DOCSLIB.ORG

Determination of Partition Coefficients and Aqueous Solubilities by Reverse Phase Chromatography--I

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Determination of Partition Coefficients and Aqueous Solubilities by Reverse Phase Chromatography--I War. Res. Vol. 20, No. 11, pp. 1433-1442, 1986 0043-1354/86 $3.00+0.00 Printed in Great Britain Pergamon Journals Ltd DETERMINATION OF PARTITION COEFFICIENTS AND AQUEOUS SOLUBILITIES BY REVERSE PHASE CHROMATOGRAPHY--I THEORY AND BACKGROUND WALTER J. WEBER JR*, Yu-PING CHINt and CLIFFORD P. RICE~ Water Resources and Environmental Engineering Program, 181 Engineering Building l-A, The University of Michigan, Ann Arbor, MI 48109, U.S.A. (Received January 1986) Abstract--Water solubilities and octanol/water partition coefficients are widely used to predict par- titioning and bioconcentration phenomena for hydrophobic organic pollutants in aqueous systems. This paper is the first in a two part series describing the application of high performance reverse phase liquid chromatography (HPRPLC) for indirect estimation of these two physicochemical parameters to facilitate environmental fate and transport predictions for organic compounds. In the first part, thermodynamic factors which control partitioning processes, water solubilities, and reverse phase retention behavior are discussed, and models for interlinking these three properties are summarized. The second part presents the results of aqueous solubility and octanol/water partition coefficient predictions for a number of organic contaminants from measurements of their HPRPLC behavior, and compares the modeling capabilities of some of the theoretical partitioning/solubility equations developed in the first paper. Key words--organic pollutants, soil/sediment sorption, bioconcentration, activity coefficient, solubility, octanol/water partition coefficient, high performance reverse phase liquid chromatography NOMENCLATURE AHm = enthalpy of mixing Roman symbols AH/= enthalpy of fusion AH v = enthalpy of vaporization A and C = regression coefficients correlating reten- Ko~ = octanol/water partition coefficient tion times and octanol/water partition Kp = partition coefficient coefficients KRp = reverse phase partition coefficient a and b = regression coefficients correlating par- k' = capacity factor tition coefficients for different organic MW = molecular weight solvent/water systems ni = moles of solute aX; a,y = solute activity in phases x and y p = organic modifier proportionality constant b(T) and C(T) = regression coefficients correlating the free R = universal gas constant energy of transfer to the solute cavity RM=thin layer chromatography retention surface area factor b'= coefficient correlating the free energy of S~ = molar solubility transfer to retention time AS/= entropy of fusion C, = molar concentration (tool 1- ~) T = temperature (°K) CSA = solute cavity surface area T,, = solute melting point temperature ACp = change in solute heat capacity during t, = solute retention time phase transition to = mobile phase retention time d = regression coefficient correlating organic tc = corrected retention time solvent/water and hypothetical pure t7 = hypothetical pure water corrected reten- water retention times tion time AE = cohesive energy t~/°rg=corrected retention time in a binary AEm = cohesive energy of mixing water/organic solvent mobile phase f~ = fugacity of crystalline organic solid V = volume f0 = pure liquid component standard state 17 = molar volume fugacity 17~ = solute molar volume 17o = octanol molar volume 17ow = water saturated oetanol molar volume V, = stationary phase volume *Professor of Environmental Engineering and Chairman of Vt = total volume of mobile phase required to the University Water Resources Program. elute a solute 1"Graduate Research Assistant in the Water Resources V~ = void space volume Program. XX; X,Y = solute mole fraction in x and y :~Research Associate in the Great Lakes Research Division. X,~ = mole fraction solubility in water. 