anion Electr.
(ˈænaɪən)
[a. Gr. ἀνιόν (a thing) going up, neut. of pr. pple of ἀνι-έναι to go up, f. ἀνά up + ἰ- go.]
An ion carrying a negative charge which moves towards the anode (positive electrode) during electrolysis. Opposed to cation. Hence anion exchange, ion exchange involving anions; also attrib.; so anion exchanger, a substance capable of anion exchange. Also anion-active a., having an active anion.
| 1834 W. Whewell Let. 5 May in I. Todhunter W. Whewell (1876) II. 182 If you take anode and cathode, I would propose for the two elements resulting from electrolysis the terms anion and cation,..and for the two together you might use the term ions. 1834 Faraday Res. Electr. (1849) I. 198, I propose to distinguish such bodies by calling those anions which go to the anode of the decomposing body. 1870 Ferguson Electr. 162 In acids, hydrogen forms the cation, and the acid radical the other constituent, the anion. 1931 S. Mattson in Soil Science XXXI. 325 Cation exchange predominates at high pH values whereas anion exchange predominates at low pH values. 1941 Industr. & Engin. Chem. XXXIII. 1271/2 The high-capacity anion-exchange resin was Amberlite IR-4. Ibid., Table I indicates that a practical equilibrium adsorption value is attained with both anion-exchangers after 6-hour contact with either hydrochloric or sulfuric acid. 1946 Nature 26 Oct. 585/2 It is well known that the addition of divalent metallic ions greatly enhances the surface-active properties of anion-active detergents. 1963 A. J. Hall Textile Sci. vi. 296 Surface active agents or surfactants can be usefully classified into three main groups—anion-active, non-ionic, and cation-active. Ibid. 297 All the above surface active types are anion-active, that is, the effective hydrophobic component is present in the anion when the substance is dissolved in water and ionises into anions and cations. |
Hence aniˈonic adj., (a) of or pertaining to anions; (b) = anion-active.
| 1922 Chem. Abstr. 3417 Evidence of salt properties is further verified by identity of negative charges with the no. predicted for the periodic group in which the anionic metal is found. 1928 Jrnl. Chem. Soc. ii. 906 It would..be expected that the tendency to migration of different potentially mobile anions (X) contained in systems otherwise identical would follow the order of anionic stability. 1948 Q. Rev. (Chem. Soc.) II. 312 Although there are many examples of systems in which cationic exchange is known to take place, there are relatively few reports of the anionic exchange. These are almost all in the field of inorganic chemistry. The term ‘anionic exchanger’ is often applied, however, to materials which absorb acid molecules from aqueous solution. 1950 Thorpe's Dict. Appl. Chem. X. 800/1 The anion is the active part of the molecule, hence the term anionic agents. The best detergents are in this class. 1962 Lancet 26 May 1109/2 The drug slowly exchanges with cations (or anions in the case of anionic drugs) in the lumen of the alimentary tract and is then free to be absorbed. |
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Add: 2. Special Comb. anion gap Physiol., the difference between the total concentration of (positive) sodium and potassium ions and the total concentration of (negative) chloride and bicarbonate ions in blood plasma.
| 1969 Minnesota Med. LII. 659 A large increase in the concentration of unmeasured anions, i.e., the ‘*anion gap’. 1973 Lancet 13 Oct. 848/2 It is not necessary to use the anion gap as a routine quality-control device. 1982 T. M. Devlin Textbk. Biochem. xxiii. 1126 In the plasma of a normal individual the sum of Na+ and K+ is greater than the sum of Cl- and HCO3- . This difference is called..the anion gap. |
anionic a.(c) (as n.), an anionic surfactant.
| 1952 McCutcheon & Speel in H. C. Speel Textile Chem. & Auxiliaries xv. 299 Certain non-ionics can be sulfonated to anionics. 1970 New Scientist 15 Oct. 132/2 Difficulty with perborate and anionics could be foreseen, but the effect of phosphate was unexpected. 1989 Pharmaceutical Jrnl. 16 Sept. 341/2 Transitions due to lipid melting that were removed by the anionics alone were protected by the added non-ionics. |