DE3007453A1 - SPECTRAL PHOTOMETER FOR DOUBLE-WAVELENGTH SPECTROPHOMETRY - Google Patents

Description

PATENTANWÄLTE DipL-Phys. JÜRGEN WEISSE · DipL-Chem. Dr. RUDOLF WOLGAST

BÖKENBUSCH41 D 5620 VELBERT U-LANGENBERG P.O. Box 110386 ■ Telephone: (02127) 4019 · Telex: 8516895

Patent application

Bodenseewerk Perkin-Elmer & Co. GmbH, D-7770 Überlingen / Bodensi Spectrophotometer for the double wavelength spectrophotometr

The invention relates to a spectrophotometer for double wavelength spectrophotometry, comprising: 15th

(a) a light source

(b) an optical system for generating a measuring beam emanating from the light source,

(c) a monochromator, onto whose entrance slit the measuring light beam is directed, with a wavelength drive for scanning a wavelength range,

(d) Means for passing the measuring light beam through a sample and

(e) a detector separated from that by monochromator and

Sample exposed through the measuring light beam is.

Such spectrophotometers are used to determine a searched component in a sample from the height of an absorption characteristic for the component ^{o =>} bande.

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Normally, in conventional spectrophotometry, the total absorption of the sample at a Wavelength measured by comparison with a reference sample. These are common two-beam spectrophotometers a measuring light beam and a reference light beam are provided, one of which is through the to be examined Sample and the other is passed through the reference sample to a common detector, the both light bundles by a chopper arrangement

"IO take effect alternately. With this usual Spectrophotometry can cause errors due to differences in the beam paths of the two light bundles, e.g. as a result of different cuvettes or different arrangements of the cuvettes occur. There is also one Determination of the required component is no longer possible if the sample solution has a different background contains, caused for example by turbidity or mutually influencing components will.

In double wavelength spectrophotometry, light at two wavelengths is alternately passed through one to be examined Sample passed through. The one wavelength of the absorption band corresponds to the one sought Substance, while the other wavelength lies outside this absorption band and a reference signal supplies.

The second wavelength is preferably chosen so that the absorption value is at this wavelength the pure interfering component is exactly as large as with the first wavelength. It can then be the component you are looking for from the absorption spectrum of the unknown sample simply can be determined from the difference in absorption at the first and second wavelength. There are none Wavelength at which the interfering component is exactly the same

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absorbed as at the first wavelength, then becomes for a suitably selected second wavelength, a factor K corresponding to the ratio of the absorption values the spurious component at the first wavelength and the second wavelength determined. When examining an unknown sample, it will be at the first wavelength measured absorption with: der-multiplied by the factor at which. second wavelength measured Corrected absorption.

'■'

. This determination of the sought; Component is known with a conventional spectrophotometer by evaluating the recorded spectra of the pure searched component, the pure interfering component and a unknown sample carried out. The spectra of the two pure components are recorded. It will from the spectrum of the component sought, the first wavelength selected as the measurement wavelength, the one Corresponds to a maximum of an absorption band. The spectrum of the interfering component becomes the second wavelength defined as a wavelength lying outside the absorption band, at which, the interfering component in absorbed in the same way as at the predetermined first wavelength. It will eventually be that Record the spectrum of the unknown sample and the difference in ordinate values for the first and the second wavelength measured.

This procedure is cumbersome and time consuming.

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It is also a spectrophotometer for the dual wavelength Spektrophotbmetrie known (Shozo Shibata "dual wavelength Spektrömetrie" in "Angewandte Chemie" 88 (1976), pages 750-757) in ^OJ which the of a continuous spectrum light source emitting outgoing light in two

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Beam is split. The two bundles of rays are each directed to a grating monochromator. One grating monochromator delivers a light beam with the first wavelength, and the second grating monochromator supplies a light beam with the second wavelength. The two Light bundle in the sequence "first light bundle, zero signal, second light bundle, zero signal" through a sample cuvette directed to a photomultiplier. 10

A similar arrangement is described in the company publication "Double-Wavelength Double-Beam Spectrophotometer-Hitachi Model 557 "from The Perkin-Elmer Corporation, Norwalk.

