Calibration solutions for

Various methods can be used to analy2e succinic acid and succinic anhydride, depending on the characteristics of the material. Methods generally used to control specifications of pure products include acidimetric titration for total acidity or purity comparison with Pt—Co standard calibrated solutions for color oxidation with potassium permanganate for unsaturated compounds subtracting from the total acidity the anhydride content measured by titration with morpholine for content of free acid in the anhydride atomic absorption or plasma spectroscopy for metals titration with AgNO or BaCl2 for chlorides and sulfates, respectively and comparison of the color of the sulfide solution of the metals with that of a solution with a known Pb content for heavy metals. 

The pure substances are provided with a statement of the purity and serve as authentic reference compounds to prepare calibration solutions for measurement of trace levels of the compound in natural matrix samples. 

A further distinction is made between pure solutions and matrix-based RMs. The former are available for many organic and inorganic analytes, with certified concentrations, but their role in quality control and assessment is limited. They may be used for the preparation of calibration solutions for a particular measurement but more usually these materials represent the base for traceability, through secondary... 

Normally, the uncertainties in the concentrations of the calibration solutions (variable x) are small in relation to the uncertainties of the response of the measurement system (variable y), so that the regression parameter can be estimated using ordinary least squares (OLS). In exceptional cases, the test quantity SeJSx (Sex2 means the variance in the concentration of the calibration solutions for a particular calibration level, and Sx2 indicates the total variance in concentration) can be calculated, and if Sex/Sx>0.2 the regression parameters should be estimated by orthogonal distance regression (ODR) [10],... 

In atomic absorption spectroscopy (AAS) both ionization and chemical interferences may occur. These interferences are caused by other ions in the sample and result in a reduction of the number of neutral atoms in the flame. Ionization interference is avoided by adding a relatively high amount of an easily ionized element to the samples and calibration solutions. For the determination of sodium and potassium, cesium is added. To eliminate chemical interferences from, for example, aluminum and phosphate, lanthanum can be added to the samples and calibration solutions. 

As a calibrant solution for the AgNOs titrant, Standard Seawater was prepared that had certified values for both chlorinity and salinity. Unfortunately, the above salinity-chlorinity relationship was derived from only nine seawater samples that were somewhat atypical. It has since been redefined using a much larger set of samples representative of oceanic waters to become... 

The British standard for the pH scale is an aqueous solution of potassium hydrogen phthalate (0.05 M), which has a pH of 4.001 at 20 °C and is often used as a calibration solution for pH meters. 

Calibration solutions. For the determination of the calibration factor prepare at least three calibration solutions by mixing 20 ml of the internal standard solution with different amounts between 1 and 10 ml of the reference solution and by diluting to 50 ml with anhydrous ethanol. 

TABLE 4-2 Example of Two-Level Calibrating Solutions for Measurement of pH and Electrolytes by Direct Potentiometry ... 

Each laboratory used its own optimised procedure for the sample preparation, clean-up, method of injection, calibration and gas chromatographic conditions [33]. Calibrants were obtained as pure crystalline certified materials from BCR [32] in addition, CBs 105, 128, 149, 156, 163 and 170 were obtained from BCR after characterisation in an independent laboratory of the identity of the compound by elemental analysis, NMR and melting point determination, and of the purity of the crystalline materials by GC-MS, GC-ECD [32] these pure compounds were used to prepare calibration solutions for these congeners. Each laboratory prepared separate calibration solutions in iso-octane of the appropriate concentration to calibrate the detector within the approximately linear range. Calibration procedures used by the participants are described in details in the certification report [32]. 

L.F. Almeida, M.G.R. Vale, M.B. Dessuy, M.M. Silva, R.S. Lima, V.B. Santos, et al., A flow-batch analyzer with piston propulsion applied to automatic preparation of calibration solutions for Mn determination in mineral waters by ET AAS, Talanta 73 (2007) 906. 

Burton, I.W., Quilliam, M.A., and Walter, J.A., Quantitative H NMR with external standards use in preparation of calibration solutions for algal toxins and other natural products. Anal. Chem., 77, 3123, 2005. 

National Research Council of Canada, Certified Reference Materials Program. Certified Calibration Solution for Yessotoxin, NRC CRM-YTX, 2006. 

Flame atomic emission spectrometry Basic information on FAES is presented elsewhere in this encyclopedia. Sodium measurements are performed at 590 nm with the use of a propane flame (1925°C). Physiological samples for sodium determination are highly diluted before measurement. The diluent and the calibrator solution contain the same concentration of lithium ions so as to balance flame instability by a concomitant measurement of lithium in the reference beam (the so-called lithium guideHne). At the same time, lithium ions inhibit the ionization of sodium atoms. This procedure cannot be used in the case of therapy with lithium salts. That is why some authors prefer the concomitant measurement of caesium to that of lithium. Dilution adjusts the viscosity of the sample to that of the calibrator solution to produce identical aspiration rate and drop size on nebulization. As other electrolytes interfere with sodium measurement, their concentration in the caH-brator solution must be similar to their concentration in the sample. For the measurement of sodium in urine, calibrator solutions different from those for serum measurement are needed as the electrolyte concentrations in urine samples are quite different from those in serum and their relations are very variable. As the concentration of the electrolytes in serum is rather constant, calibrator solutions for serum measurements can fulfill their function better than those for urine in other words, urine determinations are usually less accurate. FAES proved to be sufficiently reliable to be used as the basic principle of the sodium reference measurement procedure. In routine use, however, FAES is less accurate. Its application is given up by most clinical laboratories in favor of potentiometric measurements... 

Very pronounced pH insensitivity in commercial buffers used as calibrating solutions for multiparameter clinical analyzer, with stability of readout within 1 mV in the pH range 7.0-7.8, was observed for the PEDOT-MES films. On the other hand, the PEDOT film doped with benzenesulfonic acid (BSA, which cannot form a buffer pair) indicated much stronger pH sensitivity [18, 19]. 

The calibration solutions for analysis have to be prepared in the same final medium as the samples in order to get a matrix, which is the same as in the samples. The final medium is 0.8 M H,SO,. 

The amount of internal standards added must be approximately in the same proportion as that added to the calibration solutions. For example, if 2 g of benzene-d6 was added per lOO-mL solutions for cidibrations, then add 0.2 g for 10 mL of sample. The sample solution is then mixed 30 s on a vortex mixer and analyzed by GC/MS as described above. 

Note 4—Mix all calibration solutions for at least 30 s on a Vortex mixer after preparation or equivalent. Highly precise sample robotic sample preparation systems arc available commercially. Th systems may be used provided that the results for the quality control reference material (Section 11) are met when prepared in this manner. 

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. 

The flasks or vials are then filled to 100 mL with n-heptane. This procedure generates calibration solutions for the C9 aromatics in the range of 0.5 to 5 volume %. 

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