High purity standards

Riedel-de Haen, High Purity Standards, Seelze, BRD (1998). 

Element LA-ICP-MS Certified value (High Purity Standards)... 

Bismuth nitrate (analytical grade) lppm high-purity standard solutions of the nitrate salts of Pb and Cd prepared using supporting electrolyte solutions and acetate buffer (0.1 M, pH 4.5) as supporting electrolyte prepared in Milli-Q water. 

Method validation is important to ensure that the analytical method is in statistical control. A method may be validated by the so-called method evaluation function (MEF) (Christensen et al., 1993), which is obtained by linear regression analysis of the measured concentrations versus the true concentrations. A true concentration in a solution can be obtained by use of a high purity standard obtained from another manufacturer or batch than the one used for calibration. Both the high purity standard and the solvent are weighed using a traceable calibrated balance. If certified reference material is available this is preferred. The method evaluation includes the most important characteristics of the method as the following elements (see Figure 2.7) ... 

The excellent development of nonaqueous batteries (mostly lithium, metal based and Li ion rocking chair type batteries) created a market for the Li battery grade materials which are manufactured at high purity standards. These materials are manufactured by companies whose expertise lies in the production and distribution of the highly pure solvents and salts. Currently, a great part of... 

Stock Solutions [Because of the difficulty in preparing matrix modifier stock solutions with the required purity, purchasing modifier stock solutions and using them to prepare working modifier solutions is recommended. A palladium (0.3%) and magnesium nitrate (0.2%) solution may be purchased from High Purity Standards, or equivalent.]... 

Solvolysis (chemolysis) is defined as a techniqne which obtains the raw materials, snch as TPA, DMT, EG monomers and oligomers as the reverse process of PET prodnction by saponification or transesterification with water, methanol or EG. For the process of PET production raw materials of high purity are obligatory. Polycondensation is not a chain reaction, but a step reaction. Impurities can stop the polycondensation at low molar masses, so high-purity standards are also reqnired for the solvolysis prodncts. The choice of process depends on the starting material and the demand for solvolysis prodncts. 

Fillers are used by the pharmaceutical industry for three main functions as colorants, disintegrants, and glidants. Each application demands special properties, as discussed below. Pharmaceutical grade fillers differ from those used by other industries in that they must comply with a high purity standard. The purity of material for pharmaceutical use is not only defined in terms of chemical composition but microbiological contamination is strictly limited. 

More than half of the synthetic hydrocarbon products made at Ohio State have been sent to APIRP 6 for purification to make the two series of high purity standard samples of hydrocarbons prepared, first at the National Bureau of Standards, now at the Carnegie Institute of Technology. Most of the hydrocarbon compounds that have been purified by APIRP 6 were prepared by APIRP 45. 

Substrates and reduction products were identified on a Hewlett Packard HP6890 gas chromatograph equipped with an FID detector and employing a 30m Restek RTX-200 eapillary column (trifluoropropylmethyl polysiloxane pacing). Yields of the resulting alcohols from these reductions were based on area percents correlated to known quantities of high purity standards (Aldrich). 

Another method for the detection of the PANs involves thermal decomposition to NO2 and direct measurement with an NO chemiluminescence monitor. This instrument relies on the reaction of NO with O3 to produce excited NO2. The NO2 emission is a broadband chemiluminescence starting at about 600 run and peaking at A = 1.27 /rm (1270 nm). A red-sensitive photomultiplier is required to monitor the emission. To monitor NO2, the sample is first passed over a hot catalyst which converts the NO2 to NO. A number of atmospheric nitrates, including HNO3 and the PANs, are also decomposed by the hot catalyst to NO. The main drawback of this method for PAN detection is its sensitivity, which is limited to 1 to 2 ppbv because of the lack of sensitivity of commercial phototubes at the emission wavelength. This method is useful for calibration of other detectors with high purity standards under controlled laboratory conditions. 

The determination of chemical species in an environmental or biological sample can be difficult and time consuming. The accuracy and precision generally achieved for this type of work is not as good as that for total elemental analysis, even for laboratories with a proven track record in speciation analysis. Only a limited number of high purity standards are available, and so calibration of the method is an important area for improvement in methodology. Standard additions and external calibration strategies have been applied and recently, the use of IDMS has been described. 

High purity standards and reagents should be used, and should be characterised where appropriate. 

Figure 10.37 Precision and recovery data for Trace Metals in Drinking Water Certified Reference Material (CRM) by ICP-MS. The ICP-MS used was a PE SCIEX Elan 6000 and the CRM is from High Purity Standards, Charleston, SC. (From Wolf et al. 1995, used with permission.)...

Analytic data were obtained using an atomic absorption spectrometer (Varian Spectra AA-30). High purity standards were used for calibration. All results were based on the average of at least four separate sample solutions aspirated into the spectrometer. Samples rerun at a later time gave essentially no change in the analysis. Magnetic measurements were taken using an EPR spectrometer (IBM 2000). 

To maintain high-purity standards of the product, several precautions must also be taken in the design of the drying chamber and installation [8]. 

Quantitative analysis by ICP-MS is usually done with external calibration standards and the addition of internal standards to all standards and samples. When a large number of elements across the periodic table are to be determined, it is usual to add Li, Y, In, Tb, and Bi and measure the ions Li, " In, Tb, and ° Bi as internal standards (unless you need to measure one of these elements as an analyte). Not all of the internal standard elements are used to quantitate every analyte. The internal standard that is most closely matched in first ionization potential to the analyte is generally used, since this will compensate for ionization interferences in matrices containing easily ionized elements such as Na. Results obtained using this approach are generally very accurate and precise. Table 10.23 presents typical spike recovery and precision data for ICP-MS determination of 25 elements in a certified reference material (CRM) Trace Elements In Drinking Water from High-Purity Standards, Charleston, SC. 

Note The CRM is from High-Purity Standards, Charleston, SC. 

DSC provides a rapid, accurate and precise method for determining absolute purity. A small amount of sample (milligrams) is required and it is not necessary to use a high-purity standard of the compound for an accurate purity determination. The calorimetric purity method is accepted by the US Pharmacopeia/National Formulary [12] as a reference test method. 

Prepare tris buffer with known purity tris and high purity, standardized HCl. Make up with nitrogen-purged deionized or distilled water. 

Experience at NBS in the certification of high-purity Standard Reference Materials has illustrated the point that on most real samples, trace element analysis below the ppm level gives values of questionable accuracy. All trace methods of analysis except activation analysis must deal realistically and directly with problems of blank contamination, i.e., contamination introduced into the sample through preliminary handling and/or subsequent processing in the analytical procedure. 

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