Silica calibration curve

It is known that Selenium catalyzes reaction of some dye reduction by Sulphide. On this basis spectrophotometric and test-techniques for Selenium determination are developed. Inefficient reproducibility and low sensitivity are their deficiencies. In the present work, solid-phase reagent on silica gel modified first with quaternary ammonium salt and then by Indigocarmine was proposed for Selenium(IV) test-determination. Optimal conditions for the Selenium determination by method of fixed concentration were found. The detection limit of Se(IV) is 10 ftg/L = 2 ng/sample). Calibration curve is linear in the range 50-400 ftg/L of Se(IV). The proposed method is successfully applied to the Selenium determination in multivitamins and bioadditions. 

PMMA, on the unmodified porous glass and silica gel, and the universal calibration curves for polystyrenes and poly(methyl methacrylates) did not coincide (10,12,19). 

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. 

Burrell and Hurtubise (.32) investigated calibration curves extended well beyond the normal linear range for RTF and RTF of benzoCf)quino-line adsorbed on a silica gel chromatoplate under neutral and acidic conditions. As the benzoCf)quinoline concentration increased, the RTF curves leveled off, whereas the RTF curves passed through a maximum and then decreased. The extended calibration curves along with fluorescence and phosphorescence spectra and phosphorescence lifetimes for benzoCf)quinoline revealed differences in the RTF and RTF phenomena. For example, it was determined that RTF could arise from molecules adsorbed on the surface and in multilayers of molecules, whereas phosphorescence was only generated from molecules adsorbed on the surface of the chromatoplate and not in the multilayers. ... 

Figure 4. SEC calibration curve for silica sol separation (hard sphere particles, single pore size column) (1), Column PSM-1500 (8.9 fim), 30 X 0.78 cm mobile phase O.IU Na.HPO -NaH.PO, pH 8.0...

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. 

Results and Discussion. The 2-ethyl polyaniline concentration in the silica gel film was determined by constructing a Beer s law calibration curve from solutions of known concentration. Assuming an average molecular weight of 5000, the 2-Et PANi concentration in the silica gel was found to be 9.6 x 10 4 M. The refractive indices of CS2 and 2-Et PANi SiC>2 were estimated to be 1.6 and 1.4 at 1.06 im, respectively. The emeraldine base doped silica gel was found to have low losses due to scatter, and exhibited good transparency at 1.06 im. Spectrophotometric measurements at 1.06 fim yielded absorption coefficients of 0.1 cm-1 (> 99% T over 1 mm pathlength) for the CS2 reference and 4 cm 1 (96% T over 1 mm pathlength) for the 2-Et PANi doped silica film. 

A selective, sensitive, and rapid hydrophilic interaction liquid chromatography with electrospray ionization tandem mass spectrometry was developed for the determination of donepezil in human plasma [32], Donepezil was twice extracted from human plasma using methyl-ferf-butyl ether at basic pH. The analytes were separated on an Atlantis HILIC Silica column with the mobile phase of acetonitrile ammonium formate (50 mM, pH 4.0) (85 15, v/v) and detected by tandem mass spectrometry in the selective reaction monitoring mode. The calibration curve was linear (r = 0.9994) over the concentration range of 0.10-50.0 ng/ ml and the lower limit of quantification was 0.1 ng/ml using 200 /d plasma sample. The CV and relative error for intra- and inter-assay at four quality control levels were 2.7% to 10.5% and —10.0% to 0.0%, respectively. There was no matrix effect for donepezil and cisapride. The present method was successfully applied to the pharmacokinetic study of donepezil after oral dose of donepezil hydrochloride (10 mg tablet) to male healthy volunteers. 

Lin and Wu [137] established a simple capillary zone electrophoresis method for the simultaneous analysis of omeprazole and lansoprazole. Untreated fused-silica capillary was operated using a phosphate buffer (50 mM, pH 9) under 20 kV and detection at 200 nm. Baseline separation was attained within 6 min. In the method validation, calibration curves were linear over a concentration range of 5-100 /iM, with correlation coefficients 0.9990. RSD and relative error were all less than 5% for the intra- and interday analysis, and all recoveries were greater than 95%. The limits of detection for omeprazole and lansoprazole were 2 fiM (S/N = 3, hydroxynamic injection 5 s). The method was applied to determine the quality of commercial capsules. Assay result fell within 94—106%. 

Place 50 mL sample in a Nessler tube. Add 1 mL of 1 1 HC1 and 2 mL ammonium molybdate reagent. Shake well. Let the solution stand for 5 min. Add 2 mL oxalic acid solution, shake thoroughly, and allow the solution to stand for another 5 min. Measure the absorbance of the yellow color developed at 410 nm. Run a blank using 50 mL distilled water following the above procedure. Compare the absorbance of the sample solution with the standards and determine the concentration of silica from the calibration curve. 

Figure 2.14 Molecular weight calibration curves for porous silica microsphere columns. Chromatography conditions column, 10 X 0.78 cm mobile phase, tetrahydrofuran, 22°C flow rate, 2.5 ml/min detection, UV absorbance at 254 nm sample, 25 pi solutions of polystyrene standards, (a) Four individual columns showing four different calibration ranges (b) four columns in series with two distinct pore sizes (60,60,750,750A), providing a single calibration curve with a broader molecular weight range than the individual columns. (Adapted from Ref. 54 with permission.)...

As a means of comparing the potential for quantitative determinations on the TLC and HPTLC pre-coated plates silica gel 60, the calibration curves of S-BHC were recorded. 

It can be seen that in both cases a well correlating calibration curve in the shape of a straight line is obtained. It is also evident that for equal applied quantities the peak heights on the HPTLC plate are slightly more than twice as high as on the TLC plate. For this reason and on account of the fact that the baseline noise is markedly less on the HPTLC plate evaluated in reflectance mode as a result of its more homogeneous and smoother surface, the detection limit for S-BHC under the given conditions on the HPTLC pre-coated plate silica gel 60 is considerably less at 18 ng than on the TLC pre-coated plate silica gel 60 at 40 ng. 

Figure 1. Calibration curves for 8-BHC on a TLC pre-coated plate silica gel 60 ( leftj and on an HPTLC pre-coated plate silica gel 60 fright) (abscissae applied quantity (ng) ordinates peak height (mV))...

For quantitative determination of the individual Trevespan 6038 components, calibration curves were drawn up for the HPTLC pre-coated plate silica gel 60 and for the HPTLC pre-coated plate cellulose. 

Well correlating calibration curves in form of straight lines are obtained on both types of HPTLC plate for all three sample substances in the range of quantities examined. Although the applied quantities are identical, the peak heights on the HPTLC pre-coated plate cellulose are somewhat higher than those obtained on the HPTLC pre-coated plate silica gel 60. The detection limits determined by the peak heights and by the baseline noise for the three substances examined are listed in Table VII. 

Figure 1. Typical calibration curve obtained from silica gel...

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... 

For demonstration, the SEC behavior of different polymethacrylates is given in Fig. 6. On silica gel as the stationary phase and methyl ethyl ketone as the eluent, all polymethacrylates elute in the SEC mode. The calibration curves of elution volume vs. molar mass for poly(methyl methacrylate) (PMMA), poly(ferf-butyl methacrylate) (PtBMA), poly( -butyl methacrylate) (PnBMA) and po-ly(decyl methacrylate) (PDMA) reflect the inability of the system to separate dif-... 

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