DE2537494A1 - PHOTOMETER - Google Patents

Description

PATENT LAWYERS! A. GRÜNECKER

DIPL.-INQ.

H. KINKELDEY

DR.-ING.

_{Q /} W. STOCKMAIR

K. SCHUMANN

DR. RER. NAT. · DIPL.-PHYS.

P. H. JAKOB

DIPL.-INQ.

G. BEZOLD

DR. RER. NAT. · DIPL.-CHEM.

MUNICH E. K. WEIL

DR. RER. OEC. INQ.

LINDAU

MUNICH 22

MAXIMILIANSTRASSE 43

P 94-76

22nd August 1975

The Perkin-Bucket Corporation
Norwalk, Gonnecticut, USA

Photometer

The invention relates to a photometer with high stability and sensitivity.

In general, the invention relates to an arrangement of photometers, detectors and amplifiers as used for automatic analysis is used; In particular, with such a device the absorption capacity or measure the absorbance of liquids.

In this way, in particular, very small amounts of a

6098U / 0665

TELEPHONE (OSS) 22 28 62 TELEX O5-2Θ38O TELEGRAMS MONAP

Mixtures containing components that react with one another analyze automatically. These mixtures contain, for example, a serum sample containing a mixed diluent and reagents are added.

Such a photometer produces reactive serum samples introduced into a flow cell through which the light beam passes. At the same time another part becomes of the light beam, which is used as a reference beam or comparison beam, in a further optical beam path guided. So that the light energy of the beam after passing through the reacting mixture for determination the extinction of the mixture can be exploited, a device must be provided to increase the brightness of the light determine and amplify the measured variable to a voltage value that has a corresponding size. Various devices for generating such an output signal have been developed. In general these devices contain a photodetector in addition to various amplifier stages. To the right one To obtain output signal, the gain must also include amplifiers with logarithmic input or feedback, so that an output signal is produced that is proportional to the extinction. Although many such systems were developed they all have poor accuracy and / or a poor signal-to-noise ratio.

With conventional sensitive and stable photometers for measuring small changes in absorptivity or the absorbance of samples, this sensitivity and stability was achieved through the use of a double beam and an optical modulation system, wherein a beam with spectrally filtered radiation or Parts of the beam from the source are alternately directed along a beam path through the sample while the light of the reference beam does not pass through the sample. The ones that propagate in the two beam paths Beams are combined on a single detector

609811/0665

ORIGINAL INSPECTED

ned to generate a signal that is periodic with the time changes. This mandatory structure is based essentially on the limited possibilities of the previously used photodetectors. The periodic signal is then demodulated to produce a signal which is a measure of the difference in extinction in the sample or comparison beam path. The lower limit of measurement for such a photometer is 5 x 10 absorption or extinction units; i.e. that the photometer still shows a change in absorption as the lower limit determine of approximately 5 σ 10 ectinction units can. Furthermore, relatively large amounts of sample had to be used with these photometers. But can even relatively small amounts of sample can be analyzed, so the amount of sample material or reagents can be reduced, which are necessary for the analysis, so that the examination costs decrease.

The invention is therefore based on the object of a photometer to create the specified type, which has a higher accuracy and the absorption capacity or the Can measure absorbance in extremely small sample quantities, by improving the signal / noise ratio.

This object is achieved according to the invention by a stable, sensitive optical system with two beams and without chopper, the first: beam passing through the sample located in a cell, while the second beam serves as a reference beam, through a first and second PIN diode detector on which the first. or second beam imaged and those proportional to the incident light syrup Generate output signals, through a first and second parametric amplifier, whose inputs respectively are coupled to the outputs of the first and second detectors, and through one of the output signals of the first and second parametric amplifier as input signals receiving arrangement to the logarithms of the output signals to calculate and to form the difference of the logarithms, so that one is proportional to the absorbance in the cell

609-8 11/066 5

ORIGINAL IMSPECTED

proportional output signal is generated.

