Three-step dilution

In the example above, the sample preparation contributed 75% of the error. When multiple steps such as those shown in Figure 1.2 are involved, the uncertainty is compounded. A simple dilution example presented in Figure 1.5 illustrates this point. A 1000-fold dilution can be performed in one step 1 mL to 1000 mL. It can also be performed in three steps of 1 10 dilutions each. In the one-step dilution, the uncertainty is from the uncertainty in the volume of the pipette and the flask. In the three-step dilution, three pipettes and three flasks are involved, so the volumetric uncertainty is compounded that many times. A rigorous analysis showed [3] that the uncertainty in the one-step dilution was half of what was expected in the three-step process. 

A solution can be diluted by a factor of 200 using readily available pipets (f-mL to fOO-mL) and volumetric flasks (fO-mL to fOOO-mL) in either one, two, or three steps. Limiting yourself to glassware listed in Table 4.2, determine the proper combination of glassware to accomplish each dilution, and rank them in order of their most probable uncertainties. 

Figure 2 illustrates the three-step MIBK process employed by Hibernia Scholven (83). This process is designed to permit the intermediate recovery of refined diacetone alcohol and mesityl oxide. In the first step acetone and dilute sodium hydroxide are fed continuously to a reactor at low temperature and with a reactor residence time of approximately one hour. The product is then stabilized with phosphoric acid and stripped of unreacted acetone to yield a cmde diacetone alcohol stream. More phosphoric acid is then added, and the diacetone alcohol dehydrated to mesityl oxide in a distillation column. Mesityl oxide is recovered overhead in this column and fed to a further distillation column where residual acetone is removed and recycled to yield a tails stream containing 98—99% mesityl oxide. The mesityl oxide is then hydrogenated to MIBK in a reactive distillation conducted at atmospheric pressure and 110°C. Simultaneous hydrogenation and rectification are achieved in a column fitted with a palladium catalyst bed, and yields of mesityl oxide to MIBK exceeding 96% are obtained. 

In this reaction, three steps, ie, acylation, cyclization, and replacement of the chlorine atom by the hydroxyl group, take place simultaneously in concentrated sulfuric acid. In the course of cyclization 2,7-dichlorofluoran (31) may be formed as a by-product presumably through the carbonium ion (30) ihustrated as follows. The addition of boric acid suppresses this pathway and promotes the regular cyclization to form the anthraquinone stmcture. The stable boric acid ester formed also enables the complete replacement of chlorine atoms by the hydroxyl group. Hydrolysis of the boric acid ester of quinizarin is carried out by heating in dilute sulfuric acid. The purity of quinizarin thus obtained is around 90%. Highly pure product can be obtained by sublimation. 

Extraction and purification (Shimomura, 1991b). The luciferin precursors PS-A and PS-B are extracted from the dried fruiting bodies of Panellus stipticus (5 g) with methanol, and the extract is evaporated under reduced pressure to remove most of the methanol. The residue (pH 6.3) is diluted with a small amount of water and extracted with ethyl acetate, and the extract is evaporated to dryness. The precursors in the residue are purified by three steps of silica gel chromatography and one step of HPLC, while monitoring the absorbance of eluate at 220-230 nm. The procedure is summarized below ... 

Adsorption and desorption can be avoided much better and adaptation minimised when concentrations are presented with ascending concentration levels. A series of at least 5 dilution steps is recommended in the Netherlands starting two or three steps under the... 

The field of alkyl radical macrocyclization reactions was further augmented with an n + 1) strategy, which incorporates a CO unit in the macrocycle [93], Thus, in the presence of highly diluted (0.005-0.01 M) (TMS)3SiH, co-iodoacrylates underwent an efficient three-step radical chain reaction to generate 10- to 17-membered macrocycles in 28-78% yields, respectively (Reaction 7.82). 

Disubstituted 2-phenyl-277-1,2,3-triazole-1-oxides (150) can be easily obtained from the corresponding bis(hydroxyimino)butanes 148 in three steps. Thus, treatment of dioximes 148 with diluted HCl in dioxane with subsequent interaction with PhNHNH2/EtOH/AcOH afforded a-hydrazinooximes 149 in excellent yields. Reaction of 149 with A-iodosuccinimide (NIS) in CCI4 or with CUSO4 in aqueous pyridine afforded triazoles 150 (equation 65) . Similar cyclization in the presence of SOCI2 also leads to... 

In Great Britain, the Imperial Chemical Industries, Ltd., has developed a fluidized coal gasification process (32) using combustion of part of the fuel with air to supply the heat necessary for the endothermic steam-carbon reaction. This procedure is divided into three steps carbonization, air-blowing, and steam-blowing. The first and third steps operate with fluidized beds, and the second with a dilute suspension. Powdered coal is fed into the carbonization vessel, where it is heated by combustion of some of the carbonization gases. The powdered char is blown into a feed hopper connected with the air-... 

Perform TBA reaction and measure absorbance (steps 7 to 11) using the three TMP-spiked samples (step 15) and the three TMP dilutions (step 16). 

In m-xylene the two methyl groups agree in activating the same positions, and this is the only one of the three isomeric xylenes which can be nitrated satisfactorily to yield a trinitro derivative. Since the three isomers occur in the same fraction of coal tar and cannot readily be separated by distillation, it is necessary to separate them by chemical means. When the mixed xylenes are treated with about their own weight of 93 per cent sulfuric acid for 5 hours at 50°, the o-xylene (b.p. 144°) and the m-xylene (b.p. 138.8°) are converted into water-soluble sulfonic acids, while the p-xylene (b.p. 138.5°) is unaffected. The aqueous phase is removed, diluted with water to about 52 per cent acidity calculated as sulfuric acid, and then heated in an autoclave at 130° for 4 hours. The m-xylene sulfonic acid is converted to m-xylene, which is removed. The o-xylene sulfonic acid, which remains in solution, may be converted into o-xylene by autoclaving at a higher temperature. The nitration of m-xylene is conveniently carried out in three steps. The effect of the two methyl... 

Conversion of CHNH2 to, C=0.2 A convenient three-step conversion of alkyl 6-aminopenicillanates (1) into 6-oxopenicillanates (3) involves ditrifluorometha-nesullonation to give a ditriflamide (2), which in the presence of base eliminates trifluoromethanesulfinic acid to form an imine (a). Hydrolysis of a to the ketone 3 is effected with dilute HC1. 

The new antihypertensive agents 194 and 195, which function in part through interaction with a-andrenoreceptors198, have been 14C-labelled199 in three steps starting from ethylene-14C2 oxide (equation 77). The overall radiochemical yields for 194 and 195 were 69% and 62%, respectively, and the specific activities of both compounds before final dilutions were initialy 22.6 mCi mmol-1. 

Sutherland R. A. (2002) Comparison between non-residual A1 Co, Cu, Fe, Mn, Ni, Pb and Zn released by a three-step sequential extraction procedure and a dilute hydrochloric acid leach for soil and road deposited sediment. Appl. Geochem. 17, 353 —365. 

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