Aliquot method

Since 60 mg of the drug is not weighable on a Class A prescription balance, aliquot method has to be followed. Lactose is used as a diluent. The drug and lactose together weigh 120 mg and are therefore weighable. 

Weigh out 2100 mg of sulfasalazine powder, 28 mg of prednisone (use aliquot method for weighing this quantity), and add sufficient lactose to obtain a total of 2730 mg of the powder. Fill 195 mg in each of the 14 capsules that are required to be dispensed. 

We are including here the description of use of Giles flask in analysis of mixed acids by aliquot method, as was done by Clift Fedotoff (Ref 2, Chap I, Part I, pp 1 to 4) at Triton Chemical Corp, Glen Wilton, Va and at Keystone Ordnance Works, Meadville, [Pg.716]

For faster reactions, it maybe necessary to monitor the progress of the reaction in an NMR tube in a thermostatted NMR probe. If an aliquot method is used, it should be possible to remove an aliquot rapidly and quench it by adding cold solvent - reaction rates are lower under colder, more dilute conditions. In reactions involving bases or acids, reactions may be quenched by addition of acidic or basic buffer solutions. Of course, whether or not the reaction can be quenched efficiently, the aliquots should be analysed as expeditiously as possible to reduce the possibility of further reaction or degradation. 

Batch methods can be separated further into two general types, experiments that sacrifice the entire volume of an individual reactor and experiments that remove sample aliquots from a single larger reactor. Both types of experiment require that the material of interest be placed in a vessel and stirred continuously to ensure that the effect of transport processes is minimized. In the sacrificial method, at certain time during the course of an experiment, a small-volume reactor is sacrificed and used for analysis. This method eliminates the concentrating effect of removing sample aliquots however, it requires a matrix of experimental vessels to define the system. The aliquot method does restrict the number of samples able to be withdrawn from the system however, it is less labor intensive in terms of the experimental matrix and allows for easier alteration of system conditions. 

The methods of ED determination described above involve the measurement of many subsamples. Several separate subsamples, or aliquots, are used for measurement of each point on the growth curve, so that between 20 and 60 aliquots are used for each ED determination. An alternative to such multiple aliquot methods is to make all the measurements on a single aliquot. The methods used are very similar to those for multiple aliquots, with both additive dose and regenerative measurements possible. 

The advantages of single aliquot methods are that there is no implicit assumption that all aliquots are equivalent, that it becomes practical to make replicate ED determina-... 

Illustration showing the method of standard additions in which separate aliquots of sample are diluted to the same final volume. One aliquot of sample is spiked with a known volume of a standard solution of analyte before diluting to the final volume. 

With conventional nonspectroscopic detectors, other methods must be used to identify the solutes. One approach is to spike the sample by adding an aliquot of a suspected analyte and looking for an increase in peak height. Retention times also can be compared with values measured for standards, provided that the operating conditions are identical. Because of the difficulty of exactly matching such conditions, tables of retention times are of limited utility. 

To verify the method a 1.00-mL aliquot of a standard solution of 40.0-ppm glucose was added to 1.00 ml of the combined reagents, requiring 34.6 s to produce the same extent of reaction. Determine the calculated concentration of glucose in the standard and the percent error for the analysis. 

The complication of matching the matrix of the standards to that of the sample can be avoided by conducting the standardization in the sample. This is known as the method of standard additions. The simplest version of a standard addition is shown in Figure 5.5. A volume, V, of sample is diluted to a final volume, Vf, and the signal, is measured. A second identical aliquot of sample is... 

Procedure. The method to be described is especially suitable for ceramic materials such as fireclay, firebrick, or silica brick. The finely ground sample should be dried at 110 °C. The weight of sample to be employed depends largely upon the silica content of the material, since not more than 35 40 mg of silica should be present in the aliquot employed for the determination. For samples... 

Three related methods based on the quasiisostatic method are used to measure permeability. The most commonly used technique allows the permeant gas or vapor to flow continuously through one chamber of the permeability cell. The gas or vapor permeates through the sample and is accumulated in the lower-concentration chamber. At predetermined time intervals, aliquots are withdrawn from the lower cell chamber for analysis. The total quantity of accumulated permeant is then determined and plotted as a function of time. The slope of the linear portion of the transmission-rate profile is related to the sample s permeability. 

The thin-layer technique (CA 60, 6691) utilizes aliquots of proplnt ether extract (I) and the ether soln (II) of a known mixt. II consists of nitrates of glycerol and glycol, di-Bu or di-Et phthalates, Et or Me centralites, DNT, and diphenylamine. The chromatoplates are made of 85 15 silica gel and plaster of Paris. These plates, containing spots of I and 11, are developed with 1 1 C6H6-petroleum ether, then sprayed with specific detectors by color. The method is much quicker and easier than chemical analysis and simpler than infrared spectroscopy and column chromatography... 

Carbon was estimated by a variation of the Van Slyke method.(2) A 30-100 mg sample was heated for 30 minutes with 0.5 g K2Cr207, lg KIOj, 10 mL 20% fuming H2S01( and 5 mL HjPO in a closed flask swept by a purified N2 stream. The N2 stream carried the evolved C02 to an absorption solution of 0.5M Na0H-0.3M N H. After the wet combustion, the absorbed C02 was released from an aliquot of the NaOH solution with lactic acid in a manometric apparatus. Corrections were applied for the vapor pressure of water and for reagent blank. 

Removal of Aliquots at Intervals. Each aliquot is then analyzed as in method... 

The second analytical method uses a combustion system (O Neil et al. 1994) in place of reaction with BrF,. This method was used for the crocodiles because they were represented by very thin caps of enamel. The enamel was powdered and sieved (20 mg), pretreated in NaOCl to oxidize organic material and then precipitated as silver phosphate. Approximately 10-20 mg of silver phosphate were mixed with powdered graphite in quartz tubes, evacuated and sealed. Combustion at 1,200°C was followed by rapid cooling in water which prevents isotopic fractionation between the CO2 produced and the residual solid in the tube. Analyses of separate aliquots from the same sample typically showed precisions of 0.1%o to 0.4%o with 2 to 4 repetitive analyses even though yields are on the order of 25%. 

Tooth enamel precipitated as silver phosphate and reacted via this method gave values similar to corrected laser data from aliquots of the same tooth enamel (Table 6.1). Thus, the data from the crocodile samples are considered directly comparable with the data from the mammal tooth enamel. 

A series of calibration standards (CS) is made up that covers the concentration range from just above the limit of detection to beyond the highest concentration that must be expected (extrapolation is not accepted). The standards are made up to resemble the real samples as closely as possible (solvent, key components that modify viscosity, osmolality, etc.). A series of blinded standards is made up (usually low, medium, high the analyst and whoever evaluates the raw data should not know the concentration). Aliquots are frozen in sufficient numbers so that whenever the method is again used (later in time, on a different instrument or by another operator, in another laboratory, etc.), there is a measure of control over whether the method works as intended or not. These so-called QC-standards (QCS) must contain appropriate concentrations of all components that are to be quantified (main component, e.g., drug, and any impurities or metabolites). 

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