The advantages achieved with the invention are in particular that a photometer with the structure proposed here is extremely stable and has a very high sensitivity, so that extremely small quantities can be measured. The increased measurement sensitivity for extremely small changes in the extinction of a liquid sample can be obtained with a certain wavelength of interest. It also increases the sensitivity of the measurement of the rate of change in absorbance of a liquid sample over a short period of time, as required in kinetic measurements of the rate of reactions catalyzed by enzymes. Furthermore, the dynamic range of the extinction is broadened, in which a small change in the extinction can be measured $ only small volumes in the range of 100 microliters or less have to be used. Also, in the photometer according to the invention, no M dulation _o required, while nevertheless a sensitivity is achieved, which is better than an order of magnitude in conventional photometers. This device can measure changes in the extinction of liquid samples down to 5 x 10 "^ absorption or extinction units. These advantages are achieved through a very stable, optical system with an unmodulated double beam and an accurate electronic circuit.

Here, light from a source with a previously selected wavelength is formed into a beam, the beam space of which is defined will. The beam is then split into two separate beams, one of which passes through the sample cell onto one directing the first detector, the beam passing through the cell so as not to contact the walls of the cell; the two beams are imaged onto their respective detectors so that they are completely in their sensitive areas lie.

609811/066 5

7537494

In addition, the sample cell itself is in a cavity thermally insulated and kept at a predetermined temperature. Because of this thermal insulation the sample remains, which is preheated on its way through the photometer cell, and the cell during the entire process Measuring cycle at a constant temperature. The sample is heated by passing it through a metal block, whose temperature is regulated; the temperature is adjusted by means of a control system that includes a thermistor and includes a heat pump.

The detectors at the outputs of the photometer are silicon PIN diode detectors, their output signals as input signals given to parametric amplifiers. This combination surprisingly leads to a signal accuracy, which is far: above the accuracy that could be expected for the individual components. The output signals the parametric amplifiers are based on operational amplifiers with logarithmic elements in their Coupled feedback paths, wherein the logarithm of the respective output signals is formed. The two so created Logarithms v / ground are then subtracted in a further operational amplifier, so that finally an output signal arises, which is proportional to the extinction or the absorption capacity in the sample cell. the Accuracy can be further increased by at least the logarithmic amplifier in a thermostatic Enclosed housing, its temperature in a predetermined range of fluctuation around a desired Value is held.

The PIN diode detectors are therefore particularly well suited because the response sensitivity is relatively constant over its active area. Furthermore, their responsiveness depends does not depend significantly on the course of the lighting, i.e. they store the invaded ones Rays of light only to a very small extent; in addition, their responsiveness at any given temperature leads to

609811/066 5

ORIGINAL INSPECTOR

7537494

door to reproducible results. Such PIN diode detectors however, have an extremely small active area, so that an optical system is required as described here; With such a system, the light rays can be very sensitive to these. Areas to be aligned. By this combination of the optical part and the electronic part of the photometer, an extremely high accuracy, better sensitivity and good reproducibility can be achieved reach.

The invention thus creates a photometer that is in one Analyzer can be used to measure the absorbance or absorbance of a sample in a sample cell to eat; light from a light source comes with it previously selected wavelengths formed into a beam, des: en-'Strahlermum is defined; the beam is then split into two separate beams, one of which is through the sample cell is directed to a first detector while another beam is directed to a reference detector will; the first ray passes through the cell so that it does not touch the cell walls; the two rays are mapped onto their respective detectors so that they are completely in the sensitive area of the detectors lie.

This sensitive, stable two-beam system without a chopper is combined with a precise electronic Pühl circuit. The circuit includes PIN diode detectors which the two rays of the optical system are mapped. A ray is a reference ray that changes one of the light source detects and compensates for it, while the other is a signal beam passing through the sample cell runs. The output signals of the PIN diodes are grounded as Input signals given to parametric amplifiers. The output signals from the amplifiers are then sent to circuits which are used to calculate the logarithms of these two signals; thus the logarithms of the

609811/0665

formed both signals; then the difference between the two logarithms is determined, so that finally an output signal which is proportional to the absorbance in the cell.

The invention is illustrated below with the aid of exemplary embodiments explained in more detail with reference to the accompanying schematic drawings.

Show it:

Fig. 1 shows a representation of the opto-mechanical Part of the photometer according to the present invention ;

FIG. 2 shows in detail a cross section through the sample cell according to FIG. 1;

Figure 3 is a cross-section of the device used to control sample temperature can be;

Figure 4 is a block diagram of the detector and amplifier circuit of the present invention; and

5 is a block diagram of FIG Detector and amplifier circuit according to FIG. 4.

