Photometric Detection Research Articles

Lab on a Chip for the Colorimetric Determination of Nitrite in Processed Meat Products in the Jordanian Market.

Nitrite and Nitrate have been used extensively as additives in various meat products to enhance flavor, color, and to preserve the meat from the bacterial growth. High concentrations of nitrite can threat human health since several studies in the literature claim that nitrite is associated with cancer incidences, leukemia, and brain tumors. Therefore, it is vital to measure the nitrite concentrations in processed meat products. In this study, an in-lab miniaturized photometric detection system is fabricated to inspect the nitrite concentration in processed meat products in Jordan. The analytical performance of nitrite detection is evaluated based on three key statistical parameters; linearity, limit of detection, and limit of quantitation. Respectively, for the fabricated system, the three values are found to be equal to 0.995, 1.24 × 10−2 ppm, and 4.12 × 10−2 ppm. Adherence to Beer’s law is found over the investigated range from 2.63 ppm to 96.0 ppm. The developed system is utilized for photometric detection of nitrite in processed meat products available in the Jordanian market like pastrami, salami, and corned beef. In all of the analyzed samples, the nitrite content is found to be lower than 150 ppm, which represents the maximum allowable nitrite limit.

Review of the analysis of insecticide residues and their levels in different matrices in Ghana

This review reports on how Ghanaian scientists analyse insecticide residues in various matrices in their laboratories as well as the levels of insecticides found in Ghana. It covers different sample preparation methods such as solid-liquid and liquid-liquid extraction. The main technique used for this analysis was gas chromatography (GC) with various detectors such as electron capture, flame photometric, nitrogen phosphorus, and mass spectrometric detection. Liquid chromatography (LC) with mass spectrometric detection was sometimes used to determine the levels of very polar insecticide residues. From the articles reviewed 74% of the insecticides detected were organochlorines with DDTs, lindanes, and endosulfans as most abundant ones. Levels of the insecticides of interest analysed, varied from below the detection limits to clearly above the safety limits. The lowest detected concentration of insecticide residues reported in fruits and vegetables was δ-lindane in pawpaw (0.06 mg/kg) while the highest was fenvalerate (25.6 mg/kg). Insecticide residues reported in sediment were predominantly organochlorines with concentrations ranging from 9.68 ng/kg to 10.98 µg/kg. Endosulfan and its metabolites were the main insecticides found in water bodies with concentrations ranging from 0.036 µg/L to 62.3 µg/L. DDT and its metabolites were the dominant insecticides found in human fluids.

A mechanized urease activity assay

Two fully mechanized flow analysis systems for urease activity assays have been developed, characterized and compared. Both of them are based on almost the same compact system of solenoid micropumps and microvalves controlled and actuated by highly effective, low-power and economic Arduino microcontroller. For photometric detection of ammonia formed in the course of enzymatic hydrolysis of urea, the Berthelot method and the Nessler reaction have been examined. For both these detection schemes very simple dedicated optoelectronic flow-through detectors made of paired light emitting diodes have been developed. In both systems single enzyme assay lasting a few minutes allows determination of urease in activity range 0.02–5.3 U mL−1 with detection limit 0.02 U mL−1 and in 1.3–5.3 U mL−1 range with 0.75 U mL−1 detection limit for Nessler reaction and Berthelot method based systems, respectively. When compared with mechanized Berthelot method, the bioanalytical system based on Nessler reaction offers higher sensitivity, lower detection/determination limits, better selectivity and lower cost of the assay. It has been demonstrated that the developed bioanalytical flow systems could be useful for urease determination in complex biological matrix like plant extracts and media for microbial cultures as well as for inhibitive determination of heavy metals at sub-ppm levels.

Persistence of pesticides in green vegetables of Satna District of Madhya Pradesh

Astudy was conducted forthe qualitative and quantitative estimation of 51 pesticides comprising 16 organochlorines, 23 organophosphates, eight synthetic pyrethroids and four herbicides in commonly consumed green vegetables i.e spinach, coriander, chilli, ladyfinger, bottle gourd and bitter gourd collected from various tehsils of Satna district, Madhya Pradesh. Gas chromatography-Electron Capture Detector (GC-ECD), Flame Photometric Detector (GC-FPD) were used for estimation of pesticides and Gas chromatography-Mass Spectrometry (GC-MS) was used for confirmation. Out of 144 samples, 59 samples were found contaminated with pesticide residue. It was observed that most of the bitter gourd samples were contaminated with chlorpyrifos whereas spinach and okra were contaminated with cypermethrin. Nagod samples were found most contaminated (10 out of 18) whereas Rampur Baghelan were least contaminated (6 out of 18). Contamination of chlorpyrifos was predominant in samples of Nagod, Raghurajnagar and Birsinghpur whereas cypermethrin contamination was so in Majhagawa samples. Profenofos and monocrotophos were detected only in Nagod and Raghurajnagar samples.

