Half-wash time

Two parameters have been demonstrated to be fundamental in calculating the performance characteristics of a continuous analyser, the lag phase and the half-wash time they afford a correlation between the approach to steady state, fraction of steady state reached in a given time and the interaction between samples. The half-wash time (Wy ) is the time for the detector response to change from any value to half that value, the lag phase L is defined in the ensuing discussion. 

Fig. 2.IS Graphical representation of lag phase L and half-wash time...

B = steady states related to the plateau and baseline S and W = sampling arm in the sample and blank solution cups a = lag phase two.s = half wash time. Adapted from Anal. Chim. Acta 78 (1975) 145, J. Ruzicka, E.H. Hansen, Flow Injection Analyses. Part I. A new concept of fast continuous flow analyses, with permission from Elsevier (Ref. [6]). 

The half wash time corresponds to the time interval required to achieve a reduction of 50% in the sample volumetric fraction, X. Provided the rise and fall profiles of the recorded peak are equal to each other, the two.s value... 

Since adequate washing cannot realistically be obtained in less than about 50 msec, the complex half-life must be at least 250 msec (k i < 2.8 s ) for reasonable binding measurements to be obtained. Uirfortunately, the dissociation rates of many important receptor-ligand complexes are faster than this and these are not amenable to measurement by these techniques. To study the equilibrium binding of [ Hjmuscimol, we routinely use a filtration (wash) time of 0.5 sec and a wash volume of 2 ml. 

As with TF-2, this fixer will wash out of negative and print materials more rapidly than will an acid fixer. It has the added advantage of fixing films and papers in less than half the time of the TF-2 alkaline fixer. 

The washing time can be shortened by at least half by placing the print for 10 to 20 seconds in a 3% solution of sodium carbonate. If this method is used, handle the prints carefully. This is because carbonate considerably softens the emulsion. Redevelop the image with any non-staining developer (e.g., Kodak D-72) for 2 to 5 minutes. The print should be washed for about Vi hour. Always use a fresh developer for print intensification. 

Note Kinetics of the inhibition of photosystem II electron flow in these macrophytes by 50 pg/L linuron and the subsequent recovery of inhibition by washing with uncontaminated well water are expressed as half-life times (f1/2). 

For simple washing, the wash rate is 0.8 x 0.016 = 0.0128 ft /s, and the washing time is 68.07/0.0128 = 5318 s or 1.48 h. For more thorough washing the wash liquid is sent to every other plate so that it flows through the entire thickness of each cake. This means that the thickness is doubled and the area cut in half relative to the final period of cake formation. Therefore the wash rate is (0,8 X 0.0l6)/4 = 0.0032 ft /s, and the washing time is 5.91 h. 

Chloroplasts have been prepared from spinach. The ATP-synthase was brought into the active, reduced state by illumination in the presence of thioredoxin and dithiothreitol. Washing of the chloroplasts drastically reduced the content of endogeneous ADP and ATP. Then, the ATP-synthases are activated by a ApH/Areduced state and contain no enzyme-bound ADP and only one enzyme-bound ATP per CFqFq. The maximum rate of ATP hydrolysis (at 1 mM ATP, pH 8.2) is about 100 before and after the washing. The enzyme remains in the active state for about 450 s (half-life time). All following experiments are carried out with such chloroplasts preparations. 

For the gels studied here, a washing time of 18 h is needed. After that, no significant change in the properties is observed. This is because the gel and water phases reach equilibrium. K the gel is washed once with the same volume of pure water, the equiUbrium composition will come to lay around half of the initial Na" concentration. Hence, for a complete removal, multiple washings are required [40]. In addition, the use of larger volume equivalents of the washing fluid or a continuous process with a countercurrent flow can help... 

Fig. 3 left shows the relative photovoltage of the second flash in the time range between 2o ps and 3 s in tris- washed chloroplasts. FLg.3 ri t shews a logarithmic plot of the data. The kinetics in the long time range can be described by a first order reaction with a half life time of 1.2 s (bottom). 

If the mother-liquor from the crude product (together with the washings) is concentrated to nearly half its original volume by gentle distillation, and is then cooled and seeded with a trace of the first crop, a second and less pure crop of the a-methylglucoside is obtained. This should be purified by recrystallisation from the mother-liquor obtained from the recrystallisation of the first crop, and then if necessary recrystallised a second time from a small quantity of fresh methanol. Yield of second crop, about... 

Cool the flask in ice, acidify with 10 ml. of cold 1 1-hydro-chloric acid and distil under reduced pressure (water pump) until most of the alcohol is removed. Add water to the residue, extract several times with ether, wash the combined ethereal extracts with N ammonia solution until a test portion gives no precipitate upon acidification. Extract the combined alkahne solutions once with a fresh portion of ether, and add the aqueous solution to an excess of dilute hydrochloric acid the final mixture should still be acidic to Congo red. Collect the crystalhne half-ester by filtration at the pump, wash it with water and dry at 100°. The yield is 14-5 g., m.p. 122-125°. Recrystallise by dissolving in about 40 ml. of warm benzene and adding an equal volume of petroleum ether (b.p. 40- 60°) 13 -5 g. of the colourless half-ester, m.p. 125-126°, are obtained. 

The phenol (Imol) in 5% aqueous NaOH is treated (while cooling) with benzoyl chloride (Imol) and the mixture is stirred in an ice bath until separation of the solid benzoyl derivative is complete. The derivative is filtered off, washed with alkali, then water, and dried (in a vacuum desiccator over NaOH). It is recrystalUsed from ethanol or dilute aqueous ethanol. The benzoylation can also be carried out in dry pyridine at low temperature ca 0°) instead of in NaOH solution, finally pouring the mixture into water and collecting the solid as above. The ester is hydrolysed by refluxing in an alcohol (for example, ethanol, n-butanol) containing two or three equivalents of the alkoxide of the corresponding alcohol (for example sodium ethoxide or sodium n-butoxide) and a few ca 5-10) millilitres of water, for half an hour to three hours. When hydrolysis is complete, an aliquot will remain clear on dilution with four to five times its volume of water. Most of the solvent is distilled off. The residue is diluted with cold water and acidified, and the phenol is steam distilled. The latter is collected from the distillate, dried and either fractionally distilled or recrystalUsed. 

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