Development of Aedes aegyptiL. under the action of light radiation at different wavelengths

Aedes aegypti is a holometabolous insect, vector of medical importance for arboviral transmission, and has shown the ability to develop chemical larvicides resistance, which are the worldwide used to control mosquitoes' population because of their low cost. Due to the well-known photophobia, a striking characteristic of the behavior of A. aegypti larvae, this study aimed to observe the development of this insect in its larval stage under the action of certain ranges of light radiation and its possible biological effects. For that, the experiments used larvae in L1, observed during seven days under the action of LEDs (light-emitting diode) that emitted light at different wavelengths, with six different colors, one for each experiment. Some were tested with a light-dark interval every 10 minutes and others every two minutes, with three repetitions. At the end, mosquitoes, pupae and larvae were counted and the data submitted to statistical evaluation. The experiment showed a significant difference between the control and the different wavelengths used, when exposed at two-minute intervals. LEDs that emitted blue (λ = 457.9 nm) and white (λ = 448.58 nm) wave frequencies were the most promising for the development of equipment that could act synergistically with other forms of control in order to improve its efficiency.(AU)

A digital image-based method for determining of total acidity in red wines using acid-base titration without indicator.

This work proposes the use of digital image-based method for determination of total acidity in red wines by means of acid-base titration without using an external indicator or any pre-treatment of the sample. Digital images present the colour of the emergent radiation which is complementary to the radiation absorbed by anthocyanines present in wines. Anthocyanines change colour depending on the pH of the medium, and from the variation of colour in the images obtained during titration, the end point can be localized with accuracy and precision. RGB-based values were employed to build titration curves, and end points were localized by second derivative curves. The official method recommends potentiometric titration with a NaOH standard solution, and sample dilution until the pH reaches 8.2-8.4. In order to illustrate the feasibility of the proposed method, titrations of ten red wines were carried out. Results were compared with the reference method, and no statistically significant difference was observed between the results by applying the paired t-test at the 95% confidence level. The proposed method yielded more precise results than the official method. This is due to the trivariate nature of the measurements (RGB), associated with digital images.

An inexpensive, portable and microcontrolled near infrared LED-photometer for screening analysis of gasoline.

A microcontrolled, portable and inexpensive photometer is proposed. It uses a near infrared light emitting diode (NIR LED) as radiation source, a PbSe photoresistor as infrared detector and a programmable interrupt controller (PIC) microcontroller as control unit. The detector system presents a thermoresistor and a thermoelectric cooling to control the detector temperature and keep the noise at low levels. The microcontroller incorporated total autonomy on the proposed photometer. As its components are inexpensive and of easy acquisition, the proposed NIR LED-photometer is an economical alternative for chemical analyses in small routine, research and/or teaching laboratories. By being portable and microcontrolled, it also allows carrying out field chemical analyses. The instrument was successfully applied on the screening analysis to verify adulteration in gasoline samples.

Digital image-based titrations.

The exploitation of digital images obtained from a CCD camera (WebCam) as a novel instrumental detection technique for titration is proposed for the first time. Named of digital image-based (DIB) titration, it also requires, as a traditional titration (for example, spectrophotometric, potentiometric, conductimetric), a discontinuity in titration curves where there is an end point, which is associated to the chemical equivalence condition. The monitored signal in the DIB titration is a RGB-based value that is calculated, for each digital image, by using a proposed procedure based on the red, green, and blue colour system. The DIB titration was applied to determine HCl and H3PO4 in aqueous solutions and total alkalinity in mineral and tap waters. Its results were compared to the spectrophotometric (SPEC) titration and, by applying the paired t-test, no statistic difference between the results of both methods was verified at the 95% confidence level. Identical standard deviations were obtained by both titrations in the determinations of HCl and H3PO4, with a slightly better precision for DIB titration in the determinations of total alkalinity. The DIB titration shows to be an efficient and promising tool for quantitative chemical analysis and, as it employs an inexpensive device (WebCam) as analytical detector, it offers an economically viable alternative to titrations that need instrumental detection.