Aliquot, definition

Sodium Chloride.—The weighed ash is dissolved in water, the dilution made up to a definite volume and filtered, and an aliquot part used for tin- volumetric or gravimetric estimation of the chlorine. 

The above methods cannot be used if the spirit contains chlorides, as may happen if it has been broken down with water containing these salts. In this case the total hydrocyanic acid may be determined by distilling 100 c.c. of the spirit and collecting at least three-quarters (which will contain all the hydrocyanic acid present) in a dilute solution of silver nitrate of known titre. The liquid is then made up to a definite volume and filtered, the excess of silver in an aliquot part of the filtrate being titrated with thiocyanate as already described. The free hydrocyanic acid, in presence of chlorides, should be determined colorimetrically as follows a solution of about 0-05 gram of potassium cyanide per litre is prepared and its exact content of HCN determined by titration with silver nitrate and ammonium thiocyanate. In a series of test-tubes are placed such quantities of this... 

Ferric Oxide.—The filtrate from the preceding determination is made up, together with the wash water, to a definite volume (e.g., 250 c.c.) and an aliquot part of it (50 or 100 c.c.) precipitated with ammonia in presence of ammonium chloride the predpitate is collected on a filter and washed. If alumina is present only in negligible quantity, the weight of the caldned predpitate gives the ferric oxide. In the contrary case, the washed and still wet predpitate is dissolved in dilute sulphuric acid and the solution made up to 100 c.c. with water 10 c.c. of this solution are reduced with zinc and the ferrous iron titrated with permanganate (see Vol. I, Limestones and Marls, p. 142). 

The ability to perform the same analytical measurements to provide precise and accurate results is critical in analytical chemistry. The quality of the data can be determined by calculating the precision and accuracy of the data. Various bodies have attempted to define precision. One commonly cited definition is from the International Union of Pure and Applied Chemistry (IUPAC), which defines precision as relating to the variations between variates, i.e., the scatter between variates. [l] Accuracy can be defined as the ability of the measured results to match the true value for the data. From this point of view, the standard deviation is a measure of precision and the mean is a measure of the accuracy of the collected data. In an ideal situation, the data would have both high accuracy and precision (i.e., very close to the true value and with a very small spread). The four common scenarios that relate to accuracy and precision are illustrated in Figure 2.1. In many cases, it is not possible to obtain high precision and accuracy simultaneously, so common practice is to be more concerned with the precision of the data rather than the accuracy. Accuracy, or the lack of it, can be compensated in other ways, for example by using aliquots of a reference material, but low precision cannot be corrected once the data has been collected. 

Procedure (See Chromatography, Appendix IIA.) Set attenuation (usually 4) of the chromatograph s thermal energy analyzer detector so that an injection of 30 pg of NDMA gives a definite peak with acceptable background. Using this attenuation, analyze 5- to 6-pL aliquots, in duplicate, of NDMA Standard Solutions of 5, 10, 20, and 40 ng/mL. (Note the volume injected.)... 

The Liquid Master Store at Roche uses a 96-tube version of the microtube plate described in Section 1.4 a description of the 96-tube plate is found on the web site www.remp.com. The individually accessible tubes in 96-tube plates in the Liquid Master Store hold a few definite sample volumes, e.g. 26 J,L and 140 J,L per tube. Storage and retrieval of HTS master solutions with fixed sample volumes facilitate the sample logistics considerably. Upon retrieval from the Liquid Master Store, the master solutions in the 96-tube plates are thawed and transferred to 384-well plates before they enter the downstream aliquoting process. This sample-handling concept avoids repetitive freeze-thaw cycles of HTS master solutions and thereby improves the stability and integrity of the compound samples used in HTS. 

