Determination Of Concentration Values Research Articles

The Effect of Honeybee Propolis on Escherichia coli Biofilm Formation in vitro

Background: Colibacillosis is an infectious disease that affects livestock such as cattle, pigs, goats, sheep, horses and poultry caused by the bacterium Escherichia coli. E. coli can form biofilms when environmental conditions are unfavorable. The purpose of this research is to determine the effect of honeybee propolis on the formation of E. coli biofilm in vitro. Methods: The research began with the dilution of propolis using the microdilution technique and determination of concentration values with a modified minimum inhibitory concentration (MIC). Biofilm inhibition assays were conducted in microplates with five propolis concentration treatments: 0.39 mg/mL, 0.78 mg/mL, 1.56 mg/mL, 3.125 mg/mL and 6.25 mg/mL, along with negative and positive controls, with eight replications. Subsequently, crystal violet quantification and absorbance value readings were done using an ELISA reader with a wavelength of 595 nm. Result: The results showed that between concentrations of 3.125 mg/mL, 6.25 mg/mL and the negative control, there was no significant difference with mean values of 0.09963, 0.078857 and 0.079375, respectively. Honeybee propolis extract has the potential to act as an antibiofilm against E. coli in vitro, with the minimum concentrations capable of inhibiting biofilm formation being 3.125 mg/mL and 6.25 mg/mL.

Nitric oxide fluxes from an agricultural soil using a flux‐gradient method

Soil emission of nitric oxide may be a significant source of NOx in rural areas. Agricultural practices may enhance these emissions by addition of nitrogen fertilizers. A system that enables continuous measurement of NO fluxes from agricultural surfaces using the flux‐gradient method was developed. Hourly differences in NO concentrations in air sampled at two intake heights (0.6 and 1 m) were determined using a chemiluminescence analyzer. Eddy diffusivities were determined using wind profiles (cup anemometers), and stability corrections calculated using a 5 cm path sonic anemometer. Fast switching of sampling between air intake heights (every 30 s) and determination of concentration values at a frequency of 2 Hz minimized the errors due to fluctuations in background concentration. Low travel times for air samples in the tubing (∼8 s) were estimated to result in small errors in flux values (<0.5 ng N m−2 s−1) due to chemical reactions. The overall resolution of the system was estimated as ∼1 ng N m−2s−1. NO fluxes from a bare soil were measured quasi‐continuously from January to June 1995 at Elora, Canada, comprising a total of 1833 hourly values. Daily NO fluxes before nitrogen fertilization were small, increasing after nitrogen fertilizer was added (>10 ng N m−2 s−1). Monthly NO fluxes estimated were similar to those observed in previous studies. The designed system could be easily modified to measure NOx and NO fluxes by using an additional chemiluminescence analyzer. The system also could be adapted to measure fluxes sequentially from various plots, enabling testing of agricultural practices on NO emissions.

Measuring concentration: Sampling design issues, as illustrated by the case of perfectly stratified samples

Using the artificial example of perfectly stratified samples, we have shown the effect different sampling designs have on the determination of concentration values. More concretely, we have studied the following four cases: sampling of items in the case the number of sources is known (we have further considered the cases when there are ‘many’ items in every source and when this is not so); sampling of items in the case the number of sources is unknown, and finally, sampling of sources.

Differential method for the determination of the order of reaction and the rate constants

AbstractA method is proposed whereby the orders and rate constants for processes obeying the rate law −dA/dt = kAn may be determined. The method is illustrated in two ways. First, simulated data for processes of various orders are treated, and the treatment is shown to be capable of reproducing orders and rate constants to a high degree of accuracy. The factors affecting the accuracy with which n and k can be determined are considered. These are inaccuracy in the determination of concentration values, irregularity of the time intevals between concentration determinations, and the length of those time intervals. It is shown that if concentrations are determined at times that are close together, the effect of the other two factors is small, but if the time intervals are made longer, the errors due to the other two factors affect the calculated values of n and k much more seriously. Second, the method was applied to two homogeneous reactions, of which one was first‐order and one was second order, and three heterogeneous reactions, of which one was found by the original workers to be first order, one to be zero order, and one to vary between zero and first order, depending on the initial pressure. The present method gives results in agreement with these conclusions and reproduces the rate constants to within ±5% in all cases.