JP2012018095A - Head space gas sampler - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a head space gas sampler capable of accurately adding a fixed amount of internal standard gas to an unknown sample.SOLUTION: A head space gas sampler, which obtains sample gas from an upper space in a sample vessel and leads the sample gas into a sample vaporizing chamber of a gas chromatographic device, includes means for individually and independently measuring and obtaining the sample gas and standard gas at the outside of a sample vial and leading means for leading both of the gas which are sealed in one connected path into the sample vaporizing chamber at one time.

Description

  The present invention relates to a headspace gas sampler for sampling a gas component that volatilizes from a sample with respect to an analysis apparatus such as a gas chromatography apparatus.

  One analysis method in gas chromatography is headspace gas analysis. This is because a liquid or solid sample is sealed in a sample container with a septum lid (hereinafter referred to as a vial) with some space left on the top, and this is held at a predetermined temperature for a predetermined time, and then the upper space (head This is a method for qualitatively or quantitatively determining a volatile component in a sample by collecting and analyzing the gas in the space with a syringe or the like. A sampling apparatus for gas chromatograph that automatically performs this head space gas analysis method is a head space gas sampler, and is widely used for measuring fragrance in foods, measuring volatile organic compounds in water, and the like.

  Further, an internal standard method is often employed in order to prevent measurement accuracy from deteriorating due to fluctuations in sensitivity of the gas chromatograph apparatus and variations in sample injection amount. In the internal standard method, when multiple samples are measured continuously, the same amount (concentration) of standard gas of a component different from the component to be measured is added to all samples, and this mixed gas is injected into the column of the gas chromatograph. And measure. When all measurement conditions are ideally stable, the peak height or peak area of the standard gas appearing in the chromatogram of each sample should be the same for all samples. If there is a change in the sample injection amount or the sensitivity of the detector, the peak height or peak area of the standard gas will change. By using the fluctuation of the peak of the standard gas, it is possible to correct the influence of the fluctuation of the apparatus sensitivity and the variation of the sample injection amount that appear in the peak of the component to be measured.

  The standard gas component must be a substance that does not chemically react with the component to be measured. Moreover, it must be a substance that exhibits sufficient measurement sensitivity for the detector used for measuring the component to be measured. Considering these conditions, the optimum standard gas is selected according to the component to be measured.

  Addition of standard gas in the internal standard method is generally performed by penetrating the needle of the syringe into the upper space of the vial through a septum attached to the cap of the sample vial, and injecting the standard gas into the vial through a through hole in the center of the needle Is done by doing. Also, a syringe is often used when a mixture of standard gas and sample gas is collected from the upper space of the vial and injected into the gas chromatograph apparatus. Various methods for automating the addition of the standard gas and the injection of the sample to increase the accuracy and speed of measurement have been proposed (see, for example, Patent Document 1).

US Patent US2006 / 0263901

  Conventional standard gas addition is performed by a method in which a needle is inserted into a septum attached to the lid of the vial and the standard gas is injected into the internal space of the vial through the needle. At this time, it is necessary to ensure that the lid of the vial is tightly sealed, but there are often cases where the lid is not correctly attached due to immaturity of the measurer or carelessness. In this case, the standard gas or the head space gas leaks to the outside, which causes the accuracy of the addition amount and the measurement accuracy to be greatly degraded. The object of the present invention is to solve these problems of the conventional method by introducing a fixed amount of standard gas into a gas chromatograph without injecting it into a vial, thereby enabling accurate measurement of a headspace gas sampler. Is to provide.

