Spectrophotometrically calibrated

Bozdogan, A., Ozgur, U.M., and Koyuncu, L, Simultaneous determination of sunset yellow and Ponceau 4R in gelatin powder by derivative spectrophotometry and partial least-squares multivariate spectrophotometric calibration, Anal. Lett., 33, 2975, 2000. 

G. L. Hatch, Effect of Temperature on the Starch-Iodine Spectrophotometric Calibration Line, Anal. Chem. 1982, 54, 2002. 

The worksheet functions SLOPE known ys, known xs) and INTERCEPT(/f/ioiv/i ys, known xs) return the slope, m, and intercept, b, respectively of the least-squares straight line through a set of data points. For example. Figure 11-1 illustrates some spectrophotometric calibration curve data (concentration of potassium permanganate standards in column B, absorbance of the standards in column C). The formula =SLOPE(C4 C8,B4 B8) in cell C10 was used to obtain the slope of the straight-line calibration curve. The SLOPE and INTERCEPT functions should be used with some caution, since they do not provide a measure of how well the data conforms to a straight line relationship. 

FlameCal-xIs illustrates two methods for treating a curved spectrophotometric calibration curve. 

The photometric calibration also contributes to the uncertainty of the measured spectrum. Flux standard stars are typically measured at widely spaced wavelengths (50 A is common), and the sensitivity function of the instrument is determined by fitting a low-order polynomial or spline to the flux points. Such fits inevitably introduce low-order wiggles in the sensitivity function, which will vary from star to star. Based on experience, the best spectrophotometric calibration yield uncertainties in the relative fluxes of order 2-3% for widely-spaced emission lines the errors may be better for ratios of lines closer than 20 A apart. Absolute fluxes have much higher uncertainties, of course, especially for narrow-aperture observations of extended objects. 

Comparative Measurements of Oxygen Consumption with Spectrophotometrically Calibrated Substrates... 

The following absorbance values were obtained in preparing a spectrophotometric calibration curve blank , 0.03 A 1.00 mM standard, 0.11 A 1.00 vaM standard,... 

Standard Lamps and Spectrophotometric Calibrations. Appl. Spectroscopy 37(4) 315-333 (1983)... 

The following table contains simulated spectrophotometric calibration data for two systems obtained for blanks as well as arbitrary concentrations from 1 to 10 i n arbitrary units. Using regression analysis, determine whether data points for each the data from each system is better represented as a linear or quadratic relation of C. 

The spreadsheet s Regression fimction(/TAR,/AR,/DR) renders very simple the analysis of data such as a spectrophotometric calibration curve by linear regression... 

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. 

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

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... 

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. 

PVSA-SG film was used for determination of Fe(Phen) + and Zn + as ternary complex Zn +-Phen-bengal rose by spectrophotometric method. The calibration graph was linear in the concentration 5T0 -5T0 mol/lfor Fe(II) and FlO - 5T0 mol/1 for Zn(II). The film can be regenerated and reused. LG-PDMDA-SG film was shown to be perspective modificator of the PG electrode surface and used for voltammetric detection of Mo(VI) at ppb level. 

It was shown that Zn + adsorbed onto SG-PVSA composite film as Zn(Phen) complex. It can be detected spectrophotometrically after treatment with anionic dye Bengal Rose (BR). Ternary complex Zn + - Phen-BR formed on the surface under optimal conditions. SG-PVSA film was used for determination of Zn + by spectrophotometric method. The calibration graph was linear in the concentration range 2,5T0 - STO mol/l. 

It is known that Selenium catalyzes reaction of some dye reduction by Sulphide. On this basis spectrophotometric and test-techniques for Selenium determination are developed. Inefficient reproducibility and low sensitivity are their deficiencies. In the present work, solid-phase reagent on silica gel modified first with quaternary ammonium salt and then by Indigocarmine was proposed for Selenium(IV) test-determination. Optimal conditions for the Selenium determination by method of fixed concentration were found. The detection limit of Se(IV) is 10 ftg/L = 2 ng/sample). Calibration curve is linear in the range 50-400 ftg/L of Se(IV). The proposed method is successfully applied to the Selenium determination in multivitamins and bioadditions. 

The intensity of the colour of the extract due to ferroin is observed spectrophotometrically and may be related by calibration to the boron content of the sample. 

An alternative elution technique is to transfer the powder (e.g. for bromophenol blue) to a glass column fitted with a glass-wool plug or glass sinter, and elute the dye with ethanol containing a little ammonia. The eluted solution, made up to a fixed volume in a small graduated flask, may be used for colorimetric/ spectrophotometric analysis of the recovered dye (see Chapter 17). A calibration curve must, of course, be constructed for each of the individual compounds. 

The following procedure has been recommended by the Analytical Methods Committee of the Society for Analytical Chemistry for the determination of small amounts of arsenic in organic matter.20 Organic matter is destroyed by wet oxidation, and the arsenic, after extraction with diethylammonium diethyldithiocarbamate in chloroform, is converted into the arsenomolybdate complex the latter is reduced by means of hydrazinium sulphate to a molybdenum blue complex and determined spectrophotometrically at 840 nm and referred to a calibration graph in the usual manner. 

