A simple method for the preparation and injection of gas mixtures into a gas chromatograph using a two-component device.

Environmental sciences are expanding and are based on standardized and certified calibrations when measurements are required. When a gaseous composition is quantified, commercial standards are used. Here, we report on a two-component device for the preparation and injection of gas mixtures at the appropriate levels of pressure and volume. The two-component calibrator/injector can be used simultaneously or separately depending on the experimental objective but their combination is extremely effective for injecting gas mixtures at low concentrations. The quantity of gas introduced into a gas chromatograph with the injector can be adapted to the sensitivity of the detector or to avoid column overload. The calibrator provides for a large range of gas-mixture concentrations, from ppm to % mol/mol with an error of preparation of around 1% and an accuracy of less than 3%. This device prepares a variety of gas mixtures (hydrogen, methane and dioxide of carbon) which are compared with certified mixtures by means of gas chromatographic measurements. The results show good agreement between prepared and certified mixtures with a maximum difference of 2% which remains within the relative error of commercial standard. In addition, the preparation of dissolved methane at different concentrations in seawater is presented as a direct application of the calibrator.

Analysis of hydrogen and methane in seawater by "Headspace" method: Determination at trace level with an automatic headspace sampler.

"Headspace" technique is one of the methods for the onboard measurement of hydrogen (H2) and methane (CH4) in deep seawater. Based on the principle of an automatic headspace commercial sampler, a specific device has been developed to automatically inject gas samples from 300ml syringes (gas phase in equilibrium with seawater). As valves, micro pump, oven and detector are independent, a gas chromatograph is not necessary allowing a reduction of the weight and dimensions of the analytical system. The different steps from seawater sampling to gas injection are described. Accuracy of the method is checked by a comparison with the "purge and trap" technique. The detection limit is estimated to 0.3nM for hydrogen and 0.1nM for methane which is close to the background value in deep seawater. It is also shown that this system can be used to analyze other gases such as Nitrogen (N2), carbon monoxide (CO), carbon dioxide (CO2) and light hydrocarbons.

[Efficacy of intravitreal dexamethasone implants in macular edema excluding venous occlusions: results for a cohort of 80 patients]. / Efficacité des implants intravitréens de dexaméthasone dans l'œdème maculaire hors occlusions veineuses : résultats sur une cohorte de 80 patients.

INTRODUCTION: The intravitreal dexamethasone implant has shown efficacy in the treatment of macular edema (ME) arising after retinal venous occlusions (central or branch), and in the treatment of non-infectious uveitis. The purpose of this study was to evaluate the efficacy of this implant in the treatment of other diffuse macular edemas with an inflammatory mechanism. MATERIALS AND METHODS: We carried out a retrospective cohort study over 2 years: from January 2012 to December 2013, including all patients who received at least one injection of intravitreal dexamethasone implant, excluding venous occlusions and non-infectious uveitis. The primary study parameter was the progression of visual acuity. The study protocol had the approval of the institutional review board of the respective clinical ethics committees, and was conducted in accordance to the tenets of the Declaration of Helsinki. RESULTS: Eighty patients were included. Eighty-eight percent of patients were pseudophakic. The indications for treatment were: diabetic ME when anti-VEGF were ineffective (53%), ME after retinal detachment (RD) (22%), ME of Irvine-Gass syndrome (16%), ME after endophthalmitis (4%), macular telangiectasia (4%), ME secondary to retinitis pigmentosa (1%). The mean ETDRS visual acuity was 53.7 letters prior to injection, improving to 62.3 letters after injection (P<0.001). The average gain in visual acuity was 6.7 letters [4.53;8.84] (P<0.001) in patients treated for diabetic ME, 9.6 letters [6.1;13.1] (P<0.001) in patients with ME after RD, and 15.2 letters [10.25;20.28] (P<0.001) for Irvine-Gass syndrome. The mean duration of efficiency was 4.6 months, with a median of 3.8 months. CONCLUSION: The intravitreal dexamethasone implant appears to be an effective second-line treatment even in patients with diabetic ME after failure or in the case of contraindication of anti-VEGF. It is also effective and well tolerated in patients with ME after RD, as well as in patients with Irvine-Gass syndrome.