Pre-equilibration Time Research Articles

Microfluidic emulsification: Process and formulation variables effects in flow behavior pattern on a flow-focusing device

Formulation and process variables in surfactant/oil/water (SOW) systems can strongly modify the water/oil interfacial tension leading to different behaviors. Pre-equilibration time of the SDS/toluene/1-butanol/NaCl(aq) system was studied as a process variable and the flow regimes were described at different continuous and dispersed flow rates through a flow focusing geometry. Salinity and oil nature for the SDS/n-alkane/alcohol/NaCl(aq) equilibrated system were studied as formulation variables at fixed dispersed flow rates, changing the continuous flow rate and the formulation variable in order to get O/W or W/O emulsions in hydrophilic and hydrophobic chips, respectively. Pre-equilibration time modifies the flow regimes depending on the differences observed in the interfacial tension at t = 0 and t = 24 h of equilibration. Under very hydrophilic conditions, when γt=24 > γt=0, the entire droplet area is slightly higher for equilibrated systems. At WIII condition, when γt=0 >> γt=24, droplets are formed only in jetting regime for not equilibrated systems. For salinity scan, monodispersed oil droplets were obtained at low salinities, S = 0−0.25 % and in the oil scan, water droplets were obtained when using cyclohexane and cyclohexane-hexane mixtures. In both cases, flow regimes are reported into the formulation maps, using the Hydrophilic Lipophilic Deviation as formulation variable (HLD vs flow rate ratio). Droplet size was fitted into the same equation ( di≈αCac-0.264), and it is noteworthy that the interfacial tension in CaC is lower than in most of reported works using flow-focusing geometries and both emulsions (W/O and O/W) were obtained with the same surfactant.

Mineralization Enhancement of Pharmaceutical Contaminants by Radical-Based Oxidation Promoted by Oxide-Bound Metal Ions.

While the use of transition metal oxides in catalyzing advanced oxidation reactions has been widely investigated, very few reports have focused on how the preliminary contact of oxides with target compounds may affect the succession of reaction. In this study, we examined the adsorption and electron transfer reactions of two fluoroquinolones, flumequine (FLU), and norfloxacin (NOR), with goethite (α-FeOOH) or manganese (Mn) oxide, and their impact on the subsequent mineralization of target compounds using H2O2 or S2O82- under UVA irradiation. Intriguingly, higher total organic carbon (TOC) removal was achieved when antibiotics and metal oxides were allowed for preequilibration before starting the oxidation reaction. The rate and extent of TOC removal are strongly dependent on the molecule structure and the redox-active mineral used, and much less on the preequilibration time. This high efficiency can be ascribed to the presence of reduced metal ions, chemically or photochemically generated during the first stage, onto oxide minerals. Oxide-bound MnII plays a crucial role in catalyzing oxidant decomposition and then producing greater amounts of radical species through a photoassisted redox cycle, regardless of the underlying surface, MnIVO2 or MnIIIOOH. This finding will be of fundamental and practical significance to Mn-based oxidation reactions and wastewater treatment processes.

How good are the predictions of mobility of aged polychlorinated biphenyls (PCBs) in soil? Insights from a soil column experiment

A column leaching experiment was performed to evaluate the influence of some relevant environmental factors (soil/water contact time, temperature, saturation) on mobility of aged polychlorinated biphenyls (PCBs) in soil together with transport mediated by dissolved organic carbon (DOC) and mobile organic carbon (OC) coated fine particles/colloids. Consecutive fractions of leachates were collected after a variable pre-equilibration time (2, 5, 7, 48 days), using leaching solutions with different DOC content (tap water vs. Aldrich humic acid), in saturated vs. field capacity conditions and at different temperatures (25 °C vs. 15 °C). The data obtained were compared to the predicted values using a multimedia model (SoilPlusVeg) to evaluate model behaviour. Contact time and temperature determined a relevant effect on DOC and particle/colloid availability, with significant variations in leachate concentrations (up to 1 order of magnitude), typically overlooked by most environmental fate models. Results obtained at different temperatures show a modulation of the DOC/particles production with temperature and therefore the role of temperature changes in the environmental scenarios (e.g. seasonal variations). Transport of PCBs enhanced by Aldrich DOC was not linearly correlated to chemical hydrophobicity but revealed a threshold to ~Log KOW 6.5, likely because of the slow sorption kinetics of more hydrophobic chemicals. Additionally, variation of the saturation conditions (e.g. drying-wetting cycles) can determine contamination peaks at the beginning of an irrigation/rainfall event because of the soil/water equilibration. Model simulations, even when including DOC in the water phase, but not accounting for the particle/colloidal transport and sorption/desorption kinetics, mismatched the ratio of dissolved vs. DOC-associated and particle-associated PCBs and substantially underpredicted concentrations, especially for the high chlorinated congeners. The results indicated that some of the common assumptions and paradigms in fate modelling of such hydrophobic compounds should be revisited and models updated.

