Safety data sheet
A safety data sheet, material safety data sheet, or product safety data sheet is a document that lists information relating to occupational safety and health for the use of various substances and products. SDSs are a used system for cataloging information on chemicals, chemical compounds, chemical mixtures. SDS information may include instructions for the safe use and potential hazards associated with a particular material or product, along with spill-handling procedures. SDS formats can vary from source to source within a country depending on national requirements. A SDS for a substance is not intended for use by the general consumer, focusing instead on the hazards of working with the material in an occupational setting. There is a duty to properly label substances on the basis of physico-chemical, health or environmental risk. Labels can include hazard symbols such as the European Union standard symbols; the same product can have different formulations in different countries. The formulation and hazard of a product using a generic name may vary between manufacturers in the same country.
The Globally Harmonized System of Classification and Labelling of Chemicals contains a standard specification for safety data sheets. The SDS follows a 16 section format, internationally agreed and for substances the SDS should be followed with an Annex which contains the exposure scenarios of this particular substance; the 16 sections are: SECTION 1: Identification of the substance/mixture and of the company/undertaking 1.1. Product identifier 1.2. Relevant identified uses of the substance or mixture and uses advised against 1.3. Details of the supplier of the safety data sheet 1.4. Emergency telephone number SECTION 2: Hazards identification 2.1. Classification of the substance or mixture 2.2. Label elements 2.3. Other hazards SECTION 3: Composition/information on ingredients 3.1. Substances 3.2. Mixtures SECTION 4: First aid measures 4.1. Description of first aid measures 4.2. Most important symptoms and effects, both acute and delayed 4.3. Indication of any immediate medical attention and special treatment needed SECTION 5: Firefighting measures 5.1.
Extinguishing media 5.2. Special hazards arising from the substance or mixture 5.3. Advice for firefighters SECTION 6: Accidental release measure 6.1. Personal precautions, protective equipment and emergency procedures 6.2. Environmental precautions 6.3. Methods and material for containment and cleaning up 6.4. Reference to other sections SECTION 7: Handling and storage 7.1. Precautions for safe handling 7.2. Conditions for safe storage, including any incompatibilities 7.3. Specific end use SECTION 8: Exposure controls/personal protection 8.1. Control parameters 8.2. Exposure controls SECTION 9: Physical and chemical properties 9.1. Information on basic physical and chemical properties 9.2. Other information SECTION 10: Stability and reactivity 10.1. Reactivity 10.2. Chemical stability 10.3. Possibility of hazardous reactions 10.4. Conditions to avoid 10.5. Incompatible materials 10.6. Hazardous decomposition products SECTION 11: Toxicological information 11.1. Information on toxicological effects SECTION 12: Ecological information 12.1.
Toxicity 12.2. Persistence and degradability 12.3. Bioaccumulative potential 12.4. Mobility in soil 12.5. Results of PBT and vPvB assessment 12.6. Other adverse effects SECTION 13: Disposal considerations 13.1. Waste treatment methods SECTION 14: Transport information 14.1. UN number 14.2. UN proper shipping name 14.3. Transport hazard class 14.4. Packing group 14.5. Environmental hazards 14.6. Special precautions for user 14.7. Transport in bulk according to Annex II of MARPOL73/78 and the IBC Code SECTION 15: Regulatory information 15.1. Safety and environmental regulations/legislation specific for the substance or mixture 15.2. Chemical safety assessment SECTION 16: Other information 16.2. Date of the latest revision of the SDS In Canada, the program known as the Workplace Hazardous Materials Information System establishes the requirements for SDSs in workplaces and is administered federally by Health Canada under the Hazardous Products Act, Part II, the Controlled Products Regulations. Safety data sheets have been made an integral part of the system of Regulation No 1907/2006.
The original requirements of REACH for SDSs have been further adapted to take into account the rules for safety data sheets of the Global Harmonised System and the implementation of other elements of the GHS into EU legislation that were introduced by Regulation No 1272/2008 via an update to Annex II of REACH. The SDS must be supplied in an official language of the Member State where the substance or mixture is placed on the market, unless the Member State concerned provide otherwise; the European Chemicals Agency has published a guidance document on the compilation of safety data sheets. The German Federal Water Management Act requires that substances be evaluated for negative influence on the physical, chemical or biological characteristics of water; these are classified into numeric water hazard classes. WGK nwg: Non-water polluting substance WGK 1: Slightly water polluting substance WGK 2: Water polluting substance WGK 3: Highly water polluting substance This section contributes to a better understanding of the regulations governing SDS within the South African framework.
