Primary stock solutions

An obvious question to be settled before beginning any preparation of solutions of standards concerns the range 

Stock and spiking solutions (see below) are eventually used to make the cahbration solutions and matrix matched calibrators that are the basis for the comparative measurement of analyte concentration in the unknown analytical sample (Sections 2.6 and 8.5), so the reliability of their concentrations is directly related to that of the measured concentrations. Accordingly, meticulous care and monitoring of these primary solutions is every bit as important as that expended in weighing the analytical standard in the first place (Sections 2.3). 

Another important concern is related to the chemical stability in solution of the analyte or SIS itself. Special consideration should also be given to the dangers inherent in use of protic solvents (water, alcohols etc.), e.g., hydrolysis or transesterification of ester analytes, D/H back exchange of a D-labeled SIS. 

The stability of the reference substance in a stock solution made from a particular solvent and stored nnder a given set of conditions should be established prior to use (Section 10.2.7). Method development studies can commence prior to establishing known stability but the analyst must be aware that the analyte could be degrading in solution (or during all phases of sample processing) and take that into consideration especially when unusual or unexpected results are obtained during development. In no instance should solutions without established analyte stabihty be used for sample analysis. Also, additional stability data should be generated for any other solutions that are prepared in a different solvent and/or stored under 

Once stabihty is established, storage containers should be clearly labeled with the solution name or ID, appropriate storage condition and expiration date. Any solution that is found to be past the estabhshed expiration date should be removed from the refrigerator or freezer and destroyed. 

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Prepare two primary stock solutions for ribavirin each in 50% methanol containing 20 mM ammonium acetate and 0.1% formic acid at a concentration of 1 mg/mL in 20 mL glass vials. The stock solutions should be kept in the refrigerator. For validation purposes, the stock solutions from the two weighings must have less than a 5% difference in the LC-MS/MS response. 

The majority of titrations involving basic analytes, whether conducted in aqueous or nonaqueous solvents, use HCl, HCIO4, or H2SO4 as the titrant. Solutions of these titrants are usually prepared by diluting a commercially available concentrated stock solution and are stable for extended periods of time. Since the concentrations of concentrated acids are known only approximately,the titrant s concentration is determined by standardizing against one of the primary standard weak bases listed in Table 9.7. 

Stamm-farbe, /, primary color = Stamman-satz, -flotte, /. (Dyeing) stock liquor, stock solution. 

The high-pressure cells and temperature control units are similar to the ones described by Betts and Bright (29). Samples for analysis were prepared by directly pipetting the appropriate amount of stock solution into the cell. To remove residual alcohol solvent, the optical cell was placed in a heated oven (60 °C) for several hrs. The cell was then removed from the oven, connected to the high-pressure pumping system (29), and a vacuum (50 pm Hg) maintained on the entire system for 10-15 minutes. The system was then charged with CF3H and pressurized to the desired value with the pump (Isco, model SFC-500). Typically, we performed experiments at 10 /xM PRODAN and there was no evidence for primary or secondary interfilter effects. HPLC analysis of PRODAN subjected to supercritical solvents showed no evidence of decomposition or additional components. 

Prepare a plot of A4S0 versus the log of the inverse antibody dilution (a 1 10 dilution = 1, a 1 100 dilution = 2, etc.). Plot the data from all five primary antibody samples on a single graph for comparison. If the assay was successful, each antibody solution should produce a sigmoidal curve in this type of plot (see Fig. 17-5). The various primary antibody stock solutions were diluted prior to performing twofold serial dilutions across each row (see step 4). Keep this in mind when you construct your graph. 

From the stock solutions of DNP-alanine, DNP-aspartate, DNP-serine and DNP-threonine provided make up working standards containing 0.05 mg mp methanol of each of the DNP-amino acids. Inject 5 pi of each of these working standards and record the retention of each DNP-amino acid. Make up the calibration mixtures shown in Table 9.5, containing the volumes (pi) shown of each of the primary standards. To each calibration mixture add 1 ml methanol. Inject 5 pi of each calibration mixture. Identify the terminal amino acid of the protein sample as follows. React the protein with FDNB and then hydrolyse the derivative (6M HCl, 110°C, 20 h). Extract the hydrolysate with diethyl ether (3x5 ml) and evaporate to dryness take up the residue in 1 ml of methanol. Chromatograph these solutions using the conditions established above. 

Dissolve approximately 0.01 g of sodium lauryl sulfate in between 50 and 10 mL of MeOH in a 50-mL beaker. Transfer the contents of the beaker to a 10-mL volumetric flask and adjust to the mark with MeOH. This yields a stock solution whose concentration is 1000 ppm. Transfer 1 mL using a glass pipette and pipette pump to a 10-mL volumetric flask. Adjust to the mark with DDL This yields a primary dilution reference standard whose concentration is 100 ppm. 

Acids and bases in Table 10-3 can be purchased in forms pure enough to be primary standards. NaOH and KOH are not primary standards because the reagent-grade materials contain carbonate (from reaction with atmospheric CO2) and adsorbed water. Solutions of NaOH and KOH must be standardized against a primary standard. Potassium hydrogen phthalate is convenient for this purpose. Solutions of NaOH for titrations are prepared by diluting a stock solution of 50 wt% aqueous NaOH. Sodium carbonate is relatively insoluble in this stock solution and settles to the bottom. 

A stock solution was prepared by dissolving the enriched isotope. Diluted solutions were prepared from this stock solution on a weight basis. The isotopic composition of this solution was determined experimentally by GC-MS analysis of the chelate. The internal standard solution was calibrated by reverse isotope dilution GC-MS using the atomic absorption primary standard. Weighed amounts of the primary standard solution were mixed with weighed amounts of the enriched isotope solution. Chelates were prepared from the spiked samples (as described below) and were used for mass spectrometric determination of isotope ratios. Concentration of the trace metal in the spike solution was calculated using the experimentally determined isotope ratios, the weights of the standard and... 

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