Electrocoalescence based serial dilution of microfluidic droplets PMC

As shown in Figure 7(b), the duration of coalescence is nearly constant for voltages greater than 10 V. This indicates that there exists a threshold voltage for achieving “body” type coalescence, and for the specified geometry and fluidic conditions, the threshold is 20 V. Figure 4(a) shows the DF as a function of number of coalescence events for three capillary numbers (Ca). The applied signal was a sinusoidal voltage of magnitude of 50 V and frequency of 5 kHz for all studies unless specified otherwise. In all the cases, the flow rate ratio between the oil phase (Qo) and the dispersed water phase (Qw) was kept constant at 3. This resulted in uniform size of diluting droplets, since it is well-known that the size of the droplets in a T-junction is a function of the ratio between the flow rates.26 The dilution factor is approximately linearly related to the number of coalescence events up to a large number of events.

All other interior boundaries were set to continuity of the current density and the exterior boundaries of the model were set to electric insulation. The conductivities of PDMS and the continuous phase were assumed to be zero, and the conductivity of the dispersed phase was set to 5.5 μS/m. Differential scanning calorimetry was also obtained on (DL)-malic acid, and that thermogram is shown in Figure 9. The sole thermal event observed was a single endotherm identified as the melting phase transition.

Second, the electric field was alternately switched on or off such that every other moving droplet coalesced with the parked droplet. Finally, the field was kept on so that every moving droplet coalesced with the parked droplet. It is also possible to add more functionality by incorporating multiple traps storing different sample liquid for on-demand storage and multiplexed dilution and mixing. To investigate how the proposed design of the channel electrodes facilitates coalescence by generating electric field lines in the the one which decreases with dilution is desired region, we performed simulations in COMSOL Multiphysics® 3.5. Since solving the coupled problem of hydrodynamics, drop deformation, and electrical stresses is quite challenging, we pursue a simpler route by taking representative static (deformed) drop shapes and calculating the resulting electric field distribution. As we discuss below, this simplified approach provides useful insights into regions where electrical stresses are strongest, thus aiding in device design and understanding the mechanisms of coalescence.

Variation of Molar Conductivity with Concentration

When it comes to electrical current, the Arrhenius equation or principle is utilised to define electrolytic conduction. A substance’s molar conductivity is a measurement of how well it conducts electrical current or water. Concentration dependence of a) osmotic coefficient (ϕ), b) enthalpy of dilution (ΔHdil), and c) fraction of free hydrogen counterions (fC) in aqueous solutions of the PSS–CP complex at 25 °C for various degrees of complexation (1 − f). Each cylinder encases an easily removable assembly, itself mainly consisting of the heat flow-meter and exchanger J, of the adsorption cell K and of the lid L. The latter is made of semi-conductive elements (Cambion, type 801) and the whole assembly is pressed by a spring F against the aluminum block I acting as a heat sink.

The onset of melting was noted at 103.3°C, and the peak maximum was observed at 105.3°C. The enthalpy of fusion computed for this sample was calculated as 201 J/g, and the quality of the DSC thermogram suggests that purity determination by DSC would be a viable method. 231Pa/233Pa isotope ratios were measured with a precision of 0.5%, with an LOD of 200 ag mL−1.

However, experimental controls in which the T-RFLP analysis was applied to DNA from a pure culture were also performed and a single T-RLFP peak was generated in each case. Another possible explanation is that because an individual organism can contain multiple, heterogeneous copies of the 16S rRNA gene (20, 27, 30, 43, 44), each organism type could actually have been responsible for more than one T-RFLP peak. However, the extent to which such sequence deviations occur has not been well studied and it is unlikely that the detection of multiple, divergent copies of a 16S rRNA gene can account for the results presented here. In this study, a sterile SM was also used in an attempt to increase the number of types to compare when calculating the diversity index. Unfortunately, the colonies that grew on the SM were quite small and generally lacked morphological distinctiveness, making a comparison among treatments impossible. Another concern with regard to the use of culture-based procedures is the difficulty in accurately and consistently identifying community members, given the fact that very similar colony morphologies can occur among taxonomically distinct groups of organisms.

