Sulfur calibration

The amount of sulfur in aromatic monomers can be determined by differential pulse polarography. Standard solutions are prepared for analysis by dissolving 1.000 mb of the purified monomer in 25.00 mb of an electrolytic solvent, adding a known amount of S, deaerating, and measuring the peak current. The following results were obtained for a set of calibration standards... 

If it is inconvenient to add sulfur tetrafluoride directly from a cylinder, it may first be condensed in a calibrated trap containing a boiling chip and cooled in a acetone-dry ice bath. When cooled to — 78°, 119 g. of sulfur tetrafluoride is about 62 ml. The sulfur tetrafluoride can be added to the cooled flask by allowing it to distil slowly from the trap. 

Fig. 38 Companson of manual dipping (A) with mechanized dipping (B) on the basis of scans and calibration curves [114] — 1 = cM-diethylstilbestrol, 2 = traw-diethylstilbestrol, 3 = ethinylestradiol Scanning curve 2 ng of each substance per chromatogram zone = 313 nm, /n > 390 nm Dipping solution water — sulfuric acid — methanol (85 + 15 + 1)...

It is convenient to condense sulfur dioxide from a cylinder in a calibrated trap cooled in a dry ice bath. 

The checkers used acetylene available from Matheson Gas Products. The gas was purified by passing it through concentrated sulfuric acid and then through a tower filled with potassium hydroxide pellets. The gas was then passed into a 1-1. safety flask which was connected to the gas inlet tube by means of rubber tubing. The checkers used a rotameter that was calibrated with air to determine the flow rate of acetylene. 

Fig. 31 Evolution of the Raman spectra of a high-pressure and photo-induced sample of Se while decreasing the pressure at ca. 300 K [109]. The spectrum at 3.9 GPa shows the onset of the transformation S6 p-S. The asterisks indicate the Raman signals typical for p-S whereas the peaks of two stretching vibrations of p-S coincide with those of Se at about 458 cm and 471 cm (not indicated by asterisks). The Raman spectrum of the sample recovered at ambient pressure (0 GPa) is evidently a superposition of the spectra of a-Sg and polymeric sulfur, Sj, arrows indicate plasma lines of the Ar ion laser at 515 nm, which have been used for calibration). For Raman spectra under increasing pressure, see Fig. 23 in [1] and references cited therein...

The XANES spectra of Se, Ss, Sio, S12, S14 [222] and polymeric sulfur [223, 224] are all very similar as far as the peak positions are concerned but the relative intensities of the two peaks differ considerably. The spectra are characterized by an absorption line at 2471.7 eV (so-called white line) and a broad absorption in the region 2477-2480 eV [222] see Fig. 35 (energies calibrated to the white line of ZnS04 defined as 2481.4 eV). Since the spectra of the components of a mixture are additive, quantitative analyses are possible, even for mixtures of samples as similar as Ss and polymeric sulfur, for instance [224]. The interpretation of the spectra is, however, still somewhat controversial see [225]. 

Application to solid polymer/additive formulations is restricted, for obvious reasons. SS-ETV-ICP-MS (cup-in-tube) has been used for the simultaneous determination of four elements (Co, Mn, P and Ti) with very different furnace characteristics in mg-size PET samples [413]. The results were compared to ICP-AES (after sample dissolution) and XRF. Table 8.66 shows the very good agreement between the various analytical approaches. The advantage of directly introducing the solid sample in an ETV device is also clearly shown by the fact that the detection limit is even better than that reported for ICP-HRMS. The technique also enables speciation of Sb in PET, and the determination of various sulfur species in aramide fibres. ETV offers some advantages over the well-established specific sulfur analysers very low sample consumption the possibility of using an aqueous standard for calibration and the flexibility to carry out the determination of other analytes. The method cannot be considered as very economic. 

