Apparatus for flow analysis
BACKGROUND OF THE INVENTION 
     This invention relates to a method and an apparatus for flow analysis, and particularly to a method and an apparatus suitable for rate assay. 
     A method comprising providing a flow cell in a carrier liquid passage, introducing a sample and a reagent solution into a stream of a carrier liquid, and observing a state of reaction therebetween by a photometer is known as flow analysis, whose specific structure is disclosed in U.S. Pat. No. 4,022,575, where a reaction solution of a sample and a reagent is introduced into a single flow cell through a reaction coil and thus colorimetric analysis is carried out continuously and efficiently by successively introducing samples into the passage. 
     The conventional flow analyzer is suitable for end point assay, and not suitable for rate assay. Rate assay by the conventional flow analyzer is poor in analytical treatment efficiency, because, if a zone of a reaction solution of a sample and a reagent solution enters into a flow cell, solution transfer must be stopped for the necessary time for observation. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a method and an apparatus for rate assay without retaining a reaction solution in a flow cell for a long time, that is, a method and an apparatus for efficient analysis. 
     Another object of the present invention is to provide a method and an apparatus capable of readily meeting changes in reaction time for one sample to another for observation. 
     According to the present invention, a plurality of flow cells are provided in a light path of a photometer, and are connected to one after another through reaction tubes. When a zone of a reaction solution of a sample and a reagent solution, as introduced into the flow passage, enters into a first flow cell, a first light absorbancy is measured, and then, when the zone of the reaction solution enters into a second flow cell, a second light absorbancy is measured. Reaction rate of a given analytical item is determined from the difference between the first and second light absorbancies. Reaction tubes having various lengths are made ready for the connection between the flow cells, and a reaction tube having an appropriate length is selected in view of the necessary time for observation. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a flow diagram showing an arrangement according to one embodiment of the present invention. 
     FIG. 2 is a schematic arrangement of a photometer and members relating to it according to another embodiment of the present invention. 
     FIG. 3 is another schematic arrangement of a photometer and members relating to it according to further embodiment of the present invention. 
     FIG. 4 is a diagram showing results of measurement acccording to the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In FIG. 1, a carrier liquid, which is distilled water, is placed in reservoir 10, and is taken into suction tube 11 by suction, and led to flow passages 13 and 14 by transfer pump 12, which is a peristaltic pump. The carrier liquids, which have passed through passages 13 and 14, are joined together in passage 17, and passed through flow cell 42, reaction tube 44, flow cell 46 and passage 48, and then discharged. Passage resistances 15 and 16 are adjusted according to a flow rate proportion of passage 13 to passage 14. 
     Passage 13 extends through metering perforation 40 of rotary switch valve 34. Sample 30 is provided for introducing a predetermined volume of a sample into the carrier liquid stream in passage 13. A plurality of sample cups 31 each containing a sample is provided on turn table 32. When a given sample cup 31 is positioned at a suction point, suction tube 33 is inserted into sample cup, and a sample is taken into rotary switch valve 34 by suction generated by working of transfer pump 36. When the sample fills the metering perforation of switch valve 34, working of transfer pump 36 is discontinued. Rotary switch valve 34 is comprised of fixed members 37 and 38 and rotary member 39. Rotary member 39 has a large number of metering perforations 40, each having a volume of 10 μl. When rotary member 39 turns by one step around shaft 41, the next metering perforation is communicated with suction tube 33. Turn table 32 advances by one step, and another sample in the next sample cup is introduced into the metering perforation communicated with suction tube 33 therethrough. When metering perforation 40 containing the sample is communicated with passage 13, the sample is transferred by the carrier liquid stream. 
     On the other hand, passage 14 extends through 6-way switch valve 25. When transfer pump 24 works, a reagent solution for measuring GOT (glutamate oxalate transaminase) in reservoir 20 is taken into passage 23 through passage 21 and metering tube 22. When the reagent solution fills metering tube 22 having a capacity of 200 μl, the working of transfer pump 24 is discontinued. Then, six-way switch valve 25 is switched as shown by dotted lines in FIG. 1, and the carrier fluid pushes the reagent solution from metering tube 22 into passage 17. 
     A zone of the sample sandwiched between the carrier liquids from passage 13 and a zone of the reagent solution sandwiched between the carrier liquids from passage 14 are joined together in passage 17 to form a zone of reaction solution. The reaction solution gradually undergoes reaction while it passes through the passage. 
