Reference standardization

The physics of X-ray refraction are analogous to the well known refraction of light by optical lenses and prisms, governed by Snell s law. The special feature is the deflection at very small angles of few minutes of arc, as the refractive index of X-rays in matter is nearly one. Due to the density differences at inner surfaces most of the incident X-rays are deflected [1]. As the scattered intensity of refraction is proportional to the specific surface of a sample, a reference standard gives a quantitative measure for analytical determinations. 

Based on known ocpcrimontal AG values, and Q, were estimated. The system phenol-HMPA in CCI4. was chosen as the reference standard the H-boud free energy factors C, and Q were set at -2.50 (phenol) and 4,00 (HMPA) respectively. 

The actual value of the enthalpy of hydrogenation of 1,3-butadiene is —243 k,l rnol Both are hydrogenated to the same product, u-biitaiie hence the enthalpy diagram (Fig. 7-4) shows that bnta-1,3-diene is 11 kJ rnol. lower in enthalpy than it ought" to be on the basis of the reference standard, bnt-l-ene. 

Using cyclohexene as the reference standard, calculate the resonance energies of cyclohexa-1,3-diene = —224 kJ moU ), cyclohexa-1,4-diene =... 

Spectroscopically determined values of P vai y, but they aie usually around —2.4 eV. In the section on resonance stabilization, we saw that thermodynamic measurements of the total resonance stabilization of butadiene yield 11 and 29 kJ mol according to the reference standard chosen. Calculate the delocalization energy of buta-1,3-diene in units of p. Determine two values for the size of the energy unit p from the thermochemical estimates given. Do these agree well or poorly with the spectroscopic values ... 

For the secondary pH reference standards, the buffer value is 0.070 for potassium tetroxalate and 0.09 for calcium hydroxide. 

For example, if a carbonaceous sample (S) is examined mass spectrometrically, the ratio of abundances for the carbon isotopes C, in the sample is Rg. This ratio by itself is of little significance and needs to be related to a reference standard of some sort. The same isotope ratio measured for a reference sample is then R. The reference ratio also serves to check the performance of the mass spectrometer. If two ratios are measured, it is natural to assess them against each other as, for example, the sample versus the reference material. This assessment is defined by another ratio, a (the fractionation factor Figure 48.2). 

For two samples A and B measured against the same reference standard X, the relationship between the a and 5 values can be approximated by the expression shown in Equation 48.1 (see also Figure 48.5). 

Handbook 105-1, Specifications and Tolerancesfor Reference Standards andEield Standard Weights and Measures, National Institute of Standards and Technology, Gaithersburg, Md., 1990. 

There are no estabHshed specifications for the standard reference samples used in general chemical analysis. Many such substances, however, are analyzed and certified by the National Institute of Standards and Technology (NIST), formerly the National Bureau of Standards (NBS). Specific reference standards are required for many of the analyses included in the USP and NE standards for dmgs. 

Reference Standards. Many of the identification tests and assays require the use of reference standards. These standards are available for purchase from the USPC. 

United States Pharmacopeia. Reference standards are requited in many USP and NF tests, and in a few FCC tests. The USPC distributes such standards domestically and has authorized international distribution by a number of organizations or companies. There are well over 1000 USP Reference Standards, including several for melting points, and also specimens of narcotics and other controlled substances. New standards are constantly under development as needed in various USP, NF, and FCC testing methods. 

Specifications for hGH products are defined by the governmental licensing authorities, eg, the U.S. Pood and Dmg Administration. Draft monographs for hGH have been prepared by both the EnitedStates Pharmacopia and the European Pharmacopeia commissions and should be formally adopted by 1995. These specifications are suitable for biosynthetic hGH. The much less purified pituitary-derived hGH has virtually disappeared from commercial production. An international reference standard for pituitary-derived hGH (lot 80/505) has been used for caUbration, particularly for bioassay purposes. A highly purified biosynthetic hGH standard (lot 88/624) has been prepared and should be formally adopted by 1995, or before. 

Analytical standards imply the existence of a reference material and a recommended test method. Analytical standards other than for fine chemicals and for the NIST series of SRMs have been reviewed (6). Another sphere of activity ia analytical standards is the geochemical reference standards maintained by the U.S. Geological Survey and by analogous groups ia France, Canada, Japan, South Africa, and Germany (7). 

Reasonable grounds in support of tolerance petition Analytical reference standard(s)... 

Entry into Confined Spaces. In 1993 OSHA adopted a confined space entry rule (93) requiring employers to evaluate the workplace to (/) determine if it contains any confined spaces, (2) mark or identify such confined spaces, and (2) develop and implement a permit program for entry into such spaces. The program must include a permit system which specifies the steps to be taken to identify, evaluate, control, and monitor possible electrical, mechanical, and chemical ha2ards select and use equipment institute stand-by attendance and estabflsh communications. The reference standard (93) should be studied for details. 

