Calibration volumetric internal standard

Application of such a calibration to quantitative analysis of sample extracts requires that these extracts be spiked with the identical quantity Qvis.a of volumetric internal standard as used in the calibration experiments. (It is emphasized that all of these spiking procedures, i.e. calibration solutions plus sample extracts, should be done at the same time, to minimize any drift in the value of Cyis as a result of uncontrolled evaporation.) Then it is straightforward to show that ... 

The need for a surrogate internal standard (SIS) and the ways in which it is used in practice were discussed in Sections 2.6.3 and 8.5.2. Questions concerning choice and availability of an SIS were introduced in Section 2.2.3 and Table 2.1, and are discussed further below. All of the concerns about chemical and chiral purity, applicable to the analytical standard (Section 9.4.4), apply also to the SIS however, the absolute chemical purity is not as crucial for the SIS in cases where both calibration and measurement are performed using response ratios of analyte SIS where the absolute quantity of SIS detected does not enter into the final determination (Section 8.5.2b, essentially the signal from the SIS is used as a normalizing factor for the analyte responses). In the few instances where a volumetric internal standard is required (Sections 2.2.4 and 8.5.2a) the only concern is that the VIS is stable and provides no interferences (direct or indirect) that co-elute with the analyte. 

A chromatographic mobile phase consisting of acetonitrile/0.1 M sodium acetate buffer pH 4.0 (70 30) is prepared. Separate stock solutions in 250 ml of chromatographic mobile phase containing miconazole nitrate (200 20 mg) and econazole nitrate (200 20 mg) (internal standard) are prepared. 25 ml of econazole nitrate stock solution is transferred to five 100 ml volumetric flasks and varying amounts of miconazole stock solution 15, 20, 25, 30 and 35 ml are added to the five flasks. The flasks containing the calibration series are diluted to volume with mobile phase. A sample of cream containing 20 mg miconazole nitrate is shaken with 25 ml... 

The volumetric marks on volumetric ware are called calibrations. How they were located on the volumetric ware is called calibration. All volumetric ware is calibrated to provide its stated volume at 20°C. The International Standards Organization has recommended that the standard volumetric temperature should be changed to 27 °C. However, so far there has not been any significant movement toward this goal. The ASTM recommends that those labs in temperate climates that are unable to maintain an environment at 20°C should maintain one at 27°C. 

Calibration Standards Prepare four HQ calibration standards as follows Add 0.50, 1.00, 2.00, and 3.00 mL of HQ Stock Solution into separate 10-mL volumetric flasks, then add 2.00 mL of Methyl Benzoate Stock Solution (internal standard) to each, dilute to volume with pyridine, and mix. In the same manner, prepare four DTBHQ Stock Solution calibration standards. Prepare the trimethylsilyl derivative of each standard as follows Add 9 drops of calibration standard to a 2-mL serum vial, cap the vial, evacuate with a 50-mL gas syringe, add 250 p,L of A.O-bistrimethylsilylacetamide, and heat at about 80° for 10 min. 

Etofenprox calibration solution. Weigh in duplicate (to the nearest 0.1 mg) about 0.06 g of etofenprox standard (M and Mg) into two 50-ml stoppered volumetric flasks. Add 10ml of di-cyclohexyl phthalate internal standard solution, shake to dissolve the etofenprox and dilute to 50 ml with methanol/tetrahydrofuran (50 50, v/v) (solutions and Cg). Keep the solutions in a thermostat bath if room temperature varies by more than 2°C. 

Three or more calibration mixtures are made from pure samples of the analyte(s). A known amount of internal standard is added to each calibration mixture and to the unknown. Usually the same amount of standard is added volumetrically, e.g., 1.00 mL. All areas are measured and referenced to the area of the internal standard, either by the data system or by hand. 

Combining appropriate amounts of the stock solutions of analytical and internal standards, and subsequent dilution, can again be done volumetrically or gravimetrically (via a weighed syringe) the choice can only be determined by considerations of fitness for purpose, but most often careful manipulation of standard flasks and pipets (possibly re-calibrated for the purpose by weighings) is adequate for trace analysis (see Section 9.5.4 for details) as other uncertainties can considerably exceed those introduced in preparing the calibration solutions. 