The sample cell is shown in FIG. 1 together with the optical elements of the photometer according to the present invention shown, which schematically shows the opto-mechanical construction. In the photometer according to the present invention Due to the use of certain, particularly zv / angular parts, an improved sensitivity and Stability achieved. At the beginning of the beam path, a light source is provided, the light with previously determined

609811/066 5

Wavelengths emitted. In the embodiment shown in FIG a HolSkathodenampe 271 ~ a, a manganese light source, and a hollow cathode lamp 271b, a cobalt light source, is used; the manganese light source is selected so that it emits light at about 4-04 nm, while which emits cobalt-like light at about 3ΨΟ nm. There If the emitted wavelengths are those of the atoms of the light source cathodes, these are the wavelengths extremely stable and reproducible, which contributes significantly to the stability of the photometer. In front of the light sources 271a Lenses 272a and 272b are provided, respectively, so that light rays are formed. A 404 nm filter 273 is in front of the lens 272a arranged. The two ray paths intersect at a point 275. At this point there is one about an axis rotatable mirror 277 arranged. Which of the light sources used depends on the experiment to be performed. Depending on the result of this selection, the mirror will be by an output signal from a parameter memory or an auxiliary setting panel in the solid lines position shown for light at 404 nm or the position shown with dashed lines for light at 340 nm rotated. In In connection therewith, a movable filter 281 is arranged so that it passes only a wave range which is the selected one Contains wavelength. The light beam with the selected wavelength is then planted along the optical axis towards a cell 71. Next essential Step is the radiation space (etendu geometrique), i.e. the extent, in particular the shape and cross section, of the Defined beam. This is essential in order to produce a beam of known and controlled light flow; as a result, it is still possible to move the beam into a signal beam path and split a reference beam path, each beam path also being a known one and controlled light flow. For the definition of the radiation space and for the generation of the ray it is essential that that the light source has an area of substantially uniform brightness; furthermore the picture must have this Area of uniform brightness so large

60 9 Ö 1 1/0665

that it has a larger area than the first aperture on which it is imaged; then the entire cross-section of the beam has the same, even brightness despite small mechanical movements of the source. The beam space ~ is defined by the use of a field stop S1 and an aperture stop S2, between which a lens 285 is arranged. Before the light beam strikes the apertures S1 and S2, it passes a shutter 284. The shutter is normally kept closed and only opened for a predetermined period of time during which the measurement is being carried out; the reasons for this are described below. The shutter is controlled by the output signal of a suitable timer. The beam with the beam space defined in this way is then directed onto a beam splitter, a coated beam splitter being expediently used; this ensures uniform irradiation in both beam paths. Beam splitter 287 is coated so that it transmits approximately 90 fo of the beam and reflects the remaining 10% of the beam. The two rays thus formed have a lower intensity than the original ray; However, both have a very uniform illuminance over their respective cross-sections. The portion of the beam that has passed through, that is, the portion which contains 90 % of the energy, enters the cell 71, where it first passes a lens 289. The lens 285 images the field stop S1 onto an area near the entrance of the cell, while the lens 289 images the stop S2 onto an area near the exit of the cell. These lenses are only mentioned as examples; of course, any other equivalent lens arrangement can also be used which images the diaphragms in this way. This mapping is intended to ensure that the light path is kept away from the sides of the cell; furthermore, the limits of the beam should be precisely defined, so that small mechanical movements of the parts

609811/0665
ORIGINAL INSPECTED

can happen without the rays affecting either the Walls of the cell or the edge areas of optical parts can hit. This will allow the light to flow through stable in the beam with respect to small mechanical or optical disturbances. Another lens 291 is on the Output end of the cell 71 is provided. This lens images the Blexle · S1 onto a condenser lens arrangement 500. the Condenser lenses shown as two lenses image the diaphragm S2 onto a detector 295. It is essential that these lenses have as large an angle of incidence as possible so that they can scatter as much light as possible can collect. Although the propagation of the beam through cell 71 is very precisely defined, that contained therein can Liquid scatter the jet to some extent; those with the photometer according to the present invention The improved results obtained are due, at least in part, to this ability to almost all of the scattered To collect light. It is also essential that the lenses 300 emit light very precisely within the limits of the active Image area of the detector 295, so that despite small mechanical movement of the optical parts, a movement of the beam cause almost all of the light energy emitted by the cell to be measured. That on the beam splitter Light reflected 287 is directed through a lens 297 and a pair of condenser lenses 298. The lens 297 images the field stop S1 onto the first lens and the stop S2 onto the second lens. The second lens forms the Imaging S1 on a second detector 299. It is again essential that the entire beam is within of the sensitive area of the detector 299 is imaged.

