptible to a reaction. This means that the sealing element consisting of salt cut bricks develops early supporting pressure against the creeping rock salt of the rock mass compared to crushed salt, has a low initial porosity and already shows a strong sealing effect in the short term (regression of the loosened zone). One can also assume that cohesive bonding between the surrounding rock and the sealing element can already be achieved by introducing the joint filling or by wetting the contact surfaces of the salt cut bricks (no or reduced separation planes in the contact zone). Essential prerequisites for the investigation of the geomechanical-geohydraulic effectiveness of a sealing element made of salt cut bricks included the development and construction of a pilot plant to analyze the mechanical and hydraulic material properties of the bonding system comprising salt cut bricks and joint sealing (FKZ 02E11223, FKZ 02E11425), as well as preliminary investigations on the production of salt cut bricks and joint sealant (→ cutting technique/processing of salt cut bricks; maufacture/workability of jointing material) and on the spatial arrangement of the salt cut bricks (→ avoidance of continuous axial joints in the bonding system, Fig. 1). The presentation includes the results of the research work on the development, construction and commissioning of the pilot plant, as well as the first successful test results demonstrating the functionality of sealing elements made of salt cut bricks.

Hysteresis of the water retention curves of geosynthetic clay liners in the high suction range

This paper examines two needle-punched geosynthetic clay liners' water retention behaviour at high suction ranges using the vapour equilibrium technique where super-saturated salt solutions controlled the relative humidity. This study shows that the bentonite form and its mineralogy affect the absorption/desorption of GCLs and their corresponding water retention curves. In particular, a granular bentonite-based GCL was found to absorb more and release less water than a powdered bentonite-based GCL due to its higher montmorillonite content and larger pores. The water retention curves of both GCLs exhibited very little hysteretic behaviour at high suction. Repeated wetting-drying cycles shifted the WRCs of both GCLs slightly downward with minimal impact on their degree of hysteresis.

Multifractal Approaches of the Ring Tensile Rupture Patterns of Dried Laver (Porphyra) as Affected by the Relative Humidity.

Texture properties are the most important quality attributes for commercial dried laver (DL) products. The relative humidity influences the texture properties of DL during production, storage, shipping, and consuming. This study well characterized the effect of the relative humidity on the texture properties of DL using the tensile tests under microclimate conditions. This information is very practical and can be immediately applied to control the relative humidity of the packaging and the storage room for DL.

Effect of Humidity on Development ofPseudogymnoascus destructans, the Causal Agent of Bat White-Nose Syndrome

The invasive fungal pathogen that causes white-nose syndrome (WNS), Pseudogymnoascus destructans, has decimated bat populations in the United States, causing significant mortality since the winter of 2006–2007. Temperatures inside many bat hibernacula are ideal for fungal growth, yet data are limited on the effects of humidity on the development of the fungus. The aim of our study was to determine optimum relative humidity (RH) levels for vegetative growth and sporulation of P. destructans growing at optimal temperatures. We cultivated P. destructans isolate MYA-4855 at 13 °C in individual humidity chambers where RH was maintained between 70.5 and 96.5% using supersaturated salt solutions. We quantified vegetative growth and conidia formation for 3 weeks and implemented single linear regression and ANCOVA analyses to ascertain the effects of RH. Mycelial growth increased significantly with increasing RH by 2 and 3 weeks post inoculation (P < 0.001, r = 0.49, 0.61). This effect was most pronounced up to 81.5% RH, after which no significant increases in growth were detected. Conidiation increased linearly with increasing RH by 3 weeks post inoculation (P < 0.05, r = 0.33). Similar to mycelial growth, there was no difference in conidia production once RH exceeded 81.5%. The RH range permissive for significant mycelial development is fairly wide, and RH levels at 81.5% and above at 13 °C support similar levels of vegetative growth. However, our results indicate that at 13 °C, RH of 70% or lower impedes mycelial growth, which could restrict infection severity and/or colonization of organic matter. Finally, lower RH does not restrict production of conidia, which serve as important transmission propagules. Our study suggests that lowering RH could stem infection serverity but may be of limited value as a means of mitigating pathogen dispersal from infected to healthy bats.

