Carbon dots derived from citric acid and urea as fluorometric probe for determining melamine contamination in infant formula sample.

Melamine has been intentionally added into food products to increase the protein count at less cost, especially in dairy products for infant resulting in serious adverse effects on health of consumers. Therefore, this study aimed to develop a method to quantify melamine in dairy products based on the change of fluorescent properties of carbon dots (CDs) as sensing probe. CDs with green-fluorescent emission were synthesized from citric acid and urea under microwave irradiation. The synthesized CDs emitted fluorescence at the maximum wavelength of 538 nm with excitation wavelength of 410 nm. Thus, they provided high sensitivity and selectivity on melamine detection by which fluorescent emission of the CDs was increasingly quenched upon increasing melamine concentrations. Optimal conditions for melamine determination using the CDs was under pH 6, volume ratio between CDs and sample of 2:8 and reaction time of 15 min. The developed method provided high precision of melamine determination with less than 5% of %RSD (n = 5), wide detection range from 1.0 to 200.0 ppm, and high sensitivity with limit of detection (LOD) of 0.47 ppm and limit of quantification (LOQ) of 1.56 ppm, which is within the regulated level by the Food and Drug Administration of the United States for melamine in dairy products. Several analytical characterization techniques were conducted to elucidate the reaction mechanism between CDs and melamine, and the hydrogen bonding interaction was proposed.

Transparent Cross-Flow Platform as Chemiluminescence Detection Cell in Cross Injection Analysis.

This work presents the use of a transparent 'Cross Injection Analysis' (CIA) platform as a flow system for chemiluminescence (CL) measurements. The CL-CIA flow device incorporates introduction channels for samples and reagents, and the reaction and detection channels are in one acrylic unit. A photomultiplier tube placed above the reaction channel detects the emitted luminescence. The system was applied to the analysis of (i) Co(II) via the Co(II)-catalyzed H2O2-luminol reaction and (ii) paracetamol via its inhibitory effect on the catalytic activity of Fe(CN)63- on the H2O2-luminol reaction. A linear calibration was obtained for Co(II) in the range of 0.002 to 0.025 mg L-1 Co(II) (r2 = 0.9977) for the determination of Co(II) in water samples. The linear calibration obtained for the paracetamol was 10 to 200 mg L-1 (r2 = 0.9906) for the determination of pharmaceutical products. The sample throughput was 60 samples h-1. The precision was ≤4.2% RSD. The consumption of the samples and reagents was ca. 170 µL per analysis cycle.

Microfluidic paper-based analytical device for determination of sucrose in sugarcane juice using Benedict's reagent.

This work presents a microfluidic paper-based analytical device (µPAD) for the determination of sucrose using the Benedict's test. An asymmetric dumbbell-shaped hydrophobic barrier was produced by rubber stamping the barrier pattern onto a laboratory filter paper. Hydrochloric acid and solution containing sucrose were successively deposited onto the sample reservoir of the µPAD attached to a glass slide. The device was placed in a plastic bag and dipped into boiling water for accelerating the hydrolysis of sucrose into the reducing sugars. Then the Benedict's reagent was added at the narrow straight channel connecting the two circular zones of the µPAD, which was replaced in the plastic bag and heated again for reduction of Cu(II) by the reducing sugars. Precipitate of brick-red copper(I) oxide was formed. The image of the µPAD was recorded by a smartphone. The ratio of the red to blue intensities gave linear correlation with the concentration of sucrose in the range of 0.5-10% w/v. The relative standard deviation of the measurement was less than 5% for 2 and 4% w/v sucrose (n = 10), with limit of determination, calculated using standard deviation of regression divided by slope of calibration, of 0.26% w/v sucrose. The method was successfully validated using the dinitrosalicylic acid method for sucrose measurement. Percent recoveries of sucrose were evaluated using ten sugarcane samples. The recoveries were in the range of 89 to 101%, demonstrating that there were no significant sample matrix effects on the quantification.

Simple gunshot residue analyses for estimating firing distance: Investigation with four types of fabrics.

