scholarly journals Changes in the Surface Area of Silica-supported 12-Molybdophosphoric Acid in Relation to the Degree of Loading and the Calcination Temperature

1994 ◽  
Vol 11 (2) ◽  
pp. 83-93 ◽  
Author(s):  
L.B. Khalil ◽  
W.E. Mourad ◽  
B.S. Girgis
Keyword(s):  
Aqueous Solution ◽  
Surface Area ◽  
Silica Gel ◽  
Heteropoly Acid ◽  
Surface Acidity ◽  
Molybdophosphoric Acid ◽  
Surface Species ◽  
Considerable Decrease ◽  
Acidic Aqueous Solution

A technical silica gel (Grace-113) was impregnated with 12-molybdophosphoric solution to attain loadings of 0.72–13.4 wt.%. The air-dried solids were then calcined for 3 h at 400, 600 and 800°C, respectively, followed by determination of their N2 adsorption isotherms. The silica gel was thermally stable and suffered about 15% loss in area at 800°C. The impregnated silicas showed considerable decrease in surface area as a function of their heteropoly acid content. Two processes are suggested as taking part in the modification of pore structure: (1) diffusion of the aqueous heteropoly acid solution and its subsequent deposition; and (2) dissolution of silica gel in the acidic aqueous solution followed by interaction with HPMo to form either molybdosilicate or P–Si exchange products. Correlation with the previously studied catalytic conversion of isopropanol indicated that the activity was independent of the surface area. Catalytic dehydration on the 600°C and 800°C products seems to be associated with silicate, molybdate or MoO3 surface species rather than being due to surface acidity or the extent of the surface area.

scholarly journals Parabens Adsorption onto Activated Carbon: Relation with Chemical and Structural Properties

Molecules ◽  
2019 ◽  
Vol 24 (23) ◽  
pp. 4313 ◽  
Author(s):  
Astrid Roxanna Moreno-Marenco ◽  
Liliana Giraldo ◽  
Juan Carlos Moreno-Piraján
Keyword(s):  
Aqueous Solution ◽  
Activated Carbon ◽  
Surface Area ◽  
Endocrine Disruptor ◽  
Emerging Contaminants ◽  
Activated Carbons ◽  
Elaeis Guineensis ◽  
Acid Sites ◽  
Co2 Atmosphere

Parabens (alkyl-p-hidroxybenzoates) are antimicrobial preservatives used in personal care products, classified as an endocrine disruptor, so they are considered emerging contaminants. A raw version of activated carbons obtained from African palm shell (Elaeis guineensis) modified chemically by impregnation with salts of CaCl2 (GC2), MgCl2 (GM2) and Cu(NO3)2 (GCu2) at 2% wt/v and carbonized in CO2 atmosphere at 1173 K was prepared. The process of adsorption of methyl (MePB) and ethylparaben (EtPB) from aqueous solution on the activated carbons at 18 °C was studied and related to the interactions between the adsorbate and the adsorbent, which can be quantified through the determination of immersion enthalpies in aqueous solutions of corresponding paraben, showing the lowest-value carbon GM2, which has a surface area of 608 m2 × g−1, while the highest values correspond to the activated carbon GCu2, with a surface area of 896 m2 × g−1 and the highest content of surface acid sites (0.42 mmol × g−1), such as lactonic and phenolic compounds, which indicates that the adsorbate–adsorbent interactions are favored by the presence of these, with interaction enthalpies that vary between 5.72 and 51.95 J × g−1 for MePB adsorption and 1.24 and 52.38 J × g−1 for EtPB adsorption showing that the process is endothermic.

Spectrophotometric Determination of Cyclamate in Foods: NMKL Collaborative Study

1987 ◽  
Vol 70 (3) ◽  
pp. 588-590
Author(s):  
Anna-Maija K Sjoberg ◽  
Timo A Alanko
Keyword(s):  
Aqueous Solution ◽  
Ethyl Acetate ◽  
Spectrophotometric Determination ◽  
Spectrophotometric Method ◽  
Collaborative Study ◽  
Soft Drinks ◽  
Uv Absorption ◽  
Acidic Aqueous Solution ◽  
Coefficients Of Variation

Abstract A spectrophotometric method for the determination of cyclamate was collaboratively studied in 9 laboratories. Ethyl acetate is added to extract cyclamate from acidic aqueous solution into water, and the cyclamate is then quantitatively converted to /V,./V-dichlorocyclohexylamine by adding excess hypochlorite. A',A'-Dichlorocyclohexylamine is determined by measuring its UV absorption at 314 nm. Six samples, 3 soft drinks with cyclamate levels of 0.36-0.47 g/kg and 3 jams with levels of 1.23-1.50 g/kg, were included in the study. Average recoveries of cyclamate were 99.7% in the soft drinks and 103.8% in the jams. Reproducibility coefficients of variation were 6.7% for the soft drinks and 4.4% for the jams.

scholarly journals Spectrofluorometric Determination of Citalopram in Pharmaceutical Preparations and Spiked Human Plasma Using Organized Media

2006 ◽  
Vol 89 (5) ◽  
pp. 1288-1295 ◽  
Author(s):  
Dina T El-Sherbiny
Keyword(s):  
Aqueous Solution ◽  
Human Plasma ◽  
Fluorescence Intensity ◽  
Pharmaceutical Preparations ◽  
Citrate Buffer ◽  
Acidic Aqueous Solution ◽  
Sds Micelles ◽  
Spectrofluorometric Determination ◽  
Organized Media

