JP4061794B2 - Flame atomic absorption spectrophotometer - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a flame atomic absorption spectrophotometer that atomizes a sample by introducing an atomized sample liquid into the frame.
[0002]
[Prior art]
In an atomic absorption spectrophotometer, it is necessary to vaporize a sample. Atomization methods include a flame method using a chemical flame and a flameless method not using a chemical flame. In the flame type atomic absorption spectrophotometer, fuel gas and auxiliary combustion gas supplied separately are mixed inside the chamber, and this is ejected from the slit opening of the burner and burned to form a frame. .
[0003]
In such a frame-type atomic absorption spectrophotometer, the types of fuel gas and auxiliary combustion gas, the flow rate of the fuel gas, and the burner height (vertical direction position) optimum for the analysis differ depending on the target element. Therefore, it is necessary to appropriately change these parameters according to each measurement element. Specifically, acetylene gas is most widely used as the fuel gas, and air is often used as the auxiliary combustion gas. However, an element that produces a strong oxide in the flame (aluminum, titanium, etc.) Etc.), dinitrogen monoxide capable of forming a flame having a higher temperature and a strong reducing atmosphere is used as a combustion gas. Therefore, when measuring a plurality of target elements sequentially, it may be necessary to switch the type of auxiliary combustion gas.
[0004]
However, since the combustion speed varies depending on the type of auxiliary combustion gas, for example, when the auxiliary combustion gas (for example, air) having a low combustion speed is switched to the auxiliary combustion gas (for example, dinitrogen monoxide) having a high combustion speed, the fuel gas is insufficient and ignition occurs. The point moves to the inner side of the burner, and backfire is likely to occur. In order to prevent this backfire, conventionally, when such auxiliary combustion gas is switched, control is performed to increase the flow rate of the fuel gas by a predetermined amount prior to that. This control is achieved by opening a valve provided in the bypass pipe for increasing the fuel gas.
[0005]
[Problems to be solved by the invention]
By the way, it is known that in a flame atomic absorption spectrophotometer, it is advantageous to keep the fuel gas flow rate as small as possible in order to improve the detection sensitivity of the target element. However, when the fuel gas flow rate is reduced, the combustion itself tends to become unstable. Therefore, when the auxiliary combustion gas is switched as described above, the stability of the combustion state is further lowered by the switching operation of the auxiliary combustion gas switching valve and the fuel gas bypass pipe valve, and the movement of the burner, so that the flame is blown out or flashback. The possibility of causing such troubles increases. In order to prevent this, it is conceivable that the auxiliary combustion gas switching valve and the fuel gas bypass pipe valve can be structured so that the switching operation can be performed more smoothly, or the moving speed of the burner can be made slower, but such a switching valve is expensive. In addition, there is a disadvantage that the time required for analysis is prolonged if the moving speed of the burner is slowed down.
[0006]
The present invention has been made to solve the above-described problems, and the object of the present invention is to provide a flame even when the type of auxiliary combustion gas is switched when the fuel gas flow rate is set to be relatively small. The object of the present invention is to provide a flame atomic absorption spectrophotometer that can prevent blowout and flashback.
[0007]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present invention provides a flame type atomic absorption method in which a fuel gas and an auxiliary combustion gas are burned by a burner to form a frame, and a sample liquid is sprayed into the frame to atomize the sample. In the spectrophotometer,
a) a flow path switching means for alternatively selecting a plurality of types of auxiliary combustion gas and supplying the same to the burner;
b) a flow rate adjusting means for adjusting the flow rate of the fuel gas supplied to the burner;
c) moving means for moving the burner in the height direction;
The d) the supporting gas Saishi To adjust the height of the burner with switching from gas A in the gas B, one of the fuel gas flow rate required for stable combustion for each combination of gas A and gas B and the fuel gas The flow rate adjusting means is controlled so that the larger value is obtained, the flow path switching means is subsequently controlled to switch the auxiliary combustion gas, and then necessary for stable combustion by the combination of gas B and fuel gas. The flow rate adjusting means adjusts the height of the burner by the moving means in a state in which the fuel gas flow rate is ensured, and then achieves a fuel gas flow rate so that optimum analysis can be performed by a combination of gas B and fuel gas. Control means for controlling
It is characterized by having.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
In the flame type atomic absorption spectrophotometer according to the present invention, before the auxiliary combustion gas is switched from the gas A to the gas B, the control means each of the auxiliary combustion gases (gas A and gas B) and the fuel gas before and after the gas switching. In this combination, the fuel gas flow rate is once set so as to be the larger value of the fuel gas flow rates at which combustion is performed stably. After that, the auxiliary combustion gas is switched, and after the auxiliary combustion gas is switched to an almost steady flame state, that is, stable combustion, the fuel gas flow rate is analyzed by the combination of the gas B and the fuel gas after switching. Set to be optimal. Usually, the optimal fuel gas flow rate for analysis by the combination of gas A and fuel gas is smaller than the fuel gas flow rate required for stable combustion for the combination, but by the above control, gas A and fuel gas are switched at the time of switching of the auxiliary combustion gas. Since the fuel gas flow rate required for stable combustion by the combination with the above is ensured, it is possible to prevent the flame from being blown off or backfired by the operation of the flow path switching means. In this case, the switching operation of the flow path switching means may not be so smooth, and it is not necessary to provide an expensive valve or the like.
