JP2006337158A - Sample concentration device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sample concentration device capable of effectively separating collected components, using a simple constitution. <P>SOLUTION: After a sample component is collected by passing a sample gas through a low-temperature collection pipe 2, the collection pipe 2 is heated and a valve 5 is changed-over to allow a purge gas (also used as a carrier gas) through the collection pipe 2, in a direction opposite to the flow direction of the sample gas; while the captured sample components are separated from the collection pipe 2 to be introduced into the analyzer 10 of a rear stage. An orifice 13 is provided in the flow channel, on the inflow side of the purge gas provided in close vicinity to the collection pipe 2. According to this constitution, the flow velocity of the purge gas is throttled by the orifice 13 at heating and separation, and is increased in the collection pipe 2, the pressure of the purge gas is allowed to fall due to the Bernoulli effect, and accordingly, the separation efficiency of the collected components is enhanced. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a sample concentrator for collecting and concentrating a small amount of a measurement target component substance in a sample air and introducing it into an analyzer, for example, in analyzing environmental pollutants in the air.

  Environmental pollutants in the air, such as various volatile organic compounds (VOC), are urgently required to establish measurement techniques as causative substances for sick house problems. Although it is said that there are over 100 VOCs that can be a source of environmental pollution, there are many gas chromatograph mass spectrometers (GC / MS) with high separation and qualitative capabilities as analyzers for separating and qualitatively quantifying these various substances. Used. Since the concentration of VOC in the air is extremely small and cannot be detected even if it is introduced into an analyzer such as GC / MS as it is, it is common to use a sample concentrator as the pre-analysis stage. is there.

  As a sample concentrating device, a solid-phase adsorption / heat desorption method has been conventionally used. In this method, a sample gas (for example, air) is passed through a low-temperature collection tube filled with a collection agent such as an adsorbent, and a component material to be measured such as VOC contained in the gas is adsorbed to the collection agent. Then, the collection tube is heated and purge gas is flowed to expel the collected VOC and the like and introduce it into the analyzer (see, for example, Patent Document 1).

FIG. 2 shows a configuration example of a conventional sample concentrator. This example is configured as an analyzer that combines a sample concentrator and a gas chromatograph.
The operation of the sample concentrator is divided into a collection process and a desorption process.
In the figure, first in the collection process, the sample air is sucked into the pump 4 and flows from the sample introduction port 1 through the valve 5 through the collection tube 2 cooled by the cooling and heating device 11, A component substance to be measured in the air is collected in the collection tube 2. During this time, the carrier gas for gas chromatography flows from the carrier gas source 8 through the valve 5 to the column 6 and the detector 7. Next, the process proceeds to the desorption process, and when the collection tube 2 is heated and the valve 5 is switched, the carrier gas flows as a purge gas by detouring to the collection tube 2 and is collected in the collection tube 2. The material is expelled and introduced into the column 6 where component separation takes place. Each separated component is converted into an electric signal by the detector 7, appropriately processed by the data processing device 9, and recorded.

  In the above example, the gas flow direction in the collection tube 2 is the same in the collection process and the desorption process. However, by exchanging the positions of the sample introduction port 1 and the pump 4 in FIG. The flow directions of the sample air and the purge gas in the inside can be reversed (reverse purge). Since reverse purge is more advantageous for quickly desorbing the high boiling point component from the collection tube 2, desorption by reverse purge has been widely used.

  When the subsequent analyzer is a gas chromatograph (including GC / MS) as in the above example, the carrier gas also serves as the purge gas, so there are two names for the same gas. The carrier gas when flowing in the pipe 2 is referred to as a purge gas in order to clarify its function.

