Thymol determination

Figure 14.30. Temperature-dependence of the contact angle, 6, of glycerol on solid thymol, determined from the capillary rise, /i, on a flat vertical surface, and the temperature-dependence of the resulting surface tension, /sv, of thymol in the solid state (from ref. (52))...

The results of the complexation study of Cu(II), Pb(II), Zn(II), Fe(III), Hg(II), Cd(II), Sn(IV), Zr(IV), Ti(IV) with arsenazo III, sulfonazo III, SPADNS, Eriochrome T, Acid Chrome Dai k Blue, Xylenol Orange, Methyl Thymol Blue, Pyrocatechol Violet, Chrome Azurol S, Eriochrome Cyanin R, Basic Blue K, Methyl Violet, Brilliant Green, Rhodamine C and Astraphoxin in solid phase. The obtained data ai e used for the working out of a new method of metal determination. 

The alkaline solution of thymol is made up to 100 or 200 c.c. as the case may require, using a 5 per cent, soda solution. To 10 c.c. of this solution in a graduated 500 c.c. flask is added a normal iodine solution in shgbt excess, whereupon the thymol is precipitated as a dark reddish-brown iodine compound. In order to ascertain whether a sufficient quantity of iodine has been added, a few drops are transferred into a test tube and a few drops of dilute hydrochloric acid are added. When enou iodine is present, the brown colour of the solution indicates the presence of io ne, otherwise the liquid appears milky by the separation of thymol. If an excess of iodine is present, the solution is slightly acidified with dilute hydrochloric acid and diluted to 500 c.c. From this 100 c.c. are filtered,off, and the excess of iodine determined by titration with normal solution of sodium thiosulphate. For calculation, the number of cubic centimetres required is deducted from the number of cubic centimetres of normal iodine solution added and the resultant figure multiplied by 5, which gives the number of cubia centimetres of iodine required by the thymol. 

A slight excess of 10 per cent barium chloride solution is added to the hot solution to precipitate the carbonate as barium carbonate, and the excess of sodium hydroxide solution immediately determined, without filtering off the precipitate, by titration with the same standard acid phenolphthalein or thymol blue is used as indicator. If the volume of excess of sodium hydroxide solution added corresponds to timL of 1M sodium hydroxide and u mL 1M acid corresponds to the excess of the latter, then v — v = hydrogencarbonate, and V— v — v ) = carbonate. 

The basicities of [18] were determined by photometric titrations in ethanol relative to thymol blue [(log/flrei = 0] (Tuning and Muller, 1989). 

CHARACTERIZATION. The intrinsic viscosity of the soluble fractions was determined in toluene at 30 C. The MAH content of the soluble fractions was determined by heating a 0.5-1.0g portion in refluxing water-saturated xylene for 1 hr and titrating the hot solution with 0.05N ethanolic KOH using 1% thymol blue in DMF as indicator. 

Although litmus paper, cabbage juice, and phenolphthalein can indicate whether a substance is acidic or basic, they have limitations in that they cannot determine an exact pH. To do this, an acid-base indicator called universal indicator can be used. Universal indicator is actually a mixture of several different acid-base indicators (usually phenolphthalein, methyl red, bromthymol blue, and thymol blue). This mixture produces a wide range of colors to indicate different pHs. Under very acidic conditions, universal indicator is red. It turns orange and then yellow between the pHs of 3 to 6. It is green at neutral pH and turns greenish-blue as a solution becomes more alkaline. In very basic conditions, universal indicator turns a dark purple color. 

Other SC- and BSC-PEG derivatives were prepared using the same general protocol. The active carbonate contents of the products were determined according to Kalir et al. (77) by reacting aliquots of the polymers with an excess of benzylamine and back titration of the latter with perchloric acid in dioxane using thymol blue as an indicator. The results of these determinations are summarized in Table I. 

Spengler and Jumar [90] used a spectrophotometric method and thin layer chromatography to determine carbamate and urea herbicide residues in sediments. The sample is extracted with acetone, the extract is evaporated in vacuo at 40°C and the residue is hydrolysed with sulphuric acid. The solution is made alkaline with 15% aqueous sodium hydroxide and the liberated aniline (or substituted aniline) is steam distilled and collected in hydrochloric acid. The amine is diazotized and coupled with thymol, the solution is cleaned up on a column of MN 2100 cellulose power and the azo-dye is determined spectrophotometrically at 440nm (465nm for the dye derived from 3-chloro- or 3.4-dichloroaniline) with correction for the extinction of a reagent blank. 

Fluorescent pH indicators offer much better sensitivity than the classical dyes such as phenolphthalein, thymol blue, etc., based on color change. They are thus widely used in analytical chemistry, bioanalytical chemistry, cellular biology (for measuring intracellular pH), medicine (for monitoring pH and pCC>2 in blood pCC>2 is determined via the bicarbonate couple). Fluorescence microscopy can provide spatial information on pH. Moreover, remote sensing of pH is possible by means of fiber optic chemical sensors. 

Determination of Acidity or Alkalinity of NG. Place a lOg sample of the NG by pipet into a tared beaker and retare. Add 100ml of benzene and transfer to a 250-ml separatory funnel when dissolved. Wash twice with 50-ml portions of neutral distd w, combining the washes in a 250-ml beaker. Add several drops of bromo-thymol blue indicator and immediately titrate with 0.01N NaOH if yellow, or with 0.01 N sulfuric acid if blue. Run a blank on 100ml of benzene and correct the first titratiaQ value. Then, % acidity (as sulfuric acid) or alkalinity (as sodium carbonate) = kVN/W, where k is... 