[0009]
When the fuel gas flow rate at which stable combustion is possible for the combination of gas A and fuel gas is greater than the fuel gas flow rate at which stable combustion is possible for the combination of gas B and fuel gas, the auxiliary combustion gas is switched. After that, the fuel gas flow rate is temporarily reduced to a fuel gas flow rate at which stable combustion can be performed for the combination of gas B and fuel gas, and after the combustion is stabilized in this state, analysis by the combination of gas B and fuel gas is performed. Reset to the optimal fuel gas flow rate. According to this, fuel gas is not wasted immediately after the auxiliary combustion gas is switched, and incomplete combustion due to excessive fuel gas can be avoided.
[0010]
Further, by atomic absorption spectrophotometer according to the present invention, adjustment of the height of the wake cormorants burner switching of combustion aid gas after controlling the flow path switching unit, a stable combustion in combination with the gas B and the fuel gas It is performed in a state where a necessary fuel gas flow rate is secured. In other words, after the auxiliary combustion gas is switched as described above, the flow rate adjusting means is controlled so as to temporarily drop the fuel gas flow rate to the fuel gas flow rate at which stable combustion is possible for the combination of gas B and fuel gas. may have line movement of the burner waiting for the substantially stable combustion in this state, then again controls the flow rate adjusting means so that the fuel gas flow rate, such as can be performed optimally analysis in combination with gas B and the fuel gas do it. On the other hand, if the flow rate of the fuel gas is not temporarily reduced immediately after the auxiliary combustion gas is switched, the burner is moved after the auxiliary combustion gas is switched and the combustion is substantially stabilized in that state, and then the gas B and the fuel are moved. What is necessary is just to control a flow volume adjustment means so that it may become the fuel gas flow volume which can perform the optimal analysis by the combination with gas. According to this, even when the burner moves, it is possible to prevent the flame from being blown out and backfire. In addition, since it is not necessary to slow down the burner moving speed, the time required for analysis is not prolonged.
[0011]
【Example】
Hereinafter, an embodiment of a flame type atomic absorption spectrophotometer according to the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram of a flame atomic absorption spectrophotometer according to this embodiment. The burner 14 for forming the frame 15 is movable in the vertical direction (direction indicated by an arrow in FIG. 1) by a burner moving motor 13 controlled by the motor control unit 12. The fuel gas pipe 16 connected to the acetylene gas cylinder 22 filled with acetylene gas (C ₂ H ₂ ) as a fuel gas is provided with a flow rate control valve 19 capable of arbitrarily setting the flow rate. A bypass pipe 18 provided so as to pass through the control valve 19 is provided with a valve 20 whose flow rate when opened is a predetermined value (here, 5 L / min). On the other hand, the auxiliary combustion gas pipe 17 having one end connected to the burner 14 is connected to a dinitrogen monoxide cylinder 23 filled with dinitrogen monoxide (N ₂ O) via a three-way switching valve 21 or an air compressor 24 that supplies air. It is selectively connected to either one.
[0012]
The analysis control unit 10 includes a control program corresponding to the analysis procedure and a memory storing various parameters necessary for the analysis. According to this control program, the operation of the motor control unit 12 and the valves 19, 20, and 21 is performed. The gas control unit 11 that controls the gas is controlled.