     Flow cells 42 and 46 have the same structure as shown in FIG. 2. Flow cells 42 and 46 in FIG. 1 are within photometer 50 and arranged in series to light path 58. White light from light source 51 irradiates flow cell 42, and the light transmitted through flow cell 42 irradiates flow cell 46. The light transmitted through flow cell 46 enters into spectrometer 52, in which concave refractive lattice 53 and a large number of photoelectric detectors 54 and 55 are provided. Detector 54 is arranged at a position corresponding to the position of wavelength absorbed by a given analytical item, and detector 55 is arranged at a position corresponding to the position of wavelength not absorbed by the analytical item, and thus light measurement of dual wavelength is carried out by comparing and computing two signals of wavelength by computer section 56. A microcomputer provided in computer section 56 controls functioning of transfer pumps, turn table 32, rotary switch valve 34, six-way switch valve 25 and a multiplexer of taking out light signals of dual wavelength. Results of computation are displayed on display section 57 with CRT and a printer. 
     In FIG. 1, spectrometer 52 of photometer 50 is provided after the series of flow cells, but it can be provided before flow cells, as photometer 60 shown in FIG. 2. According to the structure of FIG. 2, a dispersing member is provided in spectrometer 60, where monochromatic light of single wavelength or dual wavelength irradiates flow cells. Flow cells 42 and 46 have the same shapes. Light transmission windows 65, 66, 75 and 76 of quartz are provided at both ends of flow cell bodies 62 and 72. Inlet 63 of flow cell 42 is connected to passage 73, and outlet 74 of flow cell 46 is connected to passage 48. End parts of reaction tube 44 are comprised of fluorine resin tube having a low elasticity. One end of reaction tube 44 is engaged with outlet 64 of flow cell 42, and other end thereof is engaged with inlet 73 of flow cell 46. The ends of reaction tube 44 are detachable by detachable fixing means. The monochromatic light transmitted through the flow cells is detected by detector 61. 
     While the zone of reaction solution formed in passage 17 of FIG. 1 stays in flow cell 42, a first light absorbancy based on the reaction solution is measured. Then, the zone of reaction solution flows through reaction tube 44 and enters into flow cell 46. During the transfer, reaction further proceeds between the sample and the reagent. While the zone of reaction solution stays in flow cell 46, a second light absorbancy based on the reaction solution is measured. Zones of other reaction solutions can be successively fed into the passage by synchronizing functions of sampler 30 and six-way switch valve 25. 
     In FIG. 4, results of measurement according to the present invention are shown, where two samples are successively passed by a carrier liquid stream to measure light absorbancies. Peak 86 shows a result of first measurement of a first sample, peak 87 a result of second measurement of the first sample, peak 91 a result of first measurement of a second sample, and peak 92 a result of second measurement of the second sample. The difference between peaks 86 and 87 and that between peaks 91 and 92 are changes due to the progress of reaction. Since the reaction solution or liquid mixture diffuses into the carrier liquid while the reaction solution or liquid mixture is transferred through reaction tube 44, the zone of reaction solution is broader at the second measurement. In that case, the change can be corrected by determining the area of each peak. 
     Flow cells 42 and 46 each are 0.8 mm in inner diameter and 10 mm in path length, and reaction tube 44 is 0.5 mm in inner diameter and 200 cm in length. 
     In the embodiments of FIG. 1 and FIG. 2, passage 21 is inserted into another reagent reservoir, when GOT measurement of a series of samples on turn table 32 is completed. At that time, a reagent, for example, for GPT (glutamate pyruvate transaminase) is made ready as another reagent solution. At the same time, reaction tube 44 is replaced with another reaction tube with different length, whereby a suitable time interval between a first measurement and a second one for GPT observation can be selected. 
     In the embodiment of FIG. 3, spectrometer 60 is provided after a series of flow cells, and there is a mechanism of selecting the length of reaction tube between the outlet of flow cell 42 at the upstream side and the inlet of flow cell 46 at the downstream side. That is, passage 81, which is connected to the outlet of flow cell 42 at one end, is connected to switch valve 80 at another end. Passage 84, which is connected to the inlet of flow cell 46 at one end, is connected to long reaction tube 82 and short reaction tube 83 at another end. Three or more reaction tubes can be used. 
     According to the structure of FIG. 3, a time interval between a first measurement of light absorbancy and a second measurement of light absorbancy for observation can be readily selected in view of the kind of sample or difference in analytical items. 
     In the foregoing embodiments, two flow cells are provided, but three or more flow cells can be provided in series in the same light path of a photometer. In that case, number of observations is increased in accordance with the number of flow cells.