This work presents two simple methods for estimating the firing distance from the gunshot residues (GSRs) on fabric targets. Four types of fabric targets, namely twill weave denim cotton-polyester (80/20), jersey knitting 100% cotton, plain weave cotton-polyester (80/20) and plain weave cotton-polyester (60/40), were employed. The firing tests were carried out using these white fabrics as targets at distances of 5-100 cm, respectively. In the first method, digital images of the black GSRs on fabric materials were recorded inside an illuminated box and the inverted gray intensity values were plotted against the firing distances. Since the plots of all fabrics are not significantly different, the estimation of firing distance employs the same exponential curve for all test fabrics. Although simple, the imaging method is not suitable for dark-colored materials. A chemical-based method was therefore developed as an alternative method. In the second method, a small disposable microfluidic paper-based analytical device (µPAD) was employed for detecting Pb(II) extracted from the GSRs. The µPAD method uses the measurement of the length of a narrow band of a pink color resulting from reaction between rhodizonate reagent and the Pb(II) extract. The plots indicated that the data of thick denim material are significantly different to other test fabrics which are much thinner. These three fabrics share the same estimation curve. However, it is recommended that the separate estimation curve for denim materials must be used. Both methods are suitable for short range firing distance, no further than 60 cm, since at greater distances the inverted gray intensity and the 'band-length' methods are unable to detect the GSRs.

Development of a microfluidic membraneless vaporization flow system for trace analysis of arsenic.

A new design of a membraneless vaporization (MBL-VP) unit coupled with a specific flow system is presented for the determination of arsenic at trace levels using a hydride generation process. The MBL-VP unit contains two concentric conical reservoirs, with the outer cone selected as the donor reservoir. The volume of the outer donor reservoir is thereby greater than the acceptor volume, necessary for holding sufficient sample and reagents for the generation of arsine gas by reaction between As(iii) and sodium borohydride under acidic conditions. The arsine gas diffuses into the narrow headspace and is absorbed by an aliquot of 150 µL of mercuric chloride acceptor solution. The resulting reaction produces hydronium ions which is monitored by the absorbance change at 530 nm of the methyl orange indicator added in the acceptor solution. To decrease the detection limit, the aspiration and removal of the donor plug, comprising the sample, borohydride and acid, into and out of the donor cone are repeated several times, while the acceptor solution is kept unchanged. As a result, analysis of arsenic was achieved in the range of 10 to 100 µg L-1 with a detection limit of 8 µg L-1. Application to surface water was investigated. Percent recoveries of spiked surface water samples were in the range of 94-110%. For comparison of total arsenic (As(iii) and As(v)), the results obtained from the developed method are not statistically different from the ICP-OES method.

Paper-based colorimetric biosensor of blood alcohol with in-situ headspace separation of ethanol from whole blood.

This work presents a novel development that exploits the concept of in-situ gas-separation together with a specific enzymatic colorimetric detection to produce a portable biosensor called "Blood Alcohol Micro-pad" for direct quantitation of ethanol in whole blood. The thin square device (25 mm × 25 mm × 1.8 mm) comprises two layers of patterned filter paper held together with a double-sided mounting tape with an 8-mm circular hole (the headspace). In operation, the reagent is deposited on one layer and covered with sticky tape. Then 8 µL of a blood sample is dispensed onto the opposite layer and covered with sticky tape. Diffusion of ethanol across the 1.6 mm narrow headspace permits selective detection of ethanol by the enzymatic reagents deposited on the opposite layer. This reagent zone contains alcohol oxidase, horseradish peroxidase and 2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt, as the chromogenic reagent. The color intensity, measured from the recorded digital image, resulting from the enzymatic assay of ethanol, correlates with the concentration of blood alcohol. The results obtained with spiked mice and sheep blood samples, using an external calibration in the range of 1-120 mg dL-1ethanol, gave recoveries of 93.2-104.4% (n = 12). The "Blood Alcohol Micro-pad" gave good precision with %RSD <1 (50 mg dL-1 ethanol, n = 10) and limit of quantification (10SD of intercept/slope) of 11.56 mg dL-1. The method was successfully validated against a headspace gas chromatography-mass spectrometric method. It has good potential for development as a simple and convenient blood alcohol sensor for on-site testing.

Simple flow system with in-line gas-diffusion unit for determination of ethanol employing hypsochromic shift of visible absorbance band of methyl orange.

