JPH0715435B2 - Device for measuring water content in liquid - Google Patents

Description

TECHNICAL FIELD The present invention relates to an apparatus for measuring water content in a liquid. More specifically, the present invention relates to a moisture measuring device capable of easily measuring the amount of moisture in various liquid substances such as petroleum products, organic solvents and refrigerants, and in particular, capable of performing quantitative analysis with excellent reproducibility of trace moisture.

(B) Conventional technology The Karl-Fisher method, the gas chromatographic method, and the like have been known as methods for quantifying the amount of water in petroleum and organic media. However, all of these methods require a long time for analysis, and the Karl Fisher method, which is considered to be the most reliable method, requires a titration operation, which consumes a complicated titration reagent and results in at least 30 There is a problem in that it takes more than a minute and further requires the skill of the analyst.

In this regard, the simplest method in operation is to heat and vaporize a liquid sample, and then to vaporize the vaporized sample, a so-called moisture sensor for gas, that is, resistance due to absorption and absorption of moisture in gas, electric capacity, A method is conceivable in which a sensor that electrically detects a physical change in weight or the like is brought into contact with the sensor and the water concentration or amount in the liquid sample is determined based on the output. And more specifically, a known vaporizer is diverted for gas chromatography etc. to heat and vaporize a liquid sample under the flow of a carrier gas containing substantially no moisture, and transfer it into a moisture measuring cell containing a moisture sensor. Then, a method of performing the measurement can be considered.

However, when the vaporization and transfer system of such a gas chromatograph is used as it is and connected to the moisture measurement cell by a pipeline, good reproducibility can be obtained even if the conditions such as the sample injection amount, carrier gas flow rate and vaporization temperature are kept constant. It is difficult to obtain a good measurement result, especially due to a slight difference in the injection operation, which causes a large variation in the measured value.
It is said that the quantitative determination of a trace amount of water of 10 ppm or less is far from practical use.

(C) Object of the invention The present invention has been made in view of the above-mentioned conventional problems, and is composed of a combination of a liquid sample vaporization system and a moisture measuring cell, and has sufficient practicability for quantitative determination of a trace amount of moisture. In addition to the above, the present invention intends to provide a moisture measuring device having good reproducibility.

(D) Structure of the Invention Thus, according to the present invention, ... Is provided. "Thus, according to the present invention, a liquid sample which is provided with a carrier gas supply mechanism substantially containing no water and a heating means and which is injected by a syringe through a liquid sample injection part in the non-flow of carrier gas is provided. A vaporization chamber consisting of a vaporizable capillary tube and a moisture measurement cell with a built-in moisture sensor are connected in this order to form a flow channel.At the time of vaporization of a liquid sample, this vaporization chamber is bypassed to generate a carrier gas. Provided is a device for measuring water content in a liquid, which is provided with a bypass flow path to be introduced into a water content measurement sensor, and further provided with a pair of open / close valves for switching the flow path between the vaporization chamber side and the bypass flow path side. To be done.

The most important feature of the present invention is that the on-off valves are provided in front of and behind the vaporization chamber, and they are closed during vaporization so that only the vaporization process can be performed independently. In order to avoid an adverse effect on the moisture sensor due to the temporary stop of the flow of the carrier gas, a bypass passage for the carrier gas is additionally provided.
With such a feature, the vaporization of the liquid sample can be stably performed in the non-flow of the carrier gas, and a uniform vaporized sample can be generated in the vaporization chamber without substantially causing the uneven distribution of the vaporized sample in the pipe due to the injection operation. You can Therefore, when vaporization is completed, by opening both open / close valves and introducing carrier gas, the vaporized sample can be transferred into the moisture measurement cell to measure moisture with improved reproducibility. Moreover, since the carrier gas can always be kept supplied to the moisture measuring cell, the moisture sensor will not be adversely affected by the opening and closing of the on-off valve.

