Freezing Point Osmometry Research Articles

Comparison of vapour pressure osmometry, freezing point osmometry and direct membrane osmometry for determining the osmotic pressure of concentrated solutions

Osmometry is the analytical method of measuring osmotic pressure (π) and related colligative properties. Accurately measuring π is essential for applications that use osmosis, including drug delivery systems and water filtration methods such as forward osmosis. The three most common forms of directly or indirectly measuring π are vapour pressure osmometry (VPO), freezing point osmometry (FPO), and direct membrane osmometry (DMO). In this report, the performance of VPO, FPO, and DMO are compared for various aqueous solutions, including small molecule and polymer solutes, and potentially more difficult samples such as concentrated, carbonated, or viscous solutions. Potential problems with each of the three methods are examined. Good practices can avoid inaccuracies in DMO due to external concentration polarization and solute diffusion through the membrane. Similarly, it is important to be aware of and avoid weaknesses in VPO and FPO in order to obtain reliable results. Even with care, however, the three methods still give different values of π for concentrated aqueous solutions.

Direct evidence for dynamics of cell heterogeneity in watercored apples: turgor-associated metabolic modifications and within-fruit water potential gradient unveiled by single-cell analyses

Watercore is a physiological disorder in apple (Malus × domestica Borkh.) fruits that appears as water-soaked tissues adjacent to the vascular core, although there is little information on what exactly occurs at cell level in the watercored apples, particularly from the viewpoint of cell water relations. By combining picolitre pressure-probe electrospray-ionization mass spectrometry (picoPPESI-MS) with freezing point osmometry and vapor pressure osmometry, changes in cell water status and metabolisms were spatially assayed in the same fruit. In the watercored fruit, total soluble solid was lower in the watercore region than the normal outer parenchyma region, but there was no spatial difference in the osmotic potentials determined with freezing point osmometry. Importantly, a disagreement between the osmotic potentials determined with two methods has been observed in the watercore region, indicating the presence of significant volatile compounds in the cellular fluids collected. In the watercored fruit, cell turgor varied across flesh, and a steeper water potential gradient has been established from the normal outer parenchyma region to the watercore region, retaining the potential to transport water to the watercore region. Site-specific analysis using picoPPESI-MS revealed that together with a reduction in turgor, remarkable metabolic modifications through fermentation have occurred at the border, inducing greater production of watercore-related volatile compounds, such as alcohols and esters, compared with other regions. Because alcohols including ethanol have low reflection coefficients, it is very likely that these molecules would have rapidly penetrated membranes to accumulate in apoplast to fill. In addition to the water potential gradient detected here, this would physically contribute to the appearance with high tissue transparency and changes in colour differences. Therefore, it is concluded that these spatial changes in cell water relations are closely associated with watercore symptoms as well as with metabolic alterations.

In Vitro Comparison of Different Nebulizers Delivering 7% Hypertonic Saline.

Nebulized 7% hypertonic saline is used to treat patients with cystic fibrosis. Clinical trials supporting its use were conducted with breath-enhanced nebulizers (BEN). It is not uncommon for the specific nebulizer used in studies or prescribed by a physician to be unavailable to patients. The investigator compared the aerosol characteristics of hypertonic saline delivered by nebulizers of different operating principles. A continuous-output nebulizer (CON), a breath-actuated (BAN) jet nebulizer, and 2 brands of BEN (Pari LC Plus and Sidestream Plus) were tested. Airway delivery and aerosol characteristics of nebulizers loaded with 7% hypertonic saline were determined with 3 breathing simulations (ie, infant, child, and adult breathing patterns) and cascade impaction, respectively. Solutes were analyzed with freezing point osmometry. Aerosols generated with the BEN and BAN had similar mass median aerodynamic diameters (3.43-3.67 µm), geometric standard deviations (2.12-2.34), percentage of particles < 5 µm (63.1-68.9%), and percentage of particles 1-3 µm (35.9-37%). The CON produced a larger aerosol than BEN and BAN. The 2 BENs had similar airway delivery values that were greater than those for both CON and BAN. Hypertonic saline aerosols generated with the BEN and BAN devices were similar, while that generated with the CON was different. Airway delivery was similar between the BEN devices, but higher than that observed with the BAN and CON devices.