As can be seen from the following in detail, the output signal of the detector 299 »of a reference detector is used to filter out or compensate for all changes in the output signal resulting from variations from the output signal of _{the detector 295 5 of the signal detector}

609811/0665

of the light sources 271a and 271b result. All changes, which occur before the splitting of the beam 287 can be filtered out in this way * The signals from the detectors are amplified in amplifiers 296 and 294, respectively and then processed in a manner to be described below. The shutter 284 only operates during one Measurement cycle open I.e. when samples are entered or removed, the lock remains closed. This causes inaccuracies due to a response time effect of detectors 295 and 299 avoided. That means that the detectors simultaneously with the corresponding Real levels are applied. If the shutter were left open, the reference detector 299 would always acted upon by light, while the detector 295 would under certain circumstances only respond with a delay to a sample, entered in the cell. Under such circumstances errors could arise due to the difference in the course of the irradiation of the two detectors.

If the above measures are carried out very carefully, thus the ratio of the signals detected in the two beams becomes essentially only through a change influences the absorption capacity or extinction of the sample.

Despite all precautionary measures, small mechanical and optical disturbances occur; some of these disorders can cause the images to move or their size on the sensitive areas of the detectors change. It is therefore advantageous if the detectors have a uniform response sensitivity over their entire active area for light.

Furthermore, since ^f depends on the sensitivity of the detectors for light on its temperature, it is essential that the two detectors are kept at the same temperature, and that this temperature is maintained

6 0 9 8 11/0665
ORIGINAL! MSPECTED

the measurement does not change. A detailed illustration of the cell 71 is shown in FIG. The cell itself consists of silver, the region 901 in which the sample is located during the measurement being provided with a cutout as shown. The cell has an essentially cylindrical shape, with cutouts 903 being provided at the edges with which the cell rests in a plastic block, as will be described below. Two openings 904 and 905 are provided in the cell, through which the sample can be introduced or removed. A nipple 906 made of stainless steel is inserted into each of the openings 904 and 905. Silver is used as a material for the cell because of its high thermal conductivity. It is essential that the sample is kept at a certain temperature during the measurement. However, it is more important that the temperature does not change in the slightest during the measurement. It is sufficient if the temperature of the sample in the cell up to 0.2 ⁰ g of the desired temperature, 30 ⁰ C, passes. The temperature during the measurement interval, however, should no longer change than 0.01 ^0C. Fig. 3 shows an arrangement controlled by a thermostat to bring the sample to a desired temperature and to keep it at that temperature. A basic block 907 made of aluminum is provided, the temperature of which is regulated. This block contains a cylindrical passage 909 into which a stainless steel tube 911 is inserted. The upper end of the stainless steel tube 911 is connected to a flexible plastic conduit fitting to a nipple 906 which connects to the cell 7I. The cell itself rests on a V-shaped plastic block 913 which is attached to the top of the block 907. A cover 915, also made of aluminum, contains a recess 917 for the block 913> the cell 71 and the lines and is arranged over the block 907 and fixed in its position by means of bolts. In block 907 there is an incision

609811/0 6 65

into which a thermistor 921 is inserted. On the side of the block, under the thermistor, is a heat pump 923 attached, according to a preferred embodiment is a Peltier element such as Borg Warner Element No. 930-17. The thermistor 921 is on a control arrangement 925 is connected, the output signals for operating or controlling the heat pump 923. On the other side of the 923 heat pump is another Metal block 927 provided with a passage 929, through which water flows; this allows the heat to be dissipated from the heat pump when it is working in cooling mode. This structure is surrounded by an insulation 931, e.g. made of plastic scKaim. The heat pump 923 controls the temperature of the aluminum block 907 to the desired value. This leads to, that the space in the recess 917 is approximately the desired That is, close enough to that value to allow accurate results. As mentioned above, however, the sample must not change its temperature during the measurement. This is done through the use of the silver cell and their isolation by the V-shaped plastic block 913 ensured. The high thermal conductivity of silver causes it to reach the equilibrium temperature very quickly achieved with the sample. The heat pump changes the temperature of the aluminum block proportionally in addition, in a small amount, i.e. when the temperature of the block drops slightly, the heat pump increases its heat flow, to increase the temperature. The temperature changes only in a narrow range; this little change is enough however, from influencing the measurement if it is noticeable on the cell. Installation of the V-shaped plastic blocks 913, which is a good insulator, prevents that these small changes in block 907 reach and act on the sample in cell 91, i.e. it acts as a heat filter. The detectors, which are also located in the recess, are also grounded on an im kept substantially constant temperature.