Water vapour adsorption and desorption in GCLs

Super-saturated salt solutions are used to control relative humidity (RH) and to infer the hydration (water uptake and loss) behaviour of three needle-punched geosynthetic clay liners (GCLs) with respect to time under conditions of both free swell and 20 kPa applied stress. It is shown that RH and applied stress play a key role in the hydration behaviour with time when GCL specimens were in equilibrium with water vapour. It was also observed that water uptake and loss was affected by the bentonite form (powdered or granular) and mineralogy of the bentonite. However, the effect of GCL structure (i.e. difference in geotextiles and bonding of needle-punched fibres to the carrier geotextile) on their hydration behaviour for GCLs with similar form of bentonite was not significant for RH ≤ 97.7%. The effect of GCL structure became more apparent at 100% RH (for all GCLs). The results presented in this study can be used to better assess the hydration of GCLs in field applications such as waste containment liners and cover systems at different RH and overburden stress conditions.

Using PXRD and PONKCS to Determine the Kinetics of Crystallisation of Highly Concentrated NH4NO3 Emulsions

A technique that is known as PONKCS (Partial or no known crystal structure) has become useful in the quantitative determination of solid phases in powder samples that have no known crystal structure, or that have poorly determined crystal structures. This technique was shown to be useful with commercial software, such as Topas®, to quantitatively determine the amorphous phase content of powdered samples that contain a number of crystalline phases within the bulk material. In this study, the method of analysis was applied to the crystallization process of highly concentrated emulsions of ammonium nitrate (HCE of AN) composed of a supersaturated salt solution within a continuous hydrocarbon phase that was stabilized with a variety of surfactants and additives. These emulsions are thermodynamically unstable, and would with time crystallize into the crystalline room temperature phase IV of AN. It was found that by applying slightly different mixing times during the preparation steps, emulsions with different droplets sizes would be obtained. Powder X-ray diffraction was shown to be a useful tool in studying the crystallization process of HCE of AN, where the fresh emulsion would have a characteristic amorphous halo that over time, would then show typical diffraction peaks to appear that correspond with the solid phases of crystalline AN. An assumption was made that the emulsion crystallizes close to about 80 % solid content, thereby allowing for a relative quantification to be made over time. The change with time in the degree of crystallization of the emulsions prepared with different droplet sizes could then be modeled with the well-known Johnson–Mehl–Avrami–Kolmogorov kinetic equation. A crystallization time-related constant and an empirical exponent that reflects the type of nucleation that occurred during the process was determined. The results showed that for a set of emulsions that were prepared by varying only the mixing times and their effective droplet sizes, that the emulsion with the smaller droplet had higher crystallization stability.

Caking of sodium chloride: Role of ambient relative humidity in dissolution and recrystallization process

Both, producers and users of divided solids regularly face the problem of caking after periods of storage and/or transport. Particle agglomeration depends not only on powder water content, temperature and applied pressure, but also on the interactions between the solid substance and water molecules present in the atmosphere, i.e., on relative humidity (RH) at which the product is stored. Ambient humidity plays an important role in most of events leading to caking: capillary condensation of water at contact points between particles, subsequent dissolution of a solid and formation of saturated solution eventually followed by precipitation of solid during evaporation of water. Here we focus on the kinetics of dissolution followed by evapo-recrystallization of hygroscopic powder sodium chloride under controlled temperature and RH, with the aim of anticipating caking by predicting rates of water uptake and loss under industrial conditions. Precise measurements of water uptake show that the rate of dissolution is proportional to the difference between the imposed RH and deliquescence RH and follows a model based on the kinetic theory of gases. Evaporation seems to be governed by more complex phenomena related to the mechanism of efflorescence and crystal growth from supersaturated salt solution. The proposed methods provide values of Deliquescence Relative Humidity (DRH) and Efflorescence Relative Humidity (ERH) for sodium chloride in good agreement with literature data.

