A modified Grob closed‐loop‐stripping device is currently being used to concentrate organic contaminants from drinking water. The identification and quantification of organic contaminants at the nanogran per litre (part‐per‐trillion) level are accomplished by a computerized glass capillary gas chromatography–mass spectrometry system. Applications of closed‐loop‐stripping analysis (CLSA) for monitoring water by water utilities, for studying the use and effects of alternative disinfectants in drinking water, and for providing data on the removal of organic contaminants from water by granular activated carbon (GAC) treatment are discussed. An attempt to validate the method using statistical computations is also included.

The mechanism of flocculation by polymers has been examined by a study of fluorite suspensions. The "bridging" theory accounts qualitatively for the data-e.g., the influence of mol. wt., the much stronger mutual adhesion of particles (and hence the more open structure of flocs) than those resulting from electrolytic coagulation, etc. However, the quantitative theory of refiltration curves developed by Smellie and La Mer5 is shown to be invalid, because it is based on erroneous assumptions as to the origin of the permeability maximum. The mechanism of adsorption of polymers by ionic crystals such as calcium fluoride has been considered, and the possibility of dipole interaction of non-ionic groups with the electrostatic field of the crystal lattice is suggested.Water-soluble polymers are widely used for flocculating suspensions of finelydivided minerals, either for clarification of the water or for recovery of the solids.1 It is generally accepted that such flocculants act by adsorption and " bridging " and this theory is in accord with the following evidence. (i) Polymers produce larger, " tougher " flocs than do simple electrolyte coagulants. (Hydrolyzing coagulants, such as alum must, however, be classed as polymeric bridging agents?) (ii) Effectiveness of polymers of a given chemical type increases greatly with increase of molecular weight .3 (iii) Linear macromolecules are more effective flocculants than highly branched compounds of comparable molecular weight and chemical type.4 (iv) At high concentrations, flocculants become protective colloids. Smellie and La Mer 5 suggested that optimum flocculation is obtained when about half the available adsorption sites are occupied by polymer. (v) Highly charged particles are not flocculated by polymer until their zeta-potential has been reduced to a low value, either by use of a polyelectrolyte of opposite sign or by addition of suitable supplementary electrolyte.laThe selection of a flocculant for a particular mineral suspension is largely by trial and error, the main obstacle to a theoretical approach being inadequate knowledge of the surface chemistry of the minerals in water and the specific mechanisms of adsorption of the polymers.Kuzkin and Nebera 1 have concluded that the following adsorption mechanisms can be distinguished. (a) General electrostatic interaction; where a surface and a polyelectrolyte are of opposite sign, flocculation can always be obtained. (b) Local electrostatic adsorption-e.g., on to individual charged sites on a, more-or-less, iso-electric surface or by a more-or-less iso-electric protein.6 (c) Hydrogen-bonding adsorption (e.g., of uncharged polyacrylamide on to alumina or freshly prepared silica 7). ( d ) Chemisorption of more specific type, such as co-ordinate bonding. In addition, it should be possible to attach polymeric ions to surfaces of like sign of charge by use of di-or tri-valent ions of opposite sign-by analogy with the use of " activators " to promote the sorption of collector ions in flotation of minerals (e.g., Pbzf with c...

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