Method for transforming phase spectra to absorption spectra

Abstract

A device and method for determining analyte concentrations within a material sample are provided. A modulating temperature gradient is induced in the sample and resultant, emitted infrared radiation is measured at selected analyte absorbance peaks and reference wavelengths. The modulating temperature gradient is controlled by a surface temperature modulation. One embodiment provides a transfer function relating the surface temperature modulation to a modulation of the measured infrared radiation. Phase and magnitude differences in the transfer function are detected in the presence of the sought-after analyte. These phase and magnitude differences, having a relationship to analyte concentration, are measured, correlated and processed to determine analyte concentration in the material sample. Another embodiment provides a method for transforming thermal phase spectra to absorption spectra for consistent determination of analyte concentration within the sample.

What is claimed is:  
     
         1 . A method for determining a concentration of an analyte within a material sample, said method comprising: 
 inducing said material sample to emit electromagnetic energy in a time-varying manner;    measuring, at at least one wavelength, said induced electromagnetic energy emitted by said material sample;    determining a phase of said electromagnetic energy;    converting said phase into an absorption value; and    determining said concentration of said analyte based at least in part on said absorption.    
     
     
         2 . The method of  claim 1 , wherein converting said phase into an absorption value comprises converting said phase into a normalized absorption.  
     
     
         3 . The method of  claim 2 , wherein determining said concentration of said analyte based on said absorption comprises determining said concentration of said analyte based on said normalized absorption.  
     
     
         4 . The method of  claim 1 , wherein measuring comprises analyzing said material sample with an optical measurement system.  
     
     
         5 . The method of  claim 4 , wherein said optical measurement system comprises an array of wavelength-specific detectors.  
     
     
         6 . The method of  claim 4 , further comprising correcting said optical measurement system for temporal variations in performance.  
     
     
         7 . The method of  claim 1 , wherein inducing said material sample to emit electromagnetic energy in a time-varying manner comprises inducing a periodically modulated thermal gradient in said material sample.  
     
     
         8 . The method of  claim 1 , wherein said electromagnetic energy comprises infrared radiation.  
     
     
         9 . A method for determining a concentration of an analyte within a material sample, said method comprising: 
 determining at least a portion of a phase spectrum based on electromagnetic energy emitted by said material sample;    converting said at least a portion of said phase spectrum into at least a portion of an absorption spectrum; and    determining said concentration based on said at least a portion of said absorption spectrum.    
     
     
         10 . The method of  claim 9 , wherein converting said phase spectrum into an absorption spectrum comprises converting said phase spectrum into a normalized absorption spectrum.  
     
     
         11 . The method of  claim 10 , wherein determining said concentration of said analyte based on said absorption spectrum comprises determining said concentration of said analyte based on said normalized absorption spectrum.  
     
     
         12 . The method of  claim 9 , wherein said phase spectrum comprises an ideal phase spectrum.  
     
     
         13 . The method of  claim 9 , wherein determining a phase spectrum comprises analyzing said material sample with an optical measurement system.  
     
     
         14 . The method of  claim 13 , wherein said optical measurement system comprises an array of wavelength-specific detectors.  
     
     
         15 . The method of  claim 13 , further comprising correcting said optical measurement system for temporal variations in performance.  
     
     
         16 . The method of  claim 9 , further comprising inducing a periodically modulated thermal gradient in said material sample.  
     
     
         17 . The method of  claim 9 , wherein said electromagnetic energy comprises infrared radiation.  
     
     
         18 . An analyte detection system comprising: 
 a detector array;    a processing circuit in communication with said detector array; and    a module executable by said processing circuit whereby said processing circuit converts a phase spectrum, said phase spectrum based on electromagnetic energy emitted by a material sample and measured by said detector array, into an absorption spectrum and determines a concentration of an analyte within said material sample based on said absorption spectrum.    
     
     
         19 . The analyte detection system of  claim 18 , further comprising means for inducing said material sample to emit electromagnetic energy in a time-varying manner, said means for inducing being in communication with said processing circuit.  
     
     
         20 . The analyte detection system of  claim 18 , further comprising means for inducing a periodically modulated thermal gradient in said material sample, said means for inducing being in communication with said processing circuit.  
     
     
         21 . The analyte detection system of  claim 18 , wherein said electromagnetic energy comprises infrared radiation.  
     
     
         22 . A method of estimating analyte concentration in a sample comprising: 
 applying a time varying temperature to a portion of a sample;    measuring time varying infrared radiation intensity received from said sample in at least one wavelength band;    calculating an absorption coefficient α in said wavelength band based at least in part on said time varying infrared radiation intensity received from said sample.    
     
     
         23 . The method of  claim 23 , additionally comprising calculating a phase difference θ between said time varying temperature and said time varying infrared radiation intensity and calculating said absorption coefficient α based at least in part on said phase difference θ.  
     
     
         24 . The method of  claim 24 , wherein said absorption coefficient is calculated from said phase difference according to the formula  
       
         
           
             
               
                 
                   tan 
                    
                   
                     [ 
                     
                       θ 
                        
                       
                         ( 
                         λ 
                         ) 
                       
                     
                     ] 
                   
                 
                 = 
                 
                   
                     - 
                     γ 
                   
                   
                     [ 
                     
                       
                         α 
                          
                         
                           ( 
                           λ 
                           ) 
                         
                       
                       + 
                       γ 
                     
                     ] 
                   
                 
               
               , 
               
                 
                   wherein 
                    
                   
                       
                   
                    
                   γ 
                 
                 = 
                 
                   
                     
                       ω 
                       / 
                       2 
                     
                      
                     
                         
                     
                      
                     β 
                   
                 
               
               , 
             
           
           
           
               
           
         
       
       wherein ω is the angular modulation frequency in radians/sec, and β is the coefficient of thermal diffusivity of the sample.