Barite recrystallization in the presence of 226Ra and 133Ba

Despite the long history of studies on (Ba,Ra)SO4, various recent investigations aimed at improving our understanding of its formation processes and thermodynamics. Accumulation of natural Ra isotopes (mainly 226Ra and 228Ra) in (Ba,Ra)SO4 plays an important role in many geotechnical applications and water desalination facilities. In the near field of a nuclear waste repository, barite formation may be expected e.g. as a consequence of contact of spent nuclear fuel or vitrified high level waste with sulfate containing ground water, and may control the potential release of Ra from waste forms upon leakage.Here, we present results of long term batch-type barite recrystallization experiments conducted in the simultaneous presence of 226Ra and 133Ba as a function of initial Ra2+ concentration and pH with the same type and charge of barite powder as used in previous studies (Curti et al., 2010; Klinkenberg et al., 2014; Brandt et al., 2015). Due to the simultaneous measurement of 133Ba and 226Ra our data allow for a direct relation of 226Ra uptake with barite recrystallization, which leads to more accurate partition coefficients compared to previous studies. During a reaction period of five years, barite is continuously recrystallizing. Within the investigated radium concentration range (Ba(1−X)RaXSO4 with X < 0.0006), we measure a partition coefficient of D = 2.1 ± 0.5. The partition coefficient is constant within uncertainty during almost five years (1793 days) of experimental duration. This value is in line with a description of (Ba,Ra)SO4 as an ideal solid solution based on the solubility products (KSP) of the endmembers barite (log10(KSP(barite)) = −9.97) and radium sulfate (log10(KSP(RaSO4)) = −10.26; dimensionless Guggenheim parameter, a0 = 0.0 ± 0.3). Apparent discrepancies to previous theoretical results (a0 = 1.0 ± 0.4) may be resolved when the uncertainties related to the solubility of RaSO4 are considered.Compared to results of previous publications, recrystallization is extremely slow in the experiments presented here. While previous authors suggested complete equilibration of bulk microcrystalline barite within less than three years, a recrystallization of less than 7% of the barite mass is observed within five years. We describe the progress of recrystallization with a new modified homogeneous recrystallization model. Observed recrystallization rates are in the range 0.11–1.5 nmol/(m2 s) and increase with decreasing pH. According to this modified homogeneous recrystallization model, complete bulk barite equilibration is expected in about 1400–16,900 years.The strongly decreased recrystallization kinetics in our experiments is likely related to a strongly prolonged pre-equilibration time (0.8 years), which according to XRD investigations, leads to a higher crystallinity (higher crystal domain size and lower Debye-Waller parameters) of the barite powder.

Polymerization of Silicate on Hematite Surfaces and Its Influence on Arsenic Sorption

Iron oxides and oxyhydroxides are important sorbents for arsenic in soils, sediments, and water treatment systems, but their long-term potential for arsenic retention may be diminished by the formation of polymeric silicate on their surfaces. To study these interactions, we first investigated the sorption of silicate to colloidal hematite (α-Fe(2)O(3)) in short-term (48 h) and long-term (210 days) batch experiments. The polymerization of silicate on the hematite surface was monitored by attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. The pH dependence of silicate sorption exhibited a maximum between pH 9.0 and 9.5. The condensation of silicate on hematite surfaces adsorbed from monomeric silicate solutions steadily continued over the 210 day period, whereby surface polymerization was slower at pH 3 than at pH 6. The effect of silicate surface polymerization on arsenate and arsenite sorption was studied by use of hematite pre-equilibrated with silicate for different time periods of up to 210 days. The competitive effect of silicate on arsenate and arsenite sorption increased with increasing silicate pre-equilibration time. Only under strongly acidic conditions (pH 3), where silicate sorption was weakest and surface polymerization was slowest, was arsenate and arsenite sorption not affected by the presence of silicate. We conclude that the long-term exposure to dissolved silicate can decrease the potential of natural iron (oxyhydr)oxides for adsorbing inorganic arsenic.

