Method and apparatus for measure of sulfate

Abstract

A method and apparatus for sulfate analysis in a sample are provided. A portion of the sulfate contained in the sample is converted to sulfur dioxide, and at least a portion of the sulfur dioxide can be determined. The amount of sulfur dioxide determined can be used to quantify the amount of sulfate in the sample.

1 . A method comprising: 
 providing a sample comprising sulfate;    converting at least a portion of the sulfate to sulfur dioxide; and    continuously determining the sulfur dioxide.    
     
     
         2 . The method of  claim 1  wherein the sulfate is particulate sulfate.  
     
     
         3 . The method of  claim 1  wherein at least a portion of the sulfate is ammonium sulfate.  
     
     
         4 . The method of  claim 1  wherein the at least a portion of the sulfate is converted to sulfur dioxide by passing the sample over a surface.  
     
     
         5 . The method of  claim 4  wherein the surface is at an elevated temperature.  
     
     
         6 . The method of  claim 4  wherein the surface comprises a transition metal.  
     
     
         7 . The method of  claim 6  wherein the surface comprises stainless steel.  
     
     
         8 . The method of  claim 6  wherein the surface comprises chromium.  
     
     
         9 . The method of  claim 1  wherein the sulfur dioxide is determined by pulsed fluorescence detection.  
     
     
         10 . The method of  claim 1  further comprising quantifying the amount of sulfur dioxide determined.  
     
     
         11 . The method of  claim 10  further comprising determining the amount of sulfate converted to sulfur dioxide.  
     
     
         12 . The method of  claim 1  wherein at least 50% of the sulfate is converted to sulfur dioxide.  
     
     
         13 . The method of  claim 12  wherein at least 90% of the sulfate is converted to sulfur dioxide.  
     
     
         14 . The method of  claim 10  further comprising: 
 removing at least a portion of any particulate matter from at least a portion of the sample to produce a background sample essentially free of particulate sulfate; and    detecting a positive or negative sulfur dioxide response in the background sample.    
     
     
         15 . The method of  claim 14  further comprising subtracting the positive or negative response from the amount of sulfur dioxide determined.  
     
     
         16 . The method of  claim 1  wherein the at least a portion of the sulfate is continuously converted to sulfur dioxide.  
     
     
         17 . The method of  claim 1  wherein the sample is a fluid.  
     
     
         18 . The method of  claim 17  wherein the fluid is air.  
     
     
         19 . A method comprising: 
 passing a sample comprising sulfate over a surface, the surface comprising a transition metal and being at an elevated temperature;    reducing at least a portion of the sulfate to sulfur dioxide; and    continuously determining at least a portion of the sulfur dioxide.    
     
     
         20 . The method of  claim 19  wherein at least 50% of the sulfate is reduced to sulfur dioxide.  
     
     
         21 . The method of  claim 20  wherein at least 80% of the sulfate is reduced to sulfur dioxide.  
     
     
         22 . The method of  claim 21  wherein at least 90% of the sulfate is reduced to sulfur dioxide.  
     
     
         23 . The method of  claim 22  wherein at least 95% of the sulfate is reduced to sulfur dioxide.  
     
     
         24 . The method of  claim 19  wherein the temperature is greater than 500° C.  
     
     
         25 . The method of  claim 24  wherein the temperature is greater than 800° C.  
     
     
         26 . The method of  claim 25  wherein the temperature is greater than 1000° C.  
     
     
         27 . The method of  claim 26  wherein the temperature is about 1100° C.  
     
     
         28 . The method of  claim 19  wherein the sample is a fluid.  
     
     
         29 . The method of  claim 28  wherein the fluid is air.  
     
     
         30 . The method of  claim 19  wherein the sulfate comprises particulate matter.  
     
     
         31 . The method of  claim 19  further comprising removing at least a portion of any sulfur dioxide that may be in the sample prior to reducing the sulfate to sulfur dioxide.  
     
     
         32 . The method of  claim 19  comprising removing particles of a size greater than about 2.5 μm from the sample prior to passing the sample over the surface.  
     
     
         33 . The method of  claim 19  wherein the sulfur dioxide is determined quantitatively.  
     
     
         34 . The method of  claim 19  wherein the determining is performed with a pulsed fluorescence sulfur dioxide detector.  
     
     
         35 . The method of  claim 19  wherein the sulfur dioxide is determined at a rate of more than one reading per hour.  
     
     
         36 . The method of  claim 35  wherein the sulfur dioxide is determined at a rate of more than one reading per minute.  
     
