Quantitation spectrophotometric method

EDTA forms colored complexes with a variety of metal ions that may serve as the basis for a quantitative spectrophotometric method of analysis. The molar absorptivities of the EDTA complexes of Cu +, Co +, and Ni + at three wavelengths are summarized in the following table (all values of e are in cm )... 

Introduction of photoelectric cells led to the replacement of the Duboscq colorimeter and so to quantitative spectrophotometric methods of analysis which met biochemical requirements. This introduction of spectrophotometry as a routine procedure was one of the earliest technological advances underpinning the elucidation of biochemical pathways between 1930-1960. Micromanometric methods also became available about the same time, and offered a means to measure cell respiration. Manometry was developed in Warburg s laboratory in Berlin and was one of the main techniques used by H.A. Krebs in his studies on the citric acid and urea cycles (Chapters 5 and 6). 

Quantitative spectrophotometric methods for pectin utilize carbazole (diphenyleneimine Bitter and Muir, 1962) and m-hydroxydiphenyl (Kintner and Van Buren, 1982). The intense red-to-brown color with carbazole in sulfuric acid, relatively specific for uronans (pectin and alginate), is much less intense with ketohexoses, aldohexoses, and pentoses (Snell and Snell, 1953). The m-hydroxydiphenyl assay is subject to less interference than the carbazole assay. 

A fundamental feature of the spectrophotometric analysis is that the absorbance is an additive function. The Lambert-Beer law states that absorbance is proportional to the number or molecules that absorb the radiation at each wavelength, and this principle is valid even for different absorbing species. This means that the absorbance of a mixture at a given wavelength is equal to the sum of the absorbance of each component of the sample at that wavelength and this is at the bases of all quantitative spectrophotometric methods. Very importantly, this is no longer the case when two or more of the present species interact or react with one another. 

A spectrophotometric method for the quantitative determination of Pb + levels in blood yields an Sjtand of 0.474 for a standard whose concentration of lead is 1.75 ppb. How many parts per billion of Pb + occur in a sample of blood if Ssamp is 0.361 ... 

A second spectrophotometric method for the quantitative determination of Pb + levels in blood gives a linear normal calibration curve for which... 

A third spectrophotometric method for the quantitative determination of the concentration of in blood yields an Sjamp of 0.193 for a 1.00-mL sample of blood that has been diluted to 5.00 mb. A second 1.00-mL sample is spiked with 1.00 )J,L of a 1560-ppb Pb + standard and diluted to 5.00 mb, yielding an Sspike of 0.419. Determine the concentration of Pb + in the original sample of blood. 

A fifth spectrophotometric method for the quantitative determination of the concentration of Pb + in blood uses a multiple-point standard addition based on equation 5.6. The original blood sample has a volume of 1.00 mb, and the standard used for spiking the sample has a concentration of 1560 ppb Pb +. All samples were diluted to 5.00 mb before measuring the signal. A calibration curve of Sjpike versus Vj is described by... 

A sixth spectrophotometric method for the quantitative determination of Pb + levels in blood uses CQ+ as an internal standard. A standard containing 1.75 ppb Pb + and 2.25 ppb CQ+ yields a ratio of Sa/Sis of 2.37. A sample of blood is spiked with the same concentration of Cu +, giving a signal ratio of 1.80. Determine the concentration of Pb + in the sample of blood. 

Ln(II) in LnFj Ln(II) were determined after samples dissolution in H PO in the presence of a titrated solution of NFI VO, which excess was titrated with the Fe(II) salt. It was found that dissolution of the materials based on CeF CeFj in H PO does not change the oxidation state of cerium, thus phosphate complexes of Ce(III, IV) can be used for quantitative spectrophotometric determination of cerium valence forms. The contents of Ln(II, III) in Ln S LnS may be counted from results of the determination of total sulfur (determined gravimetric ally in BaSO form) and sum of the reducers - S and Ln(II) (determined by iodometric method). 

Uranium and thorium are the first members of natural radioactive chain which makes their determination in natural materials interesting from geochemical and radioecological aspect. They are quantitatively determined as elements by spectrophotometric method and/or their radioisotopes by alpha spectrometry. It is necessary to develop inexpensive, rapid and sensitive methods for the routine researches because of continuous monitoring of the radioactivity level. 

A multiwavelength approach might have been considered as an alternative to chemical derivatisation. Ruddle and Wilson [62] reported UV characterisation of PE extracts of three antioxidants (Topanol OC, Ionox 330 and Binox M), all with identical UV spectra and 7max = 277 nm, after reaction with nickel peroxide in alkaline ethanolic solutions, to induce marked differentiation in different solvents and allow positive identification. Nonionic surfactants of the type R0(CH2CH20) H were determined by UV spectrophotometry after derivatisation with tetrabromophenolphthalein ethyl ester potassium salt [34]. Magill and Becker [63] have described a rapid and sensitive spectrophotometric method to quantitate the peroxides present in the surfactants sorbitan monooleate and monostearate. The method, which relies on the peroxide conversion of iodide to iodine, works also for Polysorbate 60 and other surfactants and is more accurate than a titrimetric assay. 