Sorption of 2,4-D and other phenoxy herbicides to soil, organic matter, and minerals

We review 2,4-dichlorophenoxyacetic acid (2,4-D) and other phenoxy herbicide sorption experiments. A database with 469 soil–water distribution coefficients K d (in liters per kilogram) was compiled: 271 coefficients are for the phenoxy herbicide 2,4-D, 9 for 4-(2,4-dichlorophenoxy)butyric acid, 18 for 2-(2,4-dichlorophenoxy)propanoic acid, 109 for 2-methyl-4-chlorophenoxyacetic acid, 5 for 4-(4-chloro-2-methylphenoxy)butanoic acid, and 57 for 2-(4-chloro-2-methylphenoxy)propanoic acid. The following parameters characterizing the soils, solutions, or experimental procedures used in the studies were also compiled if available: solution CaCl2 concentration, pH, pre-equilibration time, temperature, soil organic carbon content (f oc), percent sand, silt and clay, oxalate extractable aluminum, oxalate extractable iron (Oxalate Fe), dithionite–citrate–bicarbonate extractable aluminum, dithionite–citrate–bicarbonate extractable iron (DCB Fe), point of zero negative charge, anion exchange capacity, cation exchange capacity, soil type, soil horizon or depth of sampling, and geographic location. K d data were also compiled characterizing phenoxy herbicide sorption to the following well-defined sorbent materials: quartz, calcite, α-alumina, kaolinite, ferrihydrite, goethite, lepidocrocite, soil humic acid, Fluka humic acid, and Pahokee peat. The data review suggests that sorption of 2,4-D can be rationalized based on the soil parameters pH, f oc, Oxalate Fe, and DCB Fe in combination with sorption coefficients measured independently for humic acids and ferrihydrite, and goethite. Soil organic matter and iron oxides appear to be the most relevant sorbents for phenoxy herbicides. Unfortunately, few authors report Oxalate Fe and DCB Fe data.

Specific Soluble Oligomers of Amyloid-β Peptide Undergo Replication and Form Non-fibrillar Aggregates in Interfacial Environments

Aggregates of amyloid-β (Aβ) peptides have been implicated in the etiology of Alzheimer disease. Among the different forms of Aβ aggregates, low molecular weight species ranging between ~2- and 50-mers, also called "soluble oligomers," have emerged as the species responsible for early synaptic dysfunction and neuronal loss. Emerging evidence suggests that the neurotoxic oligomers need not be formed along the obligatory nucleation-dependant fibril formation pathway. In our earlier work, we reported the isolation of one such "off-pathway" 12-18-mer species of Aβ42 generated from fatty acids called large fatty acid-derived oligomers (LFAOs) (Kumar, A., Bullard, R. L., Patel, P., Paslay, L. C., Singh, D., Bienkiewicz, E. A., Morgan, S. E., and Rangachari, V. (2011) PLoS One 6, e18759). Here, we report the physiochemical aspects of LFAO-monomer interactions as well as LFAO-LFAO associations in the presence of interfaces. We discovered that LFAOs are a replicating strain of oligomers that recruit Aβ42 monomers and quantitatively convert them into LFAO assemblies at the expense of fibrils, a mechanism similar to prion propagation. We also found that in the presence of hexane-buffer or chloroform-buffer interfaces LFAOs are able to associate with themselves to form larger but non-fibrillar aggregates. These results further support the hypothesis that low molecular weight oligomers can be generated via non-fibril formation pathways. Furthermore, the unique replicating property of off-pathway oligomers may hold profound significance for Alzheimer disease pathology.

