Spectrophotometric

S-hydroxyquinoline, oxine, C9H7ON. Light brown needles, m.p. 15-16 C. Forms insoluble complexes with metals. The solubilities of the derivatives vary with pH, etc. and hence oxine is widely used in analysis. Used for estimating Mg, Al, Zn and many other metals. Many oxinates are extracted and the metal is estimated spectrophotometrically. Derivatives, e.g. 2-meIhyl tend to be specific, for, e.g.. Copper derivatives are used as fungicides. 

An illustrative example generates a 2 x 2 calibration matrix from which we can determine the concentrations xi and X2 of dichromate and permanganate ions simultaneously by making spectrophotometric measurements yi and j2 at different wavelengths on an aqueous mixture of the unknowns. The advantage of this simple two-component analytical problem in 3-space is that one can envision the plane representing absorbance A as a linear function of two concentration variables A =f xuX2). 

Simultaneous Cr O " and MnOj" detemiination (Ewing, 1985) is a multivariate spectrophotometric analysis that requires detemiination of a matrix of four calibration constants, one for each unknown at each of two wavelengths. 

Davies and Warren have investigated the nitration of naphthalene, ace-naphthene and eight dimethylnaphthalenes in acetic anhydride at o °C. Rates relative to naphthalene were determined by the competition method, and the nitro-isomers formed were separated by chromatographic and identified by spectrophotometric means. The results, which are summarised in the table, were discussed in terms of various steric effects, and the applicability of the additivity rule was examined. For the latter purpose use was made of the data of Alcorn and Wells (table 10.2) relating to the nitration of monomethyl-naphthalenes at 25 °C. The additivity rule was found to have only limited utility, and it was suggested that the discrepancies might be due in part to the... 

Diazo coupling involves the N exocyclic atom of the diazonium salt, which acts as an electrophilic center. The diazonium salts of thiazoles couple with a-naphthol (605). 2-nitroresorcinol (606), pyrocatechol (607-609), 2.6-dihydroxy 4-methyl-5-cyanopyridine (610). and other heteroaromatic compounds (404. 611) (Scheme 188). The rates of coupling between 2-diazothicizolium salts and 2-naphthol-3.6-disulfonic acid were measured spectrophotometrically and found to be slower than that of 2-diazopyridinium salts but faster than that of benzene diazonium salts (561 i. The bis-diazonium salt of bis(2-amino-4-methylthiazole) couples with /3-naphthol to give 333 (Scheme 189) (612). The products obtained from the diazo coupling are usuallv highly colored (234. 338. 339. 613-616). 

Another line of analytical use is exemplified by the properties of l-(2-thiazolylazoi-2-naphthol (305), whose complexes with metals may be used for their spectrophotometric and titrimetric determination, as wel] as for their separation by solvent extraction (564, 568, 953-957, 1040). 

PAM,. spectropliotoniciric dctcrniination of vanadium photometric dctenniiiation of niobium in the presence of trietlianolamine spectrophotomelric determination of bismuth in the presence of 1,3-diphenylguanidinc spectrophotometric determination of yttrium in the presence of Ttephiramine formation constants of mmplexes with Hoflll) measured... 

Gives complexes of constrating colors with AI,Zn, Th. Zr, and Ga and is useful in tlie photometric analysis of these elements specific reagent of Pa(H) spectrophotometric determination of Cu(U)... 

The first identified complexes of unsubstituted thiazole were described by Erlenmeyer and Schmid (461) they were obtained by dissolution in absolute alcohol of both thiazole and an anhydrous cobalt(II) salt (Table 1-62). Heating the a-CoCri 2Th complex in chloroform gives the 0 isomer, which on standirtg at room temperature reverses back to the a form. According to Hant2sch (462), these isomers correspond to a cis-trans isomerism. Several complexes of 2,2 -(183) and 4,4 -dithiazolyl (184) were also prepared and found similar to pyridyl analogs (185) (Table 1-63). Zn(II), Fe(II), Co(II), Ni(II) and Cu(II) chelates of 2.4-/>is(2-pyridyl)thiazole (186) and (2-pyridylamino)-4-(2-pyridy])thiazole (187) have been investigated. The formation constants for species MLr, and ML -" (L = 186 or 187) have been calculated from data obtained by potentiometric, spectrophotometric, and partition techniques. 

