EP0963551A1

EP0963551A1 - Methods and apparatus for efficient combustion of samples

Info

Publication number: EP0963551A1
Application number: EP98907482A
Authority: EP
Inventors: Randy L. Wreyford; Jean-François BORNY
Original assignee: Antek Instruments GmbH; Antek Instruments Inc
Current assignee: Antek Instruments GmbH; Antek Instruments Inc
Priority date: 1997-02-28
Filing date: 1998-02-17
Publication date: 1999-12-15
Also published as: WO1998038507A1; AU6327998A

Abstract

The present invention involves the formation of oxygen-rich aerosols for subsequent combustion in an oxidation zone so that aerosol combustion does not occur near or at the nebulizer, but occurs substantially and to near completion in the oxidation zone. The use of oxygen-rich aerosols is particularly useful when near complete combustion of samples contained in large volumes of carrier solvent such as effluents for LC, MPLC or HPLC devices.

Description

TITLE: METHODS AND APPARATUS FOR EFFICIENT

COMBUSTION OF SAMPLES

BACKGROUND OF THE INVENTION

1. Field of the Invention This invention relates to a method and apparatus for efficient oxidative decomposition of a sample subsequently analyzed to determine constituents concentrations.

More particularly, the present invention relates to a method and apparatus for forming an oxygen-rich aerosol including a sample material and an oxidizing agent, directing the aerosol into a heated zone, optionally diluting the aerosol with an inert gas, oxidizing the oxidizable components of the sample material in an oxidation zone and forwarding the oxidized sample material to a detection system

2. Description of the Related Art

U.S. Patent Nos. 4,914,037 and 4,950,456 discloses a method and apparatus for analyzing a sample for nitrogen and sulfur by forming an aerosol containing the sample material and an inert gas. The aerosol is formed in the cool region of a furnace and enters an oxygen-rich atmosphere where the sample material is combusted and then the combustion gases are analyzed for nitrogen and sulfur

The current nebulizer systems suffer from certain disadvantages when operated in association with instruments running high volumes of samples contained in high purity carrier solvents such as water, methanol, THF, hexane, isooctane, or the like or combinations thereof. In such applications, efficient combustion (near complete combustion) is difficult because of the type and amount of carrier solvents in the sample stream. Thus, it would represent an advancement in the art to provide a nebulizing interface between such an instrument and a combustion zone to achieve near complete combustion of the sample material in the effluent producing combustion gases containing detectable concentrations of at least one oxide or class of oxides.

SUMMARY OF THE INVENTION

This invention provides a method for efficient oxidation of a sample contained in a large volume of at least one carrier solvent by contacting the sample, including at least one sample component, with a gas containing an oxidizing agent in a nebulizing zone to form an oxygen-rich aerosol, i. e. , the sample and solvent are dispersed in the gas in the form of small droplets. The oxidizing agent is present in an amount sufficient to convert a portion of the oxidizable components of the sample into an effective concentration of its corresponding oxides, where the concentration of oxides is sufficient to allow for post-oxidation detection and analysis.

The oxygen-rich aerosol is then forwarded to a combustion zone, maintained at an elevated temperature, where portions of oxidizable components in the sample and carrier solvents are converted to their corresponding oxides in effective concentrations for post-combustion analysis. The oxides are then forwarded to a detection system for determining the concentrations of oxides or to other units that chemically transform the oxides and detect the transformed oxides.

The present invention also provides a method for forming an oxygen-rich aerosol including contacting a sample material contained in a large volume of at least one solvent with a gas containing an oxidizing agent. The resulting mixture is then passed into and through a nebulizing zone to form an oxygen-rich aerosol. The aerosol generally contains sufficient oxidizing agent to oxidize a portion of the sample components into corresponding oxides, at least one of which is detectable. Preferably, the oxidizing agent is present in an amount in excess of the amount of oxygen equivalents needed to substantially quantitatively convert the sample components and any oxidizable solvent into corresponding oxides, where at least one of the oxides produced by oxidation of the sample components is capable of being subsequently analyzed. The oxygen-rich aerosol generally has a flow rate of at least 200 mL/min so that upon introducing the aerosol into an heated oxidation zone, the resulting combustion does not result in combustion at or near the nebulizing zone.