Osmolality of antisense oligonucleotide parenteral formulations: Implications on counterion dissociation and recommended osmometry techniques

The intrinsic osmolality of aqueous solutions of sodium salt antisense oligonucleotides (ASOs) has been studied to inform formulation practices, understand the molecular basis underlying the difference between theoretical and empirical results, and determine suitable measurement methods. It was found that regardless of nucleotide sequence, ASO concentration of ∼140mg/mL has isotonic osmolality of ∼290mOsm/kg water (SI unit: mmol osmotically-active particles/kg water), such that lower concentration formulations require excipients for tonicity adjustment. The range of osmolality values at a given active ingredient concentration can be ascribed to drug substance lot-to-lot purity differences impacting total oligonucleotide content (i.e., including oligonucleotide-related impurities). Empirical osmolality measurements were found to be ∼70% of theoretical values, which corresponds to an osmotic coefficient value of ∼0.7, thus inferring incomplete counterion dissociation. When comparing theoretical (ideal) osmolality of multiple sequences with various nucleotide compositions and chemistries at the same w/v concentration, the “average osmolar mass” (molar mass of the oligonucleotide, including the sodium counterions, divided by the ideal Van’t Hoff factor, iid) appears to be the strongest factor governing theoretical osmolality values. Other factors examined were the sequence length, backbone chemistry, 2′ sugar chemistry, and nucleotide composition. A head-to-head comparison between two osmolality techniques showed that vapor pressure osmometry is generally more suitable than freezing point osmometry for oligonucleotide solutions greater than ∼150mg/mL due to viscosity effects, but the two techniques are comparable otherwise.

Osmotic potential at full turgor: an easily measurable trait to help breeders select for drought tolerance in wheat

AbstractThis study investigated the relationship between osmotic potential at full hydration (π100) and turgor loss point (ΨTLP) in wheat (Triticum aestivum) to determine the potential of using π100 to predict ΨTLP under well‐watered (WW) and drought (WS) conditions. Two methods for determining π100 were tested: pressure–volume (PV) analysis and freezing point osmometry. The study also measured π100 in a range of 38 field‐grown wheat cultivars to determine whether there is genetic variation in π100 under field conditions. π100 correlated with ΨTLP using both methods under both water treatments, particularly WS. Genetic variation of π100 in the field, under rainfed conditions, was greater than controlled conditions and ranged from −0.94 to −1.95 MPa. Overall, the evidence supports development of π100 as a novel tool for plant breeders to screen large populations of wheat and identify genotypes with lower ΨTLP, an integrative trait that is related to drought tolerance.

Measuring Rat Serum Osmolality by Freezing Point Osmometry

Measuring Rat Serum Osmolality by Freezing Point Osmometry

Application of osmometry in quality analysis of milk

The aim of this study was to evaluate osmometry as a tool in quality analysis of milk. The osmolality of raw milk, sterilized milk, skimmed UHT (ultra-high temperature-treated) milk, pasteurized milk, standardized UHT milk and fermented milk (Lactococcus lactis culture) was determined by freezing point osmometry. The relationship between osmolality and pH of fermented milk was further investigated during spontaneous fermentation of UHT milk at 37°C for 48h. Average osmolality values (mean ± SD) were raw milk-290.2 ± 7.98, sterilized milk-290.2 ± 5.84, skimmed UHT milk-290.8 ± 3.31, pasteurized milk-283.6 ± 2.28, standardized UHT milk-281 ± 4.59 and fermented milk-466.0 ± 17.30 mOsmoles kg(-1). For fresh milk samples, 88% showed normal osmolality, 8% were hypo-osmotic and 4% hyper-osmotic. Fermentation studies revealed a high negative correlation between osmolality and pH, with a correlation coefficient of -97.49%. Hypo-osmotic milk shows mixing of milk with water along the production chain. Hyper-osmotic milk indicates fermentation of milk at high ambient temperatures or with prolonged storage. It may also reveal adulteration of fresh milk with a soluble substance. Osmolality was highest for fermented milk owing to production of lactic acid during fermentation. This was confirmed by the high negative correlation between osmolality and pH of milk in fermentation studies. Hence the osmolality of fermented milks may be used as an index of the extent of fermentation.

Activity Coefficients of Aqueous Mixed Ionic Surfactant Solutions from Osmometry

Osmotic techniques for measuring thermodynamic activities, such as isopiestic equilibration, are well established for multicomponent solutions, especially mixed salt solutions. Surprisingly, these techniques have not yet been applied to mixed ionic surfactants, despite the numerous practical applications of these systems and the importance of the Gibbs free energy for micelle stability. In this study, mass-action equations are developed for the osmotic coefficients of solutions of ionic surfactant CA + ionic surfactant CB, with common counterion C. Extended Debye–Huckel equations are used for the ionic activity coefficients. The equilibrium constants for mixed micelle formation are evaluated by Gibbs–Duhem integration of critical micelle concentrations. Fitting the derived equations to the osmotic coefficients of aqueous sodium decanoate + sodium dodecylsulfate solutions measured by freezing-point osmometry is used to evaluate the activities of the total surfactant components. Very large departures from ideal solution behavior are indicated, including stoichiometric surfactant activity coefficients and micelle activity coefficients that drop below 0.05 and 10−8, respectively, relative to unity for ideal solutions. Osmometry offers many interesting and unexplored possibilities for studies of mixed surfactant thermodynamics.

