DE4215165A1 - Miniaturised raster scanning light source, e.g. for spectral photometer - sequentially activates two or more different sources in UV to IR region by electrical switching - Google Patents

Abstract

The raster scanning light source (1) includes at least two different optoelectronic or optical, line- or bandpass-monochromatic sources (2) operating in the ultraviolet, visible or infrared region. The light sources are sequentially activated by electrical switching in a defined time sequence and for defined durations. There is a device which focusses the light from the individual sources into a common beam path. USE/ADVANTAGE - For chemical analysis. Enables spectral information to be produced without a monochromator.

Description

The present invention relates to a raster scanning light source according to An claim 1, their use in a spectrophotometer according to claim 8, and the use of the spectrophotometer in a test kit according to An Proverb 11

Optical spectroscopic measurement methods have one in chemical analysis very important. Commercial analyzers for the ultraviolet th (UV), visible (VIS) and infrared (IR) spectral range are both used for routine determinations as well as in trace analysis (for For an overview, see e.g. B. Message Chem.Tech.Lab. 37 (1989) special issue). Regarding the Categorizing the different spectrophotometers plays the question of whether the Samples of polychromatic, bandpass monochromatic or monochro matical light, play an essential role. According to these criteria The design of the light source part and the arrangement of the mono are determined chromators. The use is with all continuously scanning spectrophotometers of a monochromator is absolutely necessary, with its installation alternatively before or behind the sample is required. According to the current state of the art essentially between two basic types of optical spectrophotometers to distinguish, which are also fundamentally different in the construction of the light source part differentiate:

• - Diode array spectrometer:
  With this type of spectrometer, the light from a polychromatic source shines through the sample. Behind the sample is the monochromator, which displays the light dispersively on a photodiode array. The array and monochromator determine the wavelength resolution.

Basic disadvantages of the diode array spectrometer are:

• - The calibration of the devices is difficult because of the drift phenomena the individual diodes of the array, especially with regard to their small Temperature stability. These disadvantages can only be overcome with one size evaluation software and with frequent reference measurements to reduce,
• - The sensitivity of detection is due to the small Emp Front surfaces of the photodiodes of the array compared to conventional ones Grid spectrometers with a sensitive photomultiplier detector (PMD) much lower,
• - by polychromatic irradiation on the sample with the trigger of photoreactions and the associated changes in the con concentrations in the analyte.
• - grating spectrophotometer:
  In these devices, the monochromator is usually located in front of the sample so that monochromatic irradiation takes place on the sample. The light source part and monochromator must be of high quality and have the correct optical imaging geometry.

Disadvantages of the grating spectrometer are:

• - slow scanning due to mechanically moving parts
• - elaborate precision optics and precision mechanics
• - Large construction due to the device type
• - The detectors have to be optically and electronically complex be.

Simple designs of spectrophotometers are basically the grating spectrophotometer related.  

Single-channel photometer arrangements with light-emitting diodes (LED) and photodiodes, as described in connection with an optical biosensor in the literature (see: Lowe C.R., Goldfinch M.J., Biochem. Soc. Trans. 11, 448, 1983), are bound to a predetermined wavelength range. Such orders accordingly do not provide any spectral information. So that is the Informati ons content extremely small, so that for example drift phenomena and disturbances cannot be recognized.

The above statements on the prior art make it clear that the be only knew spectrophotometric analyzers then spectral Provide information when a monochromator, and associated optical Precision components are involved. As a result, these spectrophotometers are on maneuverable large-scale analysis devices, which are mainly for the laboratory, but not for Field trials (e.g. in environmental analysis) are suitable. They also require in usually trained operating personnel, so that both the purchase and the operation are expensive. Because the known devices due to the indispensable Monochromator (including optical precision components) is not sufficient can be miniaturized, are used for monitoring tasks (inline process control, Sensors, etc.) for signal coupling and decoupling additional complex fiber optics techniques needed.

It is therefore an object of the present invention, a novel and miniaturi to provide a light source that can be used - in a spectrophotometer or sensor used - it allows spectral information without a monochromator to obtain.  

This object is achieved by the features of claim 1, 7 or 10.

Advantageous developments of the invention result from the subclaims chen.