The vaporization chamber used in the present invention is a vaporization chamber composed of a capillary tube used in a vaporizer such as gas chromatography. That is, the shape of the vaporization chamber, which is known in analytical instruments such as gas chromatography, is usually cylindrical, and especially the ratio of its inner diameter to its length is about 1/10 and its capacity is 200-600 ml.
Many things are used. When such a cylindrical vaporization chamber is used, it takes time until the vaporized sample in the vaporization chamber is replaced by the introduction of the carrier gas and transferred, which causes a disadvantage that the tailing of the detection peak in the moisture sensor becomes large, and further the carrier gas is generated. There is a risk of uneven replacement due to. In this regard, it has been found that high precision and high sensitivity measurement can be performed without causing the above-mentioned problems by using a so-called capillary tube which is used for a vaporization chamber for a separation column in a field such as gas chromatography. It was At this time, as a capillary tube,
Any of a glass capillary tube, a quartz capillary tube, a metal capillary tube and the like can be used. In the case of a metal capillary tube, it is more preferable to select a stainless steel capillary tube in terms of corrosion resistance and mechanical durability. Furthermore, its inner diameter /
It is desirable to set the length to be 1 / (100 or more) to be a vaporization chamber, and usually 1/100 to 1/1000 is more desirable.

The above vaporization chamber depends on the target, but the entire vaporization chamber is practically used during vaporization.
The most suitable setting is such that the temperature can be raised to a temperature of 200 ° C. or higher, and these are performed by attaching a heating means such as an electric heater or an infrared heater. Further, a liquid sample injection unit is provided in the vaporization chamber, and this may be configured by applying a known structure capable of injecting with a cylinder through various septa. When the capillary tube is used, it is preferable that the liquid sample is injected near the introduction end of the tube.

The bypass passage of the carrier gas in the present invention may be independently configured to be switchably connected to the flow passages after the vaporization chamber, but normally, the on-off valve is formed by a so-called three-way valve, and in between It is preferable in terms of device configuration to connect a pipeline that functions as a bypass passage of the vaporization chamber.

When opening the open / close valve to the flow passage after vaporization in the vaporization chamber (usually sufficient for 0.5 to 1 minute), both open / close valves should be opened simultaneously or on the moisture measuring cell side. It is preferable to open the container first and to open the carrier gas later to prevent backflow of the vaporized sample and to more stably transfer the vaporized sample.

(E) Example (1) shown in FIG. 1 is a structural explanatory view illustrating the moisture measuring apparatus of the present invention. In the figure, a device (1) is a carrier gas supply mechanism (2) consisting of a nitrogen gas cylinder (21) and a dryer (22), a heating means (33) consisting of an electric heater, and a liquid sample inlet (31) consisting of a silicon septum. And a moisture sensor (4)
1) Built-in moisture measuring cell (4) and conduit (5A) (5
The flow channel (5) is constructed by connecting in sequence at B).
A pair of three-way valves (6A) and (6B) consisting of solenoid valves are provided in the pipe lines (5A) and (5B) before and after the vaporization chamber (3), and a pair of ports of each three-way valve is a flow passage on the vaporization chamber side. (Vaporizer channel: 5 ') is used for opening and closing, and the other pair of ports is used for opening and closing the bypass channel (7).

In the apparatus (1) having such a configuration, first, nitrogen gas serving as a carrier gas is dried through the dryer (22) and allowed to flow to the drain through the vaporization chamber (3) and the cell (4).
At this time, the three-way valves (6A) (6B) are set to the open state with respect to the vaporizer flow path (5 '), and the output of the recorder (42) for recording the signal of the moisture sensor (41) in this case. Is the baseline. Next, after switching the three-way valves (6A) (6B) to the carburetor flow path (5 ') and to the bypass flow path (7) to the closed state, the liquid is removed by the syringe (32). The sample is injected into the vaporization chamber (3) through the injection port (31). When the sample injection is completed, the vaporizing chamber (3) is heated to a predetermined temperature by the heating means (33) and heated for a predetermined time. Therefore, the injected liquid sample is vaporized in the vaporization chamber (3). During this period, the supply state of the carrier gas to the cell (4) does not change, so that the baseline of the recorder (42) does not change. After heating the vaporization chamber for a prescribed time at a prescribed temperature and sufficient vaporization of the liquid sample (usually 0.5 to 2 minutes), switch the three-way valve (6B) to the vaporizer flow path (5 ') side. , Three-way valve (6A) at the same time or within 10 seconds
The carrier gas is again transferred to the drain through the vaporization chamber (3) and the cell (4) by switching to the vaporizer flow path (5 ′) side, and the vaporized sample retained in the vaporization chamber (3) is stored in the cell (4). ), The output signal corresponding to the water concentration in the vaporized sample is recorded in a peak form in the recorder (42). It should be noted that these operations may be automatically controlled by the microcomputer.