This spectrophotometer facilitates the evaluation. However, it is very complex and requires two grating monochromators. It is also important that the user opts for automated double-wavelength spectrophotometry requires a specially set up spectrophotometer and cannot use existing equipment.

The invention is based on the task of automating double-wavelength spectrophotometry with the least possible outlay to enable. 25th

According to the invention, a spectrophotometer is provided to achieve this object, which is characterized by

(f) means for specifying two wavelength values,

(g) storage means for storing signals from the detector,

(h) Activation means from the wavelength drive are controlled, for switching on the two predetermined wavelength values from the detector signals supplied to the storage means and

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(i) Means for forming a linear combination of the two stored signals.

A method of determining the concentration of a component of a sample by dual wavelength spectrophotometry from the height of an absorption band of the absorption spectrum in the presence of one in the range this absorption band also absorbing interference component using such a spectrophotometer is characterized by the following procedural requirements:

(a) Specification of a first wavelength at which the absorption band to be measured of the component sought the sample lies

(b) specification of a second wavelength outside this absorption band,

(c) Determination of the ratio of the absorption values for the pure interfering component in the first Wavelength and the second wavelength,

(d) Adjustment of the monochromator by means of the shaft length drive on the first wavelength,

(e) switching on the at the first wavelength on Detector received signal on the storage means

to store this signal, 30

(f) Adjusting the monochromator by means of the wavelength drive on the second wavelength,

(g) applying the signal obtained at the second wavelength to the storage means for storing it Signals,

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(h) linearly combining the stored signals by means of of the linear combination-forming means with opposite signs, the second being Wavelength obtained signal is multiplied by the said ratio.

Further refinements of the invention are the subject matter of subclaims 2 to 4, 6 and 7.

An embodiment of the invention is as follows explained in more detail with reference to the accompanying drawings:

Fig. 1 shows schematically absorption spectra and illustrates the principle of double

wavelength spectrophotometry,

Fig. 2 is a block diagram of a spectrophotometer;
20th

Fig. 3 shows schematically the linear combination forming means in the spectrophotometer of Fig. 2.

In Fig. 1, 10 denotes a UV absorption spectrum of an unknown sample. From the height of for a sought component characteristic absorption band, the concentration of the component is to be determined. However, the sample also contains a second component, which also absorbs in the same wavelength range as the component sought and which is therefore referred to as the "interfering component". In Fig. 1, 12 is the Absorption band of the component sought and denoted by 14 the spectrum of the interfering component. It will first determine the wavelength with a known concentration of a pure solution of the component sought, at which the absorption band 10 has its maximum,

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unless this wavelength is already known. It then becomes the spectrum 14 of the pure interference component recorded and determined the wavelength λ outside the absorption band 12 at which the interference component absorbed just as strongly as at the wavelength λ · From the spectrum 10 of the unknown sample can then be the height of the absorption band caused by the searched component as the difference between the Ordinates of the spectrum 10 at the wavelengths λ

and λ can be determined.

If there is no wavelength outside the absorption band of the component sought at which the interfering component absorbed just as strongly as in the case of the wavelength λ, λ is suitably chosen so that it is outside the absorption band of the component being sought lies and the sturgeon component is noticeably absorbed there. It becomes a factor from the spectrum of the interfering component

Ordinate value at λ

K = £

Ordinate value at λ

educated. The spectrum of the unknown sample is then evaluated so that the ordinate is corrected to the multiplied with the _"ς factor K value of the ordinate at. So it becomes the linear combination

A (X _m ) - KA ( X _x )

formed when A ( X ) represents the course of the absorption spectrum.

The spectrophotometer includes a light source 16 (Fig. 2) and an optical system 18 for generating a measuring light beam 20 emanating from light source 16. The measuring light bundle 20 is directed onto the entry slit of a monochromator 22. The monochromator 22 has in the usual way a wavelength drive 24 for

130 036/0405

• Scanning a range of wavelengths. They are means provided for guiding the measuring light beam through a sample 26. A detector 28 is through from that Monochromator 22 and sample 26 passed through measuring light beam 20 acted upon.