Variation of Conductivity and Molar conductivity with Concentration

It is possible that this variation in bacterial concentration was the result of differential grazing pressure along the dilution gradient (dilution of the inoculum would also have changed the amount of predation pressure in each treatment) (17, 29, 38). However, given the low concentration of ciliates and other grazers in the undiluted inoculum (direct microscopic observation, 1.5 × 102 organisms/ml), the impact of these organisms on bacterial abundance should have been small, especially in comparisons of treatments beyond the 10−2 dilution. Ecological diversity, the variety and abundance of species in different habitats and communities, is one of the central themes of ecology. Diversity is commonly thought to be a useful indicator of the well-being of an ecological system; however, there is considerable debate over the role diversity plays in ecosystem function (4, 18, 23, 24, 26, 32, 33, 36). Most of this uncertainty arises from the practical limitations of measuring and manipulating diversity for experimental studies. Testing the effects of diversity on any community property or ecosystem function requires knowledge of the diversity of the community under examination; however, there are no methods currently available that allow microbial diversity to be measured.

In complexes with surfactant micelles, stiff chains tend to remain more expanded, consequently the apparent molar volume per monomer unit may be rather insensitive to the degree of complexation. Hence, PSS–CP complexes may be one of the exceptional cases among PSCs that form stable and clear complex solutions appropriate for studies of real solution properties. IDA is applicable for all elements with at least two stable isotopes and can also be applied for long-lived radionuclides (e.g., for 129I radionuclide determination using the stable iodine isotope 127I). Today isotope dilution mass spectrometry (IDMS) is recognized as a primary measurement method by means of which accurate results with sufficiently small uncertainties can be achieved and therefore it has been used in certifying the composition of reference materials. A requirement of isotope dilution analysis in mass spectrometry is to achieve equilibration of spike and sample so that very careful sample preparation steps, especially in solid mass spectrometry, are necessary when a homogeneous sample-spike mixture is to be prepared.

Molar conductance (λm) is the conductance furnished by all the ions present in 1 gm mole of electrolyte in its solution. Molar conductance of both strong and weak electrolytes increases with dilution. In strong electrolytes, the no. of ions is the same at all dilution but the ions are more mobile due to a decrease in inter-ionic attraction. Specific Conductance “К” is the conductance produced by the ions of 1cc of the electrolytic solution. When it is diluted, the concentration of the ions within 1cc volume decreases. This is because the number of energized ions per unit volume  in a solution decreases with dilution.

4.2 Dilution tests

All flasks were capped with sterile foam plugs to prevent contamination and kept on a shaker table, operated at 150 rpm, to maintain aerobic conditions. Each day, 20 ml of liquid was removed from each flask and replaced with 20 ml of sterile sewage. After 9 days (three retention times), flasks were harvested and analyzed.

On the R2A plates, percent culturability was high (100%) and only three colony morphologies were observed, further suggesting that diversity in these flasks was quite low. Given this information, it was surprising to find that the average number of T-RFLP fragments in the 10−6 treatment was so high (8 for MspI and 10 for HhaI). It is possible that this discrepancy is the result of a technical error with the T-RFLP, e.g., incomplete restriction digestion, which could produce a number of differently sized T-RFLP fragments for each organism type.

Chapter 6: General Principles and Processes of Isolation of Elements

As PCA is not mathematically appropriate for use with binary data, its application in this study was solely to aid in visualization of the relationships among the samples and not for statistical evaluation. Such an approach has been used several times to compare samples profiled using a variety of similar genetic techniques (6, 7, 47, 48); PCA generally provides the same information (groupings and relative distances among samples) as the above-outlined cluster analysis. Molar Conductivity is defined as the product of the Conductivity of a solution of an electrolyte divided by the Molar concentration of the electrolyte, and it is used to determine the efficiency with which an electrolyte conducts electricity in solution when it is assigned to a specific electrolyte. To put it another way, Molar Conductivity is the total conducting power of all the ions that are formed when a mole of electrolyte is dissolved in a solution.

For example, if there are 10 grams of salt (the solute) dissolved in 1 litre of water (the solvent), this solution has a certain salt concentration (molarity). If one adds 1 litre of water to this solution, the salt concentration is reduced. The diluted solution still contains 10 grams of salt (0.171 moles of NaCl). Dilution is the process of decreasing the concentration of a solute in a solution, usually simply by mixing with more solvent like adding more water to the solution. To dilute a solution means to add more solvent without the addition of more solute.