The present invention also provides an apparatus for forming an oxygen- rich aerosol including a material-to-be-oxidized supply line, an oxidizing gas supply line and a nebulizing zone where the material and the gas are converted into the oxygen-rich aerosol. The material is a sample containing at least one sample component in a solvent carrier, where the solvent comprises at least 50% of the volume of the material-to-be-oxidized..

The present invention also provides an apparatus for efficient oxidation or combustion of a sample including the apparatus for forming an oxygen-rich aerosol, a combustion zone maintained at an elevated temperature where the combustion zone is connected to the aerosol forming apparatus so that the aerosol is directed into the combustion zone, an optional supply of an inert gas to maintain a given residence time in the combustion zone, and an outlet for directing the resulting combustion gases either to a system for further chemical transformation or to a detection system. The present invention also provides an apparatus for efficient oxidation or combustion of a sample including the apparatus for efficient oxidation or combustion a sample and a detection system capable of determining the concentration of at least one oxide or class of oxides contained in the combustion gases being discharged from the combustion zone.

The present invention also includes an oxygen-rich aerosol including a material having a sample entrained in a large volume of at least one ultra-high purity solvent and an amount of an oxidizing gas where the amount of oxidizing gas is in an amount sufficient to substantially completely oxidize the oxidizable components of the sample and the solvent. Preferably, the aerosol has a ratio of material to oxidizing gas between about 1 : 1 and about 1 :500, with ratios of greater than 1 : 1 being preferred, and the aerosol has a flow rate of between about 1 and about 10,000 mL/min so that when the aerosol is directed into a combustion zone, the combustion reactions does not occur at or near a nebulizing zone or nozzle where the aerosol is formed.

DESCRIPTION OF THE DRAWINGS

The invention can be better understood with reference to the following detailed description together with the appended drawings in which like elements are numbered the same:

Figure 1 is a schematic of the nebulized combustion unit of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The inventors have found that an apparatus can be designed that is capable of high efficiency combustion of a sample stream including at least one sample component in a large volume of at least one solvent such as an effluent stream for an LC, an MPLC, or an HPLC.

Three apparatus are broadly envisioned in this invention: (1) a nebulizer assembly for producing oxygen-rich aerosols; (2) the nebulizer assembly operatively connected to a oxidation furnace assembly for converting a portion of the oxygen-rich aerosol into sufficient concentrations of at least one oxide or class of oxides capable of post oxidation detection and analysis; and (3) the nebulizer operatively connected to the furnace assembly which is in turn operatively connected to a post-furnace assembly and detection device for detecting either the oxides or class of oxides or chemical transformants derived therefrom.

Generally, the nebulizer assembly includes a sample material supply, an oxidizing gas supply and a nebulizing zone, typically, a nebulizing nozzle, which disperses the liquid sample material in the oxidizing gas to form an oxygen-rich aerosol. The term oxygen-rich means that the oxygen equivalents in the resulting aerosol are sufficient to convert a portion of the oxidizable components in the aerosol into their corresponding oxides at least one oxide or class of oxides being capable of post-oxidation detection. Thus, for example, an oxygen-rich aerosol containing sample components containing carbon and nitrogen and a non- oxidizable solvent, such as water, would be converted to oxides of carbon and oxides of nitrogen in the oxidizing zone so that sufficient concentrations of the carbon oxides and/or nitrogen oxides are present for post-combustion detection and analysis.

Of course, if the carrier solvent is combustible such as methanol, then the oxygen-equivalents in the oxidizing gas will convert portions of the sample and the carrier solvent into their corresponding oxides and the oxygen-equivalents must be sufficient to produce detectable concentration of at least one oxide or class of oxides, such as nitrogen or sulfur oxides, capable of post-combustion detection and analysis.