Determining osmotic pressure of drug solutions by air humidity in equilibrium method

Objective: To establish a new osmotic pressure measuring method with a wide measuring range.Method: The osmotic pressure of drug solutions is determined by measuring the relative air humidity in equilibrium with the solution. The freezing point osmometry is used as a control.Results: The data obtained by the proposed method are comparable to those by the control method, and the measuring range of the proposed method is significantly wider than that of the control method.Conclusion: The proposed method is performed in an isothermal and equilibrium state, so it overcomes the defects of the freezing point and dew point osmometries which result from the heterothermal process in the measurement, and therefore is not limited to diluted solutions.

Switchable polarity solvents as draw solutes for forward osmosis

Switchable polarity solvents (SPS), mixtures of carbon dioxide, water, and tertiary amines, are presented as viable forward osmosis (FO) draw solutes allowing a novel SPS FO process. In this study substantial osmotic strengths of SPS are measured with freezing point osmometry and were demonstrated to induce competitive fluxes at high salt concentrations on a laboratory-scale FO unit utilizing a flat sheet cellulose triacetate (CTA) membrane. Under the experimental conditions the SPS degrades the CTA membrane; however experiments with polyamide reverse osmosis (RO) membranes display stability towards SPS. Once the draw is diluted the major fraction of the switchable polarity solvent can be mechanically separated from the purified water after polar to nonpolar phase shift induced by introduction of 1atm carbon dioxide to 1atm of air or nitrogen with mild heating. Trace amounts of SPS can be removed from the separated water with RO in a process that avoids solution concentration polarization. The separated nonpolar phase can be regenerated to a full strength draw and recycled with the re-addition of 1atm of carbon dioxide.

Serum osmolality and effects of water deprivation in captive Asian elephants (Elephas maximus)

Serum from 21 healthy, captive Asian elephants (Elephas maximus) was evaluated by measured and calculated osmolality. Serum osmolality results for this population of Asian elephants had a median of 261 mOsm/kg and an interquartile interval of 258-269 mOsm/kg when measured by freezing point osmometry and a median of 264 mOsm/kg and an interquartile interval of 257-269 mOsm/kg when measured by vapor pressure osmometry. These values are significantly lower than values reported in other mammalian species and have important diagnostic and therapeutic implications. Calculated osmolality produced unreliable results and needs further study to determine an appropriate formula and its clinical application in this species. A 16-hr water deprivation test in 16 Asian elephants induced a small, subclinical, but statistically significant increase in measured serum osmolality. Serum osmolality, blood urea nitrogen, and total protein by refractometer were sensitive indicators of hydration status. Serum osmolality measurement by freezing point or vapor pressure osmometry is a useful adjunct to routine clinical tests in the diagnostic evaluation of elephants.

Activity Coefficients and Free Energies of Nonionic Mixed Surfactant Solutions from Vapor-Pressure and Freezing-Point Osmometry

The thermodynamic properties of mixed surfactant solutions are widely investigated, prompted by numerous practical applications of these systems and by interest in molecular association and self-organization. General techniques for measuring thermodynamic activities, such as isopiestic equilibration, are well-established for multicomponent solutions. Surprisingly, these techniques have not yet been applied to mixed surfactant solutions, despite the importance of the free energy for micelle stability. In this study, equations are developed for the osmotic coefficients of solutions of nonionic surfactant A + nonionic surfactant B. A mass-action model is used, with virial equations for the activity coefficients of the micelles and free surfactant monomer species. The equations are fitted to osmotic coefficients of aqueous decylsulfobetaine + dodecylsulfobetaine solutions measured by vapor-pressure and freezing-point osmometry. Equilibrium constants for mixed-micelle formation are calculated from the free monomer concentrations at the critical micelle concentrations. The derived activity coefficients of the micelles and free monomers indicate large departures from ideal solution behavior, even for dilute solutions of the surfactants. Stoichiometric activity coefficients of the total surfactant components are evaluated by Gibbs-Duhem integration of the osmotic coefficients. Relatively simple colligative property measurements hold considerable promise for free energy studies of multicomponent surfactant solutions.

