Impurities unknown

Purity Technical grade compound is about 92% pure nature and extent of impurities unknown... 

Into the bottom of a 25-mL filter flask place 50 mg of an impure unknown taken from the list in Table 3. These substances can be sublimed at atmospheric pressure although some will sublime more rapidly at reduced pressure. Close the flask with a rubber pipette bulb, and then place ice water in the centrifuge tube. Cautiously warm the flask until sublimation starts... 

Acetamide [60-35-5] C2H NO, mol wt 59.07, is a white, odorless, hygroscopic soHd derived from acetic acid and ammonia. The stable crystalline habit is trigonal the metastable is orthorhombic. The melt is a solvent for organic substances it is used ia electrochemistry and organic synthesis. Pure acetamide has a bitter taste. Unknown impurities, possibly derived from acetonitrile, cause its mousy odor (1). It is found ia coal mine waste dumps (2). 

Of course, the most reliable and accurate method of quantitative analysis is to calibrate each element with standards prepared in matrices similar to the unknown being analyzed. For a survey technique that is used to examine such a wide variety of materials, however, standards are not available in many cases. When the technique is used mainly in one application (typing steels, specifying the purity of alloys for a selected group of elements, or identifying impurities in silicon boules and... 

Other zinc reductions have been used extensively. Zinc dust in aqueous ammonium chloride is a standard reagent for the reductive cyclization of nitro esters to hydroxamic acids. These reactions are usually carried out at low temperatures (0°-10°) to avoid further reduction. Despite the fact that good yields can often be obtained, these reductions are highly capricious, depending on the quality of the zinc (impurities seem to improve the reaction) and other unknown factors. 

J. Ogorka, G. Schwinger, G. Bmat and V. Seidel, On-line coupled reversed-phase high-performance liquid cliromatography-gas chromatography-mass specti ometi y , A powerful tool for the identification of unknown impurities in pharmaceutical products , J. Chromatogr. 626 87-96 (1992). 

This definition outlines in very broad terms the scope of analytical chemistry. When a completely unknown sample is presented to an analyst, the first requirement is usually to ascertain what substances are present in it. This fundamental problem may sometimes be encountered in the modified form of deciding what impurities are present in a given sample, or perhaps of confirming that certain specified impurities are absent. The solution of such problems lies within the province of qualitative analysis and is outside the scope of the present volume. 

Running a blank determination. This consists in carrying out a separate determination, the sample being omitted, under exactly the same experimental conditions as are employed in the actual analysis of the sample. The object is to find out the effect of the impurities introduced through the reagents and vessels, or to determine the excess of standard solution necessary to establish the end-point under the conditions met with in the titration of the unknown sample. A large blank correction is undesirable, because the exact value then becomes uncertain and the precision of the analysis is reduced. 

TLC analysis of the crude product (elution with 50 1 pentane ether, visualization with iodine) showed three non-baseline spots Rf 0.65 (cis isomer), Rf 0.52 (unknown impurity), and Rf 0.32 (trans isomer). The unknown impurity is intensely sensitive to iodine and largely coelutes with the cw-isomer in the subsequent column chromatography. However, the ll NMR spectrum of this isomer shows excellent purity despite the presence of this spot on TLC. In 100 1 pentane ether, Rf values of the cis and trans isomers are about 0.50 and 0.15, respectively. 

The experimentally observed minimum in retention in dilute solution remains unexplained. An explanation could lie in a scavenger action by an unknown impurity. 

However, compared with the traditional analytical methods, the adoption of chromatographic methods represented a signihcant improvement in pharmaceutical analysis. This was because chromatographic methods had the advantages of method specihcity, the ability to separate and detect low-level impurities. Specihcity is especially important for methods intended for early-phase drug development when the chemical and physical properties of the active pharmaceutical ingredient (API) are not fully understood and the synthetic processes are not fully developed. Therefore the assurance of safety in clinical trials of an API relies heavily on the ability of analytical methods to detect and quantitate unknown impurities that may pose safety concerns. This task was not easily performed or simply could not be carried out by classic wet chemistry methods. Therefore, slowly, HPLC and GC established their places as the mainstream analytical methods in pharmaceutical analysis. 

SIMS intensities from the "clean" Cu/Ni surfaces cannot be used to determine Cu/Ni surface concentrations, or relative change in concentration from one surface to another. This is because trace impurities (of very low but unknown concentration) preferentially bond to Ni sites and therefore the Ni containing SIMS cluster ions are preferentially enhanced, leading to an erroneously high determination of Ni concentration. 

Ethanoiamine is used to absorb carbon dioxide. A tank that contained the absorption product combusted spontaneously in air, probably because of an unknown impurity and because an amine evaporation had stripped a heating coil of this compound. The fire went out later due to the carbon dioxide release caused by the compound s temperature rise. 

The testing of impnrities in active pharmacentical ingredients has become an important initiative on the part of both federal and private organizations. Franolic and coworkers [113] describe the utilization of PLC (stationary phase — silica gel and mobile phase — dichloromethane-acetonitrile-acetone (4 1 1, v/v)) for the isolation and characterization of impurities in hydrochlorothiazide (diuretic drug). This drug is utilized individually or in combination with other dmgs for the treatment of hypertension. The unknown impurity band was scraped off the plate and extracted in acetonitrile. The solution was filtered and used for LC/MS and NMR analysis. The proposed procedure enabled the identification of a new, previonsly nnknown impurity. It was characterized as a 2 1 hydrochlorothiazide-formaldehyde adduct of the parent drug substance. 

THF solution [290]. There had been much confusion in the past about the magnetic moment of the iron(I) species and the correct Mossbauer and NMR properties caused by impurities of the samples and possible unknown axial ligation. However, with clean crystallized samples with known molecular structure [291], the first reduction product of iron(II)(tetraphenylporyphrin), [Fe(TPP)], can be clearly characterized as a quasiplanar iron(I) complex with spin S = 1/2 (EPR = 2.28,... 

Excellent if unJutown is in reference file. Poor if unknown spectrum contains contaminant peaks. Better than whole spectrum search for Impure spectra. 

Finally, one has to consider that an unknown impurity present in the benzene is responsible for quenching the triplet state/8,12,16 We then have four viable possibilities to explain this effect. 

A study of the nomenclature problem indicates that only samples are analyzed elements, ions, and compounds are identified or determined. The difficulty occurs when the sample is nominally an element or compound (of unknown purity). Analysis of... (an element or compound) must be understood to mean the identification or determination of impurities. When the intent is to determine how much of such a sample is the material indicated by the name, assay is the proper word. ... 

The material (of unknown structure, analysing as Aui 5N9Na and possibly the impure title compound, explodes at 130°C. 

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