Long-term measurements of atmospheric PM2.5 and its chemical composition in rural Korea

Long-term measurements of ambient particulate matter less than 2.5 μm in diameter (PM2.5) and its chemical compositions were performed at a rural site in Korea from December 2005 to August 2009. The average PM2.5 concentration was 31 μg m−3 for the whole sampling period, and showed a slightly downward annual trend. The major components of PM2.5 were organic carbon, SO42−, NO3−, and NH4+, which accounted for 55 % of total PM2.5 mass on average. For the top 10 % of PM2.5 samples, anionic constituents and trace elements clearly increased while carbonaceous constituents and NH4+ remained relatively constant. Both Asian dust and fog events clearly increased PM2.5 concentrations, but affected its chemical composition differently. While trace elements significantly increased during Asian dust events, NO3−, NH4+ and Cl were dramatically enhanced during fog events due to the formation of saturated or supersaturated salt solution. The back-trajectory based model, PSCF (Potential Source Contribution Function) identified the major industrial areas in Eastern China as the possible source areas for the high PM2.5 concentrations at the sampling site. Using factor analysis, soil, combustion processes, non-metal manufacture, and secondary PM2.5 sources accounted for 77 % of the total explained variance.

Fabrication of honeycomb polyvinyl butyral film under humidity provided by super saturated salt solutions

AbstractWe introduce a novel method for making breath figure arrays (BFAs) on polyvinyl butyral (PVB) films under humidity by putting the dip coated samples inside a chamber filled with supersaturated salt solutions. With the increase in humidity or retention time, multiple porous films with bigger pore sizes and wider size distributions are generally obtained, resulting from the coalescence of the following‐up water drops. The presence of nitrogen flow accelerates the evaporation of solvents and vapor, thus increases the elastic interaction among water droplets such that films with smaller pores can be obtained. Compared to PVB/ethyl acetate solution, it is easier to obtain a film with regular honeycomb pattern by using PVB/chloroform solution. Its lower boiling point makes it evaporate faster to increase temperature gradient between film surface and the atmosphere; while its higher density makes it provide stronger support to maintain the shape of water droplets. In this study, the solubility of polymer in solvents is initially proposed to explain the BFAs formation. Higher mobility of polymer chains in a good solvent increases chances of its polar groups to interact with water droplets, thus increases the possibility of regular arrangements of water droplets on the film. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Studies on mechanical properties of films made from texturized whey protein and traditional whey protein

Introduction: In today's competitive world, development of new approaches through novel technologies is in demand to utilize the food ingredients in a better way. To achieve this goal, there is a need to understand different properties of food ingredients through basic research. Texturized whey protein concentrate (WPC) is one such novel food ingredient, which is currently being investigated by various researchers. Objective: The objective of this study was to compare a few selected mechanical properties of texturized whey protein concentrate (tWPC) films with those of the traditional WPC films. Materials and Methods: To perform this comparative study, moisture content, tensile strength, percentage elongation (PE), water vapor permeability, and water contact angle were evaluated by conditioning the films specimens for 3 h at 11%, 32%, 53%, 75%, 84%, and 100% RH with the help of supersaturated salt solutions to get a water activity of 0.11, 0.32, 0.53, 0.75. 0.84, and 0.99, respectively. Results: The results showed that as the water activity and thus the moisture content increased the PE and water vapor permeability of the tWPC films decreased significantly in comparison with the WPC-based films. On the other hand, the tensile strength and water contact angle of the tWPC films were found to be superior to those of the WPC films at all water activities. Conclusion: These results provide strong evidence that the tWPC films have improved mechanical properties of utility in package design in comparison with films made with WPC films. These attributes can be commercially exploited to advantage in fabrication of new food packaging systems and in edible coating of food products.