[0013]
As described above, in this apparatus, the fuel gas is only one type of acetylene gas, and the auxiliary combustion gas is two types of air and dinitrogen monoxide. Therefore, there are two types of combinations of auxiliary combustion gas and fuel gas: air-acetylene and dinitrogen monoxide-acetylene. The flow range of the fuel gas that stabilizes the combustion is determined depending on the type of the auxiliary combustion gas, and is about 2 L / min or more for the air-acetylene flame and about 7 L / min or more for the dinitrogen monoxide-acetylene flame. . On the other hand, as described above, in view of detection sensitivity, the optimal fuel gas flow rate for analysis is often smaller than the above value. The value of the fuel gas flow rate optimum for such analysis (hereinafter referred to as “analysis optimum value”) is obtained in advance by experiments or the like, and is stored in the memory as one of the parameters. Here, as an example, the optimal analysis value for air-acetylene flame is 0.8 L / min, and the optimal analysis value for dinitrogen monoxide-acetylene flame is 5.2 L / min.
[0014]
In this atomic absorption spectrophotometer, a flame that may be generated by switching the auxiliary combustion gas by performing characteristic control when switching from air to dinitrogen monoxide or dinitrogen monoxide to air. I try to suppress blowout and flashback.
[0015]
FIG. 4 is a flowchart of the fuel gas flow rate setting process executed by the analysis control unit 10 before switching the auxiliary combustion gas.
First, it is determined whether or not the auxiliary combustion gas for the current measurement (that is, before switching the auxiliary gas) is air (step S21). If it is not air, it is determined whether or not it is dinitrogen monoxide (step S24). . If it is neither air nor dinitrogen monoxide (that is, if another auxiliary combustion gas is connected), the process proceeds to step S30.
[0016]
If it is determined in step S21 that the currently measured auxiliary combustion gas is air, it is determined whether or not the auxiliary combustion gas in the next measurement (that is, after the auxiliary combustion gas is switched) is dinitrogen monoxide (step S22). Here, in the case of dinitrogen monoxide, the determination value D is set to 2 [L / min] (step S23). This determination value D is a flow rate of 5 L / min that is uniformly increased in the subsequent processing as described later from the lower limit value 7 L / min of the fuel gas flow rate at which combustion is stabilized in the dinitrogen monoxide-acetylene flame after the auxiliary combustion gas is switched. Is the value obtained by subtracting. If it is determined in step S22 that the auxiliary combustion gas for the next measurement is not dinitrogen monoxide, the process proceeds to step S30.
[0017]
If it is determined in step S24 that the current measurement auxiliary gas is dinitrogen monoxide, it is determined whether or not the next measurement auxiliary gas is air (step S25). If it is air, the determination value D is set to 7 [L / min] (step S26). The determination value D is obtained by adding a flow rate of 5 L / min, which is uniformly reduced in the subsequent processing as described later, to the lower limit value 2 L / min of the fuel gas flow rate at which combustion is stabilized in the air-acetylene flame after switching the auxiliary combustion gas. Value. If it is determined in step S25 that the auxiliary combustion gas for the next measurement is not air, the process proceeds to step S30.
[0018]
If the determination value D is determined in step S23 or S26, it is determined whether or not the fuel gas flow rate at that time is smaller than the determination value D (step S27), and if it is smaller, the fuel gas flow rate target value is determined. A value D is set (step S28). Then, this flow rate target value is transmitted as a control command to the gas control unit 11 (step S29). On the other hand, if it is determined that the switching of the auxiliary combustion gas is not the pattern of air → dinitrogen monoxide or dinitrogen monoxide → air, the process is performed without changing the target flow rate of the fuel gas (step S30). finish.
[0019]
Next, regarding a specific operation performed using the above flowchart, an operation when the auxiliary combustion gas is switched from air to dinitrogen monoxide will be described with reference to FIGS. FIG. 2 is a flowchart showing a procedure of processing performed by the analysis control unit 10, the gas control unit 11, and the motor control unit 12 for this auxiliary combustion gas switching processing, and FIG. It is.
[0020]
Prior to the switching of the auxiliary combustion gas, the analysis control unit 10 first executes a fuel gas flow rate setting process according to the procedure described in the flowchart of FIG. 4 (step S1). That is, in this case, the process proceeds from step S21 → S22 → S23 to D = 2. Here, if the fuel gas flow rate is set to the analysis optimum value 0.8 L / min, the process proceeds from step S27 to S28 to S29, and the gas control unit 11 is controlled to set the fuel gas flow rate to 2 L / min. Send a command.