This is the usual structure of a spectrophotometer and is therefore not described in detail.

The spectrophotometer contains means 30 for specifying two wavelength values. They are storage means for storing signals from the detector 28 as well as switching means 34 for switching on the two signals supplied by the detector 28 to the storage means 32 are provided for predetermined wavelength values. In the illustration of FIG. 2, the switching means 34 are symbolized as two switches 36 and 38, which are closed by the wavelength drive 24 at one of the predetermined wavelengths, such as is indicated by the dashed lines 40 and 42.

Means 44 are also provided for forming a linear combination of the two stored signals.

in the case shown in Fig. 1, where the spurious component absorbed just as strongly at λ as at λ, the linear-combining means 44 can simply be differentiating means, i.e. in the case of analog signals about a differential amplifier. If the aforementioned

Condition is not fulfilled, the linearly combining means can be constructed according to the type of Fig. 3: Difference forming means 46, which are shown in Fig. 3 as differential amplifiers, receive the one stored Signal A (λ) directly at an input. That

^m

other stored signal A (X _r ) is applied to multiplying means 48 together with a factor K. The output of the multiplying means 48 is applied to the other

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Entrance of the differentiating means 46. At the exit 50 the difference-forming means 46 then appears the linear combination

A (x _m ) - KA (λ _Γ ).

The factor K can be determined automatically.

For this purpose, quotient-forming means 52 are provided, to which the signals stored in the storage means 32 can be switched to form a Ratio signal, which is the ratio of the signals from the detector 28 at the first and the second wavelength, i.e. represents λ and λ. There are means 54 for Storing this ratio signal and means 56 for applying the stored ratio signal as Factor K is provided on the multiplier 48.

A method of determining the concentration of a Part of a sample by double wavelength spectrophotometry from the height of an absorption band of the absorption spectrum in the presence of one in the range this absorption band also absorbing sturgeon component using the above-described Spectrophotometer is characterized by the following process steps:

A first wavelength X _{m is} specified by means 30, at which the absorption band 12 to be measured

^{UU of} the sought component of the sample 26 is located. Furthermore, a second wavelength X is selected outside of this absorption band 12, and the ratio K of the absorption values for the pure interference component at the first wavelength λ and the second wavelength is used

λ is determined. If possible, as in Fig. 1, the second wavelength λ is chosen so that this ratio is one, i.e. the absorption values are the same.

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The monochromator 22 is by means of the wavelength drive 24 adjusted to the first wavelength λ. That obtained at the detector 28 at the first wavelength λ The signal is switched to the storage means 32 by the switching means 34 for storing this signal. The monochromator 22 is then set to the second wavelength by means of the wavelength drive 24

X "set. The one obtained at the second wavelength λ The signal is switched to the storage means for storing this signal by the switching means 34.

The order in which the first and second wavelengths are approached and the signals are switched on can of course also be the other way around.

The determination of the ratio K of the absorption values in the first and second well comprises the following process steps:

at the first and second wavelengths λ and λ

A solution with a pure stork component is used as a sample inserted into the spectrophotometer. The monochromator 22 is by means of the wavelength drive 24 on the first wavelength λ set. The signal of the detector 28 obtained at the first wavelength λ is stored in memory 32. Then the monochromator 22 is adjusted to the second by means of the wavelength drive Wavelength λ adjusted. The signal of the detector 28 obtained at the second wavelength λ is detected.

A ratio signal is formed by the quotient-forming means 52 which represents the ratio of the signals obtained at the two wavelengths λ and λ. This ratio signal is used as a factor K to form the linear combination A (X ) -ΚΑ (λ) in the

"" linear combining means 44 when measuring a to examining sample saved. The switch 58 in FIG. 2, the one after the measurement with the pure interference component

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is opened, is intended to indicate that the stored value K remains unchanged in the subsequent measurements of unknown samples remain.

