Chemical analyser

Abstract

A liquid sample is analysed for a target chemical. A sample solution is added to a measurement cell of known volume and a reagent is incrementally added to the cell until a detectable change is observed. A reference compound, of a known concentration, that does not take part in the reaction between the target chemical and reagent, is added to the reagent and by measuring the concentration of the reference compound the amount of reagent used may be determined. A single mechanism introduces a sample, adds reagent mixes cleans and flushes the measurement cell which incorporates a longitudinal chamber having a number of fluid inlets for sample and reagent and an outlet for measured sample/reagent mixtures, a detector being located in or adjacent to said chamber between the inlets and said outlet and a piston movable in said chamber carrying a series of seals such that movement of the piston sequentially opens the inlets and expels the fluid. The analyzer also includes a device for delivering a volume of reagent into a measurement cell incorporating a first port to introduce sample fluid; a second port to allow injection of fluid reagent; and a third port to allow expulsion of sample and sample/reagent mixtures to waste which includes a compressible reservoir of reagent which is positioned within a rigid container, and is surrounded by a fluid which substantially fills the space between said reservoir and the inside wall of said container and means for pressurising said fluid surrounding said reservoir to effect partial collapse of said reservoir in order to inject reagent into said measurement cell.

1 . A method of analyzing for a target chemical in a liquid sample in which a sample is added to a measurement cell of known volume and a reagent is added to the cell until a detectable change is observed, the improvement comprising the incorporation of a known concentration of a reference compound that does not take part in the reaction to the reagent and measuring the concentration of the reference compound to determine the amount of reagent added. 
     
     
         2 . A method as claimed in  claim 1  in which the detectable change is a colour change caused by the formation of a reaction product of a target chemical with the reagent and the concentration of the reference compound is calculated from the absorption at a particular wavelength characteristic of the reference compound. 
     
     
         3 . A method as claimed in  claim 1  in which free chlorine is the target chemical and the sample is water taken from a swimming pool, spa or air conditioning cooling tower. 
     
     
         4 . A device for delivering a volume of reagent into a measurement cell incorporating one or more ports to introduce sample fluid, injection of fluid reagent; and allow expulsion of sample and sample/reagent mixtures, which includes a compressible reservoir of reagent which is positioned within a substantially rigid container, and is surrounded by a fluid which substantially fills the space between said reservoir and the inside wall of said container and means for pressurising said fluid surrounding said reservoir to effect partial collapse of said reservoir in order to inject reagent fluid into said measurement cell. 
     
     
         5 . A device as claimed in  claim 4  in which the wall material of the compressible reservoir is impermeable to oxygen to preserve oxygen sensitive reagents. 
     
     
         6 . A device as claimed in  claim 4  in which the wall material of the compressible reservoir is impermeable to light to preserve light sensitive reagents. 
     
     
         7 . An analyser in which a single mechanism introduces a sample, adds reagent and cleans and flushes the measurement cell said mechanism incorporating a longitudinal chamber having a number of fluid inlets for sample and reagent and an outlet for measured sample/reagent mixtures, a detector being located in or adjacent to said chamber between the inlets and said outlet and a piston movable in said chamber carrying a series of seals such that movement of the piston sequentially opens the inlets and expels the sample/reagent mixtures. 
     
     
         8 . A control system for a re-circulating pump and chlorinator system for a swimming pool or air conditioning cooling tower which utilizes the output of an analyzer as claimed in  claim 4 .