Figures 2 and 3 (reference examples) show an example of using a capillary tube (3A) as the vaporization chamber (3) and an example of using the vaporization chamber for gas chromatograph (3B), respectively. FIG. 4 shows the temporal change of the output signal of the moisture sensor (41) actually obtained using the vaporization chamber. In addition, as a capillary tube (3 A), the inner diameter is 3 m
A coil-shaped stainless steel capillary tube having a length of 2n was used, and a tubular stainless steel container having an inner diameter of 1 cm and a length of 10 cm was used as a gas chromatograph vaporization chamber (3B). The flow rate of nitrogen gas was 200 ml / min, water (injection amount 1 μl) was used as the test sample, the vaporization chamber was heated at 200 ° C. for 1 minute, and the operation time required for one measurement was about 4 minutes. Also, the moisture sensor (41) has an oscillation frequency of 9 MHz.
The piezoelectric element plate having a diameter of 14 mm provided with a moisture sensitive film having a thickness of about 0.7 .mu.m on which a sulfonate group is introduced based on a plasma-polymerized polystyrene film on the piezoelectric element plate of JP-A-59-24234. A humidity sensor was used with a control sensor (not shown).

(A) in Figure 4 is a capillary tube (3A)
(C) is the vaporization chamber for gas chromatograph (3
It shows a similar output when B) is used. As described above, good sensitivity was obtained in all cases, but reproducibility was extremely excellent when the capillary tube was used as compared with (C) which is inferior in reproducibility, and
As shown in the figure, it can be seen that the tailing of the peak is small and ideal measurement can be performed.

In addition, FIG. 4 (B) shows the result when the measurement is carried out using the capillary tube in the same manner as the above except that the vaporization is continuously performed under the carrier gas flow except for the three-way valves (6A) and (6B). Indicates that the reproducibility is poor and the sensitivity is low. Also, FIG. 4 (D) shows the results of measurement under the same conditions as in (A) above, except that no bypass flow path was provided, and it can be seen that no reproducibility is observed in the measured values. Figure 6 shows the actual water content in benzene (0.08%).
Is the measurement result.

(C) Effects of the Invention As described above, according to the water content measuring apparatus of the present invention, the water content in a liquid sample can be easily quantified in a short time, and in particular, various petroleum products, organic solvents, organic heat transfer media, etc. It is possible to easily measure a trace amount of water in a liquid sample such as.
And the reproducibility of the obtained quantitative value is also good, especially when using the capillary tube as a vaporization chamber, it is possible to perform high-precision and high-sensitivity measurement, and the conventional operation is complicated with the Karl Fisher method. Substitution is expected.

[Brief description of drawings]

FIG. 1 is a structural explanatory view showing an embodiment of a device for measuring water content in a liquid of the present invention, FIG. 2 is a structural explanatory view illustrating an essential part of a water content measuring device of the present invention, and FIG. FIG. 4 is a configuration explanatory view illustrating a main part of the water content measuring apparatus of the reference example, and FIG. 4 shows the repeated output (A) of the water content sensor obtained by the water content measuring apparatus of the present invention as the reference example (C) and the comparative example (B). , (D) together with FIG. 5, FIG. 5 is a graph exemplifying a peak pattern by the apparatus of the present invention, and FIG. 6 is a graph exemplifying a result similarly used for measuring a trace amount of water in benzene. (1) ... moisture measuring device, (2) ... carrier gas supply mechanism, (3) ... vaporization chamber, (4) ... moisture measuring cell,
(5) …… Flow channel, (5 ′) …… Vaporizer channel, (6
A) (6B) …… 3-way valve, (7) …… Bypass flow path, (3
1) …… Liquid sample inlet, (33) …… Heating means, (41)
…… Moisture sensor, (3A) …… Capillary tube,
(3B) ... Gas chromatograph vaporization chamber.

Claims (2)

[Claims] 1. A capillary tube equipped with a carrier gas supply mechanism containing substantially no water and a heating means and capable of vaporizing a liquid sample injected by a syringe through a liquid sample injection part in the absence of carrier gas. The vaporization chamber consisting of and the moisture measurement cell with a built-in moisture sensor are connected in this order to form a flow channel, and at the time of vaporization of the liquid sample, this vaporization chamber is bypassed and the carrier gas is introduced into the moisture measurement sensor. A device for measuring water content in a liquid, further comprising a bypass flow path for controlling the flow flow path, and a pair of on-off valves for switching the flow flow path between the vaporization chamber side and the bypass flow path side. 2. The moisture measuring device according to claim 1, wherein the pair of on-off valves are three-way valves, and a bypass flow path of the vaporization chamber is connected between the three-way valves.