The three normal means of presenting the spectrophotometric data are described below by far the most common procedure is to plot absorbance against wavelength (measured in nanometres). The wavelength corresponding to the absorbance maximum (or minimum transmission) is read from the plot and is used for the preparation of the calibration curve. This point is chosen... 

Stintzing, unpublished observations). Analogous aspects were recently addressed in an extended study of anthocyanin quantification. Spectrophotometric determination is still the most preferred method that has been shown to compare well with HPLC measurements." Hence, only in rare cases have purified standards from a particular food commodity been used for calibration by HPLC-DAD. " ... 

It is always wise to calibrate physical methods of analysis using mixtures of known composition under conditions that approximate as closely as practicable those prevailing in the reaction system. This procedure is recommended because side reactions can introduce large errors and because some unforeseen complication may invalidate the results obtained with the technique. For example, in spectrophotometric studies of reaction kinetics, the absorbance that one measures can be grossly distorted by the presence of small amounts of highly colored absorbing impurities or by-products. For this reason, when one uses indirect physical methods in kinetic studies, it is essential to verify the stoichiometry of the reaction to ensure that the products of the reaction and their relative mole numbers are known with certainty. For the same reason it is recommended that more than one physical method of analysis be used in detailed kinetic studies. 

Erk [20] described a spectrophotometric method for the simultaneous determination of metronidazole and miconazole nitrate in ovules. Five capsules were melted together in a steam bath, the product was cooled and weighed, and the equivalent of one capsule was dissolved to 100 mL in methanol this solution was then diluted 500-fold with methanol. In the first method, the two drugs were determined from their measure d%/dk values at 328.6 and 230.8 nm, respectively, in the first derivative spectrum. The calibration graphs were linear for 6.2—17.5 pg/mL of metronidazole and 0.7—13.5 pg/mL of miconazole nitrate. In the second (absorbance ratio) method, the absorbance was measured at 310.4 nm for metronidazole, at 272 nm for miconazole nitrate and at 280.6 nm (isoabsorptive point). The calibration graphs were linear over the same ranges as in the first method. 

Besada [12] described a spectrophotometric method for determination of penicillamine by reaction with nitrite and Co(II). Penicillamine is first treated with 1 M NaN02 (to convert the amino-group into a hydroxy-group), then with 0.1 M CoCl2, and finally the absorbance of the brownish-yellow complex obtained is measured at 250 nm. The process is carried out in 50% aqueous ethanol, and the pH is adjusted to 5.4— 6.5 for maximum absorbance. The calibration graph is linear over the concentration range of 0.25-2.5 mg per 50 mL, and the mean recovery (n = 3) of added drug is 99.7%. Cystine, cysteine, methionine, and other amino adds do not interfere. 

Vishwavidyalaya et al. [22] used a difference-spectrophotometric method for the estimation of primaquine phosphate in tablets. One portion of powdered tablets, equivalent to 7.5 mg of primaquine phosphate, was extracted with hydrochloric acid-potassium chloride buffer (pH 2) and a second portion was extracted with phosphate buffer (pH 10). Primaquine phosphate was determined from the difference in absorbance of the acid and alkaline extracts at 254.2 nm. The calibration graph was rectilinear from 2 to 14 pg/mL of primaquine phosphate. Recovery was 98.6% and no interference was observed from excipients. Results compared with those by the British Pharmacopoeial method. 

Three anticonvulsant drugs including valproic acid were determined using different dyes as ion-pair reagents. Gentian violet was used for the spectrophotometric detection at 588 nm and acridine orange for the fluorimetric detection at 470 nm after excitation at 297 nm. Calibration graphs were linear for 5-50 pg/mL 2.5 0.50 pg/mL for the spectrophotometric and fluorimetric methods, respectively [15]. 

Another assay that is very similar to the ABTS assay is the AGV-dimethyl-p-phenylenediamine (DMPD assay). In the presence of a suitable oxidant solution at an acidic pH, DMPD is converted to a stable and colored DMPD radical cation (DMPD +). Antioxidants capable of transferring a hydrogen atom to the radical cause the decol-orization of the solution, which is spectrophotometrically measured at 505 nm. The reaction is stable, and the endpoint is taken to be the measure of antioxidant efficiency. Antioxidant ability is expressed as Trolox equivalents using a calibration curve plotted with different amounts of Trolox (Fogliano and others 1999). This method is used to measure hydrophilic compounds. The presence of organic acids, especially citric acid, in some extracts may interfere with the DMPD assay, and so this assay should be used with caution in those extracts rich in organic acids (Gil and others 2000). 

Stoll et al. [142] have described a rapid continuous-flow determination of total inorganic carbon in seawater samples. The method runs on an autoanalyser Traacs 800 spectrophotometric system and is calibrated versus certified reference materials readily available. A typical analysis speed of 45 samples per hour can be reached with an accuracy of 2-3 xM and a precision of 2.5 xM. 

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