Methods for elemental analysis by combusting a sample in a combustion tube

Abstract

Methods are provided for conducting chemical analyses by combusting a sample in a combustion tube. A primary combustion chamber receives and combusts a sample to form first combustion products. A secondary combustion chamber receives and combusts the first combustion products to form second combustion products. The secondary chamber is disposed around the primary chamber and comprises a plurality of—preferably, three—combustion compartments. Each successive compartment is disposed around the preceding compartment and defines a respective gas flow channel having an inlet opening and an outlet opening at opposite ends. Each successive gas flow channel shares its inlet opening with the outlet opening of the preceding channel. The plurality of combustion compartments define a substantially continuous gas flow conduit from the inlet opening of the innermost compartment to the outlet opening of the outermost compartment. Static gas mixers may be employed to enhance mixing of the combustion products.

What is claimed is: 
     
         1 . A method of combusting a sample in a combustion tube for combustion analysis of the sample, the combustion tube comprising: a primary combustion chamber; and a secondary combustion chamber disposed around the primary chamber and comprising a plurality of combustion compartments, each successive compartment being disposed around the preceding compartment and each compartment defining a respective gas flow channel having an inlet opening at one end and an outlet opening at the opposite end, each successive gas flow channel sharing its inlet opening with the outlet opening of the preceding channel, the method comprising the steps of:
 supplying to the primary chamber a sample and combusting the sample therein to form first combustion products; and   passing the first combustion products into the secondary chamber and further combusting the first combustion products to form second combustion products,   wherein a positive flow direction in each respective gas flow channel is defined as a direction running from its inlet opening substantially directly to its outlet opening and substantially all of the combustion products flow through each successive channel with at least a component of flow direction substantially continuously in the positive flow direction.   
     
     
         2 . The method of  claim 1 , wherein the first and/or second combustion products enter each combustion compartment through its inlet opening and exit the compartment through its outlet opening, wherein the inlet opening and the outlet opening of each compartment are substantially at opposite extremities of the respective compartment. 
     
     
         3 . The method of  claim 1 , wherein the plurality of combustion compartments define a substantially continuous gas flow conduit from the inlet opening of the innermost compartment to the outlet opening of the outermost compartment and the first and/or second combustion products follow a path through the secondary combustion chamber substantially defined by the gas flow conduit. 
     
     
         4 . The method of  claim 1 , further comprising the steps of:
 providing a background gas flow through the combustion tube; and   discharging at least the background gas as a discharge gas from the outlet opening of the outermost channel of the combustion tube,   wherein, when the sample is combusted, a concentration in the discharge gas of the second combustion products formed from that sample varies substantially as a top-hat function.   
     
     
         5 . The method of  claim 1 , wherein there are three combustion compartments, the method further comprising the step of passing the first and/or second combustion products along the outside of the primary combustion chamber three times. 
     
     
         6 . The method of  claim 1 , wherein each respective combustion compartment comprises a longitudinal sidewall and one or more of the compartments comprises a respective static gas mixer fixed to the respective sidewall, the method further comprising the steps of:
 providing a flow of the first and/or second combustion products through the compartment; and   disturbing the flow by interaction thereof with the static gas mixer to effect flow mixing in the compartment.   
     
     
         7 . The method of  claim 6 , wherein the static gas mixer comprises a plurality of longitudinally slanting first ribs which redirect at least a portion of the flow in a first direction and/or a plurality of longitudinally slanting second ribs which redirect at least a portion of the flow in a second, opposing direction. 
     
     
         8 . The method of  claim 1 , wherein the second combustion compartment has an inlet end for receiving first combustion products from the innermost compartment, the method further comprising the step of supplying oxygen into the second innermost compartment at the inlet end. 
     
     
         9 . The method of  claim 1 , wherein all substances supplied to the combustion tube and all substances discharged from the combustion tube are supplied and discharged, respectively, from the same end of the combustion tube.