Determination of Cryoprotectant for Magnetic Cryopreservation of Dental Pulp Tissue

Dental pulp, covered with dental hard tissue, is a promising source of mesenchymal stem cells and osteoprogenitor cells for regenerative medicine. Our previous studies showed that 73% of dental pulp cells isolated from magnetically cryopreserved teeth where their viability, morphology, and expression of stem cell surface markers were similar to the cells isolated from fresh teeth, suggesting that magnetic cryopreservation is an applicable method for intact tooth as well as dental pulp tissue banking. However, the cryoprotectant, concentration, contact surface, and equilibration time for magnetic cryopreservation of dental pulp require optimization. In addition, the integrity and viability of post-thawed dental pulp with and without dental hard tissue covering after magnetic cryopreservation were investigated. Lower concentration of the cryoprotectant (5% dimethyl sulfoxide [DMSO]) and shorter preequilibration time are required for magnetic cryopreservation compared with the conventional cryopreservation method. The structure of at least 33% of post-thawed pulp with dental hard tissue from the open end remained intact where >80% of cells were viable. The addition of the cryoprotectant additive trehalose did not replace or improve DMSO's efficacy for magnetic cryopreservation of dental pulp or intact tooth. Tooth banking for transplantation provides an alternative treatment to replace missing teeth. The optimized cryoprotectant conditions for dental pulp tissue during magnetic cryopreservation should lead to more satisfactory outcomes in clinical applications such as autotransplantation and the isolation and expansion of dental pulp stem cells for tissue repair.

Radium uptake during barite recrystallization at 23 ± 2 °C as a function of solution composition: An experimental 133Ba and 226Ra tracer study

High-purity synthetic barite powder was added to pure water or aqueous solutions of soluble salts (BaCl 2, Na 2SO 4, NaCl and NaHCO 3) at 23 ± 2 °C and atmospheric pressure. After a short pre-equilibration time (4 h) the suspensions were spiked either with 133Ba or 226Ra and reacted under constant agitation during 120–406 days. The pH values ranged from 4 to 8 and solid to liquid (S/L) ratios varied from 0.01 to 5 g/l. The uptake of the radiotracers by barite was monitored through repeated sampling of the aqueous solutions and radiometric analysis. For both 133Ba and 226Ra, our data consistently showed a continuous, slow decrease of radioactivity in the aqueous phase. Mass balance calculations indicated that the removal of 133Ba activity from aqueous solution cannot be explained by surface adsorption only, as it largely exceeded the 100% monolayer coverage limit. This result was a strong argument in favor of recrystallization (driven by a dissolution–precipitation mechanism) as the main uptake mechanism. Because complete isotopic equilibration between aqueous solution and barite was approached or even reached in some experiments, we concluded that during the reaction all or substantial fractions of the initial solid had been replaced by newly formed barite. The 133Ba data could be successfully fitted assuming constant recrystallization rates and homogeneous distribution of the tracer into the newly formed barite. An alternative model based on partial equilibrium of 133Ba with the mineral surface (without internal isotopic equilibration of the solid) could not reproduce the measured activity data, unless multistage recrystallization kinetics was assumed. Calculated recrystallization rates in the salt solutions ranged from 2.8 × 10 −11 to 1.9 × 10 −10 mol m −2 s −1 (2.4–16 μmol m −2 d −1), with no specific trend related to solution composition. For the suspensions prepared in pure water, significantly higher rates (∼5.7 × 10 −10 mol m −2 s −1 or ∼49 μmol m −2 d −1) were determined. Radium uptake by barite was determined by monitoring the decrease of 226Ra activity in the aqueous solution with alpha spectrometry, after filtration of the suspensions and sintering. The evaluation of the Ra uptake experiments, in conjunction with the recrystallization data, consistently indicated formation of non-ideal solid solutions, with moderately high Margules parameters ( W AB = 3720–6200 J/mol, a 0 = 1.5–2.5). These parameters are significantly larger than an estimated value from the literature ( W AB = 1240 J/mol, a 0 = 0.5). In conclusion, our results confirm that radium forms solid solutions with barite at fast kinetic rates and in complete thermodynamic equilibrium with the aqueous solutions. Moreover, this study provides quantitative thermodynamic data that can be used for the calculation of radium concentration limits in environmentally relevant systems, such as radioactive waste repositories and uranium mill tailings.

