Measuring and testing – Liquid analysis or analysis of the suspension of solids in a... – Content or effect of a constituent of a liquid mixture
Patent
1984-01-23
1985-10-15
Levy, Stewart J.
Measuring and testing
Liquid analysis or analysis of the suspension of solids in a...
Content or effect of a constituent of a liquid mixture
364498, G01N 3108
Patent
active
045466432
DESCRIPTION:
BRIEF SUMMARY
The invention relates to the analysis of effluents and more particularly, but not exclusively, is concerned with liquid phase chromatography.
In this particular field an eluent and a sample to be analysed are passed through a chromatography column. The eluent entrains various constituents of the sample selectively in the column.
At the outlet of the column, the effluent is subjected to the detection of a physical and/or chemical property, thus enabling the passage of the interesting constituents of the sample to be plotted. Detection is performed as a function of time, and supplies an analog electric signal.
The electrical signal can be regarded as comprising a "base line" having peaks, certain of which correspond to interesting constituents of the sample (useful peaks). The other peaks represent artefacts.
Any detection of a useful peak is generally accompanied by selective sampling of the effluent by means of an apparatus known as a fraction collector.
It is desirable to detect useful peaks automatically. Various techniques have been suggested for this purpose.
In the simplest, a constant threshold value is defined, slightly above the baseline. This method, which is quite suitable for certain applications, is in general not completely satisfactory: in difficult cases, the threshold must be made very low, so that an excessive number of useless samplings must be carried out.
It has therefore been proposed to take into account the slope of the detected signal, to plot the start and finish of peaks on it, as well as the minimum values between two closely adjoining slopes. There again, the technique is not entirely satisfactory.
Indeed, particularly in chromatography with a multi-component eluent with a concentration gradient the level of the baseline develops fairly quickly, thus rendering the aforementioned peak-detecting techniques inaccurate.
The present invention aims to provide a solution for these problems.
The invention provides a method of analysing effluents, in which: function of time, in the form of an electric signal, the electric signal detected comprising a baseline having peaks, certain of which represent useful information concerning the effluent; slope, with a view to selecting useful peaks in it.
According to the invention the analytical stage (b) comprises the following operations: (S.phi.); signal, plus the deviation value (L.phi.), if the slope of the detected signal is lower than the threshold; detected signal is higher than the threshold; signal which exceed the level of the pilot signal.
Preferably operation (b4) consists in freezing the pilot signal when the slope of the detected signal is higher than the threshold value (S.phi.).
Very advantageously when the slope of the detected signal becomes lower than the threshold value (S.phi.) again, the preceding value of the pilot signal is then resumed if the duration of exceeding the threshold was less than the selected duration (TMAX), or in the contrary case, a start is made again from a value equal to the sum of the detected signal and the deviation value (L.phi.).
According to another aspect of the invention the deviation value (L.phi.) and a selected duration (TMAX) can be defined by the user, the slope threshold (S.phi.) being defined as the ratio between a pre-established quantity and the selected duration.
Preferably the passage of the detected signal through a minimum is also detected, thus defining any change in useful peak.
In practice, for the majority of applications the process is completed by an operation (c) consisting in sampling the effluent at least during a useful peak.
The invention also provides a fraction detecting and/or collecting device for analysing effluents, which comprises means for performing the aforedescribed method.
Other features and advantages of the invention will become apparent from a reading of the detailed description which follows and examination of the accompanying drawings, in which:
FIG. 1 illustrates diagramatically the general structure of an installation for liquid phase chromatography;
FIG.
REFERENCES:
Anderson et al., Computer Analysis of Unresolved Non-Gaussian Gas Chromatograms by Curve-Fitting, in Anal. Chem., vol. 42(4), pp. 434-440, Apr. 1970.
Burke et al., Use of a Dedicated Computer for Real-Time Control of Gas Chromatographic Measurements, in Journ. of Chrom. Sci., vol. 8, pp. 39-45, Jan. 1970.
Bonneyrat Alain M.
Lanclais Christian L.
Gilson Medical Electronics (France)
Levy Stewart J.
Roskos Joseph W.
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