1433 1434 WALTER J. WEBER JR et aL Greek synlhols phase liquid chromatography (HPRPLC) to indi- :t and fl = regression constants which correlate rectly estimate n-octanol/water partition coefficients. activity coefficient to retention time Major advantages of this approach include ease of 7, = activity coefficient :,',' = saturation limit solute activity coefficient analysis, speed, precision, and accuracy. Several in water workers (Locke, 1974; Hakfenschied and Tomlinson, /i'= solute activity coefficient in octanol 1981) have also explored the possibility of indirectly 77" =solute activity coefficient in octanol estimating water solubility values using HPRPLC. saturated with water ,) = solubility parameter The bulk of this work to date, however, has treated 6,, = solubility parameter of octanol predictions of S," and K,,,, from HPRPLC mea- ,S' = solubility parameter of octanol saturated surements in terms of purely empirical correlations, with water thus providing no insight to processes which may t~, = chemical potential control relationships between reverse phase chro- i~i~ = standard state chemical potential Atz,~,,~= partial molar free energy of transfer matographic behavior and solubility and partitioning /) = density. behavior. The first paper in this two part series summarizes the current level of understanding of concepts underlying solubility and partitioning re- INTRODUCTION lationships, and discusses the relevance of these con- cepts to the selectivity and retention of solutes in The increased presence of anthropogenic organic reverse phase chromatography systems. Part I begins pollutants in surface and subsurface waters raises by examining the relationships of both the phase questions concerning the environmental transport partitioning behavior and solubility characteristics of and distribution of these materials and their effects on a compound to its activity coefficient(s) within a given the aquatic community and human health. The man- system. Methods for estimating activity coefficients ner in which a compound moves and is distributed are then discussed, along with their inherent limi- within an aquatic system and its associated solid tations and inaccuracies. Having established quanti- phases, both inert (soils, sediments, suspended solids) tative relationships between the activity coefficient o1" and living (flora and fauna), is influenced significantly an organic contaminant and its partitioning and by the physicochemical properties of that compound. solubility characteristics and associated parameters, Many organic contaminants are "hydrophobic", and Part I then considers diagonal relationships between tend to sorb from the aqueous phase onto or into solubility and partitioning behavior and their related phases which are thermodynamically more favorable. parameters. Finally, the technique of HPRPLC is The n-octanol/water partition coefficient (K,,,,.) and discussed, its characteristic parameters identified, and water solubility ($7) are two physicochemical par- these parameters then related and correlated to the ameters commonly used to predict soil/sediment characteristic properties of solubility and partition- sorption (Karickhoff et al., 1979, 1984; Briggs, 1973; ing. Emphasis is given to the potential application Means et aL. 1980; Chiou et al., 1982; Voice et aL, of HPRPLC for quantifying the partitioning and 1983) and biosorption or bioconcentration phenom- activity coefficients of organic pollutants in aqueous ena (MacKay, 1982; Chiou et al., 1977; Neely et aL, media. 1974) for lipophilic organic contaminants. Values for these two "predictor" parameters can be determined PHASE PARTITIONING AND ACTIVITY COEFFICIENTS either experimentally (McAuliffe, 1966; Karickhoff and Brown. 1979; Sutton and Calder, 1974; Haque The partition coefficient, Kp, quantifies the equi- and Schmedding, 1975; Chiou et al., 1982) or esti- librium partitioning of a liquid or "supercooled" mated from empirical models (Rekker, 1977; Fujita et organic solute between two phases al., 1964; Leo and Hansch, 1979; Arbuckle, 1983). Direct experimental determinations of n-octanol/ K~=--cC (~) water partition coefficients are laborious, however, and frequently suffer from lack of precision and where Ci~ and C~ are the molar concentrations of accuracy. This is particularly true for very hydro- solute i in phases x and y, respectively. phobic compounds (S~ < 50 ppb and log K,,,. > 6). For conditions of equilibrium between two immis- Conversely, estimates of water solubilities and cible solvent phases, the chemical activity, a, of n-octanol/water partition coefficients using such solute i is equal in each phase empirical models as are available do not account a' = a~ (2l quantitativel~ for steric effects and other consid- erations relating to molecular configuration. Chemically activity is quantified by the expression A number of investigators (Veith et al.. 1979; a, = 7,);'L (3) McCall, 1975: Unger et al., 1978; Eadsforth and Moser, 1983; Renberg et aL, 1980; McDuffie, 1980; where 7~ and X, are