As regulations may change, it is the responsibility of the reader to verify the validity of the regulations mentioned in text. As globalisation increased and countries engaged in cross-border trade, the quantity of hazardous material crossing international borders a
Acid dissociation constant
An acid dissociation constant, Ka, is a quantitative measure of the strength of an acid in solution. It is the equilibrium constant for a chemical reaction known as dissociation in the context of acid–base reactions. K a =; the chemical species HA, A−, H+ are said to be in equilibrium when their concentrations do not change with the passing of time, because both forward and backward reactions are occurring at the same fast rate. The chemical equation for acid dissociation can be written symbolically as: HA ↽ − − ⇀ A − + H + where HA is a generic acid that dissociates into A−, the conjugate base of the acid and a hydrogen ion, H+, it is implicit in this definition that the quotient of activity coefficients, Γ, Γ = γ A − γ H + γ A H is a constant that can be ignored in a given set of experimental conditions. For many practical purposes it is more convenient to discuss the logarithmic constant, pKa p K a = − log 10 The more positive the value of pKa, the smaller the extent of dissociation at any given pH —that is, the weaker the acid.
A weak acid has a pKa value in the approximate range −2 to 12 in water. For a buffer solution consisting of a weak acid and its conjugate base, pKa can be expressed as: p K a = pH − log 10 The pKa for a weak monoprotic acid is conveniently determined by potentiometric titration with a strong base to the equivalence point and taking the pH value measured at one-half this volume as being equal to pKa; that is because at this half equivalence point, the number of moles of strong base added is one-half the number of moles of weak acid present, while the concentrations of the conjugate base and the remaining weak acid are the same. Acids with a pKa value of less than about −2 are said to be strong acids. In water, the dissociation of a strong acid in dilute solutions is complete such that the final concentration of the undissociated acid final is low. Consider a strong monoprotic acid, such as HCl; because of their 1:1 ratio, the final concentration of the conjugate base, final, is taken to be equal to the concentration of the hydronium ion, which can be directly measured by a pH meter.
For strong monoprotic acids like HCl, final and are both nearly equal to the initial concentration of initial placed into solution. With conventional acid-base titration methods it is difficult to measure the pH of a strong acid solution and, hence, to determine the or final, with a sufficient number of significant figures to and compute the low values encountered for final, which can be as low as 10-9 mol per liter for some strong acids. Furthermore, if 100% dissociation is assumed, final is zero and the fraction within parenthesis in the equation above becomes undefined; because the second expression on the right-hand side of the above equation is therefore indeterminable by conventional titration methods, the entire equation is not as useful a means of experimentally measuring pKa for strong acids as it is for weak acids. However, pKa and/or Ka values for strong acids can be estimated by theoretical means, such as computing gas phase dissociation constants and using Gibbs free energies of solvation for the molecular anions.
It is possible to use spectroscopy in some cases to determine the ratio of the concentrations of the conjugate base produced and the undissociated acid. For example, the Raman spectra of dilute nitric acid solutions contain signals of the nitrate ion and as the solutions become more concentrated signals of undissociated nitric acid molecules emerge; the acid dissociation constant for an acid is a direct consequence of the underlying thermodynamics of the dissociation reaction. The value of the pKa changes with temperature and can be understood qualitatively based on Le Châtelier's principle: when the reaction is endothermic, Ka increases and pKa decreases with
The boiling point of a substance is the temperature at which the vapor pressure of a liquid equals the pressure surrounding the liquid and the liquid changes into a vapor. The boiling point of a liquid varies depending upon the surrounding environmental pressure. A liquid in a partial vacuum has a lower boiling point than when that liquid is at atmospheric pressure. A liquid at high pressure has a higher boiling point than when that liquid is at atmospheric pressure. For example, water at 93.4 °C at 1,905 metres altitude. For a given pressure, different liquids will boil at different temperatures; the normal boiling point of a liquid is the special case in which the vapor pressure of the liquid equals the defined atmospheric pressure at sea level, 1 atmosphere. At that temperature, the vapor pressure of the liquid becomes sufficient to overcome atmospheric pressure and allow bubbles of vapor to form inside the bulk of the liquid; the standard boiling point has been defined by IUPAC since 1982 as the temperature at which boiling occurs under a pressure of 1 bar.