The combustion zone is typically contained within a furnace assembly. The furnace assembly includes an oxidation zone which generally comprises the interior volume of an oxidation or combustion tube. The tube is generally housed in a housing designed to maintain the tube at an elevated temperature. Typically, the temperature is maintained so that at a given residence time of the aerosol in the oxidization zone, a sufficient amount of the oxygen-rich aerosol can be converted into its corresponding oxides. The temperature of the furnace assembly is generally maintained between about 300°C and about 2200 °C and the residence time is generally between about 0.1 seconds and about 100 seconds. Although higher and lower temperatures can be used as well as shorter or longer residence times, the temperature and residence time must be so that the two cooperate to promote sufficient oxidation of the sample contained in the oxygen-rich aerosol.

The furnace assembly converts the oxygen-rich aerosol into combustion gases including at least one oxide or class of oxides capable of being either directly detected in a downstream detection device or of being transformed chemically or physically into transformants that are capable of being detected by a downstream detection system.

Optionally, the aerosol can also be mixed with an inert gas just prior to entering or as it is entering the oxidation zone where the inert gas is designed to prevent the aerosol from coming into contact with surfaces of either the nebulizer or the furnace prior to combustion, to control the residence time of the sample in the oxidation zone and to improve oxidation efficiency by reducing contact of the aerosol with the tube. The downstream detecting device can include any device capable of detecting at least one oxide or class of oxides in the combustion gases. The detection device can be a chemiluminescence detection device, a UV fluorescence detection device, or any other detection device used to quantify the amount of an given oxide in an oxidized sample.

Additionally, the entire device can include additional steps and/or apparatus to convert the at least one oxide or class of oxides into species capable of being detected in the detection devices such as placing a reduction zone between the oxidation zone and the detection device where the reduction zone converts a portion of at least one oxide or class of oxides into species capable of detection in the detection device. This latter configuration is ideally suited for using ozone induced chemiluminescence to analyze a sample for nitrogen and/or sulfur content or to perform a near simultaneous detection of both the nitrogen and sulfur content of a sample as disclosed in co-pending application Ser. No. 08/760,247, incorporated therein by reference.

The methods of the present invention broadly involve: (1) forming an oxygen-rich aerosol; (2) burning the oxygen-rich aerosol in a combustion zone maintained at an elevated temperature to form combustion gases containing at least one detectable oxide or class of oxides; and (3) detecting at least one oxide or class of oxides in the combustion gases in a detection system. The method can also include one or more additional step subsequent to the burning and prior to the detecting, where the additional step or steps are designed to convert the at least one oxide or class of oxides into species capable of being detected in a given detection system.

The present invention is also related to oxygen-rich aerosols including a sample material having at least one sample component entrained in a large volume of a carrier solvent and an oxidizing gas, where an oxygen-equivalent of the oxidizing gas is greater than the number of oxygen equivalents needed to completely oxidize the sample components and/or the carrier solvent to corresponding oxides.

General Details of the Apparatus

Referring now to Figure 1, a preferred embodiment of a nebulized combustion apparatus generally 10 for forming and burning an oxygen-rich aerosol according to this invention for use with an HPLC instrument using a sample line having a diameter between about 0.2 mm and about 0.6 mm. The unit 10, in its most general form, includes a nebulizer 20 and a combustion chamber 100. The nebulizer 20 includes an outer housing 22 having associated with its first end 24 a sample receiving tube 26 designed for receiving and having a sample line 30 inserted therein. The receiving tube 26 connects to the sample line 30 at its first end 32. The tube 26 connects to the sample line 30 by a set of fittings 34, 36, and

38. The fittings 34-38 hold the sample line 30 in place after it has been inserted into the tube 26.

The nebulizer 20 also includes an oxidizing gas supply line 40, an oxidizing gas flow controller 42, an oxidizing gas source 44 and an oxidizing gas inlet 46 associated with the housing 22. The oxidizing gas supply line 40 is operatively connected to the inlet 46 by fittings 48 which allows the oxidizing gas to flow into the nebulizer 20 in a gas tight fashion. The oxidizing gas supply line 40 operatively connects and brings the source 44, the flow controller 42 and the gas inlet 46 into fluid communication with the nebulizer 20.