A schematic diagram of the arrangement of detectors and

6 09811/0685

Preamplifiers for the photometer are shown in Fig. 4-. In addition to the amplifier stages 300 and 296, the detectors 299 and 295 are used. The amplifiers output signals are supplied from the measuring points, which are designated with Eref and E sig. These Output signals are also given to a logarithmic circuit, the individual logarithmic circuits are designated by 301 and 303. The circuit 301 calculates the logarithm of the reference signal and the circuit 303 is the logarithm of the signal. These two logarithmic signals are also used as output signals too Out of measuring points, which are designated with L ref and L sig. The absorption capacity is derived from these two values or the absorbance is calculated by adding in an analog subtracter 305 the logarithm of the reference signal is subtracted from the logarithm of the signal energy. That Output signal then occurs on line 306.

The structure of this circuit arrangement is shown in detail in FIG. The detectors 295 and 299, at which the measurement signals are generated, provide input signals to the amplifiers 294 and 296, respectively. The detectors are silicon PIN photodiodes, such as those manufactured by Motorola under the designation MDR 510. These detectors have a sensitive area with a uniform response sensitivity, do not depend particularly on the previous course of the irradiation and provide reproducible results at a certain temperature. Each of the amplifiers 29 and 296 has a parametric amplifier 4-01 with negative feedback through a feedback resistor 4-03. A feedback capacitor 4-05 is provided in parallel with the feedback resistor. Typical values for the resistors 4-03 are lOOOMOhm rstärker for the V _e 296 and 3000 megohms for the amplifier 4-01. Capacitor 4-05 can have a capacitance of 5 picofarads. Each of the amplifiers is supplied with positive and negative supply voltages, which are generally at +15 volts. Between the positive and negative supply voltages and earth are

609811/0665

Decoupling capacitors 407 are provided. These capacitors have a capacitance of 6.8 microfarads. Every amplifier an adjustment or tuning potentiometer 409 is also assigned, its sliding contact with the input a corresponding amplifier is coupled. The adjustment potentiometers are between the positive and negative supply voltage, as can be seen in FIG. The amplifier manufactured by Analog Devices can be used as an amplifier Type 301 J can be used.

The output signals of the amplifiers 296 and 300 are applied to the corresponding measuring points via resistors 411. Furthermore, they are also fed to the logarithmic circuits 301 and 303 via resistors 413. Every One of the logarithmic circuits includes an operational amplifier 413 whose non-inverted input is grounded while the input signal is applied to the inverting input. With these amplifiers it can be expediently around the LM3O8AH amplifier from National Acting semi-conductor. The input resistances between amplifiers 300 and 296 and the logarithmic steps, that is, the input resistors 413 can have a resistance of 100 kOhms. By means of appropriate feedback circuits a logarithmic function is obtained. Thereby the output signal of each amplifier initially fed back through a capacitor 415 to its inverting input. After pairing through a resistor 417, the output signal is also grounded through a transistor 419 whose base and fed back through a diode 421 connected in parallel with the transistor. Typical components are 2N4023 transistors, each half of which has a 75 pico-Farad capacity. The resistors 417 can have a resistance value of 5 kOhm. The signals generated at the n outputs of the logarithmic circuits are transmitted via

609811/066 5

Resistors 413 led to measuring points. The two output signals are also matched by a pair of Resistors 425 are given to a summing amplifier 305. The output from the logarithmic circuit 303 is fed to the non-inverting input, while the reference signal from the logarithmic circuit 301 is fed to the inverting input. The amplifier 305 can be a Precision Monolithic 725C amplifier be. In the feedback path of amplifier 305 is a Resistor 427 is provided to a corresponding division or to enable change of area. Finally, appropriate compensation circuits with a Resistor 429, a capacitor 431, a capacitor 432 and a resistor 433 are used. The output signal of the subtracter is removed via a resistor 435, so that on the line 306 the above-mentioned Output signal occurs. A second output signal, the can be used in a measuring device if necessary, is picked up via a second resistor 435. The resistance 427 can have a resistance of 49.9 kOhm, while resistor 435 has a resistance of 47 ohm should have.