The heat of vaporization is the energy required to transform a given quantity of a substance from a liquid into a gas at a given pressure. Liquids may change to a vapor at temperatures below their boiling points through the process of evaporation. Evaporation is a surface phenomenon in which molecules located near the liquid's edge, not contained by enough liquid pressure on that side, escape into the surroundings as vapor. On the other hand, boiling is a process in which molecules anywhere in the liquid escape, resulting in the formation of vapor bubbles within the liquid. A saturated liquid contains as much thermal energy. Saturation temperature means boiling point; the saturation temperature is the temperature for a corresponding saturation pressure at which a liquid boils into its vapor phase. The liquid can be said to be saturated with thermal energy. Any addition of thermal energy results in a phase transition. If the pressure in a system remains constant, a vapor at saturation temperature will begin to condense into its liquid phase as thermal energy is removed.
A liquid at saturation temperature and pressure will boil into its vapor phase as additional thermal energy is applied. The boiling point corresponds to the temperature at which the vapor pressure of the liquid equals the surrounding environmental pressure. Thus, the boiling point is dependent on the pressure. Boiling points may be published with respect to the NIST, USA standard pressure of 101.325 kPa, or the IUPAC standard pressure of 100.000 kPa. At higher elevations, where the atmospheric pressure is much lower, the boiling point is lower; the boiling point increases with increased pressure up to the critical point, where the gas and liquid properties become identical. The boiling point cannot be increased beyond the critical point; the boiling point decreases with decreasing pressure until the triple point is reached. The boiling point cannot be reduced below the triple point. If the heat of vaporization and the vapor pressure of a liquid at a certain temperature are known, the boiling point can be calculated by using the Clausius–Clapeyron equation, thus: T B = − 1, where: T B is the boiling point at the pressure of interest, R is the ideal gas constant, P is the vapour pressure of the liquid at the pressure of interest, P 0 is some pressure where the corresponding T 0 is known, Δ H vap is the heat of vaporization of the liquid, T 0 is the boiling temperature, ln is the natural logarithm.
Saturation pressure is the pressure for a corresponding saturation temperature at which a liquid boils into its vapor phase. Saturation pressure and saturation temperature have a direct relationship: as saturation pressure is increased, so is saturation temperature. If the temperature in a system remains constant, vapor at saturation pressure and temperature will begin to condense into its liquid phase as the system pressure is increased. A liquid at saturation pressure and temperature will tend to flash into its vapor phase as system pressure is decreased. There are two conventions regarding the standard boiling point of water: The normal boiling point is 99.97 °C at a pressure of 1 atm. The IUPAC recommended standard boiling point of water at a standard pressure of 100 kPa is 99.61 °C. For comparison, on top of Mount Everest, at 8,848 m elevation, the pressure is about 34 kPa and the boiling point of water is 71 °C; the Celsius temperature scale was defined until 1954 by two points: 0 °C being defined by the wate
Simplified molecular-input line-entry system
The simplified molecular-input line-entry system is a specification in the form of a line notation for describing the structure of chemical species using short ASCII strings. SMILES strings can be imported by most molecule editors for conversion back into two-dimensional drawings or three-dimensional models of the molecules; the original SMILES specification was initiated in the 1980s. It has since been extended. In 2007, an open standard called. Other linear notations include the Wiswesser line notation, ROSDAL, SYBYL Line Notation; the original SMILES specification was initiated by David Weininger at the USEPA Mid-Continent Ecology Division Laboratory in Duluth in the 1980s. Acknowledged for their parts in the early development were "Gilman Veith and Rose Russo and Albert Leo and Corwin Hansch for supporting the work, Arthur Weininger and Jeremy Scofield for assistance in programming the system." The Environmental Protection Agency funded the initial project to develop SMILES. It has since been modified and extended by others, most notably by Daylight Chemical Information Systems.
In 2007, an open standard called "OpenSMILES" was developed by the Blue Obelisk open-source chemistry community. Other'linear' notations include the Wiswesser Line Notation, ROSDAL and SLN. In July 2006, the IUPAC introduced the InChI as a standard for formula representation. SMILES is considered to have the advantage of being more human-readable than InChI; the term SMILES refers to a line notation for encoding molecular structures and specific instances should be called SMILES strings. However, the term SMILES is commonly used to refer to both a single SMILES string and a number of SMILES strings; the terms "canonical" and "isomeric" can lead to some confusion when applied to SMILES. The terms are not mutually exclusive. A number of valid SMILES strings can be written for a molecule. For example, CCO, OCC and CC all specify the structure of ethanol. Algorithms have been developed to generate the same SMILES string for a given molecule; this SMILES is unique for each structure, although dependent on the canonicalization algorithm used to generate it, is termed the canonical SMILES.
