The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Rajesh K Jakher - One of the best experts on this subject based on the ideXlab platform.
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investigation of asphaltene association with vapor pressure osmometry and interfacial tension measurements
Industrial & Engineering Chemistry Research, 2000Co-Authors: H W Yarranton, Hussein Alboudwarej, Rajesh K JakherAbstract:Molar masses of both n-pentane-extracted and n-heptane-extracted Athabasca asphaltenes were measured in toluene or 1,2-dichlorobenzene with a vapor pressure osmometer (VPO). The initial asphaltene molar mass, at concentrations below 0.5 kg/m3, is ≈1800 g/mol. The asphaltene molar mass is found to increase with asphaltene concentration until a limiting value is reached at a concentration between 10 and 20 kg/m3. The limiting value ranges from 4000 to 10 000 g/mol and depends on the solvent, temperature, and asphaltene fraction. The results suggest that asphaltenes form aggregates of 2−6 molecules in aromatic solvents. Interfacial tensions of asphaltenes in toluene or 1,2-dichlorobenzene versus water were measured for asphaltene concentrations from 0.3 to 100 kg/m3 using a drop volume tensiometer. The interfacial tension decreases linearly with concentration, indicating that no micelles are formed. Hence, the aggregation observed with VPO does not appear to be micellization. Similar results are obtained for...
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investigation of asphaltene association with vapor pressure osmometry and interfacial tension measurements
Industrial & Engineering Chemistry Research, 2000Co-Authors: H W Yarranton, Hussein Alboudwarej, Rajesh K JakherAbstract:Molar masses of both n-pentane-extracted and n-heptane-extracted Athabasca asphaltenes were measured in toluene or 1,2-dichlorobenzene with a vapor pressure osmometer (VPO). The initial asphaltene ...
Azadeh Tavakoli - One of the best experts on this subject based on the ideXlab platform.
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the validity of point of care tear film Osmometers in the diagnosis of dry eye
Ophthalmic and Physiological Optics, 2021Co-Authors: Azadeh Tavakoli, Maria Markoulli, Judith Flanagan, Eric B PapasAbstract:Purpose To determine the repeatability of TearLab and I-PEN Osmometers in vivo and their accuracy in vitro. Design Prospective, single-visit study. Methods The tear osmolarity of 28 participants was evaluated with TearLab and I-PEN on two occasions in random order, over a 2-h period. Both eyes were measured in a randomised order. Coefficients of repeatability (CoR) were determined for each device, together with the bias and limits of agreement between them. For the in vitro experiment, the osmolarity was measured by both Osmometers in five solutions (290, 297, 342, 338 and 383 mOsm/L) at two different temperatures (22 and 37°C) with a total of four consecutive measures. Results The CoRs for the TearLab and I-PEN in the right and left eyes were 26.2, 21.3, 33.6 and 28.3 mOsm/L, respectively. Across the first and second repeats, TearLab showed consistency of diagnosis for 50% of participants with 29% as dry eye positive, while I-PEN indicated 68% consistency of diagnosis with 57% dry eye positive. The instruments agreed on the diagnosis in 46.5% of cases. In vitro comparison showed that the average measurement errors for TearLab and I-PEN were -10 ± 13 and 31 ± 39 mOsm/L at 22°C, and 4 ± 13 and 20 ± 51 mOsm/L at 37°C. Conclusions In vitro, both instruments showed reasonable accuracy and repeatability at mid-range osmolarities, but repeatability generally declined at higher and lower levels. While TearLab accuracy remained consistent across the osmolarity range, measurement errors for I-PEN noticeably increased outside the mid-range. In vivo, both instruments displayed poor repeatability. This casts doubt on the value of utilising either instrument to establish osmolarity as a factor in the diagnosis of dry-eye, according to currently recommended diagnostic guidelines (TFOS DEWS II), if only a single measurement is taken from each eye.
H W Yarranton - One of the best experts on this subject based on the ideXlab platform.
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investigation of asphaltene association with vapor pressure osmometry and interfacial tension measurements
Industrial & Engineering Chemistry Research, 2000Co-Authors: H W Yarranton, Hussein Alboudwarej, Rajesh K JakherAbstract:Molar masses of both n-pentane-extracted and n-heptane-extracted Athabasca asphaltenes were measured in toluene or 1,2-dichlorobenzene with a vapor pressure osmometer (VPO). The initial asphaltene molar mass, at concentrations below 0.5 kg/m3, is ≈1800 g/mol. The asphaltene molar mass is found to increase with asphaltene concentration until a limiting value is reached at a concentration between 10 and 20 kg/m3. The limiting value ranges from 4000 to 10 000 g/mol and depends on the solvent, temperature, and asphaltene fraction. The results suggest that asphaltenes form aggregates of 2−6 molecules in aromatic solvents. Interfacial tensions of asphaltenes in toluene or 1,2-dichlorobenzene versus water were measured for asphaltene concentrations from 0.3 to 100 kg/m3 using a drop volume tensiometer. The interfacial tension decreases linearly with concentration, indicating that no micelles are formed. Hence, the aggregation observed with VPO does not appear to be micellization. Similar results are obtained for...