Investigations of the information content of a color screened spectralpho tometry compared to normal scanning devices have surpassed shendingly shown that the use of the raster scanning according to the invention Light source in a spectrophotometer with only one detector, but without Monochromator (raster scanning spectrophotometer), simple and inexpensive In addition to quantitative analysis results, it is also a good idea to use qualitative nisse about the nature of the ingredients. This information he to recognize specific spectral patterns and the composition or assign the concentration ratios in the analyte.

With the aid of the raster scanning light source according to the invention, quantita tive and qualitative optical investigations of gaseous, liquid and supercritical fluid media in the UV / VIS and near IR range will. By sequential electrical switching of the individual color channel beam and by using different colored LEDs or other optical or optoelectronic sources, such as laser diodes, Kleinla or miniaturizable quartz halogen lamps with pre-filters that line up bandpass monochromatic characteristics are the prerequisite conditions for a raster scan in the light source part. The duration of the light Source activation can affect the respective measurement problem and the light source cha characteristics can be adjusted. As a rule, the time is less than 1 second sufficient for each channel.  

By bundling into a beam path through, for example, a mirror or Optical fiber optics ensure that in a spectrophotometer or sensor when passing through the sample space during the wavelength raster scan the same sample volume is always irradiated in the analyte. The detection is easily done with a single photodetector, such as egg ner photodiode or a photovoltaic detector realized. With the help of Measured spectral information can be used in addition to quantitative determinations determine the composition of the analyte, or can give it if necessary, overlapping interferences are recognized.

Compared to spectral photometers according to the prior art, a spectral shows a series of photometers with the raster scanning light source according to the invention of advantages:

• - robust construction,
• - no monochromator and only one detector required,
• - No mechanically moving components and no polychromatic radiation on the sample to be analyzed,
• - relatively fast spectral analysis in seconds thanks to sequential raster scan Area,
• - easy and quick access to meaningful spectral patterns,
• - Avoidance of photoreactions by having appropriate color channels selectively selected in a simple manner or not ak in the raster scan be activated. Avoiding complex additional filters,
• - modular design,
• - higher quantitative detection sensitivity due to the larger radiation cross section and above all due to the larger detector area than the usual diode array spectrometers,  
• - Wide range of applications for tests in the laboratory, for process transfer monitoring and for the field of environmental analysis,
• - Suitability for reaction kinetic measurements due to the short scan times in the Comparison to the grating spectrophotometers,
• - Easy adaptation to special analysis problems due to the possibility of Adjustment of the wavelength and sensitivity range of the photodetector and due to the use of various inexpensive light sources,
• - Possibility of miniaturizing the grid according to the invention Scanning spectrophotometers (including miniaturized raster scanning Light source) for monitoring tasks such as inline process control and Senso rik, thereby access to miniaturized single-rod sensor arrangements with the Construction and measurement principle of the raster scanning spectrophotometer; to this Wise avoidance of reflection mirrors, such as those found in expensive fiber optic systems orders with Y light guides are required (see e.g. Camman K. et al., Appl. Chem. 103 (1991), 536),
• - suitable for field trials (e.g. in environmental analysis),
• - Can be used by laypeople, therefore also applicable in the form of a test kit,
• - The informative value of measurements with the raster scanning spectrophotometer can be expanded in connection with methods of an AI software. There through is a learnable, meaningful and yet fault-tolerant pattern Recognition accessible.

In comparison to conventional spectrophotometers, another is ent decisive advantage of a raster scanning spectrophotometer, thanks to the raster Scanning light source, which is much cheaper to implement. Leave it very good results compared to expensive devices with a fraction achieve effort and cost.

Further advantages and features of the present invention result from the following description and with reference to the drawing.

Show it:

Fig. 1 shows a schematic view of a particular embodiment of the erfindungsge MAESSEN raster scanning light source,

Fig. 2 shows a schematic view of a particular embodiment of the erfindungsge MAESSEN raster scanning spectrophotometer

Fig. 3a-c, 4 u. 5 explanatory illustrations of the examples.

