Method for automatic analysis

Abstract

This invention relates to a method for analyzing the concentration of an analyte in a sample and to automatic analyzing apparatus. The invention will be described herein with particular reference to a method and apparatus for measuring the concentration of glucose or other analytes in blood but is not limited to that use.

1 . A method for estimating the concentration of a reduced or oxidized form of a redox species in a liquid comprising the steps of: 
 (1) contacting an area of a first electrode with a sample of predetermined volume of the liquid,    (2) bringing a second electrode into a closely spaced relationship with the first electrode, thereby contacting the sample with an area of the second electrode spaced apart from the first electrode, wherein step (2) is conducted after step (1),    (3) applying a potential between the electrodes while the electrodes are sufficiently closely spaced such that reaction products formed at each electrode diffuse to the other electrode while the potential is applied,    (4) reversing the potential between the electrodes,    (5) measuring or estimating a value indicative of the change in current as a function of time and a value indicative of the steady state current, and    (6) determining from said value, said current as a function of time, and said steady state current the concentration of reduced or oxidized form of the species in the liquid sample.    
     
     
         2 . The method according to  claim 1 , wherein the step of reversing the potential occurs after waiting for the current to change by less than a predetermined amount per time.  
     
     
         3 . The method according to  claim 1 , further comprising the step of the change in current as a function of time before the potential is reversed to compensate for a slow chemical reaction step.  
     
     
         4 . The method according to  claim 1 , wherein at least one of the electrodes includes a reagent positioned thereon.  
     
     
         5 . The method according to  claim 4 , wherein the sample contacts the reagent during step (1).  
     
     
         6 . The method according to  claim 4 , wherein the sample contacts the reagent during step (2).  
     
     
         7 . The method according to  claim 4 , wherein the sample is deposited on the reagent.  
     
     
         8 . The method according to  claim 1 , wherein at least one electrode is covered with a layer which serves to define wells on the electrode surface.  
     
     
         9 . The method according to  claim 1 , wherein at least one of the electrodes is in the form of a continuous strip.  
     
     
         10 . The method according to  claim 1 , wherein a pipette deposits the sample on the first electrode.  
     
     
         11 . The method according to  claim 1 , wherein the first electrode further comprises a porous medium wherein the predetermined volume is immobilized.  
     
     
         12 . The method according to  claim 1 , further comprising the step of depositing one or more reagents on one of the electrodes prior to placing the sample on the electrode.  
     
     
         13 . The method according to  claim 1 , wherein at least one of the first and second electrodes includes at least one well.  
     
     
         14 . The method according to  claim 1 , wherein at least one of the first electrode and the second electrode is in the form of a disposable probe.  
     
     
         15 . The method according to  claim 1 , wherein at least one of the first electrode and the second electrode is in the form of a retractable probe.  
     
     
         16 . The method according to  claim 1 , wherein the first electrode comprises a first metallized electrode layer, wherein the second electrode comprises a second metallized electrode layer, and wherein the first metallized electrode layer travels transversely of the second electrode layer.  
     
     
         17 . The method according to  claim 1 , wherein the first electrode comprises a first metallized electrode layer, wherein the second electrode comprises a second metallized electrode layer, and wherein the first metallized electrode layer travels in a same direction as the second electrode layer.  
     
     
         18 . The method according to  claim 1 , wherein the sample of predetermined volume is a droplet deposited on one of said electrodes.  
     
     
         19 . The method according to  claim 18 , wherein the droplet is held between the two electrodes by surface tension.