Stabilisers are usually determined by a time-consuming extraction from the polymer, followed by an IR or UV spectrophotometric measurement on the extract. Most stabilisers are complex aromatic compounds which exhibit intense UV absorption and therefore should show luminescence in many cases. The fluorescence emission spectra of Irgafos 168 and its phosphate degradation product, recorded in hexane at an excitation wavelength of 270 nm, are not spectrally distinct. However, the fluorescence quantum yield of the phosphate greatly exceeds that of the phosphite and this difference may enable quantitation of the phosphate concentration [150]. The application of emission spectroscopy to additive analysis was illustrated for Nonox Cl (/V./V -di-/i-naphthyl-p-phcnylene-diamine) [149] with fluorescence ex/em peaks at 392/490 nm and phosphorescence ex/em at 382/516 nm. Parker and Barnes [151] have reported the use of fluorescence for the determination of V-phenyl-l-naphthylamine and N-phenyl-2-naphthylamine in extracted vulcanised rubber. While pine tar and other additives in the rubber seriously interfered with the absorption spectrophotometric method this was not the case with the fluoromet-ric method. 

He et al. [25] described an ultraviolet spectrophotometric method for the quantitative determination of miconazole in liniments. The drug was analyzed at 272 nm, the average recovery was 99.76% and the relative standard deviation was 0.3%. 

Lemli and Knockaert [33] described a spectrophotometric method for the determination of miconazole nitrate suspensions and other organic bases in pharmaceutical preparations by the use of cobalt thiocyanate. The drug and the amines (as their anhydrous hydrochlorides in dichloromethane) react with solid cobalt thiocyanate to form an ion-pair complex that contains two molecules of base to one [Co(SCN)4]2. The complex is determined quantitatively by spectrophotometry versus dichloromethane at 625 nm with rectilinear response for up to 400 pg/mL of the base. This method was applied to miconazole nitrate suspensions and the coefficient of variations were generally <2%. 

A spectrophotometric method for the quantitative determination of fenasal (niclosamide) in tablets was given [56]. The tablets were powdered and extracted with acetone at 35-45°C. The solution was treated with ethanolamine in ethanol (1 1) at pH < 8.0 the absorbance was determined at 400 nm. 

Methods for Determining Biomarkers of Exposure and Effect. Very few methods were located that could be used to determine exposure to 1,3-DNB or 1,3,5-TNB in humans. A spectrophotometric method exists (Dangwal and Jethani 1980) but is selective for nitro and amino benzene-based compounds, not for 1,3-DNB and 1,3,5-TNB specifically. The best methods for determination of exposure to 1,3-DNB and 1,3,5-TNB are HRGC/ECD (Bailey et al. 1988) and GC/MS (McEuen and Miller 1991). To date, only HRGC/ECD has been used quantitatively, and only for detection of... 

Solid-phase organic reactions are hard to quantitate spectrophotometric or fluorimetric methods are probably the best approach. A general method for... 

Analytical methods employed in soil chemistry include the standard quantitative methods for the analysis of gases, solutions, and solids, including colorimetric, titrimetric, gravimetric, and instrumental methods. The flame emission spectrophotometric method is widely employed for potassium, sodium, calcium, and magnesium barium, copper and other elements are determined in cation exchange studies. Occasionally arc and spark spectrographic methods are employed. 

Central ite 1 Analytical Procedures. Centr 1 can be detected by various colorimetric tests, such as described in Refs 1,6,12,24, 28 Sc 33. Some other qualitative tests are given in Ref 13. Quantitative detns of Centr 1 by bromination methods are described in Refs 4,5,7,9,10,14,16,17,20,27,34 Sc 35. Chromatographic and spectrophotometric methods are found in Refs-11,15,18,21,22,23,24, 29,30,32 Sc 33. Other quantitative methods, including polarographic, are in Refs 2,7a,20a,25, 26,27 Sc 30. X-ray diffraction spectra data are given in Ref 19. Detns of stabilizing action of Centr 1 by methods of Taliani and Thomas are discussed in Refs 3 8... 

Another technique which has much potential in analysis, but which to date has had only limited use, is the formation of radioactive derivatives of non-radioactive compounds for quantitation by radiocounting. A radiolabeled reagent is used to form the derivative. This approach has been of use in combination with chromatography. The advantage of this technique is that it avoids problems of sample background which are often associated with spectrophotometric methods. The 14C-methylation of carboxylic acids and the 14 C-acetylation of hydroxyl groups have been studied [39,40]. These methods are quantitative and the sensitivity is dependent on the activity of the radioactive group added to the molecules. The radioactive derivatization of lipids has been reviewed [41]. 

The limitations of the Gutzeit method for determining arsenic are well-known. The spectrophotometric molybdenum blue or silver diethyldithio-carbamate procedures tend to suffer from poor precision. Sandhu [34] has described a spectrophotometric method for the direct determination of hydrochloric acid-releasable inorganic arsenic in soils and sediments. The method provides reliable data on the quantitative recovery of 2.0 xg of arsenic(V) added to 5.0 g (0.4 mg/kg) of soil, clay, sand and sediment samples. The method is simple, reliable and relatively rapid 24 samples can be analysed in about an hour. It does not require elaborate equipment and can be routinely used for the quantitative determination of arsenic in soil and soil-like material. The detection limit has been established as 0.5 xg of arsenic. The extent of ionic interference when this method is used for arsenic determination in soil was also quantitatively evaluated. 

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