These are the lines along which the electric stresses act on the liquid-liquid interfaces, and the net effect is the deformation of the interfaces and the reduction of the continuous-phase film thickness. If the electric stresses are strong enough to bring the interfaces in contact and destabilize, the drops coalesce.33 The rest of the electric field lines is responsible for the change in contact angle of the drop on the channel walls. When the moving drop has entered the bypass escaping coalescence at its front end, shown in Figure 3(b), most of the electric field lines pass through both the drops and the continuous phase. The resulting forces deform the interfaces and are responsible for the coalescence at the body of the moving drop. Figure 3(c) portrays the scenario when the drop is inside the bypass having only the tail end in the region between the upper electrode and the trap. Since a significant number of field lines can still connect the interfaces on both drops and a liquid bridge below the PDMS wall—separating the trap from the bypass—is possible, coalescence can take place at the tail end of the moving drop.

Figure ​Figure22 demonstrates the working principle of on-demand coalescence between the moving drop and the trapped drop. In the absence of electric field, the moving drop glides past the trapped drop. Although the interfaces are pushed against each other, shown by the deformation of the left-side interface of the trapped drop, coalescence due to hydrodynamic forces does not occur. However, in the presence of electric field, when the moving drop is near the trap, coalescence and material exchange take place.

The onset of melting was observed at 130.8°C, and the peak maximum was noted at 133.8°C. The enthalpy of fusion computed for this sample was calculated as 257 J/g, and the quality of the DSC thermogram suggests that purity determination by DSC would be a viable method. Very extensive investigations into the complexation of lanthanide ions by malic acid have been performed using circularly polarized luminescence as a means to study the coordination chemistry of Tb(III) and Eu(III) complexes [14–16]. The metal-ligand binding modes were found to be strongly dependent upon solution pH and details of the complexes formed. For example, Figure 3 illustrates the change in bonding mode that accompanies relatively small changes in pH for the mixed Tb(III) complex with nitrilotriacetic acid and (L)-malic acid.

H2σ and h1σ are (following Everett’s notations (9)) the partial enthalpies of solute 2 and solvent 1 in the adsorbed state. The order of the experiments is of course chosen by taking into account the reversible (or irreversible) character of the various phenomena, so as to make the best use of the sample and of the time-consuming first temperature equilibration. The microcalorimeter is connected with the peristaltic pumps (through an 8 m long teflon tubing exchanger coiled around the insulating cylinder D and therefore immersed into the water thermostat) and with the amplifier and recorder. Various Joule effect resistors located before and after the adsorption cell allows one to calibrate the microcalorimeter. The electrical signal is amplified (Sef ram amplifier “Amplispot”) and then recorded, so that the final recording range is usually from 2.5 to 50 μV full scale.

Variation of Conductivity

The design proposed here can be adapted to serial dilution applications requiring fine gradation of dilution between successive coalescence events. Since the electric field can be turned on or off very fast, on-demand coalescence and dilution with any sequence of moving droplets can be performed with this device. If simultaneous washing or exchange is needed, all the positive (and negative) electrodes near traps can have a single connection without complicating the design and operation. In addition, active control of the applied field can be automated by implementing a droplet sensing mechanism in front of the trap. To investigate the effect of the magnitude of applied electric field on the dilution rate, we varied the amplitude of the voltage signal and maintained constant flow rates of the continuous and dispersed phases constant at 30 μl/h and 20 μl/h, respectively. The results, shown in Figure 7(a), follow the same general pattern of DF as a function of the number of coalescence events.

• Percent culturability on each growth medium was much higher in the communities regrown from the high-dilution inocula.
• To put it another way, Molar Conductivity is the total conducting power of all the ions that are formed when a mole of electrolyte is dissolved in a solution.
• However, the greatest difference for the diversity on R2A plates was between the undiluted (100) inoculum and the 10−1 dilution treatment.
• Interionic forces are strong forces of attraction between ions of opposing charges in concentrated solutions of strong electrolytes.
• Sample dilution tests should be systematically performed to determine the appropriate amount of sample to be injected before analyzing all biological samples.

To ensure a satisfactory dryness of the electrical heat flow-meter the microcalorimeter can be evacuated through a stainless-steel flexible tubing attached to port M. Net binding (adsorption) enthalpy ΔHP,A versus spectral frequency’shift ΔvOH; ads. Equation (7.86) is usually used for obtaining L¯2 from ϕL for a nonelectrolyte mixture. A graph of ϕL against m allows one to obtain the slope as (∂ϕL/∂m)n1 from which L¯2 can be calculated. For an electrolyte, equation (7.87) is usually used instead since it is easier to find the slope of ϕL against m1/2 [as seen in Figure 7.9(b)]. An alternative to ventilation to clear tobacco smoke is the use of electrostatic air cleaners which clean and recirculate air within a room.