Reactivities of Fe(II) on Calcite: Selenium Reduction

The reductive immobilization of Se(IV) by micrometer-sized (100-200 microm) calcite containing sorbed or coprecipitated Fe(II) was investigated at pH 7 under anoxic conditions (O(2) < 1 ppmv) using X-ray absorption near-edge structure (XANES) spectroscopy. The Se(IV) sorption on calcite increased in the presence of sorbed Fe(II) compared to that of Fe-free pure calcite. XANES spectra of Se K-edge shows that nearly half of the total sorbed Se(IV) is reduced to Se(0) by Fe(II) sorbed on calcite within 24 h. The extent of reduction decreases with increasing equilibration time of calcite with Fe(II) solution before Se(IV) addition. The combined results of field emission scanning electron microscopy and X-ray diffraction have shown that needle-shaped red monoclinic elemental Se with diameters of 30-50 nm and lengths of up to 100 nm is precipitated on the calcite surface. Fe(II) coprecipitated calcite does not contribute to Se(IV) reduction within 72 h. Therefore, the reduction capacity of Fe(II) linked to calcite critically depends on its location (either on the surface or in the bulk solid), and less extensively on the pre-equilibration time of calcite with Fe(II) solution. Such understanding is important to predict the transport, transformation, and attenuation of Se in subsurface and in nuclear waste repositories.

217 EFFECT OF PRE-EQUILIBRATION TIME ON THE SURVIVAL RATE OF MATURED BOVINE OOCYTES AFTER VITRIFICATION AND ON SUBSEQUENT EMBRYO DEVELOPMENT

Prolonged exposure of oocytes to cryoprotectants causes cell injury, whereas a short exposure time results in insufficient permeation because of ice formation. This study was designed to determine the optimal pre-equilibration time and its effect on the survival rate of matured bovine oocytes after warming and on subsequent embryo development. Bovine COC were matured for 20 h in TCM-199 supplemented with 5% calf serum (CS) and 0.02 AU mL–1 of FSH at 38.5°C in 5% CO2 in air. Then, the COC were partially denuded. The oocytes were pre-equilibrated in 100 μL of vitrification solution 1 (VS1) containing 7.5% ethylene glycol (EG), 7.5% DMSO, and 20% CS in TCM-199 for 0, 1, 3, and 5 min. Then, the oocytes were moved through 100-μL drops of vitrification solution 2 (VS2) containing 30% EG, 30% DMSO, 0.5 m sucrose (Suc), and 20% CS in TCM-199 for 30 s, loaded into cryotops, and immersed into liquid nitrogen. Oocytes were warmed by plunging the cryotops into 1 m Suc in TCM-199 supplemented with 20% CS for 1 min, placed in 0.5 m Suc in TCM-199 supplemented with 20% CS for 3 min, and finally in TCM-199 supplemented with 20% CS alone for 5 min. Frozen–thawed semen from a single bull (5 × 106 spermatozoa mL–1) was used for fertilization. Zygotes were vortexed to remove the cumulus cells 18 h after fertilization and cultured in CR1aa for 9 days. Data were analyzed by the chi-square test. Results are presented in Table 1. There were no differences in the survival rates of the control and vitrified oocytes. The cleavage rate of controls at both 24 and 48 h was greater (P &lt; 0.01) than that of vitrified oocytes. Among pre-equilibration times, the cleavage rate of 0, 1, and 3 min pre-equilibrations at both 24 and 48 h was greater than with the pre-equilibration time of 5 min (P &lt; 0.01). With respect to blastocyst development, the control oocytes showed greater development rates than the vitrified oocytes (P &lt; 0.01), whereas the development rates were lower with the pre-equilibration time of 5 min (P &lt; 0.01) than with the other pre-equilibration times. In conclusion, the results indicated that matured bovine oocytes could survive after vitrification and subsequently develop into blastocysts after IVF. However, the pre-equilibration time before vitrification affects cleavage and blastocyst development; a longer exposure time resulted in lower blastocyst development. Table 1. Effect of pre-equilibration time on matured bovine oocytes survival and on subsequent embryo development

