Liquid sending pipe for liquid chromatograph detector and liquid chromatograph

Abstract

A heat insulating member 13 is provided on the outer circumference of a connection pipe 11. The heat insulating member 13 includes: a tube 12; and an air layer 15 between the connection pipe 11 and the tube 12. Accordingly, it is possible to always keep the temperature of a sample component at the time of detection by a detector constant and thus prevent an influence of the temperature on an output result of the detector, in a low flow rate analysis using a modularized column unit and a modularized detection unit.

Claims

1. A liquid sending pipe for a liquid chromatograph detector, the liquid sending pipe being used for a liquid chromatograph including: a column module in which a column is housed in a temperature-regulated constant temperature bath; and a temperature-regulated detection unit module that does not include a pipe winding unit, the liquid sending pipe comprising: a) a connection pipe provided between the constant temperature bath and the detection unit module; and b) a heat insulating member for covering an outer circumference of the connection pipe wherein the heat insulating member includes: an air layer for covering the outer circumference of the connection pipe; a tube for covering the air layer; and a sealing member, which is provided at each end of the connection pipe, for sealing the air layer between the connection pipe and the tube.

2. The liquid sending pipe for a liquid chromatograph detector according to claim 1, wherein the heat insulating member includes a sponge for covering an outer circumference of the tube.

3. A liquid chromatograph including: a column module in which a column is housed in a temperature-regulated constant temperature bath; and a temperature-regulated detection unit module that does not include a pipe winding unit, the liquid chromatograph comprising: a) a connection pipe provided between the constant temperature bath and the detection unit module; and b) a heat insulating member for covering an outer circumference of the connection pipe wherein the heat insulating member includes: an air layer for covering the outer circumference of the connection pipe; a tube for covering the air layer; and a sealing member, which is provided at each end of the connection pipe, for sealing the air layer between the connection pipe and the tube.

4. The liquid chromatograph according to claim 3, further comprising a lowest flow rate in a measurement range is equal to or less than 1 μL/min.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a configuration diagram of a main part of a liquid chromatograph according to an embodiment of the present invention.

(2) FIG. 2 is a configuration diagram of a liquid sending pipe for the liquid chromatograph detector according to the present embodiment.

(3) FIG. 3 is a detailed diagram of the liquid sending pipe for the liquid chromatograph detector according to the present embodiment.

(4) FIG. 4 is a schematic diagram of a conventional liquid chromatograph detector.

(5) FIG. 5A is a graph showing an experiment result when a liquid sending pipe of the present invention is not used, and FIG. 5B is a graph showing an experiment result when the liquid sending pipe of the present invention is used.

BEST MODES FOR CARRYING OUT THE INVENTION

(6) Hereinafter, a liquid sending pipe for a liquid chromatograph detector according to an embodiment of the present invention is described in detail with reference to the attached drawings. FIG. 1 is a configuration diagram of a main part of a liquid chromatograph according to the present embodiment. In a configuration of a column module 25, a column 21 that separates each component of a sample is housed in a temperature-regulated constant temperature bath 20. A fan for agitation 22 and a heater for heating 23 are provided inside of the constant temperature bath 20. A temperature sensor 24 is provided on a surface of the column 21 to regulate the temperature to be constant.

(7) A detection unit module 30 includes a temperature regulation block 34, and the temperature of the temperature regulation block 34 is regulated by a heater, a temperature sensor, and the like, which are not shown. A region sandwiched between two double wavy lines in FIG. 1 represents the inside of the temperature regulation block 34, and a light source 33, a flow cell 31, and a photodetector 32 are provided inside thereof. Sample components eluted from the column 21 and a mobile phase reach the detection unit 30 through a connection pipe 11, and are then supplied to the inside of the flow cell 31. The flow cell 31 is irradiated with light from the light source 33, the transmitted light is detected by the photodetector 32, and the detection result is converted into light absorption characteristics of the sample components. The analysis is not limited to such measurement of light absorption characteristics, but other characteristics such as fluorescence characteristics may be measured.

(8) According to a configuration (liquid sending pipe 10) characteristic of the invention of the present application, an outer circumference of the connection pipe 11 between the column module 25 and the detection unit module 30 is covered with a tube 12 (FIG. 1). That is, an air layer 15 is formed between the connection pipe 11 and the tube 12, and a heat insulating member 13 made of the air layer 15 and the tube 12 is provided on the outer circumference of the connection pipe 11 (FIG. 2). Further, a sealing member 14 is provided at each end of the connection pipe 11, whereby the air layer 15 is sealed between the connection pipe 11 and the tube 12 (FIG. 3). The sealing member may be formed by, for example, using a heat-shrinkable tube as the tube 12 and heating and shrinking each end of the heat-shrinkable tube. Moreover, in order to enhance a heat insulating effect, the outer circumference of the tube 12 may be covered with a sponge or the like.