the activity coefficient and mole D'Amboise and Hanai, 1982; Rapaport and fraction of the solute, respectively. The activity Eisenreich, 1984) have used high performance reverse coefficient reflects the degree to which a solution Reverse phase chromatography--I 1435 deviates from ideality. It is not a constant, however, ble to develop relationships between a solute's par- and varies with X~ and ai. The two standard states tition coefficients for different organic/water systems commonly employed for defining the activity provided that the solute/organic solvent molecular coefficient are based on (1) the pure liquid or sub- interactions are limited to weak dispersion forces. cooled liquid component and (2) the "hypothetical" Collander
Load more

Recommended publications
  • Understanding Variation in Partition Coefficient, Kd, Values: Volume II
    United States Office of Air and Radiation EPA 402-R-99-004B Environmental Protection August 1999 Agency UNDERSTANDING VARIATION IN PARTITION COEFFICIENT, Kd, VALUES Volume II: Review of Geochemistry and Available Kd Values for Cadmium, Cesium, Chromium, Lead, Plutonium, Radon, Strontium, Thorium, Tritium (3H), and Uranium UNDERSTANDING VARIATION IN PARTITION COEFFICIENT, Kd, VALUES Volume II: Review of Geochemistry and Available Kd Values for Cadmium, Cesium, Chromium, Lead, Plutonium, Radon, Strontium, Thorium, Tritium (3H), and Uranium August 1999 A Cooperative Effort By: Office of Radiation and Indoor Air Office of Solid Waste and Emergency Response U.S. Environmental Protection Agency Washington, DC 20460 Office of Environmental Restoration U.S. Department of Energy Washington, DC 20585 NOTICE The following two-volume report is intended solely as guidance to EPA and other environmental professionals. This document does not constitute rulemaking by the Agency, and cannot be relied on to create a substantive or procedural right enforceable by any party in litigation with the United States. EPA may take action that is at variance with the information, policies, and procedures in this document and may change them at any time without public notice. Reference herein to any specific commercial products, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government. ii FOREWORD Understanding the long-term behavior of contaminants in the subsurface is becoming increasingly more important as the nation addresses groundwater contamination. Groundwater contamination is a national concern as about 50 percent of the United States population receives its drinking water from groundwater.
    [Show full text]
  • Henry's Law Constants and Micellar Partitioning of Volatile Organic
    38 J. Chem. Eng. Data 2000, 45, 38-47 Henry’s Law Constants and Micellar Partitioning of Volatile Organic Compounds in Surfactant Solutions Leland M. Vane* and Eugene L. Giroux United States Environmental Protection Agency, National Risk Management Research Laboratory, 26 West Martin Luther King Drive, Cincinnati, Ohio 45268 Partitioning of volatile organic compounds (VOCs) into surfactant micelles affects the apparent vapor- liquid equilibrium of VOCs in surfactant solutions. This partitioning will complicate removal of VOCs from surfactant solutions by standard separation processes. Headspace experiments were performed to quantify the effect of four anionic surfactants and one nonionic surfactant on the Henry’s law constants of 1,1,1-trichloroethane, trichloroethylene, toluene, and tetrachloroethylene at temperatures ranging from 30 to 60 °C. Although the Henry’s law constant increased markedly with temperature for all solutions, the amount of VOC in micelles relative to that in the extramicellar region was comparatively insensitive to temperature. The effect of adding sodium chloride and isopropyl alcohol as cosolutes also was evaluated. Significant partitioning of VOCs into micelles was observed, with the micellar partitioning coefficient (tendency to partition from water into micelle) increasing according to the following series: trichloroethane < trichloroethylene < toluene < tetrachloroethylene. The addition of surfactant was capable of reversing the normal sequence observed in Henry’s law constants for these four VOCs. Introduction have long taken advantage of the high Hc values for these compounds. In the engineering field, the most common Vast quantities of organic solvents have been disposed method of dealing with chlorinated solvents dissolved in of in a manner which impacts human health and the groundwater is “pump & treat”swithdrawal of ground- environment.
