Calibration standards INDEX

Analyze calibration standards and samples by HPLC with refractive index detection using the following conditions ... 

Empirical Methods. The empirical methods use calibration standards to derive sensitivity factors that can be used to determine the unknown concentration of given elements in similar matrices [3. The sensitivity factors are derived from calibration curves that plot measured secondary ion intensities versus the known concentration of standards. Three types of sensitivity factors have been used the absolute sensitivity factor, the relative sensitivity factor, and the indexed relative elemental sensitivity factor. 

Operational Qualification (OQ) is a QA approved document designed to check that the individual components operate according to specification. Pumps will be tested with calibrated flow meters to confirm that they perform to the set specification. Calibration standards will be used to assess other instrumentation such as Refractive Index (RI) or Ultra Violet (UV) detectors. Gradient performance will be checked to confirm that the solvent delivery system and mixer is working to specification. Once complete and approved by QA and Technical Management, the equipment will now be made available for use. 

When characterizing particulate matter of unknown composition, it is necessary to assume a value for the index of refraction to infer the diameter from a measured intensity ratio. This causes inherent uncertainties in any reported size distribution unless all particles are of a known and uniform composition. In the case of automobile exhaust particles, the composition is certainly unknown and would probably include some combination of carbon particles and lead halides condensed on nuclei. Figure 1 is indicative of expected variations from such a spread of particle compositions. In the range of low a, the characteristic curve for nonabsorbing particles oscillates around an average value which is approximately the n = 1.57 — 0.56i data. Thus the intensity ratio curve for the absorbing soot is a convenient one to assume as the calibration standard for automobile exhaust particulates. Here this assumption results in a maximum error of approximately 30% when measuring particles of unknown composition. 

Combining SEC with MAES to produce absolute molar mass data without molecular calibration standards also requires prior calibration of the concentration detector as well as calibration of the MAES detector itself. The latter calibration involves the determination of all geometrical contributions such that the MAES detector measures the Rayleigh excess ratio at each scattering angle. This is most easily achieved by using a turbidity standard such as toluene. Details are found in Ref. 2. Once the refractive index of the mobile phase is entered, the software [4] performs the required calibration. 

One method (ASTM D-6379, IP 436) is used to determine the monoaromatic and diaromatic hydrocarbon contents in distillates boiling in the range from 50 to 300°C (122-572°F). In this method the sample is diluted with an equal volume of hydrocarbon, such as heptane, and a fixed volume of this solution is injected into a high-performance liquid chromatograph fitted with a polar column where separation of the aromatic hydrocarbons from the nonaromatic hydrocarbons occurs. The separation of the aromatic constituents appears as distinct bands according to ring structure, and a refractive index detector is used to identify the components as they elute from the column. The peak areas of the aromatic constituents are compared with those obtained from previously run calibration standards to calculate the % w/w monoaromatic hydrocarbon constituents and diaromatic hydrocarbon constituents in the sample. 

G. Castello, Retention index systems alternatives to the w-alkanes as calibration standard, /. Chromatogr., A, 1999, 842, 51-64. 

Figure 2.12 Typical chromatograms produced automatically by the data capture and data reduction software on a modern gel permeation chromatographic instrument (a) a calibration standard and (b) a typical sample with a dispersity index of 1.86 together with a full experimental report. Both the differential and integral distribution curves are plotted. Note that the molecular...

Castello, G. Retention index systems Alternatives to the n-alkanes as calibration standards. J. Chromatogr. A, 1999, 842,51-64. 

Valko et al. [37] developed a fast-gradient RP-HPLC method for the determination of a chromatographic hydrophobicity index (CHI). An octadecylsilane (ODS) column and 50 mM aqueous ammonium acetate (pH 7.4) mobile phase with acetonitrile as an organic modifier (0-100%) were used. The system calibration and quality control were performed periodically by measuring retention for 10 standards unionized at pH 7.4. The CHI could then be used as an independent measure of hydrophobicity. In addition, its correlation with linear free-energy parameters explained some molecular descriptors, including H-bond basicity/ acidity and dipolarity/polarizability. It is noted [27] that there are significant differences between CHI values and octanol-water log D values. 

ISO/IEC Guide 14025, General Requirements for the Competence of Testing and Calibration in Laboratories, International Organization of Standardization, Geneva (2000). Also available on the World Wide Web http //www.iso.ch/iso/en/iso9000-14000/index.html. 

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