These algorithms first convert the SMILES to an internal representation of the molecular structure. Various algorithms for generating canonical SMILES have been developed and include those by Daylight Chemical Information Systems, OpenEye Scientific Software, MEDIT, Chemical Computing Group, MolSoft LLC, the Chemistry Development Kit. A common application of canonical SMILES is indexing and ensuring uniqueness of molecules in a database; the original paper that described the CANGEN algorithm claimed to generate unique SMILES strings for graphs representing molecules, but the algorithm fails for a number of simple cases and cannot be considered a correct method for representing a graph canonically. There is no systematic comparison across commercial software to test if such flaws exist in those packages. SMILES notation allows the specification of configuration at tetrahedral centers, double bond geometry; these are structural features that cannot be specified by connectivity alone and SMILES which encode this information are termed isomeric SMILES.
A notable feature of these rules is. The term isomeric SMILES is applied to SMILES in which isotopes are specified. In terms of a graph-based computational procedure, SMILES is a string obtained by printing the symbol nodes encountered in a depth-first tree traversal of a chemical graph; the chemical graph is first trimmed to remove hydrogen atoms and cycles are broken to turn it into a spanning tree. Where cycles have been broken, numeric suffix labels are included to indicate the connected nodes. Parentheses are used to indicate points of branching on the tree; the resultant SMILES form depends on the choices: of the bonds chosen to break cycles, of the starting atom used for the depth-first traversal, of the order in which branches are listed when encountered. Atoms are represented by the standard abbreviation of the chemical elements, in square brackets, such as for gold. Brackets may be omitted in the common case of atoms which: are in the "organic subset" of B, C, N, O, P, S, F, Cl, Br, or I, have no formal charge, have the number of hydrogens attached implied by the SMILES valence model, are the normal isotopes, are not chiral centers.
All other elements must be enclosed in brackets, have charges and hydrogens shown explicitly. For instance, the SMILES for water may be written as either O or. Hydrogen may be written as a separate atom; when brackets are used, the symbol H is added if the atom in brackets is bonded to one or more hydrogen, followed by the number of hydrogen atoms if greater than 1 by the sign + for a positive charge or by - for a negative charge. For example, for ammonium. If there is more than one charge, it is written as digit.
Ultraviolet–visible spectroscopy or ultraviolet–visible spectrophotometry refers to absorption spectroscopy or reflectance spectroscopy in part of the ultraviolet and the full, adjacent visible spectral regions. This means it uses light in the adjacent ranges; the absorption or reflectance in the visible range directly affects the perceived color of the chemicals involved. In this region of the electromagnetic spectrum and molecules undergo electronic transitions. Absorption spectroscopy is complementary to fluorescence spectroscopy, in that fluorescence deals with transitions from the excited state to the ground state, while absorption measures transitions from the ground state to the excited state. Molecules containing bonding and non-bonding electrons can absorb energy in the form of ultraviolet or visible light to excite these electrons to higher anti-bonding molecular orbitals; the more excited the electrons, the longer the wavelength of light it can absorb. There are four possible types of transitions, they can be ordered as follows: σ–σ* > n–σ* > π–π* > n–π*.
UV/Vis spectroscopy is used in analytical chemistry for the quantitative determination of different analytes, such as transition metal ions conjugated organic compounds, biological macromolecules. Spectroscopic analysis is carried out in solutions but solids and gases may be studied. Solutions of transition metal ions can be colored because d electrons within the metal atoms can be excited from one electronic state to another; the colour of metal ion solutions is affected by the presence of other species, such as certain anions or ligands. For instance, the colour of a dilute solution of copper sulfate is a light blue. Organic compounds those with a high degree of conjugation absorb light in the UV or visible regions of the electromagnetic spectrum; the solvents for these determinations are water for water-soluble compounds, or ethanol for organic-soluble compounds. Solvent polarity and pH can affect the absorption spectrum of an organic compound. Tyrosine, for example, increases in absorption maxima and molar extinction coefficient when pH increases from 6 to 13 or when solvent polarity decreases.
While charge transfer complexes give rise to colours, the colours are too intense to be used for quantitative measurement. The Beer–Lambert law states that the absorbance of a solution is directly proportional to the concentration of the absorbing species in the solution and the path length. Thus, for a fixed path length, UV/Vis spectroscopy can be used to determine the concentration of the absorber in a solution, it is necessary to know how the absorbance changes with concentration. This can be taken from references, or more determined from a calibration curve. A UV/Vis spectrophotometer may be used as a detector for HPLC; the presence of an analyte gives. For accurate results, the instrument's response to the analyte in the unknown should be compared with the response to a standard; the response for a particular concentration is known as the response factor. The wavelengths of absorption peaks can be correlated with the types of bonds in a given molecule and are valuable in determining the functional groups within a molecule.