  In order to solve the above problems, the present invention provides a headspace gas sampler that collects a sample gas from an upper space in a sample container and introduces the sample gas into an inlet of an analyzer, and supplies the sample gas from a standard gas container. A standard gas collecting means for collecting the standard gas, a sample gas collecting means for collecting the sample gas in the sample container, a first position for connecting the standard gas container and the sample container to the collecting means, and the There is provided a path switching means for switching the standard gas sampling means and the sample gas sampling means to a second position connecting the inlet to the introduction port as one communication path. Further, the standard gas sampling means is a measuring tube having a predetermined capacity, the sample gas sampling means is a measuring pipe having a predetermined capacity, and the path switching means is located between the first position and the second position. The standard gas collection means is connected to the 6-port valve, and the sample gas collection means is connected to the 8-port valve. ing.

  That is, in the headspace gas sampler according to the present invention, the standard gas and the sample gas are separately metered and sampled outside the sample container using sampling means independent of each other. As a result, an accurate amount can be collected without being affected by the looseness of the lid of the sample container.

  In addition, the standard gas and the sample gas are arranged as one communication path without a branch in the middle, and both are injected into the inlet of the analyzer at a time. Thereby, the sample gas and the standard gas remaining in the path can be suppressed to a very small amount.

With the headspace gas sampler according to the present invention, an accurate amount of standard gas and sample gas can be introduced into the gas chromatograph apparatus regardless of the skill of the analyst, and high-precision analysis becomes possible. In addition, since there is no branch point in the flow path configuration of the present invention, standard gas and headspace gas do not remain in the line. This prevents cross contamination between samples.

It is a flow-path block diagram in the standby state of the head space gas sampler which concerns on this invention. It is a flow path lineblock diagram at the time of line washing of a head space gas sampler concerning the present invention. It is a flow-path block diagram at the time of vial pressurization of the head space gas sampler which concerns on this invention. It is a channel lineblock diagram at the time of sample collection of the head space gas sampler concerning the present invention. It is a channel lineblock diagram at the time of injection of a head space gas sampler concerning the present invention. It is a flow path lineblock diagram at the time of line washing of a head space gas sampler concerning the present invention.

  The headspace gas sampler according to the present invention is constituted by two multi-port valves, two metering tubes and one needle.

  FIG. 1 shows an embodiment of a headspace gas sampler according to the present invention.

  The valve 1a is a six-port valve having six ports indicated by a, b, c, d, e, and f in the drawing. The valve 1a can take two positions. In the first position, the path ab, the path cd, and the path ef communicate with each other inside the valve 1a. In the second position of the valve 1a, bc, de, and fa communicate with each other inside.

  The valve 1b is an eight-port valve having eight ports indicated by symbols g, h, i, j, k, l, m, and n in the drawing. Similarly to the valve 1a, the valve 1b has two positions. At the first position of the valve 1b, the paths hi, jk, lm, and ng communicate with each other, and the second position At positions, gh, ij, kl, and mn communicate with each other internally.

  The standard gas is supplied from the standard gas cylinder 3 to the port a of the valve 1a via the stop valve 5a, and the stop valve 5a is opened and closed by a control device (not shown) according to the phase of the device.

  A measuring tube 2a in which a thin tube is wound in a loop shape is connected between a port b and a port e of the valve 1a, and accurately collects a standard gas having a volume determined by the total length from the port b to the port e of the measuring tube 2a. Used for. The amount of gas to be collected is changed by adjusting the inner diameter and length of the measuring tube 2a.

  The port f of the valve 1a is connected to the outside air by the pipe 7a through the stop valve 5b. Further, the port c and the port d of the valve 1a are connected to the port i and the port g of the valve 1b, respectively.

  A thin tubular needle 6 is connected to the port m of the valve 1b, and a vial 4 containing a sample is placed below the needle 6. The vial 4 can be moved upward by a vertical drive mechanism (not shown), and the needle 6 can be inserted into the septum of the vial 4.

  A measuring tube 2b in which a thin tube is wound in a loop shape is connected between the port 1 and the port h of the valve 1b, and is used for collecting the head space gas inside the vial 4. The gas sampling amount is changed by adjusting the inner diameter and length as in the case of the measuring tube 2a.