With a calibrated pipettor, prepare the final internal standard solution by diluting 125 pL of this intermediate solution to 250 mL with 5% v/v nitric acid in a clean PP, PMP, or PFA volumetric flask. Store aU solutions at room temperature. 

For calibration, a set of standard solutions in the range of 0.005-1.0 mg/L is prepared. Therefore, appropriate volumes of the standard mix stock solution and the internal standard solution (200 pL) are transferred to 50-mL volumetric flasks, filled up with extraction buffer and sonicated for 5 min. 

For quantitative studies, stock solutions of the internal standard (5.02 x 10 g/ml mesitylene tricarbonylchromium) and of the other complexes were prepared by dissolving accurately weighed amounts (0.05 gram) of each complex in the solvent and diluting to a known volume. Subsequent volumetric dilutions yielded calibration solutions ranging in concentration from 1.00 x 10 to 1.50 x 10 " g/ml for each complex, and a constant amount (1.00 x 10 g/ml) of internal standard. Synthetic mixtures were prepared in a similar manner. Because solutions of all the complexes are somewhat light sensitive and show some decomposition over a period of several days, flasks were stored in the dark when not in use. All solutions were analyzed on the same day they were prepared. 

Weigh in turn into a 1- cm volumetric flask 1.0 cm n-undecane, internal standard plus 1.0 cm of any of the above aromatic hydrocarbons it is requited to determine. Dilute to 10 cm with propylene oxide and then further dilute 0.25 cm of the solution to 25 ml with propylene oxide. Chromatograph 5 ul of the calibration blend. This calibration procedure should be carried out daily. 

Internal standard elements can be added to the calibration standards and the samples by a simple volumetric addition to the appropriate solutions. Although this provides an accurate means of adding internal stan-... 

Bring the internal standard and the sample to be analyzed to identical temperatures, preferably 2S C. Make sure that the temperature of the sample is consistent with that of the calibration standard prepar in Section 11. Pipet SO.O pL of internal standard into a 50-mL volumetric containing 50.00 mLs of sample. Mix well. 

Place 30 to 60 mL of the cyclohexane sample to be analyzed into a 100-mL volumetric flask. Accurately add, using a micropipet or microsyringe, 25 pL of the internal stan rd to the flask and then All to the calibration mark with additional sample. Based on using 2,2-dimethylbutane as the internal standard with a density of 0.649 g/mL and cyclohexane with a density of 0.780 g/mL, the concentration of the internal standard will be 0.021 wt%. Similar calculations must be made for any alternative internal standard that may be used. Mix the above, blend thoroughly, and analyze using the chromatographic conditions stated in Table 2. 

With a microsyringe, add 50 pL of internal standard to a 100-mL volumetric flask about three-fourths full of the calibration mixture. Mix well. Add calibration mixture to mark and again mix well. If n-heptane is used as the internal standard, using a density of 0.684 for n-heptane and 0.906 for styrene, this solution will contain 0.0377 weight % n-heptane. 

For each above Set 1, 3, 5, 10, IS, and 20 mL aliquots of each component are pipetted into respective 100 mL volumetric flasks or vials while accurately recording the masses. For example, for Set 1, into flask one add 1.0 mL MTBE, 1.0 mL DIPE, 1.0 mL ETBE, 1.0 mL TAME into flask two add 3.0 mL MTBE, 3.0 mL DIPE, 3.0 mL ETBE, 3.0 mL TAME and so forth. Add the oxygenate in reverse order of their boiling points. The above procedure produces six calibration solutions for each set with the concentrations of each analyte at 1, 3, S, 10,15, and 20 volume %. 10.0 mL of DME (internal standard) is then added at constant volumes to each flask or vial while recording its mass. The flasks or vials are then filled to 100 mL total volume with toluene. It is not necessary to weigh the amount of solvent added since the calculations are based on the absolute masses of the calibration components and the internal standard components. 

Add 1.0 mL of internal standard into a 10.0 mL volumetric flask or vial and record the mass (Add 9.0 mL of gasoline sample to the flask or vial, and record the mass (Wg). The sample/intemal standard solution is then mixed 30 s on a vortex mixer and analyzed by GC/FTIR according to the instrument manufacturer s directions using the same conditions as for calibrations. 

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