Abstract The native fluorescence of citalopram (CIT) was (obtained in citrate buffer of pH 6.5 with and without β-cyclodextrin (β-CD) or sodium dodecyl sulfate (SDS) as fluorescence enhancers at 305 nm using 242 nm for excitation. Micellar systems of ionic and nonionic surfactants were investigated by measuring the fluorescence intensity of the analyte-surfactant system. In slightly acidic aqueous solution of pH 6.5, CIT was better incorporated in CDs and SDS micelles. The luminescence emission from CIT was found to be greatly enhanced by SDS micelles. The fluorescence intensity enhancements in CDs medium and in SDS as ionic surfactant relative to slightly acidic aqueous solution were 125 and 250%, respectively. Organized media-enhanced spectroflourometric methods were developed for the determination of CIT, in pure form as well as in pharmaceutical preparations. The fluorescence intensity-concentration plots were rectilinear over the ranges 0.06 to 0.64, 0.04 to 0.40, and 0.02 to 0.26 μg/mL with lower detection limits of 0.02, 0.01, and 0.007 μg/mL, either in citrate buffer only or in β-CD and SDS as organized media, respectively. Furthermore, the high sensitivity attained by using SDS as organized medium allowed in vitro spectrofluorometric determination of CIT in spiked human plasma. Interference from endogenous amino acids has been overcome by using the solid-phase extraction technique; the mean recovery (n = 5) was 100.1 ± 0.8%

scholarly journals Solvent Extraction of Thorium Using 5,11,17,23-Tetra[(2-ethyl acetoethoxyphenyl)(azo)phenyl]calix[4]arene

2016 ◽  
Vol 2016 ◽  
pp. 1-6 ◽  
Author(s):  
Quang Hieu Tran ◽  
Van Tan Le ◽  
Van Cuong Nguyen
Keyword(s):  
Aqueous Solution ◽  
Solvent Extraction ◽  
Molar Absorptivity ◽  
Tolerance Limits ◽  
Acidic Aqueous Solution ◽  
Selective Method ◽  
Chloroform Layer ◽  
Effects Of Ph ◽  
Synthetic Solution

A rapid, sensitive, and selective method for determination of thorium based on the complex withortho-ester tetra-azophenylcalix[4]arene (TEAC) was described. In the presence of pH of 4–6, TEAC-Th(IV) complex is extracted from an acidic aqueous solution into chloroform layer. The absorbance intensity of complex was measured by UV-Vis spectrometer at 525 nm and the molar absorptivity was found to be 2.4 × 104. Beer’s law was obeyed in the range of 1.0 to 25 × 10−5 M thorium(IV). The effects of pH, TEAC concentration, and shaking time were also studied. The tolerance limits for several metal ions were calculated. The proposed method was applied to the determination of thorium in synthetic solution and in the monazite sand samples with good results.

scholarly journals Determination of molybdenum(VI) in aqueous solution using trioctylmethylammonium chloride loaded silica gel.

1996 ◽  
Vol 45 (2) ◽  
pp. 175-179 ◽  
Author(s):  
Kimitoshi SATO ◽  
Motoyuki SUZUKI ◽  
Kusdiana HILMAN ◽  
Takashi GOTO
Keyword(s):  
Aqueous Solution ◽  
Silica Gel

scholarly journals Simple spectrofluorometric determination of p-aminobenzoic and p-aminosalicylic acids in biological fluids by use of terbium-sensitized luminescence

1996 ◽  
Vol 42 (10) ◽  
pp. 1659-1665 ◽  
Author(s):  
E S Lianidou ◽  
P C Ioannou
Keyword(s):  
Aqueous Solution ◽  
Biological Fluids ◽  
Optimum Conditions ◽  
Serum Samples ◽  
Solution Ph ◽  
Acidic Aqueous Solution ◽  
Selective Method ◽  
Spectrofluorometric Determination ◽  
Aminosalicylic Acids

Abstract A novel, sensitive, and selective method has been developed for determination of p-aminobenzoic (PABA) and p-aminosalicylic (PAS) acids in the N-benzoyl-L-tyrosyl-PABA/ PAS test. PAS is measured as a ternary complex with terbium and EDTA (lambda(ex) = 324 nm, lambda(em) = 546 nm) in alkaline aqueous solution (pH approximately 12.6), whereas both compounds (PABA and PAS) are measured as ternary complexes with terbium and tri-n-octylphosphine oxide (lambda(ex) = 292 nm, lambda(em) = 546 nm) in weakly acidic aqueous solution (pH approximately 5.5). We inve stigated and implemented optimum conditions for formation of these complexes, yielding respective detection limits for PABA and PAS of 0.07 and 0.02 micromol/L and ranges of application of 0-10 and 0-40 micromol/L (final concentration). The method has been successfully applied to determinations of PABA and PAS in urine and, after alkaline hydrolysis, to determinations of PABA in serum that has been deproteinized with acetonitrile. Within-run imprecision of the PABA determination ranges from 0.8% to 4.2 % for urine samples and from 3.9% to 8.2% for serum samples; day-to-day imprecision varies from 3.2% to 10% for serum samples.

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