Fig. 1 shows an advantageous embodiment of a raster scanning light source 1. Here, the color channels can be brought together in a circular arrangement via concentrically arranged, slightly angled light guides 3 , which can be made of glass for the visible area. The number of light guides used is preferably up to four, but more can also be used. The optional installation of a converging lens 5 results in a significant improvement in the luminous efficacy, especially with a greater layer depth.

A variety of optoelectronic or optical components can be used as sources, such as light-emitting diodes (LEDs) 2 (e.g. fastened with plastic holders 4 ), laser diodes, small lasers, miniaturizable micro-halogen lamps with auxiliary filters, etc. The Individual color channels are switched on sequentially by an electronic control unit, for example via reed relays or semiconductor switches, and switched off again immediately after stabilization and measurement. To achieve a constant light intensity, the LEDs and light sources are supplied with simple adjustable current stabilizers if necessary.

Fig. 2 shows a preferred embodiment of a raster scanning spectrophotometer 8 using a raster scanning light source 1 according to the invention.

The spectrophotometer 8 consists of 4 modules:

• - The light source part, in the form of the raster scanning light source 1 according to the invention
• - the cuvette part 6
• - The detector part 7
• - the control and evaluation electronics.

The construction of the cuvette part 6 depends on the given analytical task. For example, 10 mm standard / semi-micro cells or cylindrical flow cells made of plastic or stainless steel can be used.

The detector part 7 consists of only a single photodetector 9 . Si photodiodes can be used for a wide spectral range. In addition, there is the possibility of restricting the spectral range of the detector with filter windows, for example to block out unwanted IR radiation. There is a large selection of commercially available components from the consumer or professional optoelectronics market. A particularly compact design enables the integration of a preamplifier on the Si photodetector, which can be implemented using SMD hybrid technology. This allows a significantly better signal-to-noise ratio to be achieved. With very small signal levels, the temperature drift of the photodiode can have a significant effect. An improvement brings a simple way of thermostatting the detector and cuvette unit. Measurements of the temperature dependence of the open circuit voltage of the photodiode have shown that the dependency can be linearized in the usual temperature range from 20 to 28 ° C. Measuring the temperature with a semiconductor resistance sensor enables analog-electronic or computer-aided correction of the photodiode signal.

The light source part, the cuvette part and the detector part are in one light sealed housing.

The main components of the control and evaluation electronics are:

• - signal amplifier,
• - A / D converter with interface,
• - evaluation computer,
• - control electronics (sequence programming, light channel control),
• - Power supplies and constants.

Alternatively, all functions can be carried out on an electronic unit with an integrated downloadable microprocessor.  

The following application examples are intended to illustrate the invention further.

Example 1: Specific spectral patterns of different analytes

• a) Chrome alum solutions:
  0.005 mol KCr (SO ₄ ) ₂ [2.497 g KCr (SO ₄ ) ₂ .12H ₂ O] are weighed into 1000 ml water. A reference measurement of the open circuit voltage (EMF) of the photodiode is carried out for the four color channels red, yellow, green and blue in the cuvette filled with approx.2.5 ml of water. The cuvette is then filled with the same amount of chrome alum solution. The open-circuit voltage values obtained for the analyte by the raster scanning spectrophotometer are subtracted from the respective reference value. In Fig. 3a, these are related to the value of the red color channel intensity values of the individual color channels in a histogram. Since the course of the intensity / concentration curves for chrome alum is approximately linear in the range from 0.001 to 0.1 mol / l, the histogram represents a spectral pattern for chrome alum that is independent of the concentration for this area.
• b) Potassium dichromate solutions:
  2 mg K ₂ Cr ₂ O₇ are dissolved in 1000 ml water and a measurement is carried out accordingly 1a). For the range up to about 3 mg / l, the course of the intensity / concentration curves for potassium dichromate is approximately linear, so that a spectral pattern that is concentration-independent for the specified range is also obtained here (see FIG. 3b).
• c) Nitrite test:
  For the nitrite detection according to Griess (Griess P., reports, 12, 426-428, 1879), for example, the test reagent set Spektroquant® No. 14 776 nitrite from E. Merck, Darmstadt can be used. The set of reagents contains, among other things, a precise procedure and additional references. 1 mg NaNO ₂ who dissolved the in 1000 ml of water. An aliquot of the solution is mixed with the reagent mixture according to the instructions using the dosing spoon included in the reagent set and measured in the raster scanning spectrophotometer after the prescribed waiting time analogously to example 1a). Since the signal / concentration curve in this detection is approximately linear in the range up to 1.5 mg / l nitrite, the histogram FIG. 3c represents a spectral pattern independent of the concentration of nitrite for the azo dye obtained in proportion to the amount of nitrite.