The nebulizer 20 also includes a diameter reduction section 50 that reduces an internal diameter of the receiving tube 26 to form an internal sample capillary line 52. The sample line 30 butts up to the reduction section 50 so that the sample flows out of the sample line 30 and into the internal line 52. The reducing section 50 reduces the diameter of the receiving tube 26 from a diameter sufficient to accommodate the sample line 30 to a diameter of about 0.1 mm or less. The reduction section 50 acts to increase the flow rate of a sample through the internal sample line 52 by reducing the diameter of the sample line prior to the sample being nebulized by the oxidizing gas. The housing 22 of the nebulizer 20 tapers to a nozzle 54 at its second end 56. The capillary line 52 at its terminus 58 terminates in a central region 60 of the nozzle 54 just prior to the nebulizer tapered second end 56. As the sample (which is a liquid, solution, emulsion, dispersion, or the like) exits the terminus 58 of the capillary line 52, the sample is nebulized by the oxidizing gas to produce an oxygen-rich aerosol. Preferably, the housing 22, the tube 26, the reduction section 50, the capillary line 52, the tapered end 56 and the nozzle 54 can be constructed of a single material such as metal, glass, quartz, plastic, Teflon, or the like and preferably comprise a unitary construction.

The nozzle end 54 and a region 62 of the nebulizer 20 are inserted into a tube 64 at its first end 66 and held in place and connect to the tube 64 by fittings 68 which holds the nebulizer 20 properly in the tube 64 in a gas tight fashion. The tube 64 is operatively connected to or is integral with a combustion tube 102 of the combustion chamber 100. The fittings 68 are equipped with an inert gas inlet 70 connected in a gas tight fashion to an inert gas source 72 by an inert gas supply line 74 having a flow controller 76 associated therewith. The inert gas may optionally be supplied to the tube 64 to prevent the oxygen-rich aerosol exiting the nebulizer 20 through the nozzle 54 from contacting inner walls 78 of the tube 64 and to help forward the oxygen-rich aerosol to the combustion chamber 100. If the oxygen-rich aerosol contacts the walls 78 of the tube 64, sample can stick to the walls 78 which can result in lower oxidation efficiencies and downstream detector sensitivity, and increased corrosion and deposit problems, etc. The sample flow rate (flow rate of the sample material) is generally controlled by the analytical device supplying the sample, but can be separately controlled by any control device known in the art such as a pump. Typical analytical devices used to supply the sample are devices such as an LC (liquid chromatography device), MPLC (medium performance or pre-LC), HPLC (high performance LC), or similar devices.

Generally, the sample material enters the nebulizer 20 through the sample line 30 at a flow rate between about 1 μL/min and about 10 mL/min, with flow rates between about 20 μL/min and about 1 mL/min being preferred, and flow rates between about 40 μL/min and about 200 μL/min being particularly preferred. Generally, an oxidizing gas flow rate is maintained at between about 50 inL/min and about 1500 mL/min, with flow rates between about 100 mL/min and about 1200 mL/min being preferred, and flow rates between 350 mL/min and about 900 mL/min being particularly preferred. Thus, the oxygen-rich aerosol exiting the nebulizer 20 through nozzle 54 will generally have a flow rate which is roughly the sum of the flow rates for the sample material and the oxidizing gas.

The combustion chamber 100 includes the combustion tube 102 which is integral with the tube 64 as shown or can be connected to the combustion tube 102 in a gas tight fashion. The chamber 100 also includes an outer housing 104 containing a temperature controllable heater 106 which surrounds the combustion tube 102. The tube 64 and the combustion tube 102 are preferably formed from metal, quartz, ceramic or the like. Preferably, the chamber 100 also includes a first ceramic tube 110 which is inserted into the combustion tube 102 in a central region 112 thereof. The combustion tube 102 preferably expands at two expansion sections 114. A first end 116 of the first ceramic tube 110 is associated with one expansion section 114. At the other expansion (reduction) section 114, a second end 118 of the first ceramic tube 110 is surrounded by a high temperature material 120 such as a high temperature fiber including glass wool in a high temperature matrix, a ceramic compound or any similar high temperature material which brings the tube 110 into fluid communication with a second, smaller ceramic tube 122 and directs the flow from the tube 110 into the tube 122. An interior 124 of the tube 110 comprises an oxidation zone for partial, near complete or complete oxidization of any sample and/or oxidizable solvents contained in the aerosol can occur.