The effect of solvent composition on the uv-visible spectrum of methyl orange was investigated for application to the quantitative determination of ethanol. At fixed pH, there was a hypsochromic shift of the absorbance band of methyl orange with increasing ethanol concentration. Using acetate buffer at pH 3.40 the change of absorbance at 530 nm of a solution of methyl orange containing known concentrations of standard ethanol was measured to provide a calibration curve. In order to apply this method to the analysis of alcoholic samples, such as distilled spirits, blended spirits and liquid herbal medicines, a simple gas-diffusion unit coupled with flow system was employed to separate the ethanol from sample matrices. Using the gas diffusion-flow system and employing an evaporation time of 2 min, a linear calibration range of 5-45% (v/v) ethanol was achieved ((ΔA = (0.0078 ± 0.0002)x(ethanol, %(v/v)) + (0.040 ± 0.005)), r2 = 0.998). The limit of detection (3σ blank/slope) was 2.23% (v/v). The developed gas diffusion-flow system was applied to the analysis of colorless distilled spirits, yellow blended spirits and dark brown herbal medicines that are available in the local markets of Bangkok, Thailand. Validation of the method was carried out by comparing the results with analysis using gas chromatography. There was no statistically significant difference at the 95% confidence level for all alcoholic samples analyzed.

T-shirt ink for one-step screen-printing of hydrophobic barriers for 2D- and 3D-microfluidic paper-based analytical devices.

This work presents the use of polyvinyl chloride (PVC) fabric ink, commonly employed for screening t-shirts, as new and versatile material for printing hydrophobic barrier on paper substrate for microfluidic paper-based analytical devices (µPADs). Low-cost, screen-printing apparatus (e.g., screen mesh, squeegee, and printing table) and materials (e.g. PVC ink and solvent) were employed to print the PVC ink solution onto Whatman filter paper No. 4. This provides a one-step strategy to print flow barriers without the need of further processing except evaporation for 3-5 min in a fume hood to remove the solvent. The production of the single layer µPADs is reasonably high with up to 77 devices per screening with 100% success rate. This method produces very narrow fluidic channel 486 ±â€¯14 µm in width and hydrophobic barrier of 642 ±â€¯25 µm thickness. Reproducibility of the production of fluidic channels and zones is satisfactory with RSDs of 2.9% (for 486-µm channel, n = 10), 3.7% (for 2-mm channel, n = 50) and 1.5% (for 6-mm diameter circular zone, n = 80). A design of a 2D-µPAD produced by this method was employed for the colorimetric dual-measurements of thiocyanate and nitrite in saliva. A 3D-µPADs with multiple layers of ink-screened paper was designed and constructed to demonstrate the method's versatility. These 3D-µPADs were designed for gas-liquid separation with in-situ colorimetric detection of ethanol vapor on the µPADs. The 3D-µPADs were applied for direct quantification of ethanol in beverages and highly colored pharmaceutical products. The printed barrier was resistant up to 8% (v/v) ethanol without liquid creeping out of the barrier.

Green analytical method for simultaneous determination of salinity, carbonate and ammoniacal nitrogen in waters using flow injection coupled dual-channel C4D.

A flow injection analysis system (FIA) for the simultaneous determination of salinity, carbonate and ammoniacal nitrogen has been developed and reported in this paper. FIA incorporating membrane units was used, not only for the separation of the gaseous carbon dioxide and ammonia, but also for on-line dilution in the salinity measurement. The sample was injected via a 10-port valve with two sample loops. One loop was used for salinity and carbonate measurements and the second loop for ammoniacal nitrogen determination. A dual-channel capacitively coupled contactless conductivity detector was assembled in a single shielding box. Input voltage from the same AC power supply was fed to the input electrodes of both C4D cells. One channel of the C4D was used to monitor the change in conductivity of an acceptor stream that carried a zone of the water sample that has passed through the on-line dilution unit. Conductivity of this zone relates directly to the salinity of the sample. The same sample zone was next acidified to generate carbon dioxide gas that diffused through a hydrophobic membrane of the first gas diffusion (GD) unit. The zone of dissolved carbon dioxide in acceptor stream of water flowed into the same C4D cell as for the salinity measurement, but arriving at a later time. Concurrently, the second channel of the C4D monitored the change in conductivity of the acceptor stream in the second GD unit due to the diffusion of ammonia gas generated by the reaction of base with the sample injected from the second sample loop. The change in conductivity at this second C4D cell correlates with the concentration of ammoniacal nitrogen present in the sample. The proposed method is low cost, simple, rapid and sensitive. The limit of quantitation for salinity, carbonate and ammoniacal nitrogen are 0.31mmolL-1, 1.85 µmol L-1, respectively. Throughput of 20 samples h-1 for simultaneous analysis can be achieved with RSD of less than 3.8%. The system had been applied to the determination of salinity, carbonate and ammoniacal nitrogen in 15 water samples, with results in agreement with those obtained using comparison methods.

