Recalibrating apparatus and method

Chemistry: analytical and immunological testing – Composition for standardization – calibration – simulation,...

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422 81, 422 82, 422110, 422115, 436 18, 436 52, 436 53, 436179, 73 1R, 73 1G, 7386421, 7386422, 7386333, G01N 3508

Patent

active

055478751

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

THIS INVENTION relates to the recalibration of sensors and instruments used for chemical analysis.
Flow based methods of analysis require periodic recalibration with standards. Generally, several external standards (typically between two to five depending on the characteristics of the sensor or instrument e.g. linear or non-linear) are measured at intervals between a group of samples, but in all periodic recalibrations, a compromise exists. Very frequent recalibration improves reliability, but at the expense of sample throughput. Infrequent recalibration increases the risk of an out of tolerance condition between recalibrations, requiring the sample measurements to be reworked.
U.S. Pat. No. 5,080,866 describes a cyclic flow based analytical technique (Discontinuous Flow Analysis) where the ratio of a reagent to sample is varied during the measurement half of the cycle, and one example of the technique shows how an internal recalibration can be performed with a single standard and stepped flow profile on every sample. This overcomes the problem of the frequency of recalibration inherent in the use of external standards. However, the concentration of the internal standard relative to the sample has to be within certain limits so that the accuracy of the recalibration is not impaired. If the sample and standard are close in concentration, the step changes are small, consequently the resolution may be insufficient for an accurate recalibration. If the sample and standard are considerably different in concentration, plateau responses for each step may not be achieved due to the detector response time, or diffusion effects.
It should be noted that in all cyclic analytical techniques which use piston pumps, the cycle for each pump comprises two complementary half-cycles: a forward stroke whereby fluid is expelled from the pump, and a return stroke whereby fluid is drawn into the pump. The measurement of the sample takes place during one of the half-cycles.


SUMMARY OF THE INVENTION

An object of the present invention is to provide a rapid, effective internal recalibration for fluid delivery systems, in particular, those employing a piston pump fluid delivery system in which recalibration requires a minimal number of standards, and which provides a recalibration between successive samples.
A further object of the present invention is to provide a recalibration system which can auto-range the recalibration to suit the preceding sample.
The present invention entails the realization that substantial benefits in line with these objectives can be achieved by utilizing a novel recalibration apparatus in which a reproducible recalibration profile between two standards is formed in the half cycle complementary to the sample measurement half cycle, and the measurement of the sample in the first half of the cycle is compared to the recalibration profile of the two standards in the second half of the cycle. Additional standards may be employed so that the recalibration can be auto-ranged to suit the preceding sample.
According to one aspect of the invention there is provided a recalibrating apparatus comprising: mixture to a fluid junction; and second flow rates respectively of first and second fluid standards to the fluid junction; and a sensor means; sensor means relative to a fluid flow direction; or sample/reagent mixture and responsive to a fluid condition in the first standard, said second standard or mixtures thereof; second piston pump fluid delivery systems for controllably varying a flow rate thereof to produce a plurality of ratios of the first and second flow rates in accordance with a sequence of functional steps, each of which steps is defined by at least one of a distinct flow rate ratio, a series of distinct flow rate ratios, a distinct gradient of flow rate ratios, or a series of distinct gradients of flow rate ratios; systems operate in reciprocal modes of a pumping cycle so that in one half cycle the pump means delivers the fluid sample, reagent or sample/reagent mixture to t

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