The Woodward–Fieser rules, for instance, are a set of empirical observations used to predict λmax, the wavelength of the most intense UV/Vis absorption, for conjugated organic compounds such as dienes and ketones. The spectrum alone is not, however, a specific test for any given sample; the nature of the solvent, the pH of the solution, high electrolyte concentrations, the presence of interfering substances can influence the absorption spectrum. Experimental variations such as the slit width of the spectrophotometer will alter the spectrum. To apply UV/Vis spectroscopy to analysis, these variables must be controlled or accounted for in order to identify the substances present; the method is most used in a quantitative way to determine concentrations of an absorbing species in solution, using the Beer–Lambert law: A = log 10 = ε c L,where A is the measured absorbance, I 0 is the intensity of the incident light at a given wavelength, I is the transmitted intensity, L the path length through the sample, c the concentration of the absorbing species.
For each species and wavelength, ε is a constant known as the molar absorptivity or extinction coefficient. This constant is a fundamental molecular property in a given solvent, at a particular temperature and pressure, has units of 1 / M ∗ c m; the absorbance and extinction ε are sometimes defined in terms of the natural logarithm instead of the base-10 logarithm. The Beer–Lambert Law is useful for characterizing many compounds but does not hold as a universal relationship for the concentration and absorption of all s
An odor, or odour, is caused by one or more volatilized chemical compounds that are found in low concentrations that humans and animals can perceive by their sense of smell. An odor is called a "smell" or a "scent", which can refer to either a pleasant or an unpleasant odor. While "scent" can refer to pleasant and unpleasant odors, the terms "scent", "aroma", "fragrance" are reserved for pleasant-smelling odors and are used in the food and cosmetic industry to describe floral scents or to refer to perfumes. In the United Kingdom, "odour" refers to scents in general. An unpleasant odor can be described as "reeking" or called a "malodor", "stench", "pong", or "stink"; the perception of odors, or sense of smell, is mediated by the olfactory nerve. The olfactory receptor cells are neurons present in the olfactory epithelium, a small patch of tissue at the back of the nasal cavity. There are millions of olfactory receptor neurons; each neuron has cilia in direct contact with the air. Odorous molecules bind to receptor proteins extending from cilia and act as a chemical stimulus, initiating electric signals that travel along the olfactory nerve's axons to the brain.
When an electrical signal reaches a threshold, the neuron fires, which sends a signal traveling along the axon to the olfactory bulb, a part of the limbic system of the brain. Interpretation of the smell begins there, relating the smell to past experiences and in relation to the substance inhaled; the olfactory bulb acts as a relay station connecting the nose to the olfactory cortex in the brain. Olfactory information is further processed and forwarded to the central nervous system, which controls emotions and behavior as well as basic thought processes. Odor sensation depends on the concentration available to the olfactory receptors. A single odorant is recognized by many receptors. Different odorants are recognized by combinations of receptors; the patterns of neuron signals help to identify the smell. The olfactory system does not interpret a single compound, but instead the whole odorous mix; this does not correspond to the intensity of any single constituent. Most odors consists of organic compounds, although some simple compounds not containing carbon, such as hydrogen sulfide and ammonia, are odorants.
The perception of an odor effect is a two-step process. First, there is the physiological part; this is the detection of stimuli by receptors in the nose. The stimuli are recognized by the region of the human brain; because of this, an objective and analytical measure of odor is impossible. While odor feelings are personal perceptions, individual reactions are related, they relate to things such as gender, state of health, personal history. The ability to identify odor varies among decreases with age. Studies show there are sex differences in odor discrimination, women outperform men. Pregnant women have increased smell sensitivity, sometimes resulting in abnormal taste and smell perceptions, leading to food cravings or aversions; the ability to taste decreases with age as the sense of smell tends to dominate the sense of taste. Chronic smell problems are reported in small numbers for those in their mid-twenties, with numbers increasing with overall sensitivity beginning to decline in the second decade of life, deteriorating appreciably as age increases once over 70 years of age.