JP 2004-77384 A

The sample concentrator as described above is generally configured to desorb and remove the collected substance by heating the collection tube with an electric heater from the outside of the collection tube. In order to enhance the concentration effect, it is desirable to heat in a short time at the time of heat desorption, but since heat transfer from the outside is accompanied by a delay, it is difficult to raise the temperature to the inside of the collection tube at once, As a result, in the subsequent separation by gas chromatography, the width of the peak widens and the height of the peak also decreases, which causes a decrease in detection sensitivity and quantitative accuracy. Therefore, in designing and manufacturing the sample concentrator, it is most important to effectively desorb the collected components in a short time.
This invention is made | formed in view of such a situation, and it aims at providing the sample concentration apparatus which can desorb | save a collection component more effectively than before with a simple structure.

  In order to solve the above problems, the present invention collects sample components by passing a sample gas through a low temperature collection tube and then collecting the sample components, and then heating the collection tube and flowing a purge gas into the collection tube. In the sample concentrating device configured to desorb the sample component from the collecting tube and introduce the sample component into the analyzer, an orifice is provided in the inflow channel of the purge gas to the collecting tube. With this configuration, the flow rate of the purge gas is increased by being restricted by the orifice in the collection tube at the time of heat desorption, and the pressure is reduced by the Bernoulli effect, so that the desorption efficiency of the collected component is increased.

Since the apparatus of the present invention is configured as described above, the collected sample components have high desorption efficiency, and can be desorbed in a shorter time. This suppresses the spread of peaks in the subsequent analyzer and increases the peak height, thereby improving detection sensitivity and quantitative accuracy.
In addition, since the pressure in the collection tube increases due to the presence of the orifice in the collection process, an effect of improving the collection efficiency can be expected.

The sample concentrator provided by the present invention has the following characteristics. That is, the first feature is that an orifice is provided in the purge gas inflow passage, and the second feature is that the orifice is provided in the vicinity of the collecting pipe. Here, “nearest” means a distance within about 5 times the inner diameter of the collecting tube from the end of the collecting tube.
Therefore, the basic configuration of the best mode is a sample concentrating device in which an orifice is provided in the immediate vicinity of the collection pipe of the purge gas inflow passage.

FIG. 1 shows an embodiment of the present invention. This will be described with reference to the illustrated example.
In the figure, a straight tubular collection tube 2 is filled with an adsorbent or a collection agent 3 such as a resin-based Tenax (trade name) in an inertly coated interior. An orifice 13 for restricting the flow is attached to one end of the collecting pipe 2, and further connected to the valve 5 through a pipe 14 b, and is connected to either the carrier gas source 8 or the discharge port 15 by the valve 5. The other end of the collection tube 2 is connected to a valve 5 via a different-diameter joint 12 and a pipe 14a, and either the analysis device 10 such as a subsequent GC / MS or the pump 4 for supplying sample air is connected by the valve 5. The connection is switched to. The different diameter joint 12 is used to connect the collecting pipe 2 and the pipe 14a having different pipe diameters.

  The collection tube 2 is held by a cooling and heating device 11 having a Peltier element and an electric heater (both not shown), and the heat transfer from the cooling and heating device 11 cools and desorbs during the collection process. The process is heated and its temperature is controlled by a temperature control device (not shown).

The apparatus of this embodiment configured as described above operates as follows.
First, in the collecting process, the valve 5 is in a state where the ports are connected as shown by a solid line in the drawing, and the collecting tube 2 is cooled to a predetermined temperature. In this state, the sample air is sucked into the pump 4 and taken in from the sample introduction port 1 and flows through the collection tube 2 through the valve 5, the pipe 14a, and the different diameter joint 12 in this order, and further, the orifice 13, It is discharged from the discharge port 15 via the pipe 14b and the valve 5. In this process, the component substance to be measured in the sample air is collected by the cooled collection agent 3. Since the orifice 13 is provided on the downstream side of the collection tube 2, the resistance increases the pressure in the collection tube 2, and the collection efficiency is improved as compared with the case without the orifice 13.
During this time, the carrier gas flows from the carrier gas source 8 through the valve 5 to the analyzer 10.