[0021]
In response to this, the gas control unit 11 controls the opening degree of the flow control valve 19 (step S2). Then, as shown in FIG. 5, the fuel gas flow rate increases from 0.8 to 2 L / min at time t1. Thereafter, the analysis control unit 10 transmits an auxiliary combustion gas switching control command to the gas control unit 11 (step S3). When the gas control unit 11 receives this command, it first opens the bypass pipe valve 20 that has been closed (step S4). Since the flow rate of the fuel gas flowing through the bypass pipe 18 is 5 L / min, the flow rate of the fuel gas supplied to the burner 14 increases from 2 to 7 L / min at time t2.
[0022]
Subsequently, at time t3, the gas control unit 11 operates the three-way switching valve 21 to switch the connection to the auxiliary combustion gas pipe 17 from the air compressor 24 to the nitrous oxide cylinder 23 (step S5). Although the frame 15 itself fluctuates at the time of this switching, since the fuel gas flow rate of 7 L / min necessary for stable combustion of nitrous oxide and acetylene is secured, no blow-off or flashback occurs. After that, a predetermined time (here, 3 seconds) is waited in anticipation of the time for the frame 15 to stabilize (step S6), and then at time t4, the analysis control unit 10 causes the motor control unit 12 to burn the burner according to a predetermined parameter. A burner movement control command is transmitted to change the height of 14 (step S7). In response to this, the motor control unit 12 controls the burner moving motor 13, and the burner 14 moves vertically (step S8). Although combustion may become unstable during the movement period of the burner 14, blow-off and flashback do not occur for the above reason.
[0023]
After the time expected for the maximum time spent for the movement of the burner 14 has elapsed (or after the operation of the motor 13 has stopped), the analysis control unit 10 analyzes the fuel gas flow rate target value according to a predetermined parameter. 2 L / min is set, and this is transmitted as a control command to the gas control unit 11 (step S9). In response to this, the gas control unit 11 controls the opening degree of the flow control valve 19 (step S10). Then, at time t5, the fuel gas flow rate is reduced from 7 to 5.2 L / min, and an optimal analysis by the combination of dinitrogen monoxide and acetylene can be performed.
[0024]
If the interval between the times t2 and t3 is too long, not only is the fuel gas consumed unnecessarily, but it also contributes to the generation of soot due to incomplete combustion. Therefore, after the opening of the flow control valve 19 is controlled at t2. It is preferable that the delay time is as short as possible until the flow rate of the fuel gas actually supplied to the burner 14 increases.
[0025]
Contrary to the above description, the operation when the auxiliary combustion gas is switched from dinitrogen monoxide to air will be described with reference to FIGS. FIG. 3 is similar to FIG. 2, but the order of the processes of S14 and S15 corresponding to steps S4 and S5 is switched, and instead of opening the valve 20 in step S15, the valve 20 that has been opened so far is changed. Close. Accordingly, at this time, the fuel gas flow rate is reduced by 5 L / min.
[0026]
Prior to the switching of the auxiliary combustion gas, first, the analysis control unit 10 executes the fuel gas flow rate setting process according to the procedure described in the flowchart of FIG. 4 (step S11). That is, in this case, the process proceeds from step S21 → S24 → S25 → S26 to D = 7. Here, assuming that the fuel gas flow rate is set to the analysis optimum value of 5.2 L / min, the process proceeds from step S27 to S28 to S29, and the gas control unit 11 is controlled to set the fuel gas flow rate to 7 L / min. Send a command.
[0027]
In response to this, the gas control unit 11 controls the opening degree of the flow control valve 19 (step S12). Then, as shown in FIG. 6, at time t6, the fuel gas flow rate increases from 5.2 to 7 L / min. As a result, the combustion of the dinitrogen monoxide-acetylene flame becomes stable. Thereafter, the analysis control unit 10 transmits an auxiliary combustion gas switching control command to the gas control unit 11 (step S13). When the gas control unit 11 receives this command, first, at time t7, the gas control unit 11 operates the three-way switching valve 21 to switch the connection to the auxiliary combustion gas pipe 17 from the nitrous oxide cylinder 23 to the air compressor 24. (Step S14). Subsequently, the bypass pipe valve 20 that has been opened is closed (step S15). As a result, the fuel gas flow rate decreases from 7 to 2 L / min at time t8.
[0028]
Although the flame 15 itself fluctuates when the auxiliary combustion gas is switched, since the flow rate of the fuel gas is 7 L / min or more necessary for stable combustion of dinitrogen monoxide-acetylene, no blow-off or flashback occurs. . Note that if the interval between the times t7 and t8 is too long, not only is the fuel gas consumed unnecessarily, but it also contributes to the generation of soot due to incomplete combustion. Therefore, after actually operating the three-way switching valve 21 at t7, It is preferable that the time is longer than the delay time until the type of the auxiliary combustion gas supplied to the burner 14 is changed and is as short as possible.