For most untrained people, the process of smelling gives little information concerning the specific ingredients of an odor. Their smell perception offers information related to the emotional impact. Experienced people, such as flavorists and perfumers, can pick out individual chemicals in complex mixtures through smell alone. Odor perception is a primal sense; the sense of smell enables pleasure, can subconsciously warn of danger, help locate mates, find food, or detect predators. Humans have a good sense of smell, correlated to an evolutionary decline in sense of smell. A human's sense of smell is just as good as many animals and can distinguish a diversity of odors—approximately 10,000 scents. Studies reported. Odors that a person is used to, such as their own body odor, are less noticeable than uncommon odors; this is due to habituation. After continuous odor exposure, the sense of smell is fatigued, but recovers if the stimulus is removed for a time. Odors can change due to environmental conditions: for example, odors tend to be more distinguishable in cool dry air.
Habituation affects the ability to distinguish odors after continuous exposure. The sensitivity and ability to discriminate odors diminishes with exposure, the brain tends to ignore continuous stimulus and focus on differences and changes in a particular sensation; when odorants are mixed, a habitual odorant is blocked. This depends on the strength of the odorants in the mixture, which can change the perception and processing of an odor; this process helps classify similar odors as well as adjust sensitivity to differences in complex stimuli. The primary gene sequences for thousands of olfactory receptors are known for the genomes of more than a dozen organisms, they are seven-helix-turn transmembrane proteins. But there are no known structures for any olfactory receptor. There is a conserved sequence in three quarters of all ORs; this is a tripodal metal-ion binding site, and
In the physical sciences, a partition coefficient or distribution coefficient is the ratio of concentrations of a compound in a mixture of two immiscible phases at equilibrium. This ratio is therefore a measure of the difference in solubility of the compound in these two phases; the partition coefficient refers to the concentration ratio of un-ionized species of compound, whereas the distribution coefficient refers to the concentration ratio of all species of the compound. In the chemical and pharmaceutical sciences, both phases are solvents. Most one of the solvents is water, while the second is hydrophobic, such as 1-octanol. Hence the partition coefficient measures how hydrophobic a chemical substance is. Partition coefficients are useful in estimating the distribution of drugs within the body. Hydrophobic drugs with high octanol/water partition coefficients are distributed to hydrophobic areas such as lipid bilayers of cells. Conversely, hydrophilic drugs are found in aqueous regions such as blood serum.
If one of the solvents is a gas and the other a liquid, a gas/liquid partition coefficient can be determined. For example, the blood/gas partition coefficient of a general anesthetic measures how the anesthetic passes from gas to blood. Partition coefficients can be defined when one of the phases is solid, for instance, when one phase is a molten metal and the second is a solid metal, or when both phases are solids; the partitioning of a substance into a solid results in a solid solution. Partition coefficients can be measured experimentally in various ways or estimated by calculation based on a variety of methods. Despite formal recommendation to the contrary, the term partition coefficient remains the predominantly used term in the scientific literature. In contrast, the IUPAC recommends that the title term no longer be used, that it be replaced with more specific terms. For example, partition constant, defined as where KD is the process equilibrium constant, represents the concentration of solute A being tested, "org" and "aq" refer to the organic and aqueous phases respectively.
The IUPAC further recommends "partition ratio" for cases where transfer activity coefficients can be determined, "distribution ratio" for the ratio of total analytical concentrations of a solute between phases, regardless of chemical form. The partition coefficient, abbreviated P, is defined as a particular ratio of the concentrations of a solute between the two solvents for un-ionized solutes, the logarithm of the ratio is thus log P; when one of the solvents is water and the other is a non-polar solvent the log P value is a measure of lipophilicity or hydrophobicity. The defined precedent is for the lipophilic and hydrophilic phase types to always be in the numerator and denominator respectively. To a first approximation, the non-polar phase in such experiments is dominated by the un-ionized form of the solute, electrically neutral, though this may not be true for the aqueous phase. To measure the partition coefficient of ionizable solutes, the pH of the aqueous phase is adjusted such that the predominant form of the compound in solution is the un-ionized, or its measurement at another pH of interest requires consideration of all species, un-ionized and ionized.
A corresponding partition coefficient for ionizable compounds, abbreviated log P I, is derived for cases where there are dominant ionized forms of the molecule, such that one must consider partition of all forms, ionized and un-ionized, between the two phases. M is used to indicate the number of ionized forms. For instance, for an octanol–water partition, it is log P oct/wat I = log . To distinguish between this and the standard, un-ionized, partition coefficient, the un-ionized is assigned the symbol log P0, such that the indexed log P oct/wat I expression for ionized solutes becomes an extension of this, into the range of values I > 0. The distribution co