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investigation of asphaltene association with vapor pressure osmometry and interfacial tension measurements
Industrial & Engineering Chemistry Research, 2000Co-Authors: H W Yarranton, Hussein Alboudwarej, Rajesh K JakherAbstract:Molar masses of both n-pentane-extracted and n-heptane-extracted Athabasca asphaltenes were measured in toluene or 1,2-dichlorobenzene with a vapor pressure osmometer (VPO). The initial asphaltene ...
Peter G Steeneken - One of the best experts on this subject based on the ideXlab platform.
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graphene gas Osmometers
2D Materials, 2016Co-Authors: Robin J Dolleman, Santiago J Cartamilbueno, Herre S J Van Der Zant, Peter G SteenekenAbstract:We show that graphene membranes that separate two gases at identical pressure are deflected by osmotic pressure. The osmotic pressure is a consequence of differences in gas permeation rates into a few-layer graphene enclosed cavity. The deflection of the membrane is detected by measuring the tension-induced resonance frequency with an interferometric technique. Using a calibration measurement of the relation between resonance frequency and pressure, the time dependent osmotic pressure on the graphene is extracted. The time dependent osmotic pressure for different combinations of gases shows large differences that can be accounted for by a model based on the different gas permeation rates. In this way, a graphene-membrane based gas osmometer with a responsivity of ~60 kHz mbar–1 and nanoscale dimensions is demonstrated.
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graphene gas Osmometers
arXiv: Mesoscale and Nanoscale Physics, 2016Co-Authors: Robin J Dolleman, Santiago J Cartamilbueno, Herre S J Van Der Zant, Peter G SteenekenAbstract:Here it is shown that graphene membranes that separate 2 gases at identical pressure are deflected by osmotic pressure. The osmotic pressure is a consequence of differences in gas permeation rates into a graphene enclosed cavity. The deflection of the few layer graphene membranes is detected by an interferometric technique for measuring their tension-induced resonance frequency. Using a calibration measurement of the relation between resonance frequency and pressure, the time dependent osmotic pressure on the graphene is extracted. The osmotic pressure for different combinations of gases shows large differences that can be accounted for by a model based on the different gas permeation rates. Thus a graphene membrane based gas osmometer with a responsitivity of ~60 kHz/mbar and nanoscale dimensions is demonstrated.
Birger Holz - One of the best experts on this subject based on the ideXlab platform.
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Freezing point osmometry of milk to determine the additional water content – an issue in general quality control and German food regulation
Chemistry Central Journal, 2008Co-Authors: Britta Büttel, Markus Fuchs, Birger HolzAbstract:Background The determination of the osmolality of aqueous samples using a freezing point osmometer is a well-established, routine laboratory method. In addition to their use in clinical and pharmaceutical laboratories, freezing point Osmometers are also employed in food testing laboratories. One application is the determination of the osmolality of milk. Although cow's milk is a natural product whose water content is approximately 87%, the osmolality of milk is a significant value when the milk is collected from a larger population of animals. This value is used in milk processing to control the water content, based on the German Food Control Regulations for Milk. Results Measurement of the freezing point and osmolality of milk samples was performed with a Knauer Semi-Micro Freezing Point Osmometer. Osmolality was measured for the untreated milk samples and following their dilution (by volume) with 10% and 50% water. The measurements were made after 1, 4 and 7 days to evaluate changes over time. All measurement values for the undiluted milk were spread over a small interval with an average of 271 mOsmol/kg. After mixing the milk samples with 10% water, the average decreased to 242 mOsmol/kg, while mixing with 50% water resulted in an average osmolality of 129 mOsmol/kg. There was no significant change for the osmolality within the 7 days (measurements from days 1, 4 and 7). Conclusion The results observed demonstrate clearly that the additional water content of milk can be determined easily using a freezing point osmometer. Milk samples that contain additional water have a significantly decreased osmolality, corresponding to an increased freezing point. The effect on osmolality of ageing the milk samples could not be determined in this study's time-dependent measurements.
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freezing point osmometry of milk to determine the additional water content an issue in general quality control and german food regulation
Chemistry Central Journal, 2008Co-Authors: Britta Büttel, Markus Fuchs, Birger HolzAbstract:The determination of the osmolality of aqueous samples using a freezing point osmometer is a well-established, routine laboratory method. In addition to their use in clinical and pharmaceutical laboratories, freezing point Osmometers are also employed in food testing laboratories. One application is the determination of the osmolality of milk. Although cow's milk is a natural product whose water content is approximately 87%, the osmolality of milk is a significant value when the milk is collected from a larger population of animals. This value is used in milk processing to control the water content, based on the German Food Control Regulations for Milk. Measurement of the freezing point and osmolality of milk samples was performed with a Knauer Semi-Micro Freezing Point Osmometer. Osmolality was measured for the untreated milk samples and following their dilution (by volume) with 10% and 50% water. The measurements were made after 1, 4 and 7 days to evaluate changes over time. All measurement values for the undiluted milk were spread over a small interval with an average of 271 mOsmol/kg. After mixing the milk samples with 10% water, the average decreased to 242 mOsmol/kg, while mixing with 50% water resulted in an average osmolality of 129 mOsmol/kg. There was no significant change for the osmolality within the 7 days (measurements from days 1, 4 and 7). The results observed demonstrate clearly that the additional water content of milk can be determined easily using a freezing point osmometer. Milk samples that contain additional water have a significantly decreased osmolality, corresponding to an increased freezing point. The effect on osmolality of ageing the milk samples could not be determined in this study's time-dependent measurements.