Microfluidic Analysis with Front-Face Fluorometric Detection for the Determination of Total Inorganic Iodine in Drinking Water.

A microfluidic method with front-face fluorometric detection was developed for the determination of total inorganic iodine in drinking water. A polydimethylsiloxane (PDMS) microfluidic device was employed in conjunction with the Sandell-Kolthoff reaction, in which iodide catalyzed the redox reaction between Ce(IV) and As(III). Direct alignment of an optical fiber attached to a spectrofluorometer was used as a convenient detector for remote front-face fluorometric detection. Trace inorganic iodine (IO3- and I-) present naturally in drinking water was measured by on-line conversion of iodate to iodide for determination of total inorganic iodine. On-line conversion efficiency of iodate to iodide using the microfluidic device was investigated. Excellent conversion efficiency of 93 - 103% (%RSD = 1.6 - 11%) was obtained. Inorganic iodine concentrations in drinking water samples were measured, and the results obtained were in good agreement with those obtained by an ICP-MS method. Spiked sample recoveries were in the range of 86%(±5) - 128%(±8) (n = 12). Interference of various anions and cations were investigated with tolerance limit concentrations ranging from 10-6 to 2.5 M depending on the type of ions. The developed method is simple and convenient, and it is a green method for iodine analysis, as it greatly reduces the amount of toxic reagent consumed with reagent volumes in the microfluidic scale.

A "Dual-acceptor Channel" Membraneless Gas-diffusion Unit for Simultaneous Determination of Ethanol and Acetaldehyde in Liquors Using Reverse Flow Injection.

A new design of membraneless gas-diffusion unit with dual acceptor channels for separation, collection and simultaneous determination of two volatile analytes in liquid sample is presented. The unit is comprised of three parallel channels in a closed module. A sample is aspirated into the central channel and two kinds of reagents are introduced into the other two channels. Two analytes are isolated from the sample matrix by diffusion into head-space and absorbed into the specific reagents. Non-absorbed vapor is released by opening the programmable controlled lid. The unit was applied to liquors for measurement of ethanol and acetaldehyde using reverse flow injection. Dichromate and nitroprusside were exploited as reagents for colorimetric detection of ethanol and acetaldehyde, respectively. Good linearity ranges (r2 >0.99) with high precision (RSD <2%) and high accuracy (recovery: 90 - 105%) were achieved. The results were compared to the results by GC-FID and no significant difference was observed by paired t-test (95% confidence).

Microfluidic Paper-based Analytical Device for Quantification of Lead Using Reaction Band-length for Identification of Bullet Hole and Its Potential for Estimating Firing Distance.

A low-cost and user-friendly microfluidic paper-based analytical device (µPAD) was developed for identification of bullet hole from gunshot residue (GSR) on cotton fabric target. The device (25 × 82 mm) is made of filter paper with a printed pattern consisting of a circular sample loading reservoir (6 mm i.d.), a circular waste reservoir (4 mm i.d.) and a straight flow channel (3 mm wide and 60 mm long). A sticker with a ruler scale in millimeters was mounted alongside the channel. The straight channel is first impregnated with rhodizonate and dried at ambient temperature. Tartrate extract of the target fabric is loaded on the sample reservoir. If Pb(II) ions are present in the extract, pink streak of Pb(II)-rhodizonate precipitate is formed as the sample solution flows from the reservoir along the channel. The length of the pink strip is employed to estimate the firing distance.

Development of flow systems incorporating membraneless vaporization units and flow-through contactless conductivity detector for determination of dissolved ammonium and sulfide in canal water.

Use of membraneless vaporization (MBL-VP) unit with two cone-shaped reservoirs is presented for on-line separation and detection of non-volatile species. A flow system comprising two sets of MBL-VP units with a single in-house capacitively coupled contactless conductivity detector (C4D) was developed for dual determination of ammonium and sulfide ions. Using the continuous-flow section, two zones (280µL) of a sample, either mixed with sodium hydroxide (for ammonium) or hydrochloric acid (for sulfide), are separately delivered into the donor reservoir of the MBL-VP units. The acceptor reservoir contains either 150µL of 15µM HCl solution (for ammonia) or pure water (for hydrogen sulfide), respectively. Vaporization and trapping of the ammonia or hydrogen sulfide gas from the donor reservoir into the liquid acceptor cone occur concurrently in the two separate MBL-VP units. After trapping the gas for 3min, the two 150-µL liquid acceptors are sequentially aspirated through the C4D flow cell for recording the changes in the conductivity. Linear calibrations were obtained for ammonium from 5 to 80µM (Volt = (0.0134 ± 0.0003) [NH4+] - (0.01 ± 0.01), r2 = 0.998) and for sulfide from 5 to 200µM (Volt = (0.0335 ± 0.0009) [S2-] - (0.13 ± 0.09), r2 = 0.996). Analysis time for both analytes is only 320s. Our method was applied to analyze canal water samples. The results agree well with membrane gas-diffusion flow injection techniques, using bromothymol blue for ammonium and methylene blue for sulfide. Recoveries ranged from 95% to 104%.

