Patent GB-360402-A (GB)
Title: Improvements in or relating to hydrogen ion standard buffer solutions
IPC: G01N31/22
Filed: 1930-04-24
Abstract: Hydrogen ion standard buffer solutions are stabilized against changes caused by the carbon dioxide of the air by including in the solution a carbonate and/or bicarbonate, especially sodium carbonate and/or bicarbonate.  The buffers especially referred to are those containing phthalic, malic, succinic, glutaric, tartaric and citric acids and their salts, sodium acid phthalate being a particularly suitable buffer as the equal mobilities of its cation and anion causes it to give substantially no liquid-liquid junction potential against the usual liquid potential eliminators such as potassium chloride, ammonium chloride or rubidium bromide employed for determination of hydrogen ion concentration by means of the hydrogen or quinhydrone electrodes.  It can be mixed with solutions of dyes such as wool red, neptune green, <PICT:0360402/III/1> <PICT:0360402/III/2> patent blue or alphazurine without appreciable change in pH.  The dearth of suitable buffer solutions in the pH range 7-10 may be augmented by the use of 1-phenol-4 sulphonic acid, 1-phenol-2-chlor-4 sulphonic acid, 1-phenol-2, 6 dichlor-4 sulphonic acid and 1 phenol-2, 4 dichlor-6-sulphonic acid and their salts.  The pH ranges covered by these acids may be modified by the inclusion of further halogen or other negative group to lower the pH range or alkyl or amino groups to raise the pH range. These halogenated phenol derivatives also serve for killing bacteria, lice, ticks and the like.  The other buffers above referred to should also be sterilized against changes due to moulds and bacteria by the inclusion of disinfectants such as thymol, chloramines or formaldehyde.  Sodium acid phthalate solution may be mixed with the proper quantity of standard hydrochloric acid or standard caustic soda to make a series of buffer standards covering the pH range 2,0-7,0.  Further, anhydrous sodium acid phthalate may be mixed with the proper quantities of phthalic acid or anhydrous disodium phthalate and after being ground may be made into tablets which make buffer solutions having a known pH when dissolved in a given quantity of pure distilled water.  These tablets may also contain sodium chloride.  Sodium acid phthalate may also be mixed with predetermined quantities of solid phosphates, pyrophosphates, borates, phenolsulphonates and the like and thymol to give universal buffer solutions or buffer tablets from which a solution of any pH may be obtained by the addition of a given quantity of standard acid or standard alkali.  Solutions of sulphonphthalein indicators such as brom-phenol-blue, brom cresol green, brom cresol purple, brome thymol blue or other indicators such as methyl red, phenol red or cresol red may be added to the buffer solutions to make standard colour scales for colorimetric pH determination.  As the indicator solution has some effect on the pH of both the buffer solution and any unknown solution the pH of which is being determined, the indicator solution should be brought to the pH of the solution to which it is to be added by the addition of the correct amount of aqueous alkali before hand. In determining the pH of an unknown solution preliminary trial and error tests are necessary with indicator solutions adjusted to different pH values.  A series of <FORM:0360402/III/1> or <FORM:0360402/III/2> solutions of the appropriate indicator adjusted as to pH steps 0,2 pH apart is preferably employed.  Water, distilling; electrical precipitators.--Pure water suitable for the preparation of hydrogen ion buffer standards and having a pH of 7 is prepared in a still as shown in Fig. 1.  Steam enters through a valve K and after passing through a spray trap D enters a heating coil E. The condensed water flows into a trap L and is forced by the steam pressure through a pipe P into a scrubber F down which it flows in counter-current to a stream of carbon dioxide free air and finally passes into a boiler N.  Here it is boiled by the heat of the steam in the coil E the steam rising through a baffle plate I and porcelain tin or metallic rings J which remove any spray.  The spray-free steam is condensed by a condenser A, the condensate falling into a funnel Q and passing through a tube G in counter current with a steam of CO2-free air and a cooling coil R into a collecting vessel V through which a steam of carbon dioxide free air is bubbled.  Air from a pipe line W flows through a valve X into a soda lime scrubber C in which it is freed from carbon dioxide and after passing through a filter Y reaches a valve system Z from which it is distributed to the collecting vessel V and to a pipe 1 from which it travels up the tube G, through the condenser A and through a pipe 2 into a scrubber F. According to a modification the central tube G constructed of block tin or copper lined with block tin is filled with tin rings to act as a filming surface.  According to another modification (Fig. 2) the steam coming from the boiler passes up a tube 2 into a condenser 4 the condensate passing over tin rings 5 in counter current to CO2-free air introduced through an opening 6.  An insulated wire 8 longitudinally disposed within the tube 2 and charged at a potential of 8000 to 25000 volts is provided whereby any spray in the stream is precipitated on to an inner sleeve 12 having triangular portions split out and bent outwards to form points 14 which catch the inner wall of the tube 2.  The precipitated spray passes through the openings and returns down the inside wall of the tube 2 into the boiler.  The Specification as open to inspection under Sect. 91 (3) (a) comprises also a reference to salts of organic poly-bases such as ethylene diamine hydrochloride and salts such as disodium monobrom succinate, sodium acid itaconate, disodium itaconate, sodium acid malonate and disodium malonate as buffer salts.  This subject-matter does not appear in the Specification as accepted.ALSO:Standard buffer solutions for measurements of hydrogen ion concentration covering a pH range of 7-10 comprise 1-phenol-2-chlor-4-sulphonic acid, 1-phenol-2, 6 dichlor-4-sulphonic acid, and 1-phenol-2, 4 dichlor-6 sulphonic acid and their salts.  The pH range covered by these acids may be modified by the inclusion of further halogen or other negative groups to lower the pH range or alkyl or amino groups to raise the pH range.  These halogenated phenol derivatives also serve for killing bacteria, lice, ticks, and the like.