The resulting substance-specific raster spectral information corresponds to Aus cut from the entire continuous spectrum of the respective substances.

Example 2: Quantitative determination of nitrite

A stock solution of 3.1 mg NaNO ₂ in 1000 ml water is diluted volumetrically in aliquot parts. An analysis according to Example 1c) is carried out with the respective test solutions. A signal / concentration relationship according to FIG. 4 is obtained.

The relationship is almost linear in the lower concentration range. For higher concentration ranges or the more accurate reproduction of the combination the deviation must be taken into account.  

Example 3: Detection of interference

In an approach according to Example 1c) or 2), as much NaOH is added give that the buffer capacity of the acid buffer present in the test reagent (pH ≈ 2.3) is exhausted and a pH-related color change of the azo dye occurs.

In Fig. 5, the resulting interferences - characterized by the steepness (mV · l / mg) of the relationship between signal voltage and concentration of nitrite - are shown in the form of a histogram for four different pH values. It can be clearly seen that the intensity of the blue color channel remains almost constant with increasing pH. In contrast, the corresponding dependencies for the green and yellow color channels show a clear pH influence. The pH-related change in intensity at the same nitrite concentration would simulate a decrease in the concentration. The interference can only be recognized by the additional spectral information using the blue color channel.

The detection of such interference is much easier if the concentration-dependent measurement data of the raster scanning spectrophotometer processed with a neural back propagation network. in the If necessary, a successful modeler can be found after just 300 learning steps perform identification that influences the pH of 3.0 in the analyte compared to the target value of 2.3.

Claims (13)

1. raster scanning light source ( 1 ) comprising:

• - At least two different optoelectronic or optical, line to bandpass monochromatic sources from the ultraviolet, visible or near infrared wavelength range, which are activated sequentially by electrical switching in a predetermined time sequence and duration, and
• - A device for bundling the light of the individual sources in a common beam path.

2. Raster scanning light source ( 1 ) according to claim 1, characterized in that at least one of the sources is a light emitting diode ( 2 ). 3. raster scanning light source ( 1 ) according to claim 1 or 2, characterized in that at least one of the sources is a laser diode, a small laser or a quartz-halogen lamp with a front filter. 4. raster scanning light source ( 1 ) according to at least one of claims 1 to 3, characterized in that the device for focusing the light contains slightly angled concentrically arranged light guide ( 3 ). 5. raster scanning light source ( 1 ) according to claim 4, characterized in that the number of light guides ( 3 ) is four. 6. raster scanning light source ( 1 ) according to at least one of claims 1 to 5, characterized in that the device for focusing the light includes a converging lens ( 5 ). 7. raster scanning light source ( 1 ) according to at least one of claims 1 to 6, characterized in that it is designed in a miniaturized form. 8. Use of the raster scanning light source ( 1 ) according to at least one of the preceding claims in a spectrophotometer ( 8 ) for quantitative and qualitative optical investigations of gaseous, liquid and critical fluid media, the ( 8 ) the raster scanning light source ( 1 ), a cuvette part ( 6 ), a detection part ( 7 ) with only one detector ( 9 ), but does not contain a mo-chromator. 9. Spectrophotometer ( 8 ) according to claim 8, characterized in that it ( 8 ) is designed in the form of a miniaturized single-rod arrangement as an active sensor or transducer in a sensor. 10. Spectrophotometer ( 8 ) according to claim 8 or 9, characterized in that it ( 8 ) is constructed in a modular design. 11. Test kit, comprising the spectrophotometer ( 8 ) according to at least one of claims 8 to 10 for the qualitative and quantitative detection of contents in an analyte with simultaneous detection of interference. 12. Test kit according to claim 11, characterized in that the interference factors pH Changes are. 13. Test kit according to claim 11 and 12, characterized in that the ingredient Nitrite is, which is detected using the Griess reaction.