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Claims (7)

Claims I '1 J Spectrophotometer for the double wavelength - ^ Spectrophotometry, containing: 10 (a) a light source (b) an optical system for producing a measuring light beam emanating from the light source, 15 (c) a monochromator, on whose entrance slit the measuring light beam is directed, with a Wavelength drive for scanning a wavelength range / (d) means for passing the measuring light beam through a sample and (e) a detector that detects the measuring light beam that has passed through the monochromator and sample is acted upon, marked by (f) means (30) for specifying two wavelength values ( χ , χ), (g) storage means (32) for storing signals of the detector (28), 35 130036 / 04.05 (h) switching means (34) from the wavelength drive (24) are controlled, for switching on the at the two predetermined wavelength values (λ, λ) of the Detector (28) delivered signals to the Storage means (32) and (i) Means (44) for forming a linear combination of the two stored signals. 10 2. Spectrophotometer according to claim 1, characterized in that that the means (44) for forming the linear combination are means for forming the difference. 3. Spectrophotometer according to claim 1, characterized in that the means (44) for forming the Linear combination (I ₁ ) multiplier means (48) for multiplication with a factor (K) and of the one stored signal (A ( X)) (i_) Difference Forming Means (46) for Education the difference between the other stored signal (A (X)) and that with the factor (K) multiplied a stored signal contain.
30th 4. Spectrophotometer according to claim 3, characterized by (A) quotient-forming means (52) to which the stored in the storage means (32) Signals can be switched on to form a ratio signal, which indicates the ratio 130036/0405 of the signals from the detector (28) in the first and the second wavelength (λ or λ)
reproduces, (b) means (54) for storing this ratio signal (c) Means (56) for applying the stored ratio signal as a factor (K) to the
Multiplying means (48). 5. Method of determining the concentration of a Component of a sample by double wavelength spectrophotometry from the level of an absorption band of the absorption spectrum in the presence of a
in the area of this absorption band as well
absorbent fabric component, using
a spectrophotometer according to claim 1, characterized by the following process steps: (a) Presetting a first wavelength (λ), at
which is the absorption band to be measured (12) of the sought component of the sample (26) lies, (b) Specification of a second wavelength (λ) outside this absorption band (12),
30th (c) Determination of the ratio (K) of the
Absorption values for the pure interfering component at the first wavelength and the second Wavelength,
35 1300-36 / 0405 (d) Adjustment of the monochromator ^ (22) by means of the wavelength drive (24) to the first wavelength (x _m ), (e) switching on the at the first wavelength ( χ ) at the detector (28) received signal to the storage means (32) for storing this signal, (f) adjusting the monochromator (22) by means of the wavelength drive (24) to the second wavelength CX _r >, (g) Applying the signal obtained at the second wavelength "CX" to the storage means (32) to save this signal, (h) linearly combining the stored signals by means of the linear combination-forming means (44) with opposite signs, where the signal obtained at the second wavelength (χ) is multiplied by the said ratio '.- ' 6. The method according to claim 5, characterized in that the second wavelength (λ) is chosen so that at this second wavelength (λ) the The absorption value of the pure interfering component is equal to the absorption value of the interfering component in the first the absorption value becomes one. Wavelength (X) is making the said ratio 13O036 / 0A05 7. The method according to claim 5, characterized in that the determination of the ratio (K) of the Absorption values for the pure interference component at the first and second wavelength (λ, λ) includes the following process steps: (C ₁ ) Insertion of a solution with a pure interfering component as a sample (26) in the spectrophotometer, (C ₂ ) Setting the monochromator (22) by means of the wavelength drive (24) to the first wavelength (λ) / (C ₃ ) Save the first wave length (λ) received signal of the detector (28), (c.) Adjusting the monochromator (22) by means of the shaft drive (24) to the second wavelength (λ) / (Cc) Detection of the received at the second wavelength (λ _r )
Detector (28), length (λ) obtained signal of the Generation of a ratio signal which reproduces the ratio of the signals obtained at the two wavelengths ( χ, X) and Store this ratio signal (K) to form the linear combination in the Measurement of a sample to be examined. 130036/0405