Abstract:
A chromatographic flow cell having the capacity to handle fluid flow from one or more chromatographic systems, at widely varying flow rates without the need to change flow cells or detectors. The flow cell itself acts as a tee where two or more fluidic inlet lines intersect with a common inlet channel. The common inlet channel is configured so that the diameter and length minimizes the total volume, unswept volume, bandspreading, and backpressure. The common outlet channel, inlet lines and the outlet line are sized to provide for adequate fluidic handling at the varied flow rates.

Description:
FIELD OF INVENTION 
     The present invention relates to a method of chromatographic chemical analysis, more particularly to the design of multiple fluidic input flow cells for use in photometric measurements. 
     BACKGROUND OF THE INVENTION 
     It is well known to measure an analyte of interest by photometric detection on fluid flowing from one or more chromatographic systems. To effect such measurement at widely varying flow rates presents the need to change flow cells and/or detectors. The changing of flow cells or detectors is both costly and time consuming. Several approaches to solve the problems that occur with varying flow rates with flow cells in the prior art have been attempted with certain limitations. 
     For example the use of a tee where there are two or more fluidic input lines entering into the tee and a single fluidic line exiting from the tee and into the flow cell is illustrated in FIG.  1 . This method can be utilized when the internal diameter of the fluidic line exiting from the tee to the flow cell inlet is sized to handle the flow rates required from the two or more fluidic lines entering the tee. This approach is acceptable if the flow rates of the fluidic lines entering the tee are comparable and the same solvents are being used. A major disadvantage of this method occurs when the flow rates diverge, such as in the case of analytical flow rates which are approximately 1.0 ml/min, and preparative flow rates which are approximately 150 ml/min. If the flow rates are vastly different, such as in the above preparative flow rates, a fluidic line configured for preparative analysis would not be adaptable for analytical use. Attempts to utilize a preparative cell for analytical work results in problems such as chromatographic bandspreading. Conversely, an exiting fluidic line sized for analytical flow rates can cause damage to the column due to the very high backpressures if a preparative use is untertaken. The foregoing problem may be addressed by selecting an internal diameter tubing that will yield acceptable results for both preparative and analytical uses. However, as a practical matter selecting a tubing that will function in both high and low flow rate applications can be difficult to undertake without sacrificing the performance of the flow cell. Additionally, this approach creates the need for multiple fluidic interfaces. 
     Another method within the prior art is to use two detectors each with its own single inlet flow cell. Each of the flow cells would have different tubing internal diameters sized to accommodate either low or high flow rates. The flow cell for low flow rates could be used for method development and screening while the cell configured for higher flow rates would be used for high throughput analysis and or purification. The problem with this approach is that the detector flow cell combination used for the method development is not the same as that used for analysis or purification. The expense associated with purchasing and maintaining two detectors renders this approach impracticable. 
     Another approach is to use a single detector and interchange flow cells. In this approach the flow cell utilized is dependent upon the flow rate and type of analysis required. There are several limitations of this approach. The degree of automation within the chromatographic system is reduced because of the need to disturb the detector in order to place a different flow cell within the chromatographic system. Another limitation of this approach is that, while the same detector is used, the potential for variation in the method scale up is high due to utilizing two flow cells. 
     Consequently, there are numerous limitations associated with prior approaches to solve the problems caused by the variation of flow rates within a chromatography system. Most notably, the prior art suffers from several limitations such as cost, scalability, automation, and validation of the chromatography system. 
     SUMMARY OF THE INVENTION 
     The present invention provides a chromatographic flow cell having the capacity to handle fluid flow from one or more chromatographic streams, at widely varying flow rates, without the need to change flow cells or detectors. 
     According to the invention, the flow cell itself acts as a tee where two or more fluidic inlet lines intersect with a common inlet channel. The size of the common inlet channel is such that the diameter and length are configured to minimize the total volume, unswept volume, bandspreading, and backpressure over the varied range of flow rates. The common outlet channel and the outlet line are sized to provide for adequate fluidic handling at the varied flow rates. 
