JPH04254742A - Atomic absorption spectroscopy photometer - Google Patents

Abstract

PURPOSE:To enable execution of accurate measurement and background correction even when a point of emission of a hollow cathode lamp changes according to a current value or becomes non-uniform discretely. CONSTITUTION:A lamp holder 32 holding a hollow cathode lamp 12 has a moving mechanism which can move the hollow cathode lamp 12 along the direction of the optical axis. At the time of measurement of atomic absorption of a sample, a small current Il is made to flow through the hollow cathode lamp 12, and the lamp is positioned at a position on the optical axis whereat a photometric output at that time is maximum. At the time when background correction is executed, a large current Ih is made to flow through the lamp and it is positioned at a position whereat the photometric output at that time is maximum.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to an atomic absorption spectrophotometer, and more particularly to a self-reversing type atomic absorption spectrophotometer that performs background correction measurement by alternately passing a small current and a large current through a hollow cathode lamp as a light source. It is something.

0002

2. Description of the Related Art When a large current is passed through a hollow cathode lamp, its emission spectrum becomes concave in the center. The emission spectrum during high current drive is mainly subject to background absorption, and atomic absorption does not appear significantly. When a small current is passed through a hollow cathode lamp, its emission spectrum exhibits a single sharp peak, which is subject to both background absorption and atomic absorption. Therefore, by determining the difference in absorbance between the two, background absorption can be accurately corrected and true atomic absorption can be measured. In an atomic absorption spectrophotometer equipped with a background correction function using a self-inversion method, the position of the holocathode lamp is fixed and cannot be moved in the optical axis direction.

0003

[Problem to be Solved by the Invention] When background correction is performed using the self-inversion method, the position of the light emitting point of the hollow cathode lamp may change in the optical axis direction between small current drive and large current drive. be. In that case, accurate background correction cannot be performed. Furthermore, if the positions of the light-emitting points of the individual hollow cathode lamps vary or if the positions of the light-emitting points change during use, accurate measurement and background correction become impossible. The present invention provides a self-reversing type atomic absorption spectrophotometer that can perform accurate measurement and background correction even when the light emitting point of a hollow cathode lamp changes depending on the current value or varies individually. This is the purpose.

0004

[Means for Solving the Problems] In the present invention, the light emitting point of the hollow cathode lamp is adjusted in accordance with the current value flowing through the hollow cathode lamp so that the light emitting point of the hollow cathode lamp can always be kept at the light source position according to the optical design. Move in the axial direction.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 schematically represents one embodiment. 12 is a hollow cathode lamp as a light source, 14 and 16 are mirrors, and 18 is an atomization unit.
The measurement light from the mirrors 14 and 16 forms an image on the atomization section 18 . The measurement light that has passed through the atomization section 18 is passed through the mirror 20
, 22 and onto the entrance slit 26 of the spectrometer 24. The measurement light separated by the spectrometer 24 is passed through the exit slit 28
The light enters the photomultiplier tube 30 of the detector and is detected.

[0006] The lamp holder 32 holding the hollow cathode lamp 12 is provided with a moving mechanism capable of moving the hollow cathode lamp 12 along the optical axis direction. When measuring sample absorption and background absorption, the hollow cathode lamp 12 is positioned at a position on the optical axis (Fig. 2 (A)) where a small current Il is passed through it and the photometric output at that time is maximum, and the background absorption is measured. When measuring only a large current Ih, the sensor is positioned at a position on the optical axis (FIG. 2(B)) where the photometric output at that time is maximum. That is, since the light emitting points 34l and 34h change depending on the current value, the lamp 12 is positioned so that the light emitting points are always at the light source position in optical design.

FIG. 3 shows an example of the lamp holder 32. FIG. 4 is a sectional view taken along line X-Y in FIG. 3. In FIG. 3, the hollow cathode lamp 12 is fixed to a movable table 38 by a lamp holder 36. As shown in FIG. The moving table 38 is guided movably in the optical axis direction of the hollow cathode lamp 12 by a guide shaft 40 . 42 is a slide bearing provided on the movable table 38 for moving along the guide shaft 40. In order to move the moving table 38 in the optical axis direction, a ball screw 44 is provided in parallel with the guide shaft 40.
A ball screw nut 46 is provided which is screwed into the ball screw nut 46. A ramp moving motor 48 is used to drive the ball screw 44.
is provided.

FIG. 5 shows a control system for controlling the lighting of the lamp 12 and the lamp position. A lamp lighting circuit 50 for lighting the hollow cathode lamp 12 and a lamp moving motor 48
are respectively controlled by the light source control section 52. Reference numeral 54 is a lamp position memory section, which stores the position of the hollow cathode lamp where the photometric output is maximized when a small current is passed through the hollow cathode lamp, and the position where the photometric output is maximized when a large current is passed through the hollow cathode lamp. The position of the hollow cathode lamp is memorized.