The nozzle 54 of the nebulizer 20 should be a sufficient distance from the chamber 100 so that under standard operating conditions and aerosol flow rates, the aerosol does not start burning until the aerosol enters the chamber 100 where the aerosol is oxidized. To ensure that the nozzle 54 of the nebulizer 20 is a sufficient distance from the chamber 100, the tube 64 is preferably equipped with a stop 126 which prevents the chamber 100 from getting too close to the nozzle

54 of the nebulizer 20. Generally, the nozzle 54 should be no closer than about 2 cm from the chamber 100 and no further than about 5 cm, with a distance of about 2.5 cm being preferred.

The heater 106 maintains the oxidization zone 124 at an elevated temperature sufficient to promote partial, near complete, or complete oxidation of any sample and/or combustible solvent contained in the oxygen-rich aerosol. Preferably, the heater 106 is an electric heating element 128 surrounded by insulation 130. Of course, any heating device can be used; provide, however, that the device is capable of adequately maintaining the oxidation zone 124 at a given elevated temperature.

The combustion gases formed in the chamber 100 exit through an outlet 132. The combustion gases can then be forwarded to a variety of devices including a detector for analyzing the combustion gases such as a UV detector, a nitrogen chemiluminescence detector or other detectors. Such processes and detectors are more fully described in U.S. Patent Nos.: 4,018,563, now Re. 34,668; 4,352,779; 4,678,756; 4,914,037; 4,950,456; 5,227, 135; 5,310,683; 5,330,714; and 5,424,217, incorporated herein by reference. Alternatively and as shown in

Figure 1, the combustion gases can be split, with a portion going to a vent line 134 and a portion going to a detector line 136 for forwarding to a desired detector.

Alternatively, the combustion gases can be forwarded to a secondary treatment unit where the gases can be partially or completely transformed. Such secondary treatment units include partial or complete reduction units. The secondary combustion gases can then be forwarded to a detector. This alternate process and apparatus can be used to simultaneously analyze a sample for nitrogen and sulfur as described in co-pending application number 08/760, 247 entitled "Apparatii and Methods for Near Simultaneous Chemiluminescent Sulfur and

Nitrogen Detection" filed December 4, 1996, incorporated herein by reference.

Moreover, the detectors include all the necessaiy components to detect the detectable components in the combustion gases or transformed gases derived therefrom and convert the raw signal into concentrations of the detected components.

The apparatus and method of this invention are particularly well suited to serve as a sample introduction device for coupling a detector and quantification device to a separation device which produces a sample contained in a large volume of a carrier solvent, such as liquid chromatography devices including, in particular, high performance liquid chromatography devices or other similar sample separation devices to high efficiency oxidation furnaces that nearly completely oxidize the sample contained in the carrier to its corresponding oxides at least one of which is detectable in the detection device associated therewith.

Although the invention has been disclosed with reference to its preferred embodiments, from reading this description those of skill in the art may appreciate changes and modification that may be made which do not depart from the scope and spirit of the invention as described above and claimed hereafter.

Claims

CLAIMSWe claim:

1. A method for efficient combustion comprising the steps of: a. containing a sample in at least one solvent with a gas containing an oxidizing agent in a nebulizing zone to form an oxygen-rich aerosol, where the oxidizing agent is present in an amount to convert a portion of oxidizable components in the sample into detectable concentrations of their corresponding oxides; and b. forwarding the oxygen-rich aerosol to a combustion zone at elevated temperature to form combustion gases including detectable concentrations of at least one oxide or at least one class of oxides capable of post-combustion detection, where the aerosol has a sufficient flow rate to provide a residence time in the combustion zone sufficient to support combustion and to prevent combustion from occurring at or near the nebulizing zone and where the nebulizing zone is a sufficient distance from the combustion zone to prevent combustion from occurring at or near the nebulizing zone.

2. The method of claim 1, further comprising the step of contacting the aerosol with an inert gas after aerosol formation in the nebulizing zone and prior to forwarding the aerosol to the combustion zone where the flow rate of the aerosol is increased by an inert gas flow rate and the inert gas prevents the aerosol from contacting walls of the nebulizing zone or combustion zone prior to combustion.

