The Research On Microfluidic Chemical Sensor Of Cyanide And Sulfide In Environment

Cyanide and sulfide are the volatile acids in the environment,which are highly toxic and usually cause great harm to human health and environment.Most of the conventional analysis methods are time-consuming,complicated operation process,high pretreatment requirement,large and expensive instrument and no in-situ monitoring,which are difficult to meet the needs of rapid detection for a large number of samples.Therefore,it is urgent to develop a simple,rapid,safe and efficient method for the determination of these highly toxic volatile acids.In this paper,a PDMS hydrophobic film was used as pervaporation membrane in a flow injection-gas diffusion(FI-GD)by bonding to microfluidic chip.It was self-made by PDMS polymer diluted with TBA,followed degassing and spin coating.The effects of PDMS membrane on HCN and H2S gas transmittance and its stability and reproducibility were studied.The PDMS film thickness is about 4 ?m at the 3000 r/min speed.Its transmittance to HCN is not less than 65.7%(0.01-0.5mg/L CN),and the transmittance to H2S is up to 100%(5-100 ?mol/L S2-).The standard deviation of the LIF detection signal is 0.86-2.2%.The quality of lab-made membranes were stable since there was no significant difference between the chips when the chip was replaced.Using the FI-GD coupled with laser-induced fluorescence(LIF)detection method to real time on-line monitoring of cyanide and sulfide in environmental waters,the optimum condition of the injection pump flow rate,acid and alkali concentration and fluorescence reaction was studied and determined.The optimized experimental conditions are as follows:when the cyanide is detected,the injection pump flow rate introducing the sample and HC1 is 15 ?L/min and HCl concentration is 0.5 mol/L.NaOH acceptor concentration is 0.1 mol/L and the flow rate is 20?L/min.The NDA concentration is 0.6 mmol/L(in 8%DMF)and the glycine concentration is 2 mmol/L(in 200 mmol/L,pH 9.0 borate buffer).Similarly,when monitoring sulfide,the injection pump flow rate with sample and hydrochloric acid is 20 ?L/min,HCl concentration is 1 mol/L.The pH of NaOH acceptor is 12 and the flow rate is 20 ?L/min.The generation of methylene blue is with 0.2%DMPD and 0.1%K2Cr2O7.The limit of detection(3a/S)is 0.015 ?g/L CN-and 5 ?g/L S2-.The proposed method has the advantages such as high sensitivity,simple operation,safety,rapid detection and low reagent consumption.In addition,the electrochemical detection method is used for online monitoring of cyanide and sulfide in environmental water samples.A micro-electrochemical sensor was fabricated by combining the cyanide or sulfide ion selective electrodes lab-made by traditional selective membrane with a microfluidic chip.The CN-electrode slope of the E-lgc response curve of the PDMS membrane system is 14.5 mV/pS;The S2-electrode slope of the E-Igc response curve of the PDMS membrane system is 21.2 mV/pS.The linear response range of the electrode is wider,and the electrode potential at low concentration is higher due to the low concentration sample could be enriched through the PDMS membrane,but the sensitivity is lower.The standard deviation is between 0.58%and 1%and no memory effect is obtained after testing electrodes repeatedly.Using this microfluidic-electrochemical sensor device to test treated water samples,the recovery rate is 95?103%,and the results could fit our satisfactory.By taking advantage of laminar flow with high mass transfer efficiency,a sample pretreatment system based on the microfluidic parallel laminar flow was established.The factors such as flow rate and micro-channel modification were studied,and the pretreatment conditions for determining weak acid dissociable cyanide in water were optimized based on the microfluidic chip laminar flow technique.Spectrofluorometric measurements were carried out on CN-detection in water samples after pretreatment.Under the optimized conditions,the linearity and the detection limit of the proposed method were found to be 1 to 10 ?g/L CN-and 0.12 ?g/L CN-,respectively.The recovery was 97.4?104.8%.Compared with traditional distillation methods,our method is greener,safer with lower reagent consumption.Thus,it provides a new strategy to analyze the level of cyanide toxicity in real samples.