Fig. 6. Kinetics of immobilization of glutaryl-7-ACA-acylase on epoxy-activated polymethacrylate. The Gl-7-ACA-acylase was incubated with the epoxy-activated carrier. At definite times aliquots were taken from the reaction suspension. Supernatant and carrier-fixed enzyme were separated by centrifugation. The carrier-fixed enzyme was washed with water to remove non-covalently linked enzyme. The activities of the immobilized enzyme and supernatant were determined (5 mM potassium phosphate buffer pH 8,37°C, 2% glutaryl-7-amino cepha-losporanic acid, pH-stat 8.0). Simultaneously, an aliquot of carrier-fixed enzyme was boiled in sodium dodecylsulfate (SDS)/glycine buffer and the supernatant was subjected to SDS-polyacrylamide electrophoresis (see insert from left to right lane 1 Carrier-fixed enzyme, 2 h lane 2 Carrier-fixed enzyme, 4 h lane 3 Carrier-fixed enzyme, 6 h lane 4 Carrier-fixed enzyme, 21 h lane 5 Carrier-fixed enzyme, 69 h lane 6 Dialyzed enzyme lane 7 Supernatant, 2 h lane 8 Supernatant, 21 h lane 9 Supernatant, 69 h lane 10 Molecular weight calibration markers)...

The best example of a biosensor of this type is the glucose electrode (2). Regardless of the type of sample (i.e., a blood sample or an aliquot from a high fructose corn syrup production line) the glucose electrode is a biosensor. Here the emphasis is on the response mechanism and required components of the sensor. This second definition will be used throughout this paper. 

Reliability It is rather difficult to use the accuracy and precision concepts as these capital and basic properties are closely related in qualitative analysis. Their combination has produced a new property called reliability, which is defined as the proportion (percentage) of right yes or no answers provided by individual tests carried out on n aliquots of the same sample to identify an analyte or a family of the analytes. This definition represents the positive side of the errors in qualitative analysis false positives and false negatives. The reliability of the binary response is not an independent property as it strongly depends on the basic properties of sensitivity and selectivity. Moreover, it is in contradiction with productivity-related properties. Reliability is equivalent to certainty and, in quantitative analysis, the uncertainty of a result is a parameter associated with reliability. Indeed, the term is included in the definition of traceability as every experimental datum is affected by specific variations or doubts. As it directly affects the quality of an analytical result, it is necessary to find out an equivalent method to express vmcertainty in qualitative analysis. The term unreliabifity can be... 

Methods for determining the LOD that are based on the analysis of a field blank that does not contain the analyte of interest are problematic in many real-world applications because either such samples do not exist, or would be impossibly difficult to create. As such a circumstance is frequently encountered in environmental analysis, the USEPA adopted a detection limit procedure, termed the method detection limit (MDL), which focuses on an operational definition of detection limit. Specifically, the MDL is defined as the minimum concentration of a substance that can be measured and reported with 99% confidence that the analyte concentration is greater than zero. The MDL is determined from a replicate analysis of a sample of a specified matrix. Specifically, at least seven aliquots of sample, spiked to contain a concentration of from one to five times the method s estimated MDL, are analyzed. The MDL calculated from these results is statistically tested to determine its reasonableness. If the result fails the testing, this iterative process begins again with a new estimate of the MDL. 

It consists of two thermostated vessels, one on top of the other and joined by a conical fitting. Each one contains one of the two reactants. The lower reactor (200 mL) contains a magnetic stirrer, and has inlets to allow the measurement of pH and temperature, influx of circulating nitrogen, and removal of aliquots for analysis. The upper cylindrical vessel (100 mL) is blocked at its base by a solid machined stopper (17 mm i.d.) fastened to a control rod. This setup allows the rapid introduction of the ampoule contents into the reactor, and therefore a precise definition of the initial time. A slightly reduced pressure is maintained throughout the experiment and the temperature is defined to + 0.1 °C. 

Evans and McGuffin [824] studied the effect of injecting a 1 pL aliquot of a 5xl0" M 4-(bromomethyl)-7-methoxycoumarin-derivatized C,o fatty acid dissolved in 100% THF onto a C g column eluted with a 90/10 methanol/water mobile phase. A split peak resulted. The authors could not definitively explain the effect but noted that the best solution to the potential problem is to dissolve the sample in the mobile phase itself or in a solvent that is only slightly weaker than the mobile phase. This split peak effect is not uncommon when high percent THF solute solvents are used. 

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