     The selections of the flow rates used with the flow cell according to the present invention are controlled by the use of directing valves. The user controls the valves either manually or through an automation scheme. The valves are used to direct the sample stream from the injector of the chromatographic system to either a high flow rate or a low flow rate path. Both flow rate paths are in fluidic communication with their respective high or low flow rate inlets of the flow cell. The flow cell contains a common channel that is in communication with both the high and low flow rate inlets. Features of the invention include provisions of a flow cell that does not require a change of detectors over a varied range of flow rates. Bandspreading, for analytical work, is avoided with the flow cell, according to the invention by configuring the common inlet channel with the proper diameter and length. Damage to the column as a result of back pressure is prevented by having a outlet channel that can handle both high and low flow rates. The frequency of validation of the chromatography system is decreased by the utilization of the same flow cell and detector. The cost to the user is greatly reduced by having a single detector that handles both high and low flow rate systems. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing and other features and advantages of the present invention will be more fully-understood from the following detailed description of illustrative embodiments, taken in conjunction with the accompanying drawings in which: 
     FIG. 1 shows a schematic drawing of the prior art. 
     FIG. 2 a  shows a side sectioned schematic drawing of the present invention. 
     FIG. 2 b  shows an enlarged detail of A of FIG. 2 a.    
     FIG. 2 c  shows a top plan view with features in phantom of the present invention 
     FIG. 3 a  shows an alternative embodiment of the present invention. 
     FIG. 3 b  shows an enlarged detail of A of FIG. 3 a.    
     FIG. 4 shows a schematic of the present invention within a particular system application. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring in detail to the drawings, a flow cell utilizing multiple fluidic ports of the present invention is shown in section in FIG. 2 a . It comprises a cell body  100  that is formed from stainless steel, however, it can also be formed from materials such as titanium, PEEK, or other materials known in the art that are inert to the sample substance and solvents utilized. The cell body  100  contains within it an outlet port  101 , a first inlet port  102  and a second inlet port  103 . The outlet port  101  is configured to receive an outlet line (not shown). The outlet port  101  and the outlet line are configured to provide for adequate fluidic handling up to flow rates of approximately 150 ml/min The first inlet port  102  can be configured to provide for adequate fluidic handling of either high flow rates 150 ml/min to adequate fluidic handling of low flow rates &lt;0.5 ml/min. The second inlet port  103  can be of configured to provide for adequate fluidic handling of either high flow rates 150 ml/min to adequate fluidic handling of low flow rates &lt;0.5 ml/min. The first inlet port  102  and the second inlet port  103  are configured to receive a first inlet line and a second inlet line (not shown) for adequate fluidic handling of either of the appropriate (i.e. high or low) flow rates The cell body  100  has a common inlet channel  104 . The common inlet channel  104  is configured with a diameter and length have been selected to minimize the total volume, unswept volume, bandspreading, and backpressure over the range of flow rates generally employed within the intended application (&lt;0.5 ml/min to 150 ml/min). 
     Backpressure damage to the chromatography system is prevented in the present invention by configuring the outlet port  101  and the outlet line to handle both high and low flow rates. The intersection of the inlet lines within the common inlet channel  104  reduces the amount of unswept volumes by the placement of the low flow rate inlet close to the end of the common inlet channel  104  as shown in FIG. 3 b . The elimination of additional components such as a Tee and the union of the high and low flow rate lines directly into the flow cell  100  minimize the total volume thus reducing bandspreading. 
     Referring now to FIGS. 2 a  and  2   b , in an illustrative embodiment of the present invention, the dimension of the common inlet channel  104  is approximately 0.022 inches in internal diameter and approximately 0.055 inches in length. The fluidic outlet line is approximately 0.040 inches in internal diameter. The internal diameter of the first fluidic inlet line in this illustrative embodiment is approximately 0.009 inches and in this illustrative embodiment is the inlet line of the low flow rate. The internal diameter of the second fluidic inlet line is approximately 0.040 inches and in this illustrative embodiment is the inlet line of the high flow rate. In the illustrative embodiment utilizing the above dimension, the backpressure experienced at the column, when using an 80/20 mixture of IPA/H 2 O at a flow rate of 150 ml/min, was measured at approximately 260 psi. 