80 EFFECT OF PRE-EQUILIBRATION TIME ON THE SURVIVAL RATE OF IN VITRO-FERTILIZED BOVINE EMBRYOS AFTER VITRIFICATION

Successful cryopreservation of embryos depends on the pre-equilibration time. This study was designed to compare 2 pre-equilibration times – short (1 min) and long (5 min) – and to evaluate the re-expansion and hatching rates of different stages of embryos using the short pre-equilibration method. Cumulus–oocyte complexes (COCs) from ovaries obtained from a slaughterhouse were matured, fertilized, and cultured in vitro. In Experiment 1, expanded blastocysts between 7 and 9 days of culture were pre-equilibrated for the short time (1 min) in 100 μL of vitrification solution 1 (VS1: containing 7.5% ethylene glycol (EG), 7.5% dimethyl sulfoxide (DMSO), and 20% calf serum (CS) in TCM-199), followed by incubation in 100 μL of vitrification solution 2 (VS2: containing 15% EG, 15% DMSO, 20% CS, and 1 m sucrose (Suc) in TCM-199) for 30 s. Another group of blastocysts was subjected to the long pre-equilibration (5 min) in 100 μL VS1, followed by incubation in 100 μL of VS2 for 30 s. The embryos were placed into Cryotops® (Kitasato Supply Co., Tokyo, Japan) and immediately submerged in liquid nitrogen and kept there for 1 week. Blastocysts were warmed by plunging the Cryotops into 1 m Suc in TCM-199 for 1 min, placed in 0.5 m Suc in TCM-199 for 3 min, and finally placed in CR1aa alone for 5 min before being cultured. In Experiment 2, 8-cell embryos, morulae, and expanded blastocysts were vitrified by the previously described short equilibration method. The re-expansion and hatching rates of embryos were determined as the percentage of vitrified–warmed embryos undergoing further development in the in vitro culture. The data were analyzed by the chi-square test. Results are presented in Table 1. There was no difference between the short and long pre-equilibration times in terms of survival (94.0% v. 94.1%, respectively) and morphological appearance immediately after warming. However, re-expansion of blastocysts (ability to develop further) was slightly higher with the short pre-equilibration than with the long pre-equilibration (90.0% v. 85.9%, respectively). In Experiment 2, there were no differences in embryo re-expansion, but the hatching rates of 8-cell embryos were lower than those of morulae, blastocysts, and controls. In conclusion, the results of this study indicate that the length of pre-equilibration time prior to vitrification does not influence embryo re-expansion, and that bovine morulae and blastocysts can be vitrified with equal success. We also conclude that insufficient permeation of cryoprotectants may occur in 8-cell embryos. Table 1. Survival and hatching rates of vitrified bovine embryos after warming

Solid phase microextraction with gas chromatography–mass spectrometry: a very rapid method for identification of volatile organic compounds emitted by Carum copticum

The investigation of flower scent represents an important field of modern biological research which is directed towards special theories of biological recognition. The headspace solid phase microextraction coupled with gas chromatography–mass spectrometry was used to identify the volatile components of Carum copticum (C. copticum) cultivated in Iran. The compounds were identified according to their retention indices and mass spectra (EI, 70 eV). The effects of different parameters, such as the desorption time, the extraction temperature, the sample mass, the addition of salt, the pre-equilibration time and the extraction time, on the extraction efficiency were investigated. The optimized conditions were: the desorption time, 2 min; the extraction temperature, 58°C; the sample mass, 1.000 g in 4.0 mL 2.0 M NaCl solution; the pre-equilibration time, 25 min; the extraction time, 20 min. Finally, ten components were identified in the volatile components of C. copticum. The major components of C. copticum were thymol (68.2%), γ-terpinene (13.9%), p-cymene (11.6%), myrcene (1.0%) and β-pinene (0.6%). Precision of the proposed method is good and %RSD less than 14 was obtained.