  The carrier gas supplied to the gas chromatograph apparatus is connected to the port j of the valve 1b through the pipe 7d. Further, the port k of the valve 1b is connected to the column of the gas chromatograph apparatus by the pipe 7e.

  A vial pressurization gas source is connected to a port n of the valve 1b through a pipe 7c through a stop valve 5c. Further, the port n communicates with the outside air by the pipe 7b through the stop valve 5d.

  The vial pressurizing gas is injected into the upper space in the vial 4 in the step of FIG. 3 described below, and the gas phase in the vial 4 is pressurized to a pressure higher than the atmospheric pressure, and in the next step of FIG. This pressure is used to pump the sample gas from the vial 4 to the measuring tube 2b. In order not to contaminate the vial 4 and to prevent a chemical reaction with the sample gas, a mechanically or electrically pressure-adjusted helium gas is used as the pressurizing gas.

  FIG. 1 shows the flow path configuration of the headspace gas sampler in the standby state. In the standby state, the valves 1a and 1b are both set to the first position, and the stop valves 5a, 5b, 5c and 5d are all closed. The needle 6 and the vial 4 are in a separated state.

  Before starting the measurement, line cleaning for cleaning the inside of the flow path system is performed. FIG. 2 shows the flow path configuration during line cleaning. At this time, both the valves 1a and 1b maintain the first position as in the standby state. The needle 6 and the vial 4 are also in a separated state as in the standby state. Stop valves 5a, 5b, 5c and 5d are all opened.

The standard gas from the standard gas cylinder 3 flows from the stop valve 5a through the port a-port b-metering tube 2a-port e-port f-stop valve 5b of the valve 1a and out of the pipe 7a. Then, unnecessary gases and air remaining in this path are replaced with clean standard gas.
On the other hand, the pressurizing gas introduced from the pipe 7c is supplied from the stop valve 5c to the port n-port g of the valve 1b-port d of the valve 1a-port c-valve 1b-port i-port h-metering tube 2b. -Port 1-Port m-Flows through the needle 6 and flows out from the tip of the needle 6. As a result, the inside of this path is replaced with clean pressurizing gas.
This step is important as preventing a phenomenon in which the residue of the sample measured before causes an error in the measurement of the subsequent sample.

  In the next stage, vial pressurization is performed by the flow path configuration shown in FIG.

  At this time, the valves 1a and 1b are both kept at the first position, but the stop valves 5b and 5d are closed. Further, the tip of the needle 6 is inserted into the gas phase space in the vial 4 through the septum of the vial 4. Since the pressurizing gas supplied from the pipe 7c is pressed into the gas phase space of the vial 4 through the path indicated by the arrow in FIG. 3, the pressure of the gas phase in the vial 4 increases. When the pressure of the gas phase of the vial 4 reaches equilibrium with the supply pressure of the pressurizing gas supplied to the pipe 7c, the inflow of the pressurizing gas is stopped and the vial pressurization is completed. The standard gas is also filled in the measuring tube 2a at this point.

  Next, the head space gas in the vial 4 is collected in the measuring tube 2b by the flow path configuration shown in FIG. The positions of the valves 1a and 1b at this time are kept at the first position.

  First, the stop valve 5c is closed to stop the supply of pressurized gas, and the gas phase pressure of the vial 4 is maintained at a state higher than atmospheric pressure. Next, the stop valve 5d is opened. As a result, the gas sealed in the path from the gas phase of the vial 4 to the stop valve 5c is released to atmospheric pressure, flows through the path indicated by the arrow in FIG. 4 and flows out from the pipe 7b. At this time, the head space gas in the vial 4 flows out of the needle 6 and fills the measuring tube 2b.

  At this time, in order to fill the measuring tube 2b without excess or deficiency of the headspace gas, the optimum is determined by the sum of the volume of the gas phase portion of the vial 4, the volume of the measuring tube 2b, and the volume of the path from the tip of the needle 6 to the port m. The supply pressure of the pressurizing gas when the vial is pressurized is controlled to the above pressure.