[0029]
After that, waiting for a predetermined time in anticipation of the time for the frame 15 to stabilize (step S16), then at time t9, the analysis control unit 10 changes the height of the burner 14 according to a predetermined parameter with respect to the motor control unit 12. Accordingly, a burner movement control command is transmitted (step S17). In response to this, the motor control unit 12 controls the burner moving motor 13, and the burner 14 moves vertically (step S18). Combustion may become unstable during the movement period of the burner 14, but the fuel gas flow rate of 2 L / min or more necessary for stable combustion of air-acetylene is secured. Does not occur.
[0030]
After the time expected for the maximum time spent for movement has elapsed (or after the operation of the motor 13 has stopped), the analysis control unit 10 determines the target flow rate of the fuel gas according to a predetermined parameter as the analysis optimum value 0.8 L / min. Is transmitted to the gas control unit 11 as a control command (step S19). In response to this, the gas control unit 11 controls the opening degree of the flow control valve 19 (step S20). Then, at time t10, the flow rate of the fuel gas is reduced from 2 to 0.8 L / min, and the optimum analysis by the air-acetylene combination can be performed.
[0031]
In this way, in the atomic absorption spectrophotometer of this embodiment, it is possible to prevent the flame from being blown out or backfired even when the auxiliary combustion gas is switched. Further, since the amount of fuel gas is increased by a minimum necessary amount before and after the auxiliary combustion gas is switched, the fuel gas is not particularly wasted.
[0032]
Note that the above embodiment is merely an example, and it is obvious that the embodiment can be appropriately changed and modified within the scope of the present invention.
That is, for example, other types of auxiliary combustion gas may be used, and the numerical values in the above examples may be appropriately changed according to the flow rate of the fuel gas that can perform stable combustion in combination with the fuel gas.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a flame atomic absorption spectrophotometer according to an embodiment of the present invention. .
FIG. 2 is a flowchart showing a procedure of processes performed by an analysis control unit, a gas control unit, and a motor control unit when switching the auxiliary combustion gas from air to dinitrogen monoxide.
FIG. 3 is a flowchart showing a procedure of processes performed in an analysis control unit, a gas control unit, and a motor control unit when the auxiliary combustion gas is switched from nitrous oxide to air.
FIG. 4 is a flowchart of a fuel gas flow rate setting process executed by an analysis control unit before auxiliary gas switching.
FIG. 5 is a graph showing a change in the flow rate of fuel gas during the switching process when the auxiliary combustion gas is switched from air to dinitrogen monoxide.
FIG. 6 is a graph showing a change in the flow rate of the fuel gas during the switching processing period when the auxiliary combustion gas is switched from nitrous oxide to air.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Analysis control part 11 ... Gas control part 12 ... Motor control part 13 ... Burner movement motor 14 ... Burner 15 ... Frame 16 ... Fuel gas pipe 17 ... Combustion gas pipe 18 ... Bypass pipe 19 ... Flow control valve 20 ... Bypass pipe valve 21 ... Three-way switching valve 22 ... Acetylene gas cylinder 23 ... Dinitrogen monoxide cylinder 24 ... Air compressor

Claims (1)

In a flame type atomic absorption spectrophotometer that atomizes a sample by burning a fuel gas and an auxiliary combustion gas with a burner to form a frame and spraying a sample liquid into the frame,
a) a flow path switching means for alternatively selecting a plurality of types of auxiliary combustion gas and supplying the same to the burner;
b) a flow rate adjusting means for adjusting the flow rate of the fuel gas supplied to the burner;
c) moving means for moving the burner in the height direction;
The d) the supporting gas Saishi To adjust the height of the burner with switching from gas A in the gas B, one of the fuel gas flow rate required for stable combustion for each combination of gas A and gas B and the fuel gas The flow rate adjusting means is controlled so that the larger value is obtained, the flow path switching means is subsequently controlled to switch the auxiliary combustion gas, and then necessary for stable combustion by the combination of gas B and fuel gas. The flow rate adjusting means adjusts the height of the burner by the moving means in a state in which the fuel gas flow rate is ensured, and then achieves a fuel gas flow rate so that optimum analysis can be performed by a combination of gas B and fuel gas. Control means for controlling
A frame type atomic absorption spectrophotometer characterized by comprising:

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