The main constituent of thyme oil is thymol (37-55%) which also determines predominantly the sensory properties of the oil [794-799a]. 

A concave base must be concave and basic. Therefore, the basicities (and acidities, respectively) of concave bases and acids have been determined. Because most concave acids and bases are not soluble in water, the measurements had to be performed in an organic solvent. A photometric titration versus thymol blue in ethanol was chosen [31]. 

Equivalent Weight. Three reliable analytical methods are available to determine the equivalent weight of CTPB prepolymer (1) titration by 0.1 N sodium methylate in pyridine solution to the thymol blue end point, (2) infrared spectroscopy, and (3) nuclear magnetic resonance. Satisfactory agreement has been obtained between these instrumental analyses and the acid content as determined by titration (Table XVI). 

Besides thymol, other terpenes have been tested for their toxicity against Varroa jacobsoni. Imdorf et al. determined in vitro the effective miticidal air concentrations, but with minimal effects on the bees as follows 5-15 pg/litre air for thymol, 50-150 pg/litre for camphor and 20-60 pg/litre for menthol 1,8-cineole was too toxic for honey bees [86], Another interesting paper considered the efficacy of different isomers of menthol on Acarapis woodi [87]. The natural crystals obtained from the plant, synthetic crystals and the L-form gave more than 96% mite mortality, while the D-form crystals only a 37% mortality. 

Determination of the phenols is of special importance in the analysis of hop (carvacrol), thyme, ajOwan (thymol), aniseed, badiana, fennel (anethole), clove bud and stem (eugenol) and sassafras oils (safrole). 

S. K. Pant, P. N. Gupta, K. M. Thomas, B. K. Maitin, and C. L. Jain, Simultaneous determination of camphor, menthol, methyl salicylate, and thymol in analgesic ointments by gas-liquid chromatography, LC-GC, 8 322. 

Eugenol is used as an internal standard in the gas chromatographic determination of thymol in biological samples [4]. 

In the present experiment, you will determine the amount of HC1 neutralized by two different commercial antacid tablets. To do so we use a technique called back-titration. We add an excess amount of 0.2 N HC1 to the antacid tablet. The excess acid (more than is needed for neutralization) helps to dissolve the tablet. Then the active ingredients in the antacid tablet will neutralize part of the added acid. The remaining HC1 is determined by titration with NaOH. A standardized NaOH solution of known concentration (0.2 N) is used and added slowly until all the HC1 is neutralized. We observe this end point of the titration when the added indicator, thymol blue, changes its color from red to yellow. The volume of the excess 0.2 N HC1 (the volume not neutralized by the antacid) is obtained from the titration equation ... 

The composition of the volatile oil, which determines the odour and flavour characters, has been of particular interest to chemists. Ajowan oil is composed of phenols, terpenes and p-cymene. The essential oil contains more than 27 compounds, of which thymol (61%) is the major one, the others being paracymene (15.6%), y-terpinene (11.9%), (3-pinene (4-5%), dipen-tene (4-6%), camphene and myrcene. The essential oil composition of ajowan seed is given in Table 16.3. 

The most sensitive analysis was achieved with pentafluorobenzoate, which permits up to 10 12 g of thymol to be determined. Clarke et al. [74] compared the characteristics and ECD responses of acyl derivatives of amines. Table 4.7 shows some of their results. It follows that a different type of acyl derivative is suitable for each type of amine and at the same time other characteristics, which are not reported in the table, must also be taken into consideration. TFA derivatives have better chromatographic characteristics than chloroacetates and usually are preferred, despite their lower responses. The highest sensitivity was obtained by Clarke et al. for HFB derivatives. Other workers [75] drew attention to the dependence of the responses of haloacyl derivatives on the detector temperature. Its significance can be particularly important in trace analysis, when it is necessary to work at the maximal sensitivity of the detector. In each instance when an acyl derivative is used a compromise must be found among the sensitivity required, volatility of the derivatives, reagent availability and other factors. 

These constants determine the titration exponents pH and the best indicators for the successive hydrions. The acid can be titrated as dibasic, using methyl yellow, methyl orange or bromophenol blue, and as tetrabasic using phenolphthalein, thymolphthalein or thymol blue in the presence of a moderate excess of soluble barium salt. The values of pH in the partly neutralised acid were corrected for the salt error, and the constants Kz and jfiT4 which prevail in solutions of low concentration were thus deduced —6... 

Acidity Transfer about 25 g of sample, accurately weighed, into a 125-mL conical flask add 50 mL of toluene and 2 drops of thymol blue TS and titrate rapidly with 0.02 M sodium methoxide in toluene. Swirl the flask continuously until the yellow color changes to a dark color, and then continue the titration without stopping but slowing the addition of titrant until a single drop changes the solution to a clear blue color. The endpoint is stable for about 8 to 15 s. Not more than 1.0 mL of 0.02 M sodium methoxide is required. Lead Determine as directed for Method I in the Atomic Absorption Spectrophotometric Graphite Furnace Method under Lead Limit Test, Appendix IIIB. 

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