Membraneless Gas-Separation Microfluidic Paper-Based Analytical Devices for Direct Quantitation of Volatile and Nonvolatile Compounds.

This work presents new chemical sensing devices called "membraneless gas-separation microfluidic paper-based analytical devices" (MBL-GS µPADs). MBL-GS µPADs were designed to make fabrication of the devices simple and user-friendly. MBL-GS µPADs offer direct quantitative analysis of volatile and nonvolatile compounds. Porous hydrophobic membrane is not needed for gas-separation, which makes fabrication of the device simple, rapid and low-cost. A MBL-GS µPAD consists of three layers: "donor layer", "spacer layer", and "acceptor layer". The donor and acceptor layers are made of filter paper with a printed pattern. The donor and acceptor layers are mounted together with a spacer layer in between. This spacer is a two-sided mounting tape, 0.8 mm thick, with a small disc cut out for the gas from the donor zone to diffuse to the acceptor zone. Photographic image of the color that is formed by the reagent in the acceptor layer is analyzed using the ImageJ program for quantitation. Proof of concept of the MBL-GS µPADs was demonstrated by analyzing standard solutions of ethanol, sulfide, and ammonium. Optimization of the MBL-GS µPADs was carried out for direct determination of ammonium in wastewaters and fertilizers to demonstrate the applicability of the system to real samples.

Stopped-in-loop flow analysis system for successive determination of trace vanadium and iron in drinking water using their catalytic reactions.

An automated stopped-in-loop flow analysis (SILFA) system is proposed for the successive catalytic determination of vanadium and iron. The determination of vanadium was based on the p-anisidine oxidation by potassium bromate in the presence of Tiron as an activator to form a reddish dye, which has an absorption maximum at 510 nm. The selectivity of the vanadium determination was greatly improved by adding diphosphate as a masking agent of iron. For the iron determination, an iron-catalyzed oxidative reaction of p-anisidine by hydrogen peroxide with 1,10-phenanthroline as an activator to produce a reddish dye (510 nm) was employed. The SILFA system consisted of two peristaltic pumps, two six-port injection valves, a four-port selection valve, a heater device, a spectrophotometric detector and a data acquisition device. One six-port injection valve was used for the isolation of a mixed solution of standard/sample and reagent to promote each catalytic reaction, and another six-port injection valve was used for switching the reagent for vanadium or iron to achieve selective determination of each analyte. The above mentioned four-port selection valve was used to select standard solutions or sample. These three valves and the two peristaltic pumps were controlled by a built-in programmable logic controller in a touchscreen controller. The obtained results showed that the proposed SILFA monitoring system constituted an effective approach for the selective determination of vanadium and iron. The limits of detection, 0.052 and 0.55 µg L(-1), were obtained for vanadium and iron, respectively. The proposed system was successfully applied to drinking water samples without any preconcentration procedures.

Simultaneous determination of iodide and creatinine in human urine by flow analysis with an on-line sample treatment column.

This work presents the first flow system for direct analysis of iodide and creatinine suitable for screening of human urine samples. The system had a mini-column packed with strong anion exchange resin for on-line extraction of iodide. After injection of a sample on the column the unretained urine sample was analyzed for creatinine in one section of the flow system using the Jaffe's reaction with spectrometric detection at 520 nm. Iodide was eluted off with 1.42 mL 5 M NaNO3. A 150 µL fraction of the eluate was analyzed in another section of the same flow system for iodide using the kinetic-spectrometric Sandell-Kolthoff reaction. At the optimum condition, the sample throughput was 12 samples per h. The linear working range covered the normal levels of iodide and creatinine in human urine: 0-200 µg I L(-1) and 50-1200 mg creatinine L(-1), respectively. Recoveries tested in 10 samples were 87-104% for iodide and 89-104% for creatinine. Bland-Altman plots (n = 50) showed that the scatter of the differences between values obtained by this method and those of reference methods, for both iodide and creatinine, was within mean ± 2SD.