FIG. 6 shows an embodiment of the control system shown in FIG. The light source control section 52 is realized by a CPU 56, and the lamp position storage section 54 is realized by a memory device 58 such as a RAM. Detector 30 in FIG.
The detection signal is amplified by an amplifier 60 and then sent to an A/D converter 6
2, it is converted into a digital signal and taken into the CPU 56, where it is processed for measurement data and used for controlling the movement of the hollow cathode lamp in the present invention.

In one embodiment, a calibration procedure is provided in which the optimum position of the hollow cathode lamp is determined when a small current is passed through the hollow cathode lamp and when a large current is passed through the hollow cathode lamp, and the optimum position is stored in the memory device 58. It is shown in FIG. A small current is passed through the hollow cathode lamp 12 by the lamp lighting circuit 50,
The lamp moving motor 48 is operated to move the hollow cathode lamp 12 in the optical axis direction, and the position A of the hollow cathode lamp at which the photometric output is maximized is stored in the memory device 58. Next, a large current is applied to the hollow cathode lamp, and the lamp is similarly moved in the optical axis direction to find B at which the photometric output becomes maximum, and this is also stored in the memory device 58.

FIG. 8 shows a state in which the optimum position of the hollow cathode lamp 12 when driven with a small current and the optimum position of the hollow cathode lamp 12 when driven with a large current, which have been determined in this way, are stored in the memory device, and measurements are taken. It shows the steps to be taken. A timing diagram at that time is shown in FIG. When a small current is applied to the hollow cathode lamp 12, the lamp movement motor 48 is operated in synchronization with the current, and the hollow cathode lamp 12
is positioned at the optimum position for small current driving, which is stored in the memory device 58. In this state, the photometric output is captured. Next, a large current is applied to the hollow cathode lamp 12, and in synchronization with this, the hollow cathode lamp 12 connects to the memory device 58.
The sensor is positioned at the optimum position for high current drive stored in the memory, the photometric output is taken in, and background correction is performed. The moving mechanism for moving the hollow cathode lamp 12 in the optical axis direction is not limited to that shown in FIG. 3, and can be modified in various ways.

0012

[Effects of the Invention] In the present invention, the hollow cathode lamp is moved in the optical axis direction according to the current value flowing through the hollow cathode lamp, so that even if the light emitting point changes, the light emitting point always remains at the light source position according to the optical design. This makes it possible to perform accurate background correction. Since the luminous flux of the light source is utilized to the maximum, the S/N ratio is improved. Even if there are variations in the position of the light emitting point among the individual hollow cathode lamps, such as when the hollow cathode lamps are replaced, and a shift in focus occurs, this can be corrected by the present invention.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram showing one embodiment.

FIG. 2 is a diagram showing the position of a hollow cathode lamp according to its current value.

FIG. 3 is a plan view showing a lamp holder in one embodiment.

FIG. 4 is a sectional view taken along line X-Y in FIG. 3;

FIG. 5 is a block diagram showing a light source control system.

FIG. 6 is a block diagram of an embodiment showing a light source control system.

FIG. 7 is a flow chart diagram showing a calibration procedure in the present invention.

FIG. 8 is a flowchart showing a measurement procedure in the present invention.

FIG. 9 is a timing chart showing the measurement process of the present invention.

[Explanation of symbols]

12 Holo cathode lamp 18 Atomization section 24 Spectrometer 30 Detector 32 Lamp holder 34 Lamp light emitting point 38　　　　　　　Moving platform 40 Guide shaft 44 Ball screw 48 Lamp movement motor 50 Lamp lighting circuit 52 Light source control section 54 Lamp position memory section 56 CPU 58 Memory device

Claims (1)

[Claims] Claim 1: In a self-reversing atomic absorption spectrophotometer that performs background correction measurement by alternately passing a small current and a large current through a hollow cathode lamp as a light source, a lamp holder that holds the hollow cathode lamp in the light source section is provided. Equipped with a movement mechanism that moves the hollow cathode lamp in the optical axis direction, the position of the hollow cathode lamp where the detection output is maximum when a small current is passed through the hollow cathode lamp, and when a large current is passed through the hollow cathode lamp is determined. A lamp position memory unit that stores the position of the hollow cathode lamp where the detected output of lamp energy is maximum, and the optimum position of the hollow cathode lamp when a small current or a large current is passed through the hollow cathode lamp is recalled from the lamp position memory unit. and a light source control section that controls the moving mechanism so that the hollow cathode lamp is at that position.