A2.6540-g sample of an iron ore known to contain 53.51% w/w Fe is dissolved in a small portion of concentrated HCl and diluted to volume in a 250-mL volumetric flask. A spectrophotometric method is used to determine the concentration of Fe in this solution, yielding results of 5840, 5770, 5650, and 5660 ppm. Determine whether there is a significant difference between the experimental mean and the expected value at a = 0.05. 

Mizutani and colleagues reported the development of a new method for the analysis of 1-malate. As part of their study they analyzed a series of beverages using both their method and a standard spectrophotometric procedure based on a clinical kit purchased from Boerhinger Scientific. A summary follows of their results (in parts per million). 

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. 

Spectrophotometric titration curves for the titration of an analyte, A, with a titrant, T, to form a product, P, in the presence of a visual indicator. Titration curves are shown for cases where (a) only A absorbs (b) only T absorbs (c) only P absorbs (d) A and T absorb (e) P and T absorb and (f) only the visual indicator absorbs. 

Spectrophotometric titrations are particularly useful for the analysis of mixtures if a suitable difference in absorbance exists between the analytes and products, or titrant. Eor example, the analysis of a two-component mixture can be accomplished if there is a difference between the absorbance of the two metal-ligand complexes (Eigure 9.33). 

Spectrophotometric titration curve for the complexation titration of a mixture. 

Eulton, R. Ross, M. Schroeder, K. Spectrophotometric Titration of a Mixture of Galcium and Magnesium, /. Chem. Educ. 1986, 63, 721-723. 

In this experiment the concentrations of Ga + and Mg + in aqueous solutions are determined by titrating with EDTA. The titration is followed spectrophotometrically by measuring the absorbance of a visual indicator. The effect of changing the indicator, the pH at which the titration is carried out, and the relative concentrations of Ga + and Mg + are also investigated. 

The titration of a mixture ofp-nitrophenol (pfQ = 7.0) and m-nitrophenol pK = 8.3) can be followed spectrophotometrically. Neither acid absorbs at a wavelength of 545 nm, but their respective conjugate bases do absorb at this wavelength. The m-nitrophenolate ion has a greater absorbance than an equimolar solution of the p-nitrophenolate ion. Sketch the spectrophotometric titration curve for a 50.00-mL mixture consisting of 0.0500 M p-nitrophenol and 0.0500 M m-nitrophenol with 0.100 M NaOH, and compare the curve with the expected potentiometric titration curves. 

Sketch the spectrophotometric titration curve for the titration of a mixture of 5.00 X 10 M Bi + and 5.00 X 10 M Cu + with 0.0100 M EDTA. Assume that only the Cu +-EDTA complex absorbs at the selected wavelength. 

This experiment demonstrates the chemical limitations to Beer s law using the NO2-N2O4 equilibrium as an example. Blanco, M. Iturriaga, H. Maspoch, S. et al. A Simple Method for Spectrophotometric Determination of Two-Components with Overlapped Spectra, /. Chem. Educ. 1989, 66, 178-180. 

The concentration of anionic surfactants at the sub-ppm level in natural waters and industrial waters are determined spectrophotometrically. The anionic surfactants are extracted into a nonaqueous solvent following the formation of an ion association complex with a suitable cation. 

Data from the spectrophotometric titrations of Fe + with SCN , and of Cu + with EDTA are used to determine the stoichiometry of the resulting complexes using the method of continuous variations. 

Long, J. R. Drago, R. S. The Rigorous Evaluation of Spectrophotometric Data to Obtain an Equilibrium Constant, /. Chem. Educ. 1982, 59, 1037-1039. 

Procedures for determining the concentrations of caffeine, benzoic acid and aspartame in soda by these three methods are provided. In the example provided in this paper, the concentrations of caffeine and benzoic acid in Mello Yellow are determined spectrophotometrically. 

In this experiment mixtures of dyes are used to provide a means for determining spectrophotometrically a sample s pH. 

In the process of performing a spectrophotometric determination of Ee, an analyst prepares a calibration curve using a single-beam spectrometer, such as a Spec-20. After preparing the calibration curve, the analyst drops the cuvette used for the method blank and the standards. The analyst acquires a new cuvette, measures the absorbance of the sample, and determines the %w/w Ee in the sample. Will the change in cuvette lead to a determinate error in the analysis Explain. 

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 )... 

Saito described a quantitative spectrophotometric procedure for iron based on a solid-phase extraction using bathophenanthroline in a poly(vinyl chloride) membrane. ... 

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