Silica cell

A calibration curve for the range 0.2-10 mg fluoride ion per 100 mL is constructed as follows. Add the appropriate amount of standard sodium fluoride solution, 25 mL of 2-methoxyethanol, and 10 mg of a buffer [0.1 Af in both sodium acetate and acetic (ethanoic) acid] to a 100 mL graduated flask. Dilute to volume with distilled water and add about 0.05 g of thorium chloranilate. Shake the flask intermittently for 30 minutes (the reaction in the presence of 2-methoxyethanol is about 90 per cent complete after 30 minutes and almost complete after 1 hour) and filter about 10 mL of the solution through a dry Whatman No. 42 filter paper. Measure the absorbance of the filtrate in a 1 cm cell at 540 nm (yellow-green filter) against a blank, prepared in the same manner, using a suitable spectrophotometer. Prepare a calibration curve for the concentration range 0.0-0.2 mg fluoride ion per 100 mL in the same way, but add only 10.0 mL of 2-methoxyethanol measure the absorbance of the filtrate in a 1 cm silica cell at 330 nm. 

Use a recording spectrophotometer to plot the absorption curves of the three separate solutions, in each case using distilled water as the blank. Use silica cells and record the spectra over the range 210-310 nm. 

The ir measurements were carried out with a Perkin Elmer 580 spectrometer and fused silica cell with KBr windows allowing to outgass the zeolitic wafer at a desired temperature and to introduce and further outgass a probe molecule without contact with air. 

A much thinner piece (0.4 mm.) of porous glass was used, and a simple adsorption system with a fused silica cell was constructed (152). The adsorption isotherm could be obtained at the same time that the sample was in the light beam of the spectrometer. This obviates the necessity of measuring the temperature of the sample with the intensities of radiation normally used in infrared spectrometers this effect can be quite significant, since most adsorbents are bad conductors of heat. 

Apparatus. Absorbance measurements shall be made using a spectrophotometer with ultra-violet accessories, matched 1 cm silica cells and a blue sensitive phototube in position. A Beckman Model DU Spectrophotometer has been found to be satisfactory... 

Spectrometer was used. Normal operating conditions were used normal slit, IX expansion, 12-minute scan speed (4000-200 wave numbers), and normal gain, in accordance with Perkin-Elmer setup instructions. A Beckman 2 cm path length, near infrared silica cell (holds 8 ml sample) was used to hold the desorbing solution in the sample compartment (Figure 1). 

UV-VIS-NIR diffuse reflectance (DR) spectra were measured using a Perkin-Elmer UV-VIS-NIR spectrometer Lambda 19 equipped with a diffuse reflectance attachment with an integrating sphere coated by BaS04. Spectra of sample in 5 mm thick silica cell were recorded in a differential mode with the parent zeolite treated at the same conditions as a reference. For details see Ref. [5], The absorption intensity was calculated from the Schuster-Kubelka-Munk equation F(R ,) = (l-R< )2/2Roo, where R is the diffuse reflectance from a semi-infinite layer and F(R00) is proportional to the absorption coefficient. 

Cu+ emission spectra were recorded using a nanosecond laser kinetic spectrometer (Applied Photophysics). Cu+-zeolites were excited by the laser beam of the XeCl excimer laser (Lambda Physik 205, emission wavelength 308 nm, pulse width 28 ns, pulse energy 100 mJ). The 320-nm filter was situated between 2 mm thick silica cell and monochromator. Emission signal was detected with the photomultiplier R 928 (Hamamatsu), recorded with the PM 3325 oscilloscope and processed by a computer. All the luminescence measurements were carried out at room temperature. The Cu+ emission spectra were constructed from the values of luminescence intensity at the individual wavelengths of emission in selected times after excitation (2, 5,10, 20, 50, 100 and 200 ps). For details see Ref [7]. 

Transfer 25.0-ml. aliquots of Solution A to each of two 100-ml. graduated flasks. Dilute the contents of the first flask to 100 ml. with water Mix the solution and measure the absorbance at 242, 254, 266, and 268 m in 1-cm. silica cells against a reference solution consisting of 1 part of absolute alcohol and 3 parts of water. To the second flask add 35 ml. of 5% hydrochloric acid (reagent 5) and dilute to 100 ml. with water. Measure the absorbance of the solution at... 

In this method the soil extract and the blank and standards are evaporated almost to dryness by gentle heating and then cooled in an ice pack. Five millilitres of 80% sulfuric acid and then 1 ml of a 2% ethanolic solution of 3,4-xylenol are added. This solution is transferred to a separatory funnel with 80 ml ice-cooled distilled water. Toluene (10 ml) is added to the isolated toluene extract, and 5 ml of 1% sodium hydroxide is added to convert the phenol to the phenoxide. The lower aqueous phase is separated and evaluated spectropho-tometrically at 432 nm using matched silica cells with distilled water in the reference cell. 

Navalon et al. developed a method for the determination of trace amounts of ciprofloxacin, based on solid-phase spectrofluorimetry [9]. The relative fluorescence intensity of ciprofloxacin fixed on Sephadex SP C-25 gel was measured directly after packing the gel beads in a 1 mm silica cell, using a solid-phase attachment. The wavelengths of excitation and emission were 272 and 448 nm, respectively. The linear concentration range of the compound was 0.3-10 ng/mL, with a RSD of 1.2% (for a level of 4 ng/mL) and a detection limit of 0.1 ng/mL. This method was used for the determination of ciprofloxacin in human urine and serum samples with a recovery of 100% in all cases. 

Procedure Transfer 5.0 mL of sample, accurately weighed, into a 50-mL volumetric flask, dilute to volume with isooctane, and mix. Determine the absorbance of this solution in a 1-cm silica cell at 292 nm with a suitable spectrophotometer, using a 1 10 dilution of Antioxidant-Free Ethyl Acrylate in isooctane as the blank. From the previously prepared Calibration Curve read the micrograms of hydroquinone monomethyl ether corresponding to the absorbance of the sample solution, and record this value as w. Calculate the milligrams per kilogram of hydroquinone monomethyl ether (mg/kg HMME) in the sample by the formula... 

All the samples were further purifred by removing dust particles through 0.2 pm Millipore filter and sealed in fused silica cells or P x cells. The sample cell was embedded in a specially designed home-made cryostat or furnace. The temperatures were measured with a chromel-constantan thermocouple closely attached to a cell. The accuracy of the temperature control is within 0.1 K. The thermocouples were prepared at Chemical Thermodynamics Laboratory, Osaka University. 

Trinitroethane Solutions contained in 0.0115 silica cells, 1 mm thick 3625 3550-4100 97... 

Spectrophotometric Measurements. Spectrophotometric measurements were made with a Cary Model 14 recording spectrophotometer. Absorption spectra of solutions were obtained in silica cells. Absorption spectra of the crystalline salts were obtained using mixtures of the materials with petrolatum between glass or silica plates using the Cary Model 1417200 source. Blanks for the solid spectra were CaCOa mulls in petrolatum plus aqueous starch solution if necessary to produce a flat base line. The reference was adjusted so the base line was flat in the 520 to 600 m/x region where the U(VI) acetate complexes do not absorb. Slit widths for spectra of solids were typically <0.1 mm. 

A 2.0-cm. fused-silica cell containing an aqueous solution of cobalt(II) and nickel(II) sulfates (45.0 g./l. CoSOi-THaO and 500 g./l. NiSOi OHaO). This solution transmits 75% of the light near 2900 A., where the maximum absorption of fluorine occurs. 

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