Methanol dilute solution spectrum

In the dilute solution spectrum of methanol, three sharp peaks are observed superimposed on the broader continuum. These can be seen clearly in Figure 5.3. The sharp peaks have been assigned to OH stretch plus CH bending at 5090 cm" (1965 nm), OH stretch plus OH bending at 4960 cm" (2017 nm), and OH stretch plus CO stretch at 4710 cm" (2124 nm). There is also a second combination of OH-stretching and a different OH-bending mode at about 3970 cm (2520 nm). These sharp peaks are at different positions in other alcohols. In the neat spectrum, these peaks are seen as only one broad band centered at about 4770 cm" (2100 nm). In the mid-infrared, a diffuse OH association band related to deformation occurs at about 1420 cm" which can account for the 4770-cm near-infrared band (1420 cm" + 3350 cm" = 4770 cm". The diffuse mid-infrared band is said to disappear in dilute solutions of alcohols, where hydrogen... 

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. 

When very reactive substrates such as 121 and 141 (X = OMe, Y = Z = N02) are studied, very low reagent concentrations may be required and can be obtained by the use of buffer systems such as RC02 -RC02H and ArO -ArOH.33,36 Furthermore, in such cases the dilute solutions of the substrates in methanol and without any added MeO" are found slowly to gain a coloration due to the adduct.33,36 A detailed kinetic analysis has been carried out by Terrier et al.s6 for adducts 122 and 143 in methanol solution. By use of an appropriate set of buffers, it has been possible to carry out the measurements for equilibrium and rate constant determinations in a wide spectrum of pH values in MeOH from 5.5 to 13.7. 

Identification testing of indapamide drug substance can be accomplished by UV absorbance spectrophotometric analysis. A 35-40 mg sample of indapamide is weighed into a 50-mL volumetric flask. The drug substance is dissolved and brought to volume with methanol. The solution is then diluted 1 to 10 with methanol and a portion placed in a 1-cm cell. The spectrum is recorded from 260 to 325 nm using methanol as a blank. There should be maxima at about 286 nm and 278 nm and minima at about 282 nm and 271 nm. The resultant spectrum also exhibits characteristics at the same wavelengths as a similarly prepared and concomitantly measured indapamide reference standard. 

Protic solvents always have more complex infrared spectra because of the presence of hydrogen bonding in the liquid state. In methanol, this involves interaction of the acidic proton on the OH group in one molecule with the oxygen atom in an adjacent molecule (fig. 5.15). The infrared spectrum shows a wide band centered at 3346 cm which is due to the -OH stretch. When methanol is dissolved as a dilute solute in carbon tetrachloride, this band is sharp and appears at 3644 cm . An -OH bending mode appears at 1449 cm. Another broad band due to -OH out-of-plane deformation is centered at 663 cm. The other features of the methanol spectrum are due to the vibrational modes of the CH3- group or to skeletal vibrations [27]. 

As discussed in the Introduction to this paper, different viscosity versus concentration behavior is observed for SFS solutions in toluene/methanol and in DMF. Folyelectrolyte behavior is observed only in the latter solvent. The ESR spectrum of a 2.65 mole % Mn-SPS in these two solvents was studied at various concentrations. For both lvents, the hyperfine structure characteristic of isolated Mn ions was observed in very dilute solutions and at concentrations for which Lundberg and Phillips(10) observed strong intermolecular interactions. The ESR data indlcat that in dilute solution in both DMF and toluene/methanol, the Mn exists mainly as Isolated cations. In addition, the IR spectra indicated that the cation is removed from the anion to a similar degree in both solvents. Yet, a polyelectrolyte effect is observed experimentally only in DMF solutions. Although there was some dipole-dipole broadening of the toluene/methanol spectrum, the line width and the g-factor (g 2,000) in both cases were ldent fal. The g-factor of 2.000 is characteristic of an isolated Mn in solution ). 

A considerable contribution to the interpretation of the fine structure of IR spectra recorded at low temperature was made by an investigation of the dependence of the O—stretching bands on the electrolyte concentration. It was found by Strauss and Symons [St 78] that, in addition to the two bands in the O—H vibration range in dilute solutions (the narrower of which can be ascribed to the solvate sheath of the anion, and the broader one jointly to the free solvent and the solvate sheath of the cation), new bands appear in concentrated (1-2 M) solutions. For example, the IR spectrum measured at — 140°C had, in a methanolic solution of tetrabutylammonium chloride (where solvation of the cation can be neglected), six absorption bands (partly overlapping) in the wavenumber range 3100-3500 (see Fig. 5.4). 

When the same experiment was tried with dilute solutions of sodium carbonate in methanol (Hao and March, 2001), a surprising result was the appearance of species (NaOCH3) Na. In studies on buffer solutions based on phosphate with initial pH values on either side of neutrality, it had been observed that the pH appeared always to shift away from seven as the droplet evaporated, judging by the species detected in the mass spectrum. The appearance of the species containing NaOCHj was, nevertheless, unexpected. 

Diamonium pentachlorooxomolybdate(V) is an emerald green solid, stable in air. It is hygroscopic and should be stored in a stoppered vial in a desiccator. In concentrated HC1, a solution (> 10M) of the compound is green. In dilute HC1 (< 10M) the solution is greenish-brown or borwnish-red. The compound undergoes extensive ionic dissociation in aqueous solution. It is insoluble in benzene, chloroform, dichloromethane, and carbon tetrachloride. It is soluble (with decomposition) in ethanol, methanol, acetone, and pyridine a white solid of ammonium chloride precipitates from all these solutions immediately. The compound dissolves in dimethyl sulfoxide without decomposition. The electronic spectrum in 10 M HC1 contains the following absorptions 14,100(emax = 11), 22,500(emax = 10), 28,200(emax = 570),... 