Characterization of asphaltenes precipitated with three light alkanes under different experimental conditions

Asphaltene precipitation plays an important role in both oil production and refining processes. In this paper, asphaltenes are precipitated from a heavy oil sample under different experimental conditions by using three different light alkanes, i.e., propane, n-pentane, and n-heptane. A variety of analytical techniques are applied to characterize the precipitated asphaltenes and deasphalted heavy oil (i.e., maltenes), such as the density and viscosity measurements, vapour-pressure osmometry, freezing-point osmometry, scanning electron microscope (SEM) imaging, nuclear magnetic resonance (NMR) measurement, and simulated distillation for compositional analysis. It is found that the yields and properties of the precipitated asphaltenes and remaining maltenes strongly depend on the specific precipitant tested and the liquid precipitant-to-oil volume ratio used. The asphaltene yield decreases as the carbon number of an alkane increases, while it increases monotonically and finally reaches a plateau if the liquid precipitant-to-oil volume ratio increases up to 20–40 for n-pentane and n-heptane, respectively. As a result, n-heptane-precipitated asphaltenes (C 7-asphaltenes) have the highest molecular weight and aromaticity among the three kinds of precipitated asphaltenes. C 7-asphaltenes are bright and black particles, whereas n-pentane-precipitated asphaltenes (C 5-asphaltenes) are dull and brown powders. Propane-precipitated asphaltenes (C 3-asphaltenes) together with some amount of co-precipitated resins are found to be highly viscous and semi-solid like immediately after the flashed-off process but become more and more liquid-like afterward. Compositional analysis results of the original heavy crude oil and three different maltenes indicate that the carbon numbers of most precipitated asphaltenes are higher than C 50.

Determination of Dextrose Equivalent Value and Number Average Molecular Weight of Maltodextrin by Osmometry

Dextrose equivalent (DE) value is the most common parameter used to characterize the molecular weight of maltodextrins. Its theoretical value is inversely proportional to number average molecular weight (M(n)), providing a theoretical basis for correlations with physical properties important to food manufacturing, such as: hygroscopicity, the glass transition temperature, and colligative properties. The use of freezing point osmometry to measure DE and M(n) was assessed. Measurements were made on a homologous series of malto-oligomers as well as a variety of commercially available maltodextrin products with DE values ranging from 5 to 18. Results on malto-oligomer samples confirmed that freezing point osmometry provided a linear response with number average molecular weight. However, noncarbohydrate species in some commercial maltodextrin products were found to be in high enough concentration to interfere appreciably with DE measurement. Energy dispersive spectroscopy showed that sodium and chloride were the major ions present in most commercial samples. Osmolality was successfully corrected using conductivity measurements to estimate ion concentrations. The conductivity correction factor appeared to be dependent on the concentration of maltodextrin. Equations were developed to calculate corrected values of DE and M(n) based on measurements of osmolality, conductivity, and maltodextrin concentration. This study builds upon previously reported results through the identification of the major interfering ions and provides an osmolality correction factor that successfully accounts for the influence of maltodextrin concentration on the conductivity measurement. The resulting technique was found to be rapid, robust, and required no reagents.

Freezing point osmometry of milk to determine the additional water content – an issue in general quality control and German food regulation

BackgroundThe determination of the osmolality of aqueous samples using a freezing point osmometer is a well-established, routine laboratory method. In addition to their use in clinical and pharmaceutical laboratories, freezing point osmometers are also employed in food testing laboratories. One application is the determination of the osmolality of milk. Although cow's milk is a natural product whose water content is approximately 87%, the osmolality of milk is a significant value when the milk is collected from a larger population of animals. This value is used in milk processing to control the water content, based on the German Food Control Regulations for Milk.ResultsMeasurement of the freezing point and osmolality of milk samples was performed with a Knauer Semi-Micro Freezing Point Osmometer. Osmolality was measured for the untreated milk samples and following their dilution (by volume) with 10% and 50% water. The measurements were made after 1, 4 and 7 days to evaluate changes over time. All measurement values for the undiluted milk were spread over a small interval with an average of 271 mOsmol/kg. After mixing the milk samples with 10% water, the average decreased to 242 mOsmol/kg, while mixing with 50% water resulted in an average osmolality of 129 mOsmol/kg. There was no significant change for the osmolality within the 7 days (measurements from days 1, 4 and 7).ConclusionThe results observed demonstrate clearly that the additional water content of milk can be determined easily using a freezing point osmometer. Milk samples that contain additional water have a significantly decreased osmolality, corresponding to an increased freezing point. The effect on osmolality of ageing the milk samples could not be determined in this study's time-dependent measurements.