  Next, the standard gas collected in the measuring tube 2a and the headspace gas collected in the measuring tube 2b are simultaneously injected into the gas chromatograph device by the flow path configuration shown in FIG.

  First, after closing the stop valves 5a and 5d, the valves 1a and 1b are switched simultaneously or in conjunction with each other and set to the second position. By this switching operation, the carrier gas supplied from the pipe 7d flows through the flow path indicated by the arrow in FIG. 5, so the standard gas collected in the measuring pipe 2a and the headspace gas collected in the measuring pipe 2b Are sequentially injected into the column of the gas chromatograph apparatus by the carrier gas.

  Although not shown in FIGS. 1 to 5, a plurality of vials 4 are mounted on a turntable or the like in order to continuously measure a large number of samples. For each vial 4, the measurement proceeds by repeating the above-described line washing step in FIG. 2 to the sample injection step in FIG. 5, but each stage valve 1 a, 1 b, stop valve 5 a, 5 b, 5 c, 5 d etc. The switching is performed by a driving device that drives each valve and stop valve, which are not shown, and a control device that gives commands to them.

  After the measurement is completed for all the vials, the line cleaning shown in FIG. 6 is performed again at the final stage. The operation at this stage is exactly the same as that of the line cleaning described with reference to FIG. 2, and the entire flow path of the head space gas sampler is cleaned with the standard gas and the pressurizing gas.

  Thereafter, the apparatus is returned to the standby state shown in FIG. 1 and waits for the next measurement.

  As described above, the head space gas sampler according to the present invention uses the two independent measuring tubes for collecting the standard gas and the head space gas, and collects both gases by placing them outside the vial. A method is adopted in which a single measuring tube is enclosed in a single connected path, a carrier gas is allowed to flow through this path, and both gases are sent to the column at a time. As a result, since an accurate amount of standard gas is sent to the column, it is possible to correct the measurement value due to variation in measurement conditions by the internal standard method. Therefore, it is an optimal headspace gas sampler for use as an internal standard method for correcting variations in sensitivity of the analyzer.

  In addition, in the flow path configuration at the time of injection shown in FIG. 5, there is no branch portion in the path of the pipe 7d through which the carrier gas flows, the measuring pipe 2a, the measuring pipe 2b, and the pipe 7e, and there is no dead volume. . Therefore, the standard gas and the head space gas remain and no error occurs in the subsequent measurement.

  In the above description, the valve 1a has been described as a 6-port valve. However, as an actually used part, an 8-port valve is used, and a part of the valve 1a is communicated in advance to be used as a 6-port valve. May be.

1a, 1b Valve 2a, 2b Measuring tube 3 Standard gas cylinder 4 Vials 5a, 5b, 5c, 5d Stop valve 6 Needle 7a, 7b, 7c, 7c, 7d, 7e Piping

Claims (2)

  In a headspace gas sampler that collects a sample gas from an upper space in a sample container and introduces the sample gas into an inlet of an analyzer, a standard gas sampling unit that collects a standard gas supplied from a standard gas container; A sample gas collecting means for collecting the sample gas in the sample container; a first position for connecting the standard gas container and the sample container to the collecting means; the standard gas collecting means and the sample gas collecting means at the inlet; A head space gas sampler comprising a path switching means for switching to a second position connected as one communication path.   The standard gas sampling means is a measuring pipe having a predetermined capacity, the sample gas sampling means is a measuring pipe having a predetermined capacity, and the path switching means is in two positions, the first position and the second position. It consists of a 6-port valve and an 8-port valve that can be switched in conjunction with each other. The standard gas sampling means is connected to the 6-port valve, and the sample gas sampling means is connected to the 8-port valve. The headspace gas sampler according to claim 1.

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