(9) In order to check effects of the present embodiment, in a configuration without a pipe winding unit, an influence on the output of a detector of the liquid chromatograph was checked through an experiment for each of the cases where the liquid sending pipe of the invention of the present application was used and where the liquid sending pipe thereof was not used (that is, where only the connection pipe was used). In each experiment, a PEEK (registered trademark) pipe made of a resin was used as the connection pipe. Conventionally, a stainless-steel pipe having a relatively high heat conductivity (16.7 to 26.0 W/(m.Math.k)), for example, is used for the material of the connection pipe, in order to enhance a heat exchange function. If a PEEK pipe having a heat conductivity that is about one tenth (0.25 to 0.92 W/(m.Math.k)) of that of the stainless-steel pipe is used therefor, heat insulation properties can be enhanced. The inner diameter of the PEEK pipe was 0.13 mm, the outer diameter thereof was 1.6 mm, and the length of the pipe was 430 mm. Moreover, a Sumitube (registered trademark) that is a heat-shrinkable tube was used as the tube of the liquid sending pipe of the invention of the present application. The inner diameter of the Sumitube was 2.1 mm, the thickness thereof was 0.2 mm, and an air layer having a thickness of 0.25 mm was formed between the PEEK pipe and the Sumitube. The flow rate of the mobile phase of the liquid chromatograph was set to 0.6 mL/min. Further, the capacity of the flow cell and the capacity of the pipe from the column to the flow cell were each set to about one tenth of that in conventional techniques.

(10) The experiments were carried out in a room. The temperature of the room during the experiments slowly changed in a cycle of approximately 30 minutes due to turning on/off of an air conditioner. The fluctuation range of the room temperature at that time was about 2° C. A solution containing acetonitrile, water, and triethylamine at a ratio of 500:500:1 was used as the mobile phase of the liquid chromatograph. Triethylamine is capable of great absorption in a short wavelength region around 230 nm, and the amount of its absorption increases as the temperature rises. Hence, the mobile phase used for the experiments of this time had an absorption wavelength at 230 nm. In order to also check an influence of the absorption wavelength of the mobile phase on analytical sensitivity, data was acquired for four cases where the light wavelength of the detector used for the analysis was 350 nm, 300 nm, 250 nm, and 230 nm.

(11) FIG. 5A and FIG. 5B are graphs in which the horizontal axis is time (minute) and the vertical axis is an absorbance unit (AU) calculated from the detection intensity of the detector. First, experimental data when the liquid sending pipe 10 of the present invention was not used is described. In the graph of FIG. 5A, the detection intensity fluctuates in a relatively long cycle (about 30 minutes) (baseline fluctuation). This cycle is coincident with the fluctuation cycle of the room temperature, and it can be understood that the temperature of the mobile phase inside of the connection pipe 11 is influenced by surrounding environments (room temperature). It can also be understood that the detection intensity fluctuates in a cycle shorter than that of the baseline fluctuation. This is considered as noise that is generated because the temperature of the mobile phase inside of the connection pipe is influenced by local fluctuations of an air convection in the liquid chromatograph.

(12) Further, it can be understood that particularly the baseline fluctuation and the noise are larger at the absorption wavelength (230 nm) of the mobile phase.

(13) Next, experimental data when the liquid sending pipe 10 of the present invention was used is described. In FIG. 5B, both the baseline fluctuation and the noise are smaller than those in FIG. 5A. Table 1 shows numerical values of the baseline fluctuation and the noise in FIG. 5A and FIG. 5B. In Table 1, values of the baseline fluctuation are calculated from a difference between a local maximum value and a local minimum value of the detection intensity in each graph. Further, values of the noise are calculated on the basis of ASTM standards E1657-96, in order to eliminate an influence of the baseline fluctuation.

(14) In Table 1, “Without liquid sending pipe” represents values when the liquid sending pipe of the invention of the present application was not used, and “With liquid sending pipe” represents values when the liquid sending pipe of the invention of the present application was used. It is confirmed that the use of the liquid sending pipe of the invention of the present application can make both the baseline fluctuation and the noise smaller, and can suppress an influence on the output of the detector. At 230 nm that is the absorption wavelength, the noise after the countermeasures is improved to be equal to or less than one fifth of that before the countermeasures, and the baseline fluctuation after the countermeasures is improved to be equal to or less than one half of that before the countermeasures, which can sufficiently satisfy practical application.

(15) Although the flow rate of the mobile phase of the liquid chromatograph was 0.6 mL/min in the above-mentioned embodiment, it was also confirmed that similar effects were obtained at a flow rate of 1 μL/min or less.

(16) TABLE-US-00001 TABLE 1 Unit Au Baseline fluctuation Noise Detector With liquid Without liquid With liquid Without liquid wavelength sending pipe sending pipe sending pipe sending pipe (350 nm)  100μ  400μ  8.02μ  9.85μ (300 nm)  100μ  300μ  8.78μ  9.91μ (250 nm)  200μ  500μ  9.59μ 12.83μ (230 nm) 2000μ 4500μ 18.46μ 96.25μ

EXPLANATION OF NUMERALS

(17) 10 . . . Liquid Sending Pipe 11 . . . Connection Pipe 12 . . . Tube 13 . . . Heat Insulating Member 14 . . . Sealing Member 15 . . . Air Layer 20, 47 . . . Constant Temperature Bath 21 . . . Column 22 . . . Cooling Fan 23 . . . Heater for Heating 24 . . . Temperature Sensor 25, 48 . . . Column Module 30, 40 . . . Detection Unit 31, 43 . . . Flow Cell 32, 44 . . . Photodetector 41 . . . Pipe 42 . . . Pipe Winding Unit 33, 45 . . . Light Source 34, 46 . . . Temperature Regulation Block