Stock, dilutions from

Sybergreen 50x stock diluted from a 10,000x stock of Syber green (Molecular Probes) in dimethyl sulphoxide (DMSO, Sigma-Aldrich). 

Prepare appropriate dilutions from the stock to produce a calibration series of solutions so that (1) appropriate amounts of analyte are injected into the instrument giving consideration to its operating range and (2) the concentration of analyte which is expected in a diluted extract from the sample is at approximately the mid-point of the range of concentrations prepared in the calibration series. 

Another approach is to prepare a stock solution of high concentration, then perform serial dilution from the stock solution to obtain solutions of lower concentrations for linearity determination. This is a more popular approach, as serial dilution can be used to prepare solutions of very low concentrations. Since the low concentrations are prepared by serial dilution, this approach does not need to weigh a very small quantity of related substance. In addition, since all solutions are diluted from the same stock solution, weighing error in preparing the stock solution will not affect the linearity determination. 

At the end of the first tube s 10-min incubation, add 100 il freshly diluted 1 N Folin-Ciocalteu reagent (freshly diluted from a 2 N stock). Immediately vortex the tube for 2 to 3 sec. Continue to maintain the 15-sec intervals from step 3 for addition of the reagent to the remaining tubes. 

Store the stock solution frozen and prepare fresh dilutions from this for each batch,... 

Working solution dilute 1 ml of stock solution to 10 ml For nonpolar columns use a standard composed of C7-C18 n-alkanes For polar columns use a standard composed of C9-C30 -alkanes Over a period of time, preferential evaporation of the lower molecular weight alkanes will occur. Unless known weights of each alkane are required, this is not a serious problem. Using a working solution minimizes this problem and also avoids contamination. When the quality of the standard becomes unacceptable, a new sample can be diluted from the stock solution. 

Preparing serial dilution from stock solutions. 

The BSS in all cases is made up from 50 ml BSS xlO stock diluted to the appropriate volume with distilled water and sterilised by autoclaving (Table 1). 

Air-dry the DNA and resuspend in sterile TE. Adjust vol to 100 ng/mL. (DNA will be diluted from this stock to the appropriate concentration on the day of injection.) Confirm the identity, purity, and concentration of the DNA fragment by agarose gel electrophoresis of 500 ng with standards of known concentration. 

Procedure Prepare a series of THI-DNPH Standard Solutions serially diluted from the Stock THI-DNPH Solution. Pipet 1, 2, and 5 mL, respectively, of the Stock THI-DNPH Solution, into separate 10-mL volumetric flasks, and dilute to volume with absolute, carbonyl-free methanol. Prepare a standard curve by injecting 5 p-L of the Stock THI-DNPH Solution, and the serially diluted THI-DNPH Standard Solutions into a 250-mm x 4-mm (id), 10-lm LiChrosorb RP-8 HPLC column (Alltech Associates, Inc., or equivalent) fitted with an ultraviolet detector set at 385 nm. The mobile phase is 50 50 (v/v) methanohO.l M phosphoric acid. Inject 5 pL of sample into the column. Adjustments in the mobile phase composition may be needed as column characteristics vary among manufacturers. At a mobile phase flow rate of 2 mL/ min and column dimensions of 250 x 4.6 mm, elute THI-DNPH at about 6.3 0.1 min. Measure the peak areas. Calculate the amount of THI in the sample from the standard curve. (For THI limits greater than 25 mg/kg, prepare a series of Standard THI-DNPH Solutions in a range encompassing the expected THI concentration in the sample.)... 

Standard Curve Transfer 100.0 mg of L-tyrosine, chromatographic-grade or equivalent (Aldrich Chemical Co.), previously dried to constant weight, to a 1000-mL volumetric flask. Dissolve in 60 mL of 0.1 N hydrochloric acid. When completely dissolved, dilute the solution to volume with water, and mix thoroughly. This solution contains 100 pig of tyrosine in 1.0 mL. Prepare three more dilutions from this stock solution to contain 75.0, 50.0, and 25.0 pig of tyrosine per mL. Determine the absorbance of the four solutions at 275 nm in a 1-cm cell on a suitable spectrophotometer versus 0.006 N hydrochloric acid. Prepare a plot of absorbance versus tyrosine concentration. 

Calibration solutions (calibrators) should always be made up in the same medium as the final sample solution, and can be conveniently prepared in one dilution from stock solutions of 1000 mgr1 by using pipettes of the Eppendorf type. These pipettes provide a relative error of less than 1%. The stock solutions of standards supplied by chemical houses are cost-effective in commercial analysis. 

The standard curve is set up from malonyldialdehyde prepared from freshly hydrolysed malonyldialdehydebisacetal the standard (1 g/ml) is diluted 1 1000 in phosphate-buffered saline and diluted again 1 1000 to a working concentration of 1 ng//d. Tubes containing a range of aliquots from the diluted stock, ranging from 100 fA up to 500 fA, were brought up to a volume of 0.8 ml and then the thiobarbituric acid and the trichloroacetic acid added as described above for the samples. 

The flowsheet of the air-stripping process for bromine recovery from brines (including seawater brines) is shown in Fig. 5 [60]. The stock brine from a reservoir, mbted with H2SO4 and Clj, is directed to the top of the desorber. The bromine-free brine is collected at the bottom of the desorber, neutralized with thiosulfate and lime milk prior to disposal. Release of the chlorine/bromine air mixture from the top of the desorber is directed to the dechlorinating tower (1) where the mixture is treated with diluted FeBrj solution. The halogen exchange is described by the reaction... 

In Figure 1 we see baseline resolution of all the PTH amino adds in the standard. Roughly eqmvalent recoveries of all are noted, with the exception of His and Arg, which are somewhat broader in this system. Peak heights are equivalent to those found by manual iiyection of dilutions from a concentrated stock of PTH-AA. This indicates that no drastic losses were encountered with the use of 2% acetonitrile to redissolve the sample after R4 conversion and drying. Espedally noteworthy are the recoveries of PTH-Ser and PTH-Thr, despite the lack of DTT in the modified R4 and S4. One possibility is ihat the presence of DTT in the X2 wash of the flask between iixjections is a satisfactory substitution for inclusion in S4 and R4 for sequendng at this level. 

Make all the dilutions from the working stock solution to the required solution. Do not make a solution of lower dilution from one already prepared if you have made an error in the first dilution, it will be repeated for the second dilution. 

The well-known and widely applied TLC silica gel G plates 20 x 20 cm from Merck (Darmstadt, FRG) is used. Stock solutions from the compounds given in Table 1 were prepared. After corresponding dilution, a 1-/aL sample is applied and the plate is developed for a distance of 10 cm using n-propanol-water, 8 2 (v/v), as the mobile phase. Densitometric evaluation is performed at 365 nm with a Camag TLC Scanner II in absorbance reflection mode. The plate is first air-dried and then heated in an oven for 5 min at 100°C. Immediately after drying, the plate is inserted in a tank saturated with ammonia atmosphere (ammonia solution in... 

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