JPH07119689B2 - Flame atomic absorption spectrometer - Google Patents

Description

TECHNICAL FIELD The present invention relates to an atomic absorption spectrometer using a gas flame for atomizing a sample.

(Prior Art) In the flame atomic absorption spectrometry, a sample is introduced into a gas flame to atomize the sample, and the line emission of the element to be quantified in the flame is passed through to measure the absorbance of the line emission. In this case, the optimum setting of the combustion condition is an important operation because the combustion condition of the gas flame is related to the analysis sensitivity and accuracy, but conventionally, the combustion condition was manually set. In this case, the goal of condition setting was to simply obtain the maximum sensitivity, and the viewpoint of obtaining the optimum S / N value was not emphasized. Even if the highest sensitivity is apparently obtained, if the S / N ratio is low, the detection sensitivity quantitative accuracy will decrease when the concentration of the target element in the sample is low, and the reproducibility of the analysis will also decrease.
It is desirable to set the combustion conditions so as to maximize the N value, but in the case of manual operation, it was difficult to carry out because the operation was complicated.

(Problem to be Solved by the Invention) The present invention aims to provide an apparatus capable of automatically setting the combustion condition of a gas flame to an optimum S / N value in flame atomic absorption spectrometry.

(Means for Solving the Problems) Automatic flow rate varying means for each gas supply path for supplying a fuel gas and an auxiliary combustion gas to a burner forming a sample atomization flame, and its temporal average value and time point for an absorbance signal. A means for determining the range of fluctuation is provided, the flow rate of the gas supplied to the burner is set to a set of values, and a blank sample and a sample containing the element to be measured (concentration unknown unknown, for example, sample to be measured) are supplied to the burner. Then, the temporal average B of the absorbance signal for the blank sample, the temporal average T of the absorbance signal for the sample containing the element to be measured, and the temporal fluctuation range N for the signal are detected to obtain the S / N value. The operation calculated as is performed while changing the gas flow rate supplied to the burner, and the combination of gas weights that maximizes the S / N is detected.

Further, a burner position automatic changing means is provided to repeat the above-mentioned operation while changing the position of the light beam passing through the sample atomizing flame in the flame.

(Operation) In flame atomic absorption spectrometry, the flow rate of the fuel gas normally supplied to the burner is kept constant, and the optimum flow rate is changed to obtain the optimum conditions. In FIG. 2, the horizontal axis represents the auxiliary combustion gas flow rate, and the vertical axis represents the temporal average of the absorbance. The absorbance averages B and T of the blank sample and the sample to be measured change as shown in B and T of the figure when the flow rate of the supporting gas is changed. Conventionally, the auxiliary combustion gas flow rate is set to the point Lm where TB is maximum in this figure. In this case, since T and B are temporal averages, the actual absorbance signal fluctuates above and below this T and B, and the fluctuation width, that is, the noise width N, also changes depending on the auxiliary combustion gas flow rate. However, (T−B) / N is not always the maximum. However, conventionally, the person performing the measurement sees the fluctuation range by displaying the absorbance signal, so the fluctuation range is subjectively evaluated, and it is difficult to grasp the S / N value quantitatively, and it takes a relatively short time. There was no choice but to set the auxiliary combustion gas flow rate at a position where TB was considered to be maximum when the burner adjustment was terminated. According to the present invention, the noise width N with respect to T is obtained in addition to the data of T and B shown in FIG. 2, so that the auxiliary combustion gas flow rate that maximizes (TB) / N is automatically obtained.

The above explanation was given only when the flow rate of the supporting gas was changed, but it is exactly the same when the flow rate of the fuel gas is changed, and the position where the light beam passes through the sample atomizing flame is also the measured S / N ratio. Although related to the improvement, by performing the above-mentioned operation while changing the burner position, the optimum condition is automatically set in accordance with the burner position.

(Embodiment) FIG. 1 shows an embodiment of the present invention. H is a hollow cathode lamp of a light source, F is a flame for atomizing a sample, B is a burner forming a flame F, and Z is a position changing device of the burner.
The position varying device is driven by the control device C and is variable about three types of positions of the vertical direction of the burner, that is, the z-axis direction, and the horizontal direction orthogonal to the light beam passing through the flame F and the rotation around the z-axis. What is important above is the z-direction position and the rotational position around the z-axis, and the position adjustment in the z-axis direction is particularly important. N is a sample atomizer, S is a sample container, fuel gas is supplied to the burner B through the sample atomizer, Vf is a fuel gas flow rate control valve, Va is a supporting gas flow rate control valve, These valves are driven by controller C. M is a monochromator, which disperses the light from the light source H that has passed through the flame F, and D
Is a photodetector that receives the light emitted from the monochromator M. L
Is an absorbance converter that converts the output of the photodetector D into an absorbance signal, and AD is A / D-converts the output of the absorbance converter L. The control device takes in the output of the A / D converter AD and performs a predetermined calculation. R
AM is a data memory for performing the above calculation.