A method to reduce the equilibration time prior to data capture in ampoule-based isothermal microcalorimetric studies

This paper reports a technique for heat conduction isothermal microcalorimeters, which allows, by means of a lowering apparatus, the sample and reference ampoules to be lowered very slowly from the pre-equilibration position to the measuring position. The purpose is to minimize the effect on (total) equilibration time arising from both the pre-equilibration time and the dissipation time (i.e. the time to dissipate the thermal shock which occurs when the vessels are lowered manually). Measurements using 3 ml glass ampoules filled with water, as sample and reference, at 25 and 60 °C, showed that the extent of thermal shock was drastically diminished as the lowering speed decreased, and that the associated heat quantity was reduced to less than 0.2 mJ when lowering occurred over a period of more than 180 s. The dissipation time, the time-period required to dissipate the thermal shock, was also shortened to less than 10 min; the standard manual lowering procedure dissipation time being ca. 25 min. In practice experimental measurements of the imidazole catalysed hydrolysis of triacetin and of the solid state oxidation of ascorbic acid showed that the dissipation time was not shortened when the initial power observed was more than 5 μW, however, it was significantly shortened when the initial power observed was around ≤1 μW. The proposed ampoule lowering procedure could be expected to bring about a saving in the total measurement time for reactions with low initial power, such as those associated with long-term stability studies of relatively stable pharmaceuticals. The described procedure also eliminates operator-induced effects associated with manual lowering of ampoules. In principle the device described also would permit automated loading protocols to be developed.

Characterization of Pesticide Desorption from Soil by the Isotopic Exchange Technique

The reversibility of pesticide sorption–desorption in soil is of fundamental importance in the understanding of the fate of these agrochemicals in the environment. We used an isotopic exchange method to characterize the irreversibility of the sorption–desorption process of the insecticide imidacloprid (1‐[(6‐chloro‐3‐pyridinyl)‐methyl]‐Nnitro‐2‐imidazolidinimine) and its degradation product imidacloprid‐urea (1‐[(6‐chloro‐3‐pyridinyl)‐methyl]‐2‐imidazolidinone) on a silty clay loam (SiCL) soil, and that of the metabolite imidacloprid‐guanidine (1‐[6‐chloro‐3‐pyridinyl)methyl]‐4,5‐dihydro‐1H‐imidazol‐2‐amine) on a loamy sand (LS) soil. The exchange between 12C‐pesticide molecules and 14C‐labeled pesticide molecules in soil suspensions preequilibrated for 24 h was monitored and indicated that a fraction of the sorbed chemicals was resistant to desorption. A two‐compartment model was applied to describe the experimental sorption data points of the sorption isotherms as the sum of a reversible component and a nondesorbable, irreversible component. The quantitative estimation of the irreversible and reversible components of sorption, experimentally derived from isotopic exchange experiments, indicated degree of irreversibility (percentage irreversibly bound) in the order: imidacloprid–SiCL soil (6–32%) &lt; imidacloprid urea–SiCL soil (15–23%) &lt; imidacloprid guanidine–LS soil (32–51%), with greater irreversibility at lower pesticide concentration. Increasing the preequilibration time and decreasing pH in the imidacloprid–SiCL soil system resulted in increased sorption irreversibility. The irreversible component of sorption determined by the isotopic exchange technique also allowed accurate prediction of the sorption–desorption hysteretic behavior during successive desorption cycles for all three soil–pesticide systems studied. The isotopic exchange technique appears to be a suitable method to quantitatively characterize pesticide desorption from soil, allowing prediction of hysteresis during sorption–desorption experiments.

Separation of carbohydrate-mediated microheterogeneity of recombinant human erythropoietin by free solution capillary electrophoresis : Effects of pH, buffer type and organic additives

Free solution capillary electrophoresis has been investigated as an alternative to isoelectric focusing for the separation of the glycoforms of recombinant human erythropoietin (r-HuEPO), a primary regulator of erythropoiesis. A systematic approach was used to study the effect of pH, buffer type and organic modifiers on the resolution of the microheterogeneity of erythropoietin. The main factors for improving the resolution were the regulation of the electroosmotic flow of the running buffer and the reduction of solute-wall interaction. The best resolution of the glycoforms of r-HuEPO was obtained with a mixed buffer pH 4.0 (100 mM acetate phosphate, 10 h preequilibration time).