    [Show full text]
  • Chapter 4: Aqueous Solutions (Chs 4 and 5 in Jespersen, Ch4 in Chang)
    Chapter 4: Aqueous Solutions (Chs 4 and 5 in Jespersen, Ch4 in Chang) Solutions in which water is the dissolving medium are called aqueous solutions. There are three major types of chemical processes occurring in aqueous solutions: precipitation reactions (insoluble product) acid-base reactions (transfer of H+s) redox reactions (transfer of electrons) General Properties of Aqueous Solutions solution – a homogeneous mixture of two or more substances. solvent – usually the component that is present in greater quantity. solute(s) – the other substance(s) in the solution (ionic or molecular); present in smaller quantities. saturated solution – at a given temperature, the solution that results when the maximum amount of a substance has dissolved in a solvent. AJR Ch4 Aqueous Solutions.docx Slide 1 Electrolytic Properties electrolyte – a substance whose aqueous solutions contains ions and hence conducts electricity. E.g. NaCl. nonelectrolyte – a substance that does not form ions when it dissolves in water, and so aqueous solutions of nonelectrolytes do not conduct electricity. E.g. Glucose, C6H12O6. CuSO4 and Water; Ions present; Sugar and Water; No Ions present; electricity is conducted – bulb on. electricity is not conducted – bulb off. AJR Ch4 Aqueous Solutions.docx Slide 2 Ionic Compounds in Water Ionic compounds dissociate into their component ions as they dissolve in water. The ions become hydrated. Each ion is surrounded by water molecules, with the negative pole of the water oriented towards the cation and the positive pole oriented towards the anion. Other examples of ionic compounds dissociating into their component ions: + 2– Na2CO3 → 2 Na (aq) + CO3 (aq) + 2– (NH4)2SO4 → 2 NH4 (aq) + SO4 (aq) AJR Ch4 Aqueous Solutions.docx Slide 3 Molecular Compounds in Water Most molecular compounds do not form ions when they dissolve in water; they are nonelectrolytes.
    [Show full text]
  • Drugs and Acid Dissociation Constants Ionisation of Drug Molecules Most Drugs Ionise in Aqueous Solution.1 They Are Weak Acids Or Weak Bases
    Drugs and acid dissociation constants Ionisation of drug molecules Most drugs ionise in aqueous solution.1 They are weak acids or weak bases. Those that are weak acids ionise in water to give acidic solutions while those that are weak bases ionise to give basic solutions. Drug molecules that are weak acids Drug molecules that are weak bases where, HA = acid (the drug molecule) where, B = base (the drug molecule) H2O = base H2O = acid A− = conjugate base (the drug anion) OH− = conjugate base (the drug anion) + + H3O = conjugate acid BH = conjugate acid Acid dissociation constant, Ka For a drug molecule that is a weak acid The equilibrium constant for this ionisation is given by the equation + − where [H3O ], [A ], [HA] and [H2O] are the concentrations at equilibrium. In a dilute solution the concentration of water is to all intents and purposes constant. So the equation is simplified to: where Ka is the acid dissociation constant for the weak acid + + Also, H3O is often written simply as H and the equation for Ka is usually written as: Values for Ka are extremely small and, therefore, pKa values are given (similar to the reason pH is used rather than [H+]. The relationship between pKa and pH is given by the Henderson–Hasselbalch equation: or This relationship is important when determining pKa values from pH measurements. Base dissociation constant, Kb For a drug molecule that is a weak base: 1 Ionisation of drug molecules. 1 Following the same logic as for deriving Ka, base dissociation constant, Kb, is given by: and Ionisation of water Water ionises very slightly.
    [Show full text]
  • Partition Coefficients in Mixed Surfactant Systems
    Partition coefficients in mixed surfactant systems Application of multicomponent surfactant solutions in separation processes Vom Promotionsausschuss der Technischen Universität Hamburg-Harburg zur Erlangung des akademischen Grades Doktor-Ingenieur genehmigte Dissertation von Tanja Mehling aus Lohr am Main 2013 Gutachter 1. Gutachterin: Prof. Dr.-Ing. Irina Smirnova 2. Gutachterin: Prof. Dr. Gabriele Sadowski Prüfungsausschussvorsitzender Prof. Dr. Raimund Horn Tag der mündlichen Prüfung 20. Dezember 2013 ISBN 978-3-86247-433-2 URN urn:nbn:de:gbv:830-tubdok-12592 Danksagung Diese Arbeit entstand im Rahmen meiner Tätigkeit als wissenschaftliche Mitarbeiterin am Institut für Thermische Verfahrenstechnik an der TU Hamburg-Harburg. Diese Zeit wird mir immer in guter Erinnerung bleiben. Deshalb möchte ich ganz besonders Frau Professor Dr. Irina Smirnova für die unermüdliche Unterstützung danken. Vielen Dank für das entgegengebrachte Vertrauen, die stets offene Tür, die gute Atmosphäre und die angenehme Zusammenarbeit in Erlangen und in Hamburg. Frau Professor Dr. Gabriele Sadowski danke ich für das Interesse an der Arbeit und die Begutachtung der Dissertation, Herrn Professor Horn für die freundliche Übernahme des Prüfungsvorsitzes. Weiterhin geht mein Dank an das Nestlé Research Center, Lausanne, im Besonderen an Herrn Dr. Ulrich Bobe für die ausgezeichnete Zusammenarbeit und der Bereitstellung von LPC. Den Studenten, die im Rahmen ihrer Abschlussarbeit einen wertvollen Beitrag zu dieser Arbeit geleistet haben, möchte ich herzlichst danken. Für den außergewöhnlichen Einsatz und die angenehme Zusammenarbeit bedanke ich mich besonders bei Linda Kloß, Annette Zewuhn, Dierk Claus, Pierre Bräuer, Heike Mushardt, Zaineb Doggaz und Vanya Omaynikova. Für die freundliche Arbeitsatmosphäre, erfrischenden Kaffeepausen und hilfreichen Gespräche am Institut danke ich meinen Kollegen Carlos, Carsten, Christian, Mohammad, Krishan, Pavel, Raman, René und Sucre.