609811/0 0 65

Claims (12)

1. Photometer with high stability and sensitivity, It is characterized by a stable, sensitive optical system with two beams and without a chopper, the first beam passing through the sample in a cell (71), while the second beam serves as a reference beam through a first and second PIN diode detector (295i 299) j on which the first and second beams are imaged and which generate output signals proportional to the incident light flux, through a first and second parametric amplifier (401), the inputs of which are each connected to the. Outputs of the first and second detectors (295-299) are coupled, and by an arrangement receiving the output signals of the first and second parametric amplifier (401) as input signals in order to calculate the logarithms of the output signals and to form the difference between the logarithms, so that an output signal proportional to the absorbance in the cell (7Ό is generated. 2. Photometer according to claim 1, characterized in that the arrangement includes a first logarithm calculating circuit (301) which receives the output signal of the first parametric Amplifier (401) receives as an input signal, a second, the logarithm calculating circuit (303), the the output of the second parametric amplifier (401) receives as an input signal, and a device (3o5) for forming the difference between the output signals of the first and second logarithm calculating circuits. 3. Photometer according to claim 2, characterized in that each of the circuits calculating the logarithm (301, 303) an operational amplifier (41-3) with a logarithmic Has feedback. 4. Photometer according to one of claims 2 or 3, characterized in that that the device for forming the difference comprises a summing amplifier (305). 609811/0665 5. Photometer according to one of claims 1 to 4-, characterized through an optical system with a light source (271a, 271b), the light with a predetermined wavelength emitted, with an arrangement (272a, 272b) for generating a light beam from the light from the source (271a, 271b), with an arrangement for defining the radiation raid - "- ' with a field diaphragm (S1) and an aperture diaphragm (S2), with one splitting the beam into first and two beams Beam splitter (287) while maintaining uniformity of illuminance across both beams, the first beam passing through the cell (71) with a field stop (S1) near the entrance of the cell (71) and the aperture stop (S2) in the vicinity of the exit of the cell (71) in such a way that the imaging element (285) the first beam does not touch its sides when passing through the cell (71), with a first detector (295) »with one a complete image of the aperture diaphragm (S2) on the sensitive area of the first detector (295) generating element (300), with a second, the second beam receiving detector (299) * and with a one Complete imaging of the field diaphragm (S1) and the aperture diaphragm (S2) on the sensitive area of the second detector (299) generating element. 6. Photometer according to one of claims 1 to 5 »marked by a filter (281) arranged in the beam path of the light from the source (271a, 271b), which has only one selected wavelength range. 7. Photometer according to one of claims 1 to 6, characterized in that that the first and second PIN photodiodes (295, 299) have MDR 510 diodes. 8. Photometer according to one of claims 1 to 7 _5, characterized in that the parametric amplifiers (401) each have 301 J amplifiers. 9. Photometer according to one of claims 1 to 8, characterized 609811/0665 characterized in that the logarithmic circuits (301, 303) "can be kept at an approximately constant, predetermined temperature. 10. Photometer according to one of claims 1 to 9 »thereby characterized in that a closed space is provided, the temperature of which is controlled and the at least the amplifiers and the logarithmic feedback circuits (301, 303) encloses. 11. Photometer according to one of claims 1 to 10, characterized characterized in that it is used to measure the absorbance of a reaction mixture which is in the sample cell (71) is that an optical element (300) is provided with a large angle, around the largest possible To capture part of the light scattered by the contents of the cell, and that the output signal of the second detector (299) serves to compensate for fluctuations, which result from the changing brightness of the light beam with before result of a certain wavelength which falls on the first detector (295) and generates an output signal. 12. Photometer according to claim 11, characterized in that that the brightness of the light beam changes due to the fluctuations of the light source (271a, 271b) .. 13- photometer according to one of claims 1 to 12, characterized characterized in that when operating with two different wavelengths one more, light with another Wavelength-emitting light source, a movable mirror to reflect the light from one of the two light sources to direct the sample cell (71), a second filter which transmits light with the other wavelength range, and a device are provided to selectively arrange one or the other filter in the beam path. 14, photometer according to one of claims 1 to 131 by an arrangement to the sample cell (71) 6 0 9 8 11/0685 at a predetermined temperature, and by a device to put a sample on this. Temperature too before it is introduced into the sample cell (71). 609811/0 6 65
ORIGINAL INSPECTED Blank page