A Shielding Topology Stabilizes the Early Stage Protein–Mineral Complexes of Fetuin‐A and Calcium Phosphate: A Time‐Resolved Small‐Angle X‐ray Study

We report on the earliest stages of the formation of complexes of calcium phosphate in the presence of the serum protein alpha(2)-HS glycoprotein/fetuin-A termed calciprotein particles (CPPs). Time-resolved small-angle X-ray scattering (TR-SAXS) and stopped-flow analysis were used to monitor the growth of protein mineral particles nucleating from supersaturated salt solutions. It was found that fetuin-A did not influence the formation of mineral nuclei. However, fetuin-A did prevent the aggregation of nuclei and thus mineral precipitation. Hence, fetuin-A shielded spontaneously formed mineral nuclei, leading to stable calciprotein particles in the first stage of mineralization. Fetuin-A is therefore critically required during the earliest stages of the formation of protein-mineral complexes in order to prevent uncontrolled mineralization.

Ion projection surface structuring with noble gas ions at 75 keV

Compared to focused ion beam writing, ion projection lithography is a parallel structuring process which transfers the pattern of an open stencil mask with electrostatic demagnification optics onto the target surface. The parallel structuring process combined with the unique energy deposition characteristics (small forward scattering, small penetration depth) makes ion projection a very efficient structuring process. Using the different penetration depths of ions from a plasma source, fabrication of 3D-structures in resist, like free standing grids or T-gate structures, is possible. The ion induced intermixing of magnetic multilayers has been investigated for the creation of nano dots for data storage. The intermixing efficiency is greatly increased by using heavy ions (Ar +, Xe +). The creation of ion induced nucleation centers on p-Si allows for subsequent selective electroplating of nano structures. These nucleation centers can also start metal deposition on non-conducting surfaces (glass, polymers) by electrode less deposition in super saturated metal salt solutions. The expensive and time consuming production of open stencil masks may in future be avoided by an aperture plate with individually switchable openings. This is the aim of a European project: CHARPAN (Charged Particle Nanotech).

Time-resolved SAXS study of the effect of a double hydrophilic block-copolymer on the formation of CaCO3 from a supersaturated salt solution.

The effect of a double hydrophilic block-copolymer additive (made of polyaspartic acid and polyethyleneglycol, pAsp(10)-b-PEG(110)) on the initial formation of calcium carbonate from a supersaturated salt solution has been studied in situ by means of time-resolved synchrotron small-angle X-ray scattering (SAXS). A stopped-flow cell was used for rapidly mixing the 20 mM aqueous reactant solutions of calcium chloride and sodium carbonate. In reference measurements without polymer additive the very rapid formation of primary, overall spherical CaCO(3) particles with a radius of ca. 19 nm and a size polydispersity of ca. 26% was observed within the first 10 ms after mixing. A subsequent, very rapid aggregation of these primary particles was evidenced by a distinct upturn of the SAXS intensity at smallest angles. During the aggregation process the size of the primary particles remained unchanged. From an analysis of the absolute scattering intensity the mass density of these particles was determined to 1.9 g/cm(3). From this rather low density it is concluded that those precursor particles are amorphous, which has been confirmed by simultaneous wide-angle X-ray diffraction measurements. Upon adding 200 pm of the block-copolymer no influence on the size, the size polydispersity and morphology of the primary particles, nor on the kinetics of their formation and growth, was found. On the other hand, the subsequent aggregation and precipitation process is considerably slowed down by the additive and smaller aggregates result. The crystalline morphology of the sediment was studied in situ by WAXS ca. 50 min after mixing the reactants. Several diffraction rings could be detected, which indicate that a transformation of the metastable, amorphous precursor particles to randomly oriented vaterite nanocrystallites has taken place. In addition, a few isolated Bragg spots of high intensity were detected, which are attributed to individual, oriented calcite microcrystals that nucleated at the wall of the capillary.