FIG. 3 is a flowchart of the operation of the control device C. In this embodiment, the burner position is set in advance in the horizontal direction and the rotational position around the z-axis, only the position z in the height direction is adjusted, and the flow rate of the fuel gas is also set in advance. Only adjusted. First, while continuously supplying the blank sample to the burner (a), the burner height z is set to the lowest position Zo within the practical range (b), and the opening degree of the valve Va is also set to the minimum within the practical range (c). ),
The average absorbance B is stored in the measurement RAM (d), and it is checked whether the opening of the valve Va is the maximum Vam in the practical range (e). If NO, the current opening Va of the valve Va is only one step v. Increase (f) and the operation returns to step (d). If the step (e) is YES, the next step (g) checks whether the burner height is at the highest practical range or not, and if it is NO, raise the burner height z by one step from the current burner height. ), The operation returns to step (c). When the step (g) is YES, a sample containing the element to be quantified (which can be the sample to be measured, the concentration may be unknown) is introduced (re), and the burner position is returned to Zo (n). Return the valve Va to Vao (L), measure the average absorbance T and the fluctuation range N of the absorbance, and store it in RAM (E). Then, in the same way as for the blank sample, (W) (F) (Y) After step (ta),
If step (yes) is YES, it means that all the necessary data has been collected. Therefore, in step (le), when the auxiliary gas valve is changed for each height position of the burner. Calculate the maximum value from the above S / N value in step (SO) and set the burner height and valve Va opening that will give that S / N value for burner B and valve Va. And the operation ends.

The operation of obtaining the averages T and B of the absorbance signals in the above operation is performed as follows. The absorbance signal is sampled at constant time intervals, A / D converted, and taken by the controller C. This A / D converted data Xi (i = 1,2, ... n)
If so, the control device C To calculate. The value of X changes every time i is small,
Since the change gradually becomes smaller, the measurement is finished at the nth time when the difference between the (n-1) th X and the nth X becomes smaller than a predetermined value. There are various methods for obtaining the fluctuation range N of the absorbance, but the simplest one is to store the above Xi in the RAM one after another, while obtaining the above average X = (Σ Xi) / i and sample it n times. When the measurement is finished at the point, the difference between the calculated average X and the data Xi stored in RAM | Xi-
The maximum value of X | is found and set as N. As a more appropriate method, for all Xi data stored in RAM To N.

When the gas flow rate supplied to the burner is changed, it takes some time for the absorbance signal to stabilize. Therefore, in the flow chart of FIG. 3, it is better to insert time-waiting steps before the steps (d) and (e). The waiting time at this time may be fixedly set in advance according to the time, but this tends to take extra time, so it is recommended that the waiting time be set automatically. desirable. For this purpose, after the setting of the valve opening is completed, a moving average of, for example, 10 sampling data is obtained while sampling the absorbance signal, and the latest moving average value and the moving average value at the immediately preceding sampling are calculated. When the difference between the two becomes less than the set value, the steps in FIGS. 3 (d) and 3 (e) may be started.

(Effect of the Invention) Since it is difficult for human beings to visually recognize the fluctuation range of the measurement output, that is, the magnitude of noise, it is subjectivity, and therefore the manual setting of the burner combustion condition is set to the maximum sensitivity. However, according to the present invention, since the condition of the maximum S / N value is automatically set, the burden on the operator is reduced, the adjustment time is shortened, and the accuracy of measurement sensitivity is improved. In flame atomic absorption spectrometry, the position of the light beam passing through the flame also affects the sensitivity, but if the burner position adjustment is added to the above-mentioned burner combustion condition setting operation, a program that searches for the maximum S / N ratio condition will be created. As it is, both the burner position and the burner combustion conditions are optimally adjusted, and the effects of improving the S / N value, reducing the burden on the operator, and shortening the adjustment time are further enhanced.

[Brief description of drawings]

FIG. 1 is a block diagram of an apparatus of one embodiment of the present invention, FIG. 2 is a flowchart of an example of the operation of the above embodiment, and FIG. 3 is a graph for explaining the operation of the conventional example and the present invention. H: light source, B: burner, M: monochromator, D
...... Photo detector, L ...... Absorbance converter, AD ...... A / D converter, Z ...... Burner position changing device, N ...... Sample atomizer,
Vf: Fuel gas control valve, Va: Combustion gas control valve, C: Control device.

Claims (2)

[Claims] 1. An automatic flow rate changing means for adjusting a flow rate of both or one of a fuel gas and an auxiliary combustion gas supplied to a burner,
A means for detecting the temporal average of the absorbance signal and the fluctuation range of the temporal fluctuation, and a blank sample is introduced into the burner, and the automatic flow rate varying means is driven, and the ratio of the fuel gas and the supporting gas supplied to the burner The average B of the absorbance signal is calculated every time the temperature changes, and then the fuel containing the element to be quantified is introduced into the burner to drive the automatic flow rate changing means to drive the fuel gas and the auxiliary combustion gas supplied to the burner. Each time the ratio changes, the average T of the absorbance signal and the variation width N of the temporal variation of the absorbance signal are detected, and by the B, T and N for the same position of the automatic flow rate varying means, Is calculated, and the position of the automatic flow rate varying means for maximizing the S / N is found, and the flame atomic absorption spectrophotometer is provided with the control means for setting this position as the optimum position. 2. In addition to the invention as set forth in claim 1, automatic burner position changing means is provided, and a blank sample is introduced into the burner at one position of the burner, while the automatic flow rate changing means. The means B is driven to obtain the average B of the absorbance signals each time the ratio of the fuel gas and the auxiliary gas supplied to the burner changes, and then the sample containing the element to be quantified is introduced into the burner while the automatic flow rate is changed. Every time the ratio of the fuel gas and the auxiliary gas supplied to the burner is changed by driving the variable means, the operation of detecting the average T of the absorbance signal and the variation width N of the temporal variation of the absorbance signal is repeated while changing the position of the burner. , B, T and N for the same position of the burner and the same automatic flow rate changing means, And a flame atomic absorption spectrophotometer equipped with control means for finding out the burner position and the position of the automatic flow rate varying means for maximizing the S / N, and setting that position as the optimum position.