    [Show full text]
  • Estimation of Distribution Coefficients from the Partition Coefficient and Pka Douglas C
    Estimation of Distribution Coefficients from the Partition Coefficient and pKa Douglas C. Scott* and Jeffrey W. Clymer he use of partition coefficients has received much atten- tion in the assessment of relative lipophilicity and hy- drophilicity of a compound. Recent advances in com- putational chemistry have enabled scientists to estimate Tpartition coefficients for neutral species very easily. For ioniz- able species, the distribution coefficient is a more relevant pa- rameter; however, less effort has been applied to its assessment. Knowledge of the distribution coefficient and pKa is important The authors discuss for the basic characterization of a compound (1), particularly the relationship when assessing the compound’s potential to penetrate biolog- between the partition ical or lipid barriers (2). In addition, the majority of compounds coefficient and the are passively absorbed and a large number of new chemical en- distribution coefficient tities fail in the development stages because of related phar- and relate the two with the use of equations. macokinetic reasons (3). Assessing a compound’s relative lipophilicity dictates a formulation strategy that will ensure ab- To accurately explain this relationship, the sorption or tissue penetration, which ultimately will lead to de- authors consider the partitioning of both the livery of the drug to the site of action. In recognition of the ionized and un-ionized species.The presence value of knowing the extent of a drug’s gastrointestinal per- of both species in the oil phase necessitates a meation along with other necessary parameters, FDA has is- dissociative equilibrium among these species sued guidance for a waiver of in vivo bioavailability and bio- such as that in the water phase.
    [Show full text]
  • 1 Supplementary Material to the Paper “The Temperature and Pressure Dependence of Nickel Partitioning Between Olivine and Sili
    SUPPLEMENTARY MATERIAL TO THE PAPER “THE TEMPERATURE AND PRESSURE DEPENDENCE OF NICKEL PARTITIONING BETWEEN OLIVINE AND SILICATE MELT” A. K. Matzen, M. B. Baker, J. R. Beckett, and E. M. Stolper. In this Supplement, we provide seven sections that expand and/or illustrate specific topics presented in the main text. The first section is a sample calculation using our preferred partitioning expression, equation (5), from the main text. Section 2 compares our fitted values of ∆ r HT ,P ∆ r ST ,P − ref ref and ref ref for equation (5) to those calculated using tabulated thermodynamic R R data. In Section 3, we present details of the mass-balance calculations used to evaluate the experiments from both this work and the literature, and in Section 4 we describe in detail the construction of the Filter-B dataset. Section 5 details the construction and fits of the regular solution partitioning models. Section 6 is a comparison of the results of this work and the Beattie-Jones family of models. Finally, Section 7 lists all of the references incorporated into our database on olivine-liquid Ni partitioning. 1. EXAMPLE CALCULATION USING OUR PREFERRED PARTITIONING EXPRESSION (EQUATION 5) FROM THE MAIN TEXT Although one of the simplest equations listed in the text, we think it useful to present a detailed accounting of how to use equation (5) along with the fitted parameters presented in Table 4 to ol /liq ol /liq ol liq predict DNi (where DNi = NiO /NiO , by wt.) given the temperature and compositions of the coexisting olivine and liquid. In our example calculation, we predict the partition coefficient for one of our 1.0 GPa experiments, Run 6.
