Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Reexamination Certificate
2002-08-22
2004-10-12
Luu, Thanh X. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
C250S575000
Reexamination Certificate
active
06803594
ABSTRACT:
The present invention relates to an optical measuring system to determine the concentration of liquid samples, especially the concentration of turbid liquid samples
In absorption spectrometry (absorption photometry) the attenuation of light upon passing through a liquid sample is measured and displayed as extinction. The attenuation of the incident light occurs by absorption, the direction of light at this point remaining unaltered.
Turbidity measurement serves to determine the scattering centers in turbid liquid samples. For this purpose one can measure the intensity of scattered light that emerges in a defined angle from the sample hit by an incident light beam. The scattering of the light can be determined either by measuring the intensity decrease of the incident light beam after passing through the turbid medium, or by measuring the intensity of the laterally deflected light. In the first case, one speaks of the method of turbidimetry, and in the second of that of nephelometry. An important application is the measurement of the concentration of liquid cell- or bacteria cultures.
With the known optical measuring systems for absorption spectroscopy and with those for turbidity measurement, it is disadvantageous that they comprise special measuring cells for the accommodation of liquid samples, which have to be arranged in an optical path between a light emitter and a light sensor for measuring, and must be produced very accurately to maintain the error in measuring as small as possible. These measuring cells are conveniently cuvettes The relatively expensive cuvettes are in principle reused. To avoid contaminations and carry-over they must be subjected to complicated cleaning procedures.
However, according to German application DE 195 35 046 C2 the measuring cell can also be a pipette point with two plane-parallel windows which is arranged in the optical path of a photometer integrated into the hand-pipette when affixed thereto. The pipette point can be made from plastic material as an one-time-use article, but this has the disadvantage that it is also relatively complicated in manufacture because of the plane-parallel windows and has a reduced accessability as a special article.
Especially the known optical measuring systems for the measurement of turbidity have the disadvantage to exhibit only a limited measuring range. Extra turbid samples can often be measured only after preceding dilution. However, the dilution of liquid samples is labour intensive and may be problematic because of possible environment-alterations of the cultures. Further, in a relatively large measuring range only a minor differentiation of small concentration differences is recorded. Indeed, this can be remedied to by using special cuvettes with different path-lenghts But this is relatively labour and apparatus expensive.
Departing therefrom the present invention has the objective to provide an optical measuring system for the determination of the concentration, especially of turbid liquid samples, simply to operate and working accurately over a large measuring range and which can be practiced with less expensive measuring cells.
The objective is solved by an optical measuring system with the features of claim
1
. Advantageous embodiments of the optical measuring system are indicated in the subclaims.
The optical measuring system for the determination of the concentration especially of turbid liquids comprises:
a measuring volume for taking up the liquid samples to be measured,
a plurality of several photometric channels, each having a light source and a light sensor on different sides of the measuring volume aligned on a common optical axis, and the optical axes therefrom being disposed under different azimutal angles respective to the sample volume, and
an analysing device which evaluates the concentration of the liquid samples to be measured according to the data provided by the light sensors belonging to a plurality of different photometric channels.
Because the measuring data of a plurality of light sensors are drawn on for the determination of the concentration, inaccuratenesses (e.g. optical inhomogeneities, gauge fluctuations etc.) of a measuring cell containing the measuring volume, the walls thereof being irradiated by the photometric channels, which can especially be caused by manufacturing, are less effective in respect to the accurateness of the determined concentration. Consequently measuring cells which are manufactured with relatively little expenditure, and thus may be disposables, can be used Consequently, particularly commercially available vessels (e.g. reaction tanks, pipette points) can be used, which are widely common in laboratory use and the availability thereof is particularly high In principle, measuring cells with different shapes, e g circular or polygonal cross-section, can be used.
Particularly advantageous is the design of the measuring cell as a pipette point made from glass or plastic material. Pipette points are especially wide-spread as one-time-use articles in the plastic material make. They have at one end an aperture for the passage of liquid, and at the other end an aperture for the connection of a pipetting apparatus comprising an expulsion unit. By means of the expulsion unit, an accurately defined liquid volume can be aspirated through the point aperture into the pipette point and subsequently can be ejected again from it. The determination of the concentration in a pipette point has the particular advantage to facilitate the sample handling and to be connectable with an accurate metering of the sample liquid. In this manner one procedure can be saved, because a liquid sample conveniently is pipetted into a cuvette anyway. Also, by simply expulsing the liquid sample from the pipette point, a practically complete and contamination-free recovering of the liquid sample is possible
The analysing device can determine the concentration particularly simply based upon an averaging of data of a plurality of light sensors, e.g. based upon an arithmetrical signal averaging.
Preferably, the analysing device can determine, in a first analysing mode, concentrations based upon measuring values provided by the corresponding light sensor of the transmitted light originating from the light source belonging to the same photometric channel as the light sensor. The first analysing mode corresponds to absorption photometry, or turbidimetry respectively, and is preferably selected for an absorption-photometric measurement in the integral measuring range, and for a turbidity measurement in the range of small concentrations.
Furthermore, the analysing device can preferably determine, in a second analysing mode, concentrations based upon data which the corresponding sensor provides of scattered light that originates from at least one light source which is not belonging to the same photometric channel as the light sensor The second analysing mode corresponding to the method of nephelometry can be preferably selected if larger concentrations are to be determined by turbidimetry. In this case the range of larger concentrations can connect immediately to the range of smaller concentrations, respectively the ranges can overlap, so that added together a significantly larger measuring range can be attained by the turbidity measurement. At the same time, a good discernibility of small concentration differences is made possible over the entire measuring range.
In this way the optical measuring system enables the concentration determination of turbid liquid samples to be performed over a wide concentration range Thereby the taking into account of the data of a plurality of photometric channels at the absorption photometric measurement, and at the turbidimetric measurement in the range of smaller concentrations, and the taking into account of a plurality of measuring data of the laterally deflected light of the turbidity measurement in the range of larger concentrations, enables the use of measuring cells with inaccuracies, especially of disposables.
However, the optical measuring system can
Harnack Kurt
Spolaczyk Reiner
Eppendorf AG
Luu Thanh X.
Sidley Austin Brown & Wood LLP
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