     Turning now to FIGS. 3 a  and  3   b  an alternative embodiment of a flow cell utilizing multiple fluidic ports of the present invention is shown in section in FIG. 2 a . It comprises a cell body  200  that is formed from stainless steel, however, it can also be formed from materials such as titanium, PEEK, or other materials known in the art that are inert to the sample substance and solvents utilized. The cell body  200  contains within it an outlet port  201 , a first inlet port  202  and a second inlet port  203 . The outlet port  201  is configured to receive an outlet line (not shown). The outlet port  201  and the outlet line are configured to provide for adequate fluidic handling at the flow rate 150 ml/min. The first inlet port  202  being positioned adjacent to the second inlet port  203  can be configured to provide for adequate fluidic handling of either high flow rates 150 ml/min to adequate fluidic handling of low flow rates &lt;0.5 ml/min. The second inlet port  203  being within the same horizontal plane and adjacent to the first inlet port  202  can be of configured to provide for adequate fluidic handling of either high flow rates 150 ml/min to adequate fluidic handling of low flow rates &lt;0.5 ml/min. The first inlet port  202  and the second inlet port  203  can be configured to receive a first inlet line and a second inlet line (not shown) for adequate fluidic handling of either high flow rates 150 ml/min to adequate fluidic handling of low flow rates &lt;0.5 ml/min. The cell body  200  has a common inlet channel  204 . The common inlet channel  204  is configured such that the diameter and length have been selected to minimize the total volume, unswept volume, bandspreading, and backpressure over the range of flow rates generally employed within the intended application (&lt;0.5 ml/min to 150 ml/min). 
     Referring to FIG. 4 a schematic of the chromatography system is shown with the illustrative flow cell positioned within a configuration allowing for a high flow rate path  301  and a low flow rate path  302  A flow cell  303  according to the present invention is configured within a chromatography system to allow the use of a detector  304  for analysis of either a sample from a analytical column  305  or a preparative column  306 . The chromatography system has a first valve  307  and a second valve  308 . The first valve  307  is in fluidic communication with an injector  309 . The injector  309  delivers a high rate flow or a low rate flow. The valve  307  directs the flow to either the high flow path rate  301  or the low rate flow path  302  depending on the application and dead-ends the flow path not in use. In the illustrative embodiment depicted in FIG. 4, the valve  307  is positioned to direct the fluid to a low flow rate path  302  through the analytical column  305  of the chromatography system. The fluid exits the analytical column  305  and is directed by the valve  307  to a first inlet line  312 . The first inlet line  312  is in fluidic communication with a low flow rate inlet  310 . The first inlet line  312  and the low flow rate inlet  310  are configured for the adequate fluidic handling of low flow rates. The high flow rate path  301  in communication with valve  307  and valve  308  is dead-ended. In the alternative high flow rate path  301 , the fluid from the injector  309  is directed by the valve  307  to the high flow rate path  301 . The valve  307  is in fluidic communication with the second valve  308 . The second valve  308  directs the fluid to one of the preparative column  306 . The fluid exits the preparative column  306  and directed by the valve  308  to a second inlet line  313 . The second inlet line  313  is in fluidic communication with a high flow rate inlet  311 . The second inlet line  313  and the high flow rate inlet  311  are configured for the adequate fluidic handling of high flow rates. 
     Although the multiple port flow cell described in the illustrative embodiment uses only two inlet ports of circular cross section and certain dimensions, it should be appreciated by those skilled in the art that for other applications additional inlet ports can be implemented. Similarity, It should further be appreciated by those skilled in the art that multiple outlet ports can be implemented. 
     The present invention is not to be limited in scope by the illustrative embodiments described which are intended as specific illustrations of individual aspects of the invention, and functionally equivalent methods and components are within the scope of the invention Indeed, various modifications of the invention, in addition to those shown and described herein will be come apparent to those skilled in the art from the foregoing description. Such modifications are intended to fall within the scope of the appended claims.