    [Show full text]
  • Aqueous Solution → Water Is the Solvent Water
    Chem 1A Name:_________________________ Chapter 4 Exercises Solution a homogeneous mixture = A solvent + solute(s) Aqueous solution water is the solvent Water – a polar solvent: dissolves most ionic compounds as well as many molecular compounds Aqueous solution: Strong electrolyte – contains lots of freely moving ions Weak electrolyte – contains a little amount of freely moving ions Nonelectrolyte – does not contain ions Solution concentrations: Mass of Solute Percent (by mass) = x 100% Mass of Solution For example, if 1.00 kg of seawater contains 35 g of sodium chloride, the percent of NaCl in seawater is 35 g x 100% = 3.5% 1000 g If a solution contains 25 g NaCl dissolved in 100. g of water, the mass percent of NaCl in the solution is 25 g x 100% = 20.% (100 + 25) g (A solution that contains 20.% (by mass) of NaCl means that for every 100 g of the solution, there will be 20 g of NaCl. Therefore, if seawater contains 3.5% NaCl, for every 100 g of seawater, there are 3.5 g of NaCl.) Volume of Solute Percent (by volume) = x 100% Volume of Solution For example, if 750 mL of white wine contains 80. mL of ethanol, the percent of ethanol by volume is 80. mL x 100% = 11% 750 mL (A solution that contains 11% ethanol (by volume) means that for every 100 mL of the solution, there will be 11 mL of ethanol in it. However, unlike mass, volume addition is not always additive – meaning that if you add 11 mL of ethanol and 89 mL of water, the total is not 100 mL.
    [Show full text]
  • Calculating the Partition Coefficients of Organic Solvents in Octanol/Water and Octanol/Air
    Article Cite This: J. Chem. Inf. Model. XXXX, XXX, XXX−XXX pubs.acs.org/jcim Calculating the Partition Coefficients of Organic Solvents in Octanol/ Water and Octanol/Air † ‡ § ∥ Miroslava A. Nedyalkova,*, Sergio Madurga, Marek Tobiszewski, and Vasil Simeonov † Inorganic Chemistry Department, Faculty of Chemistry and Pharmacy, University of Sofia, Sofia 1164, Bulgaria ‡ Departament de Ciencià de Materials i Química Física and Institut de Química Teoricà i Computacional (IQTCUB), Universitat de Barcelona, 08028 Barcelona, Catalonia, Spain § Department of Analytical Chemistry, Faculty of Chemistry, Gdansḱ University of Technology (GUT), 80-233 Gdansk,́ Poland ∥ Analytical Chemistry Department, Faculty of Chemistry and Pharmacy, University of Sofia, Sofia 1164, Bulgaria *S Supporting Information ABSTRACT: Partition coefficients define how a solute is distributed between two immiscible phases at equilibrium. The experimental estimation of partition coefficients in a complex system can be an expensive, difficult, and time-consuming process. Here a computa- tional strategy to predict the distributions of a set of solutes in two relevant phase equilibria is presented. The octanol/water and octanol/air partition coefficients are predicted for a group of polar solvents using density functional theory (DFT) calculations in combination with a solvation model based on density (SMD) and are in excellent agreement with experimental data. Thus, the use of quantum-chemical calculations to predict partition coefficients from free energies should be a valuable alternative for unknown solvents. The obtained results indicate that the SMD continuum model in conjunction with any of the three DFT functionals (B3LYP, M06-2X, and M11) agrees with the observed experimental values. The highest correlation to experimental data for the octanol/water partition coefficients was reached by the M11 functional; for the octanol/air partition coefficient, the M06-2X functional yielded the best performance.