Szathmary and Luhmann [50] described a sensitive and automated gas chromatographic method for the determination of miconazole in plasma samples. Plasma was mixed with internal standard l-[2,4-dichloro-2-(2,3,4-trichlorobenzyloxy) phenethyl]imidazole and 0.1 M sodium hydroxide and extracted with heptane-isoamyl alcohol (197 3) and the drug was back-extracted with 0.05 M sulfuric acid. The aqueous phase was adjusted to pH 10 and extracted with an identical organic phase, which was evaporated to dryness. The residue was dissolved in isopropanol and subjected to gas chromatography on a column (12 m x 0.2 mm) of OV-1 (0.1 pm) at 265 °C, with nitrogen phosphorous detection. Recovery of miconazole was 85% and the calibration graph was rectilinear for 0.25 250 ng/mL. 

The amounts oi adsorption of the polymer on latex and silica particles were measured as follows. Three milliliters of the polymer solution containing a known concentration was introduced into an adsorption tube(lO ml volume) which contained 2 ml of latex (C = l+.O wt %) and silica(C = 2.0 wt %) suspensions. After being rotated(l0 rpm) end-over-end for 1 hr in a water bath at a constant temperature, the colloid particles were separated from the solution by centrifugation(25000 G, 30 min.) under a controlled temperature. The polymer concentration that remained in the supernatant was measured colorimetrically, using sulfuric acid and phenol for the cellulose derivatives(12), and potassium iodide, iodine and boric acid for PVA(13). From these measurements, the number of milligrams of adsorbed polymer per square meter of the adsorbent surface was calculated using a calibration curve. 

Use of a calibrated dropping funnel permits approximate estimation of the amount of phosgene absorbed a volume increase of 1 ml. corresponds to about 1.3 g. of phosgene, The stream of phosgene is led through a wash bottle containing concentrated sulfuric acid and should not be too fast in order to avoid loss of solvent by evaporation. 

Habicht KS, Canfield DE (1997) Sulfur isotope fractionation during bacterial sulfate reduction in organic-rich sediments. Geochim CosmochimActa61(24) 5351-5361 Habicht KS, Gade M, Thamdrup B, Berg P, Canfield DE (2002) Calibration of sulfate levels in the Archean ocean. Science 298 2372-2374... 

In the infrared detection system, the sample is weighed into a special ceramic boat which is then placed into a combustion furnace at 1371°C (2500°F) in an oxygen atmosphere. Most of the sulfur present is converted to sulfur dioxide, which is then measured with an infrared detector after moisture and dust are removed by traps. The calibration factor is determined using standards approximating the material to be analyzed. 

The checkers passed the nitrogen through a gas absorption bottle filled to a depth of 10 cm. with concentrated sulfuric acid which had been calibrated roughly for flow rate. The rate of flow used was one bubble per 7 seconds (ca. 145 ml. per hr.) for the larger furnace, and one bubble per 10 seconds (ca. 100 ml. per hr.) for the smaller furnace. 

Figure 10.18 Calibration describing the relationship between chemical shift and sulfuric acid concentration in spent acid from a refinery alkylation process.

There are several potential sources of error. Both methods of analysis use a binary model mixture, composed of sulfidic and thiophenic components. Thickness effects in the XANES of these model systems would alter the calibrations. There may be contributions from species not adequately represented by a simple dibenzothiophene-dibenzylsulfide model. While the XPS data are represented by 163.3 eV and 164.1 eV components, the model compound data base is as yet limited and not sufficient for a definitive interpretation in terms of alkyl sulfide and thiophenic forms. Examination by both XPS and XANES of a wider variety of model compounds and multiple component model compound mixtures will better define the sulfur species represented by these quantification methods. 

The area under a chromatographic peak is proportional to the concentration of the corresponding.species in the sample analysed. Using empirical calibration functions, a rapid simultaneous qualitative and quantitative analysis of sulfur mixtures by HPLC is now possible. In a similar manner the selenium rings Seg, Se, and SCg have recently been separated by HPLC... 

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