New membraneless vaporization unit coupled with flow systems for analysis of ethanol.

This work presents the development of a new design for a membraneless vaporization (MBL-VP) unit, called dual chamber MBL-VP for measurement of volatile compounds. With this unit, exact volumes of sample and reagent are introduced into their respective cone-shaped chambers from the base of the cones. Diffusion of volatile analyte then takes place. After an appropriate time interval, the acceptor solution is withdrawn from the chamber into the detector flow-cell, while the sample solution is withdrawn to waste. Unlike the previous MBL-VP design, problems with overflow of solutions are eliminated by precise control of the input volume to be less than the volume of the chamber. The developed flow system with the dual chamber MBL-VP unit was applied to the determination of the ethanol content of various liquid samples, using the oxidation reaction between potassium dichromate and the diffused ethanol. In addition, in order to accelerate the gas diffusion process, the donor chamber was aerated. As the result, relatively short analysis time of 144 s was achieved for ethanol content in the range of 5-50% (v/v). The proposed method was successfully validated against a gas chromatographic method for 17 alcoholic samples. Percentage recovery was in the range of 96-109%.

Sequential injection system for simultaneous determination of sucrose and phosphate in cola drinks using paired emitter-detector diode sensor.

This work presents the simultaneous determination of sucrose and phosphate by using sequential injection (SI) system with a low cost paired emitter-detector diode (PEDD) light sensor. The PEDD uses two 890 nm LEDs. Measurement of sucrose in Brix unit was carried out based on the detection of light refraction occurring at the liquid interface (the schlieren effect) between the sucrose solution and water. Phosphate was measured from the formation of calcium phosphate with turbidimetric detection. With careful design of the loading sequence and volume (sample--precipitating reagent--sample), simultaneous detection of sucrose and phosphate was accomplished with the single PEDD detector. At the optimized condition, linear calibrations from 1 to 7 Brix sucrose and from 50 to 200mg PO4(3-)L(-1) were obtained. Good precision at lower than 2% RSD (n=10) for both analytes with satisfactory throughput of 21 injections h(-1) was achieved. The method was successfully applied for the determination of sucrose and phosphate in cola drinks. The proposed method is readily applicable for automation and is found to be an alternative method to conventional procedures for on-line quality control process in cola drink industry.

Simultaneous injection effective mixing flow analysis of urinary albumin using dye-binding reaction.

A new four-channel simultaneous injection effective mixing flow analysis (SIEMA) system has been assembled for the determination of urinary albumin. The SIEMA system consisted of a syringe pump, two 5-way cross connectors, four holding coils, five 3-way solenoid valves, a 50-cm long mixing coil and a spectrophotometer. Tetrabromophenol blue anion (TBPB) in Triton X-100 micelle reacted with albumin at pH 3.2 to form a blue ion complex with a λ(max) 625nm. TBPB, Triton X-100, acetate buffer and albumin standard solutions were aspirated into four individual holding coils by a syringe pump and then the aspirated zones were simultaneously pushed in the reverse direction to the detector flow cell. Baseline drift, due to adsorption of TBPB-albumin complex on the wall of the hydrophobic PTFE tubing, was minimized by aspiration of Triton X-100 and acetate buffer solutions between samples. The calibration graph was linear in the range of 10-50µg/mL and the detection limit for albumin (3σ) was 0.53µg/mL. The RSD (n=11) at 30µg/mL was 1.35%. The sample throughput was 37/h. With a 10-fold dilution, interference from urine matrix was removed. The proposed method has advantages in terms of simple automation operation and short analysis time.

A multiple processing hybrid flow system for analysis of formaldehyde contamination in food.

This work proposes a flow system suitable for the rapid screening of formaldehyde contaminated in food. The system is based on the concept of a flow analyzer with a Hantzsch reaction. An operating procedure was developed for multiple tasking and high sample throughput. This resulted in a significant sample throughput of 51 samples h(-1). Under the optimized conditions, linear calibration from 10 to 100 microM was obtained. The system gave a limit of detection and a limit of quantitation of 0.06 and 0.10 mg kg(-1), respectively. The system was successfully applied to re-hydrated dry squids, vegetables and mushrooms.