Trimethoxysilyl)propyloctadecyldimethylammonium chloride (SiQAC) was obtained from Dow Coming Corporation, Midland, MI, as a 40% solution in methanol. A suitable aliquot of this solution was rotary-evaporated to remove most of the methanol and then diluted to 10 ml with an appropriate solvent. An infrared spectrum was recorded immediately after this procedure to obtain the initial methanol concentration. It was observed that complete evaporation of the methanol to solid SiQAC results in hydrolysis of the methoxy groups and condensation of the silanol groups to form siloxane bonds. Scheme 1 shows the structures and abbreviations of all the compounds used in this investigation. 

According to the Pharmacopoeia of the People s Republic of China [7], the method of identification testing of mefenamic acid in capsule and tablet preparations is based on light absorption spectrophotometry. A specific quantity of the powdered contents of capsules (or powdered tablets), equivalent to 0.25 g mefenamic acid, is dissolved in a mixture of 10 mL of 0.1 mL/L hydrochloric acid/methanol (1 99), shaken, and filtered. Then some quantity of the filtrate is diluted with the above-mixed solution to produce a solution having a concentration of about 20 pg/mL. The absorption spectrum of the solution exhibits maxima at 279 nm and 350 nm. 

Identification Transfer 50 mg of sample, accurately weighed, into a 200-mL volumetric flask, add 5.0 mL of water, and moisten the sample. Add 100 mL of a 1 1000 solution of glacial acetic acid in methanol, and shake by mechanical means in the dark until dissolved. Dilute to volume with the acetic acid-methanol solution, and mix. Transfer 2.0 mL of this solution into a 100-mL volumetric flask, dilute to volume with the acetic acid-methanol solution, and mix. The ultraviolet absorption spectrum of the solution so obtained exhibits maxima and minima at the same wavelengths as those of a similar solution of USP Natamycin Reference Standard, concomitantly measured. 

An interesting example of the combination of UV and PMR spectroscopies to structure determination in this area is found in the investigation26 of the species present in basic solutions of the 1-methylquinoxalinium cation (10). The UV spectra of dilute aqueous base (pH 10.5) and basic methanol solutions of this cation are very similar lmax = 301, 340 nm (pH 10.5) 304, 344 nm (CH30 /CH30H). In more basic aqueous solutions (pH 14.5), the only absorption maximum is at 347 nm. Two ionization constants (pK = 8.62 and 12.62) were obtained from the pH dependence of the UV spectrum. The PMR spectrum in 3 M NaOD/D20 may be readily assigned to the pseudobase anion 13 however, the PMR spectrum in basic... 

Ultraviolet Spectrum. After solution in dioxan and dilution with acid methanol—290 nm, 312 nm. 

This technique works particularly well if the cocaine is mixed with sugars, from which it can be easily separated by dissolution. Calibration standards are prepared, in methanol solution, at concentrations of 1.0, 0.5, 0.25, 0.125, 0.0625, 0.031 25 and 0.0156 mgml using serial dilutions. A UV spectrum of a holmium filter is first measured to confirm that the instrumental set-up is performing satisfactorily. 

ESMS was perfonned with a Fisons VG Quattro outfitted with a Hsons Electrospray Source. Samples were dissolved in 1.0 mL of 50% methanol-1% acetic acid, then diluted 1 10 with 50% acetonitrile-1.0 mM anmumium acetate to give 25 pmol/pL. A 10 pL aliquot of each sample was injected into a 10 pL/min stream of 50% acetonitrile-1.0 mM ammonium acetate. Data was processed using Fisons MassLynx Software. MALDI-MS was performed with a Vestec Benchtop lit linear dme-of-flight mass spectrometer, opmted in the linear mode with an N2 laser (337 nm). Samples were dissolved in 1.0 mL of 25% acetonitrile-0.1% TFA, then diluted 3 100 to give 5-10 pmol/pL. A 0.5 pL aliquot of each sample solution was added to 0.5 pL of matrix [a-cyano-4-hydroxycinnamic aci saturated solution in 50% acetonitrile-2% TFA]. Samples were dried at ambient temperature and pressure. Each spectrum was the sum of ion intensity from 10-50 larer pulses. Tlie mass axis was calibrated externally. 

Some substances only give clear spectra in diluted alkaline solution (0.1 M sodium hydroxide), and in such cases only that spectrum is shown. For those spectra a table has been included. Other substances are not sufficiently soluble in water, in which case only a methanol spectrum is shown. 

Intermolecular H bonding can be recognised in the H NMR spectrum by the fact that the shifts due to the protons concerned depend very strongly on the concentration, as the simple case of methanol (36) demonstrates (Fig. 2.22a) solvation with tetrachloromethane as a solvent breaks down the H bridging increasingly with dilution of the solution the OH shift decreases in proportion to this. In contrast, the shift of the H signal of an intramolecular bridging proton remains almost unaffected if the solution is diluted as illustrated in the example of hexafluoroacetylacetone (37), which is 100% enolised (Fig. 2.22b). 

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