Fast Membrane Osmometer as Alternative to Freezing Point and Vapor Pressure Osmometry

Osmometry is an essential technique for solution analysis and the investigation of chemical and biological phenomena. Commercially available osmometers rely on the measurements of freezing point, vapor pressure, and osmotic pressure of solutions. Although vapor pressure osmometry (VPO) and freezing point osmometry (FPO) can perform rapid and inexpensive measurements, they are indirect techniques, which rely on thermodynamic assumptions, which limit their applicability. While membrane osmometry (MO) provides a potentially unlimited direct measurement of osmotic pressure and solution osmolality, the conventional technique is often time-consuming and difficult to operate. In the present work, a novel membrane osmometer is presented. The instrument significantly reduces the conventional MO measurement time and is not subject to the limitations of VPO and FPO. For this paper, the osmotic pressure of aqueous sucrose solutions was collected in a molality range 0-5.5, by way of demonstration of the new instrument. When compared with data found in the literature, the experimental data were generally in good agreement. However, differences among results from the three techniques were observed.

Bioindicator capacity of trees towards dryland salinity

To investigate plant–soil reactions towards site salinity we chose Ruprechtia triflora as the dominant tree species in its natural habitat in dry forests of Paraguay. We applied freezing point osmometry to measure tree leaves and soil samples identically on the basis of colligative solute properties. In order to substantiate the first field findings, the relation of tree and soil in terms of salinity was further investigated under controlled conditions in the greenhouse. R. triflora shows extreme osmotic adaptability. In three independent greenhouse experiments with NaCl application, Ruprechtia seedlings and later Eucalyptus dunnii seedlings from E Australia (for inter-species comparison) showed highly significant responses to their soil salinities. We conclude that tree leaves can serve as bioindicator for soil salinity within the tree’s rhizosphere.

Novel function of the skin in calcium metabolism in female and male chickens ( Gallus domesticus)

To study the role of the skin in differential calcium metabolism in White Leghorn chickens, we compared the composition of suction blister fluid (SBF) collected from cutaneous blisters with blood and serum in female and male animals in various physiological states. As an estimate for interstitial fluid (IF), SBF was used as a determinant of local cutaneous metabolism. Sample collection was carried out under ketamine–xylazine anesthesia. Eight chickens of both sexes were raised freely in similar environmental conditions and fed with similar food during their growth from juvenile to sexually mature and fully adult state. SBF, blood and serum were examined for concentrations of ionized Ca 2+, Na + and K + with ion-selective electrodes (ISEs), and osmolalities by freezing point osmometry. pH and total protein content were also assessed. Our results showed that SBF of chickens is calcium-poor at the juvenile state and that it draws more Ca 2+ in adult males than laying females of the same age. Interestingly, Ca 2+ accumulation was observed also in females after laying had ceased. There was a positive correlation between blood and SBF Ca 2+ in females but a negative one in males. In general, it was found that SBF of chickens was rich in Na + and K +, was hypertonic compared to serum at the juvenile state and had a protein content of 36–47% of that in serum. Different from mammals, SBF in adult chickens was alkaline with the mean values of 8.7 ± 0.14 in females and 8.8 ± 0.06 in males. Age- and sex-related variability in cutaneous Ca 2+ concentrations in chickens, and the differences of SBF composition between that of mammals point to a novel role of skin functions in avians. Possible functions of the skin as a dynamic calcium source balancing the free circulating Ca 2+ levels and, also, as an excretory organ for Ca 2+ are discussed.

Measures of tear exchange under rigid contact lenses: Part II. Individual systems and a population model

Part I of this series discussed a model for using freezing-point osmometry techniques and the Cuklanz-Hill mathematical model to determine tear-exchange efficiencies of rigid contact lenses. In Part II, the model was applied, the tear-exchange percentages per blink being determined for six best-fit cornea-contact lens systems. The lenses were fitted “on-K” to the flattest corneal meridian (to the nearest 0.05 mm), all other design features (overall diameter, posterior optic zone, peripheral curve width, vertex power, center thickness, and edge lift) being identical across all of the system. The tear-exchange percentages per blink for this population ranged from 5.39% to 6.06%, with a mean value of 5.69%. The amount of exchange was not well correlated with the amount of corneal toricity present.

Measures of tear exchange under rigid contact lenses: Part I. The method

Although previous tear-exchange measurements under contact lens have been primarily qualitative in nature, Cuklanz and Hill in 1969 proposed a mathematical model to determine tear exchange based on particle movement. They first tested that model utilizing flame photometry to determine the number of particles in a given sample. The considerable sample dilution required at that time diminished the accuracy attainable. Recently available nanoliter sample freezing-point osmometry techniques, however, are introduced here to reexplore the CuklanzHill mathematical model more precisely.