Statistical control of an analysis or instmment is best demonstrated by SQC of a standard sample analysis. The preferred approach to demonstrate statistical control is to use a reference sample of the subject material that has been carefully analyzed or, alternatively, to use a purchased reference standard. Either material must be stored so that it remains unchanged, eg, sealed in ampuls or septum capped bottles. Periodically a sample can then be reanalyzed by the technique used for routine analysis. These results are plotted in a control chart. Any change in the stabihty of the test in question results in a lack of... 

Fig. 2. An SPC control chart of the purity analysis of a reference standard where (—) represents the average value and UCL and LCL are the upper and...

Rhinitis is characterized by nasal stuffiness with partial or full obstmction, and itching of the nose, eyes, palate, or pharynx, sneezing, and rhinorrhoea. If left untreated it can lead to more serious respiratory diseases such as sinusitis or asthma. Although several types of dmgs are available for treatment, nasal spray topical corticosteroids are widely regarded as the reference standard in rhinitis therapy (250). 

Analytical and Laboratory Operations. Sulfamic acid has been recommended as a reference standard in acidimetry (55). It can be purified by recrystaUization to give a stable product that is 99.95 wt % pure. The reaction with nitrite as used in the sulfamic acid analytical method has also been adapted for determination of nitrites with the acid as the reagent. This reaction is used commercially in other systems for removal of nitrous acid impurities, eg, in sulfuric and hydrochloric acid purification operations. 

The U.S. standard pertussis vacciae is used to standardize the potency of the whole ceU pertussis vacciae. The number of protective units Hi the vaccine is estimated for each lot from the results of simultaneous intracerebral mouse-protection tests of the vaccine being studied and the U.S. reference standard (14,17). The potency of the aceUular vaccines is estimated by then abUity to produce antibodies to the proteins Hi the vaccine Hi a mouse model. These vaccines also undergo a series of animal safety tests to ensure that the iaactivation and toxoiding steps were carried out correctiy (14,17). 

In 1949 the World Health Organization adopted the biological activity of 1 mg of an oil solution containing 0.025 p.g of crystalline D as the analytical standard for vitamin D. This standard was discontinued in 1972. USP uses crystalline cholecalciferol as a standard (80). Samples of reference standard may be purchased from U.S. Pharmacopeia Convention, Inc., Reference Standards Order Department, 12601, Twinbrook Parkway, Rockville, Maryland 20852. One international unit of vitamin D activity is that activity demonstrated by 0.025 ]1 of pure crystalline (7 -vitamin D. One gram of vitamin D3 is equivalent to 40 x 10 lU or USP units. The international chick unit (ICU) is identical to the USP unit. 

The standard chemical and biological methods of analysis are those accepted by the JnitedStates Pharmacopeia XXIII as well as the ones accepted by the AO AC in 1995 (81—84). The USP method involves saponification of the sample (dry concentrate, premix, powder, capsule, tablet, or aqueous suspension) with aqueous alcohoHc KOH solvent extraction solvent removal chromatographic separation of vitamin D from extraneous ingredients and colormetric deterrnination with antimony trichloride and comparison with a solution of USP cholecalciferol reference standard. 

In the CIELAB and CIELUV color spaces, the difference between a batch sample and a reference standard designated with a subscript s, can be designated by its components, eg, AAL = L — L. The three-dimensional total color differences are given by EucHdian geometry as the 1976 CIE lYa b and 1976 CIE lYu Y color difference formulas ... 

The American Association of Cereal Chemists has made avaUable a certified food grade wheat bran as a reference standard for research purposes. This bran is a blend of soft white wheat (87.3%) and club white wheat (12.7%). 

The same reference (standard) state,y, is chosen for the two phases, so that it cancels on both sides of equation 39. The products and are... 

The X-ray determination of REE in geological samples is normally complicated by the relatively low concentrations of the REE, their complex X-ray spectra, the high concentration of matrix elements and the lack of reference standards with certified values for REE. A rapid and sensitive ion exchange and X-ray fluorescence procedure for the determination of trace quantities of rare earths is described. The REE in two U.S.G.S. standards, two inhouse synthetic mixtures and three new Japanese standards have been determined and corrections for inter-rare earth element interferences are made. 

The analysis was performed by XRF method with SR. SRXRF is an instrumental, multielemental, non-destructive analytical method using synchrotron radiation as primary excitation source. The fluorescence radiation was measured on the XRF beam-line of VEPP-3 (E=2 GeV, 1=100 mA), Institute of Nuclear Physics, Novosibirsk, Russia. For quality control were used international reference standards. 

---