    [Show full text]
  • Raoult's Law – Partition Law
    BAE 820 Physical Principles of Environmental Systems Henry’s Law - Raoult's Law – Partition law Dr. Zifei Liu Biological and Agricultural Engineering Henry's law • At a constant temperature, the amount of a given gas that dissolves in a given type and volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid. Pi = KHCi • Where Pi is the partial pressure of the gaseous solute above the solution, C is the i William Henry concentration of the dissolved gas and KH (1774-1836) is Henry’s constant with the dimensions of pressure divided by concentration. KH is different for each solute-solvent pair. Biological and Agricultural Engineering 2 Henry's law For a gas mixture, Henry's law helps to predict the amount of each gas which will go into solution. When a gas is in contact with the surface of a liquid, the amount of the gas which will go into solution is proportional to the partial pressure of that gas. An equivalent way of stating the law is that the solubility of a gas in a liquid is directly proportional to the partial pressure of the gas above the liquid. the solubility of gases generally decreases with increasing temperature. A simple rationale for Henry's law is that if the partial pressure of a gas is twice as high, then on the average twice as many molecules will hit the liquid surface in a given time interval, Biological and Agricultural Engineering 3 Air-water equilibrium Dissolution Pg or Cg Air (atm, Pa, mol/L, ppm, …) At equilibrium, Pg KH = Caq Water Caq (mol/L, mole ratio, ppm, …) Volatilization Biological and Agricultural Engineering 4 Various units of the Henry’s constant (gases in water at 25ºC) Form of K =P/C K =C /P K =P/x K =C /C equation H, pc aq H, cp aq H, px H, cc aq gas Units L∙atm/mol mol/(L∙atm) atm dimensionless -3 4 -2 O2 769 1.3×10 4.26×10 3.18×10 -4 4 -2 N2 1639 6.1×10 9.08×10 1.49×10 -2 3 CO2 29 3.4×10 1.63×10 0.832 Since all KH may be referred to as Henry's law constants, we must be quite careful to check the units, and note which version of the equation is being used.
    [Show full text]
  • Procedures to Implement the Texas Surface Water Quality Standards
    Procedures to Implement the Texas Surface Water Quality Standards Prepared by Water Quality Division RG-194 June 2010 1 Contents Introduction................................................................................................. 12 Determining Water Quality Uses and Criteria........................................ 14 Classified Waters .......................................................................................................... 14 Unclassified Waters ...................................................................................................... 14 Presumed Aquatic Life Uses......................................................................................... 14 Assigned Aquatic Life Uses...................................................................................... 16 Evaluating Impacts on Water Quality...................................................... 20 General Information...................................................................................................... 20 Minimum and Seasonal Criteria for Dissolved Oxygen............................................... 21 Federally Endangered and Threatened Species ............................................................ 21 Screening Process ..................................................................................................... 22 Additional Permit Limits .......................................................................................... 22 Edwards Aquifer ......................................................................................................
    [Show full text]
  • Dissociation Constants of Organic Acids and Bases
    DISSOCIATION CONSTANTS OF ORGANIC ACIDS AND BASES This table lists the dissociation (ionization) constants of over pKa + pKb = pKwater = 14.00 (at 25°C) 1070 organic acids, bases, and amphoteric compounds. All data apply to dilute aqueous solutions and are presented as values of Compounds are listed by molecular formula in Hill order. pKa, which is defined as the negative of the logarithm of the equi- librium constant K for the reaction a References HA H+ + A- 1. Perrin, D. D., Dissociation Constants of Organic Bases in Aqueous i.e., Solution, Butterworths, London, 1965; Supplement, 1972. 2. Serjeant, E. P., and Dempsey, B., Ionization Constants of Organic Acids + - Ka = [H ][A ]/[HA] in Aqueous Solution, Pergamon, Oxford, 1979. 3. Albert, A., “Ionization Constants of Heterocyclic Substances”, in where [H+], etc. represent the concentrations of the respective Katritzky, A. R., Ed., Physical Methods in Heterocyclic Chemistry, - species in mol/L. It follows that pKa = pH + log[HA] – log[A ], so Academic Press, New York, 1963. 4. Sober, H.A., Ed., CRC Handbook of Biochemistry, CRC Press, Boca that a solution with 50% dissociation has pH equal to the pKa of the acid. Raton, FL, 1968. 5. Perrin, D. D., Dempsey, B., and Serjeant, E. P., pK Prediction for Data for bases are presented as pK values for the conjugate acid, a a Organic Acids and Bases, Chapman and Hall, London, 1981. i.e., for the reaction 6. Albert, A., and Serjeant, E. P., The Determination of Ionization + + Constants, Third Edition, Chapman and Hall, London, 1984. BH H + B 7. Budavari, S., Ed., The Merck Index, Twelth Edition, Merck & Co., Whitehouse Station, NJ, 1996.
    [Show full text]