     
         37 . The method of  claim 19  wherein the surface comprises stainless steel.  
     
     
         38 . The method of  claim 19  wherein the surface comprises a chromium alloy.  
     
     
         39 . The method of  claim 19  wherein the surface comprises a powder.  
     
     
         40 . The method of  claim 19  wherein the surface comprises tubing.  
     
     
         41 . A device comprising: 
 a surface comprising a transition metal; and    a sulfur dioxide detector in fluid communication with the surface.    
     
     
         42 . The device of  claim 41  wherein an air source is in fluid communication with the surface.  
     
     
         43 . The device of  claim 41  wherein the detector is a fluorescence detector.  
     
     
         44 . The device of  claim 41  wherein the surface comprises chromium.  
     
     
         45 . The device of  claim 41  wherein the surface comprises at least  10 %, by weight, of chromium.  
     
     
         46 . The device of  claim 44  wherein the surface comprises a chromium salt.  
     
     
         47 . The device of  claim 41  wherein the surface comprises chromium carbide.  
     
     
         48 . The device of  claim 41  wherein the surface comprises a stainless steel tube.  
     
     
         49 . The device of  claim 41  wherein the temperature of the surface is greater than about 500° C.  
     
     
         50 . The device of  claim 49  wherein the temperature is greater than about 800° C.  
     
     
         51 . The device of  claim 50  wherein the temperature is greater than about 900° C.  
     
     
         52 . The device of  claim 51  wherein the temperature is greater than about 1000° C.  
     
     
         53 . The device of  claim 52  wherein the temperature is about 1100° C.  
     
     
         54 . The device of  claim 41  wherein the surface is disposed in a quartz furnace.  
     
     
         55 . The device of  claim 50  further comprising air flowing across the surface.  
     
     
         56 . A method comprising: 
 passing air comprising particulate matter across a heated surface comprising chromium, the particulate matter comprising sulfate;    reducing at least a portion of the sulfate to sulfur dioxide; and    determining sulfur dioxide.    
     
     
         57 . The method of  claim 56  further comprising removing at least a portion of any sulfur dioxide from the air prior to passing the air across the surface.  
     
     
         58 . The method of  claim 56  further comprising excluding particles of a size greater than about  2 . 5  μm prior to passing the air across the surface.  
     
     
         59 . The method of  claim 56  further comprising pretreating the air with ammonia.  
     
     
         60 . The method of  claim 56  further comprising correlating a concentration of sulfur dioxide determined with an amount of sulfate in the air.  
     
     
         61 . The method of  claim 56  further comprising heating at least a portion of the surface to a temperature greater than about 500° C.  
     
     
         62 . The method of  claim 61  wherein the temperature is greater than about  800 ° C.  
     
     
         63 . The method of  claim 62  wherein the temperature is greater than about 900° C.  
     
     
         64 . The method of  claim 62  wherein the temperature is greater than about 1000° C.  
     
     
         65 . The method of  claim 64  wherein the temperature is about 1100° C.  
     
     
         66 . The method of  claim 56  wherein the surface comprises stainless steel.  
     
     
         67 . The method of  claim 56  wherein the particulate matter is classified as PM 10.  
     
     
         68 . The method of  claim 56  wherein the particulate matter is classified as PM 2.5.  
     
     
         69 . The method of  claim 56  wherein the air is passed continuously across the heated surface.  
     
     
         70 . The method of  claim 56  wherein the sulfur dioxide is continuously determined.  
     
     
         71 . The method of  claim 56  further comprising filtering at least a portion of the particulate matter from the air sample to produce a second air sample; 
 determining a positive or negative sulfur dioxide response in the second air sample; and    comparing the determined response in the second air sample with a response determined in the air sample.    
     
     
         72 . A method of measuring particulate sulfate content in a fluid sample comprising: 
 providing a sample comprising particulate matter;    continuously contacting the sample with means for reducing the sulfate to sulfur dioxide; and    analytically determining sulfur dioxide in the sample.    
     
     
         73 . The method of  claim 72  wherein the means comprises a surface having a temperature greater than about 500° C.  
     
     
         74 . The method of  claim 72  wherein the means comprises a surface comprising chromium, and the surface is at a temperature greater than about 800° C.  
     
     
         75 . An apparatus comprising: 
 means for continuously converting at least 50% of any aerosol sulfate in an air sample to sulfur dioxide; and    means for detecting sulfur dioxide in the air sample.    
     
     
         76 . The apparatus of  claim 75  wherein the means can convert at least 80% of any aerosol sulfate in the air sample.