Sorption kinetic of water vapour of MX80 bentonite submitted to different physical–chemical and mechanical conditions

The clay materials are widely used in industrial processes. One significant application is as a solid desiccant agent or as a dehydrator of gases. In this case, it is fundamental to investigate on the sorption kinetics of water vapour. The main aim of the current study has been to present an experimental–theoretical study on the sorption kinetics of water vapour, using as reference material MX80 bentonite. This clay mineral was submitted at different physical, chemical and mechanical conditions. Then 0.5g of the modified-sample previously dried for 24h at 110°C was placed in plastic desiccators (2l) under isothermal conditions and atmospheric pressure, here the relative humidity was controlled by a supersaturated salt solution. This instrumental system allowed us to study the sorption kinetics of water vapour of MX80 bentonite where the control parameters were the interlayer cation (bentonite exchanged with Na, Li, K, Mg, Ca), mechanical compaction (uni-axial system at 21, 35 and 63MPa), drying temperature of sample (110, 150, 250 and 500°C), relative humidity (61, 75, 87 and 95%) and the amount of the sample (0.5, 1, 2, 3, 4 and 5g).Thanks to a kinetic model of second order it was possible to estimate that the sorption kinetic of water vapour of MX80 bentonite depends directly on the relative humidity, the interlayer cation and amount of the sample. In contrast, the sorption kinetics of water vapour was lightly affected by the mechanical compaction. Finally, the sorption kinetics of water vapour was modified by the drying temperature of sample exclusively when this is very high (for example, 500°C).

Influence of interlayer cations on the water sorption and swelling–shrinkage of MX80 bentonite

The potential of water sorption and swelling–shrinkage in the expansive clays is practically defined by the nature of interlayer cations. The purpose of this paper is to estimate the effects of the cation saturation (Mg +, Ca +, Li +, Na +, and K +) on the swelling–shrinkage behaviour of the MX80 bentonite. The MX80 bentonite (a “commercial clay”) was treated with concentrated solutions (1 N) of sodium, calcium, magnesium, potassium, and lithium chlorides. This treatment was made three times with constant agitation for 1 h. Then, the clay was washed three times with distilled water. The scanning transmission electron microscopy (STEM) and inductively coupled plasma atomic emission microscopy (ICP-AES) analyses were used to verify the efficiency of the cation saturation. Finally, two techniques were employed to estimate the effect of the cation saturation on the swelling–shrinkage behaviour of the bentonite: the first one uses an isothermal system of water adsorption, where the water activity is controlled by a supersaturated salt solution. In the second, environmental scanning electron microscopy (ESEM), coupled with a digital image analysis (DIA) program, was used to estimate the swelling–shrinkage potential at different water activities. The swelling–shrinkage isotherms were always estimated on isolated aggregates. The isotherms of water adsorption and swelling–shrinkage of the bentonite MX80 show that the amount of adsorbed water and the swelling–shrinkage potential depend directly on the interlayer cation. For example, the sodium bentonite presents an excellent capacity to swell while the lithium bentonite does not swell significantly at the aggregate scale. In addition, other textural properties may be modified by the cation saturation, such as the specific surface, the particle size, porosity, etc.

Effect of the water content of cardboard on the static headspace extraction of volatile aldehydes

Due to their sensorial activity, quantification of linear, short-chained aldehydes is a routine operation in quality control in the paper and cardboard industry, especially when cellulose-based products are intended for hygienic or food packaging purposes. The ease of operation and automation favors static headspace extraction systems for the separation of volatiles from the matrix. Since the analytes are extracted into the gas phase, the determination is mostly performed by gas chromatography with flame ionization or mass selective detection. An absolute prerequisite for correct static headspace analysis is the establishment of a partition equilibrium of the analytes between the sample phase and the gas phase in the sample vial. Especially in the analysis of solid samples, this requirement is not easy to fulfil and matrix effects may severely hamper analytical work. This paper describes the effect of the water content of the cellulose matrix on the static headspace extraction of pentanal, hexanal, and heptanal. Special attention was given to performing the measurements under conditions which may be result from the climatic environment during storage. For homogenization purposes cardboard samples were cut to a size of 15 mm length and 1.5 mm width. Different water contents were established by conditioning the samples in desiccators over supersaturated salt solutions. The analytical results were compared with those obtained for untreated samples and those of samples which had been spiked with defined amounts of water. The measurements clearly indicate a significant influence of the water content of the cardboard samples on the static headspace extraction of volatile aldehydes.