3. The method of claim 1, wherein the amount of oxidizing agent is sufficient to produce a ratio of oxidizing agent to sample and solvent of at least 1 : 1.

4. The method of claim 3, wherein the ratio is between about 1 : 1 and 500: 1.

5. The method of claim 1 , wherein the ratio is greater than 1:1.

6. The method of claim 1, wherein the oxidizing agent is oxygen.

7. The method of claim 6, wherein the gas is oxygen gas or air.

8. The method of claim 1, the flow rate is between about 1 and about 10,000 mL/min.

9. The method of claim 1, wherein the distance is from about 2 cm to about 5 cm.

10 The method of claim 9, wherein the distance is about 2.5 cm.

11. A method for detecting oxides comprising the steps of : a. containing a sample in at least one solvent with a gas containing an oxidizing agent in a nebulizing zone to form an oxygen-rich aerosol, where the oxidizing agent is present in an amount to convert a portion of oxidizable components in the sample into detectable concentrations of their corresponding oxides; b. forwarding the oxygen-rich aerosol to a combustion zone at elevated temperature to form combustion gases including detectable concentrations of at least one oxide or at least one class of oxides capable of post-combustion detection, where the aerosol has a sufficient flow rate to prevent the combustion from occurring less than about 1.5 cm from the nebulizing zone; and c. forwarding the combustion gases to a detection device.

12. The method of claim 11, further comprising the step of contacting the aerosol with an inert gas after aerosol formation in the nebulizing zone and prior to forwarding the aerosol to the combustion zone where the flow rate of the aerosol is increased by an inert gas flow rate and the inert gas prevents the aerosol from contacting walls of the nebulizing zone or combustion zone prior to combustion.

13. The method of claim 11, wherein the amount of oxidizing agent is sufficient to produce a ratio of oxidizing agent to sample and solvent of at least 1: 1.

14. The method of claim 13, wherein the ratio is between about 1 : 1 and 500: 1.

15. The method of claim 11 , wherein the ratio is greater than 1: 1.

16. The method of claim 11, wherein the oxidizing agent is oxygen and the gas is oxygen gas or air.

17. The method of claim 11, the flow rate is between about 1 and about 10,000 mL/min.

18. The method of claim 11 , wherein the distance is from about 2 cm to about 5 cm.

19. An apparatus for efficient combustion comprising: a. a nebulizer including a sample supply line, a gas containing an oxidizing agent supply line and a nebulizing nozzle, where the sample comprises at least one sample component and at least one solvent, the sample and gas are brought in contact in the nebulizer at the nebulizer nozzle to produce an oxygen-rich aerosol where the oxidizing agent to oxidizable sample ratio is at least 1: 1; and b. a temperature controllable furnace including a temperature controller, a heater, a combustion tube containing a combustion zone maintained at an elevated temperature, and a nebulizer insertion tube fitted with an inert gas supply, where the nebulizer nozzle is at least 2 cm removed from an first end of the combustion tube and the flow rate of the aerosol is sufficient to prevent the aerosol from combusting at or near the nebulizer nozzle.

20. An apparatus for efficient combustion and analysis of a sample material comprising: a. a nebulizer including a sample supply line, a gas containing an oxidizing agent supply line and a nebulizing nozzle, where the sample comprises at least one sample component and at least one solvent, the sample and gas are brought in contact in the nebulizer at the nebulizer nozzle to produce an oxygen-rich aerosol where the oxidizing agent to oxidizable sample ratio is at least 1: 1; b. a temperature controllable furnace including a temperature controller, a heater, a combustion tube containing a combustion zone maintained at an elevated temperature, and a nebulizer insertion tube fitted with an inert gas supply, where the nebulizer nozzle is at least 2 cm removed from an first end of the combustion tube, the flow rate of the aerosol is sufficient to prevent the aerosol from combusting at or near the nebulizer nozzle, and the temperature and residence time of the sample in the combustion tube are sufficient to convert a portion of the sample into detectable concentrations of oxides; and c. a detection device operatively connected to a second end of the combustion tube and capable of detecting the oxides formed in the furnace.