Absorbance maximum

Hypochlorous acid can be distinguished from other chlorine species by amperometry using a membrane electrode (135). Spectrophotometry can also be used to measure HOCl via its absorbance maximum at 235 nm. Gaseous mixtures of CI2, CI2O, HOCl can be analyzed by mass spectrometry. 

A new interpretation for the shift of absorbance maximum as the initial mass of Ag increases is proposed. The most probable mechanism of the shift is more rapid increase of atomic absorption signal from the source, which describes the formation and outflow of atoms from graphite compar ed with the signal from the source, which describes the atomization from the furnace surface. 

This ester is formed from the anhydride in pyridine and is quantitatively cleaved with H2NNH2-H2O, Pyr-AcOH. The sensitivity of detection of this ester is high with its absorbance maximum of 513 nm and extinction coefficient of 78,600 in 5% CI2CHCO2H/CH2CI2 where it forms the trityl cation. ... 

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... 

The decomposition kinetics of the N-Br-amino acids was studied spectro-photometrically by following the fall in absorbance at the wavelength of the absorbance maximum of the N-bromoamino acid, in a Milton Roy Spectronic 3000 Array or a Beckman DU65 single-beam spectrophotometer, both equipped with a cell carrier thermostated to within 0.1 °C by water flow. Kinetic experiments were initiated using a hand-driven HI-TECH SFA-12 Rapid Kinetics Accessory with a 1.00 cm flow cell. 

In 1941, Mackinney ° published the first specific absorption coefficients for chlorophyll a and chlorophyll b in 80% acetone, quickly followed by other reports citing different solvents. Chlorophylls form aggregates in various organic solvent-water mixtures that may interfere strongly with the absorbance maximum wavelength and the shapes of spectra. 

This absorption was detected by using monochromatic methods at 15 nm resolution. The 625 nm value may therefore not reflect a true absorbance maximum for L. 

Fig. 2. Comparison of amide 1 + II IR absorption (left) and VCD (right) spectra of polypeptides dissolved in H2O obtained for a-helical poly-(LKKL) in high salt (top), /3-sheet poly-(LK) with high salt (middle amide F measured only in D2O), and random coil poly-K at pH 7 (bottom), where L is L-Leu and K is L-Lys. All spectra were rescaled to have an amide I absorbance maximum of A = 1.0, but are offset to avoid overlap. 

Rao and Rao [33] used a rapid, sensitive, and simple colorimetric method for the estimation of primaquine phosphate. The method is based on its reaction with sodium vandate to give a pink color, which has an absorbance maximum at 550 nm. Beer s law is obeyed for 2-30 pg/mL. 

Hassan et al. [39] used a sensitive color reaction method for the determination of primaquine in pharmaceutical preparation. Primaquine was treated with diazo-p-nitroaniline in acidic medium to give an orange-yellow product with an absorbance maximum at 478 nm. When the medium was made alkaline, bathochromic, and hypochromic shifts occurred the new maximum was located at 525 nm. The mean percentage recoveries for authentic samples amounted to 100 and 100.21 by the acid and alkaline procedures, respectively (P = 0.05). Both reactions could be used to determine primaquine salts in pharmaceutical preparations. The results obtained were in good agreement with those of the official methods. Recoveries were quantitative by both methods. 

In Fig. 3, the pepsin dissolved in HC1, without interaction with any solid, showed a maximum at 272 nm. After interaction with the disordered cancrinite and the intermediate phase, a small decrease in the absorbance maximum of the pepsin spectrum was observed. This small decrease is due to the pepsin adsorption on the solid surfaces. The pepsin activity was also determined by the proteolysis reaction of a denatured haemoglobin solution at different times. Fig. 4 shows the obtained results. One can see, that the enzymatic activities (determined as absorbance), presented by the tested solids were very similar among them. These results show that pepsin enzymatic activity is not lost after the contact the pepsin with the tested solids. Therefore, the absorbance decrease observed in Fig. 4, is produced by the pepsin adsorption on the tectosilicate surface, and not by chemical reactions between pepsin and the tectosilicates... 

An electron in a bonding a orbital is excited to the corresponding antibonding orbital. The energy required is large. For example, methane (which has only C-H bonds, and can only undergo o — o transitions) shows an absorbance maximum at 125 nm. Absorption maxima due to o — cr transitions are not seen in typical UV-VIS spectra (200 - 700 nm). 

Indicator Absorbance maximum color of acid/base forms or pKa value or pH range... 

The solvatochromic phenolbetaine Reichardt s Dye (RD) allows to calculate a single parameter that indicates the overall polarity of the polymer. It is obtained by dissolving the dye in the polymer and measuring the absorbance maximum. The molar transition energy (Ex(30)) of RD is an empirical parameter to scale solvent polarity and is obtained by calculating18 Et(30) - hcvmaxNA OT 2.859vmaX R >. 