  Next, the process proceeds to the desorption process. When the collection tube 2 is heated to a predetermined temperature by the cooling and heating device 11 and the valve 5 is switched so that the ports are connected as indicated by the dotted lines, the carrier gas is transferred to the carrier gas. The gas flows from the gas source 8 through the valve 5, the pipe 14 b and the orifice 13 as a purge gas to the collection pipe 2. At this time, the flow direction of the purge gas in the collection tube 2 is opposite to the flow direction of the sample air in the collection process. That is, reverse purging is performed, and the substance collected in the collection tube 2 is expelled and conveyed to the analyzer 10 through the different-diameter joint 12, the pipe 14a, and the valve 5, and analyzed.

  In the above desorption process, the purge gas passes through the orifice 13 immediately before flowing into the collection tube 2, so that the purge gas flows into the collection tube 2 in a state where the flow rate is reduced and the flow velocity is increased. When the flow rate increases, the pressure drops due to the Bernoulli effect, and the substance collected in the collection agent 3 is easily desorbed, and the desorption efficiency is improved.

When the flow of the purge gas constricted at the orifice 13 is examined in detail, the flow starts to shrink from the point upstream from the orifice 13 by the inner diameter d of the pipe 14b, and the flow cross-sectional area at the point downstream from the orifice 13 by d / 2 is Minimal. This point is called a contracted portion. In the contracted area, the flow velocity is maximum and the static pressure is minimum. The cross-sectional area of the flow gradually increases as it goes downstream from the constricted flow portion, that is, to the left in the drawing pipe 2, and is a point downstream from the orifice 13 by about 5 times the inner diameter D of the collection pipe 2. It is known that the cross-sectional area of the flow is equal to the cross-sectional area of the pipe.
Therefore, when the orifice 13 is provided in contact with the end of the collecting gas 2 on the purge gas inflow side, the inside of the collecting tube 2 in the range from this end to about 5D is affected by the orifice 13. A pressure drop occurs and the desorption effect is improved. From this, it is also understood that the orifice 13 should be provided in the vicinity of the collecting pipe 2 in the purge gas inflow passage.

The pressure drop ΔP at the contracted flow portion can be calculated by the following equation derived from Bernoulli's theorem.
ΔP = P2−P1
= ΡQ ² (1-k ² m ² ) / ² gC ² A ² (1)
Here, Q: volume flow rate, ρ: fluid density, P1: orifice 13 upstream pressure, P2: pressure in the contracted flow part, A: sectional area of the orifice 13, A1: orifice 13 upstream sectional area, A2: contracted flow The cross-sectional area of the flow in the part, k = A2 / A, C = Kk, m = A / A1, K: coefficient, g: gravitational acceleration.
As a representative numerical example, the result of trial calculation by substituting numerical values such as the collection tube 2 inner diameter (D) 1.6 mm, the piping 14 b inner diameter (d) 0.3 mm, the orifice 13 inner diameter 0.05 mm into the equation (1) , ΔP has a maximum value of about 10 kPa.

  Although one embodiment has been described above, the present invention is not limited to this. For example, a modification example in which two 4-port valves are used instead of the 6-port valve 5 can be given.

  The present invention can be used for analysis of trace samples such as analysis of environmental pollutants in the air.

It is a figure which shows one Example of this invention. It is a figure which shows an example of the conventional structure.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Sample introduction port 2 Collection pipe 3 Collection agent 4 Pump 5 Valve 6 Column 7 Detector 8 Carrier gas source 9 Data processing apparatus 10 Analyzing apparatus 11 Cooling heating apparatus 12 Different diameter joint 13 Orifice 14a Piping 14b Piping 15 Outlet

Claims (1)

The sample gas is collected by passing the sample gas through a low-temperature collection tube, and then the collected sample component is desorbed by heating the collection tube and flowing a purge gas through the collection tube. In the sample concentrator configured to be introduced into the sample concentrator, an orifice is provided in the flow path on the inflow side of the purge gas to the collection tube.

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