In the photometric analysis, a calibration of samples is made with the 5-30 ml of the water solutions of Congo red dye (Congo red Ind., Beijing Huagonchang) pH 5.6. This dye has the absorbance maximum 500 nm. Before the measurements, the tests are dried up on air at 50°C for 60 min. The absorbance of Congo red is also used as a blank for the absorbance measurements of AchE-biotests on the matrixes. 

The fluorescent properties of FITC include an absorbance maximum at about 495 nm and an emission wavelength of 520 nm. Fluorescent quenching of the molecule is possible. Under... 

Lowry method uses a combination of the Biuret copper-based reagent and the Folin-Ciocalteau reagent, which contains phosphomolybdic-phosphotungstic acid. Reagents react with protein, yielding a blue colour that displays an absorbance maximum at 750 nm... 

Bradford reagent contains the dye Coomassie blue G-250 in an acidic solution. The dye binds to protein, yielding a blue colour that absorbs maximally at 595 nm Copper-containing reagent that, when reduced by protein, reacts with bicinchonic acid yielding a complex that displays an absorbance maximum at 562 nm Essentially involves initial precipitation of protein out of solution by addition of trichloroacetic acid. The protein precipitate is redissolved in NaOH and the Lowry method of protein determination is then performed Interaction of silver with protein - very sensitive method... 

The most common methods used to determine protein concentration are the dye-binding procedure using Coomassie brilliant blue, and the bicinchonic-acid-based procedure. Various dyes are known to bind quantitatively to proteins, resulting in an alteration of the characteristic absorption spectrum of the dye. Coomassie brilliant blue G-250, for example, becomes protonated when dissolved in phosphoric acid, and has an absorbance maximum at 450 nm. Binding of the dye to a protein (via ionic interactions) results in a shift in the dye s absorbance spectrum, with a new major peak (at 595 nm) being observed. Quantification of proteins in this case can thus be undertaken by measuring absorbance at 595 nm. The method is sensitive, easy and rapid to undertake. Also, it exhibits little quantitative variation between different proteins. 

The sulfuric acid treated aliquot representing the blank forms a cyclic ether anhydroerythromycin.10 The alkaline treatment causes the formation of an unsaturated ketone (9-keto-10-ene) having its absorbance maximum as a shoulder at 236 nm. (e 6000).n i2 Thus, any other UV absorbing species are measured with the blank and subtracted from the absorbance before calculation of the erythromycin concentration. A typical spectrum is shown in Figure 4. 

For ammonia, the commonly employed molybdenum blue method was examined. In this case, there were a number of issues. For example, the standard method requires the use of phenol and hypochlorite. Phenol is unsuitable for health, safety and environmental reasons, and hypochlorite is commonly regarded as unstable. We found that salicylate could be substituted for phenol, with little affect on sensitivity and a relatively small movement of the absorbance maximum, and hypochlorite is stable if stored carefully, and there is very low contamination by certain catalytic metals that accelerate decomposition, such as copper and iron [20]. 

A plot of absorbance versus wavelength may be used to identify a component of a solution or to determine the wavelength of maximum absorbance (maximum molar absorptivity = a). A more common plot is one of absorbance versus concentration. For this type of plot the instrument is set at the wavelength of maximum molar absorptivity and the absorbances of solutions of various known concentrations (c) are measured. This plot should be a straight line. This linear relationship is called Beer s law and has the form of A = abc. The concentration of an unknown solution may be determined by measuring its absorbance and using the plot to find its concentration. 

The reaction of 1,3,5-trinitrobenzene (TNB) and l,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in toluene184 was also proposed to proceed by the mechanism shown in Scheme 16. The visible spectrum, recorded immediately after mixing appropriate solutions of TNB and DBU in toluene, shows a feeble absorbance maximum at 505 nm, which changes to a stable maximum at 468 nm, after variable reaction times. The first maximum was attributed to a molecular complex between TNB and DBU, and the second maximum at the Meisenheimer complex, 39, although NMR structural determinations were not possible, because of the low solubility of the complex in toluene. 

In another approach to the estimation of solvent polarities the effect of a solvent on the absorbance maximum in the visible-ultraviolet region of the charge-transfer band of a salt such as 1 -ethyl-4-carbomethoxy pyridinium iodide is measured 147). A shift of the maximum to shorter wavelengths occurs as solvent polarity increases. The wavelength, expressed in kcal, is called the Z value of the solvent. This method provides a simple and rapid measure of solvent polarity at the molecular level. 

---