Search for Optimal Parameters for Gas Chromatographic Complex When Determining Sarin in Water Samples by Flame Photometric Detection Method

Sarin is considered to be an instrument for chemical terror by the extremist organizations due to the availability of technologies and components for its production. This fact became evident after the use of sarin by several members of the extremist organization «Aum Shinrikyo» for air infection of the capital`s subway in 1995 in Japan and by ISIL bands in Syria in 2013. Because of its physical and chemical properties, as well as its ability to be dissolved in water in any ratios, sarin can infect water sources for the long period of time. But the sensitivity of flame photometric detectors (FPD) is not always sufficient for the analysis of water samples for the presence of sarin, its precursors and products of destruction, especially in cases of necessity to detect the concentrations less than 0,03 ppm (3×10 -5 mg/ml). We have found out that higher sensitivity of the detector can be achieved in case of the increase of the gas carrier (helium) pressure in the injector up to 25 psi, and the temperature – to 250 °C, single-segment temperature rise in the thermostat with a speed of 10 °C/min from 40 °C (1 min) to 280 °C (5 min) at a hydrogen stream in PFD – 75 ml/min, air – 100 ml/min, helium – 60 ml/min. In comparison with the initial method, the offered one is more sensitive in case of sarin concentration in water in the range from 6×10 -6 to 1×10 -4 mg/ml to 1,7 times. The approbation of the offered optimal parameters was carried out during the gas chromatographic detection of sarin in water samples during the OPCW Proficiency Tests, during the analysis of arbitration samples, during the scientific research and the obtaining of national accreditation of the Laboratory of Chemical Analytical Control of the 27 Scientific Centre of the Minstry of Defence of the Russian Federation. These parameters can be used successfully during the studies of any organophosphorous chemicals by GC analysis with flame photometric detection

Photometric detection of internal gravity waves in upper main-sequence stars

Context.Main sequence stars with a convective core are predicted to stochastically excite internal gravity waves (IGWs), which effectively transport angular momentum throughout the stellar interior and explain the observed near-uniform interior rotation rates of intermediate-mass stars. However, there are few detections of IGWs, and fewer still made using photometry, with more detections needed to constrain numerical simulations.Aims.We aim to formalise the detection and characterisation of IGWs in photometric observations of stars born with convective cores (M ≳ 1.5M⊙) and parameterise the low-frequency power excess caused by IGWs.Methods.Using the most recent CoRoT light curves for a sample of O, B, A and F stars, we parameterised the morphology of the flux contribution of IGWs in Fourier space using an MCMC numerical scheme within a Bayesian framework. We compared this to predictions from IGW numerical simulations and investigated how the observed morphology changes as a function of stellar parameters.Results.We demonstrate that a common morphology for the low-frequency power excess is observed in early-type stars observed by CoRoT. Our study shows that a background frequency-dependent source of astrophysical signal is common, which we interpret as IGWs. We provide constraints on the amplitudes of IGWs and the shape of their detected frequency spectrum across a range of mass, which is the first ensemble study of stochastic variability in such a diverse sample of stars.Conclusions.The evidence of a low-frequency power excess across a wide mass range supports the interpretation of IGWs in photometry of O, B, A and F stars. We also discuss the prospects of observing hundreds of massive stars with the Transiting Exoplanet Survey Satellite (TESS) in the near future.

Determination of florfenicol residues in swine tissues using high-performance liquid chromatography with ultraviolet photometric detector

Determination of florfenicol residues in swine tissues using high-performance liquid chromatography with ultraviolet photometric detector

Compensation method of error caused from maladjustment of optical path based on microfluidic chip

Photometric detection plays a significant role in microfluidics technology. However, the mismatch between the solution concentration and the optical path length will increase detection error. In this study, we proposed a round microfluidic chip for concentration detection to obtain the continuous gradient distribution of concentration. The optimum absorbance can be found by dynamic accurately searching. The solution concentration will be accurately calculated finally according to the relationship between arc length and solution concentration. The overall detection process runs automatically. Under the optimization of injection velocity and concentration, the experimental result shows that the compensation ratio increases as the solution concentration increases. The compensation ratio in the detection of pesticide residue has already reached 14.22% and the reproducibility is acceptable. Therefore, this novel method lays the theoretical foundation for the research of high precision microfluidic photometric detection equipment.

A method for determining glyphosate and its metabolite aminomethyl phosphonic acid by gas chromatography-flame photometric detection

As a globally popular herbicide, glyphosate (GLY) and its metabolite aminomethylphosphonic acid (AMPA) pose potential hazards to the ecological environment. In this study, a sensitive and reliable method for detecting GLY and AMPA was utilized to facilitate exposure risk assessment of the analytes in environmental systems such as water and soil. GLY and AMPA were extracted from the sample using a solid-phase extraction (SPE) procedure, derivatized by heptafluorobutyric anhydride and heptafluorobutanol, and detected by gas chromatography-flame photometric detection (GC-FPD). The linearities of GLY and AMPA in the range of 10–1000 ng/mL were good (r=0.9998, r=0.9991), and the limits of quantitation (LOQ) for GLY and AMPA were 0.37 and 0.81 ng/mL, respectively. The method has been successfully applied for detecting GLY and AMPA in water, soil and monitoring the degradation of GLY under different environmental conditions. Simulated migration characteristics of GLY and AMPA in soil were investigated for evaluating the potential hazards of GLY and AMPA to the ecological environment.

Fabrication of graphene oxide incorporated polymer monolithic fiber as solid phase microextraction device for determination of organophosphate esters in soil samples

A novel solid phase microextraction fiber named graphene oxide incorporated poly acrylamide-ethylene glycol dimethacrylate (GO-poly AM-EDGMA) monolithic fiber has been successfully prepared in a fused silica capillary tube (250 μm, i.d.) via thermally initiated polymerization using acrylamide (AM) as the monomer, ethylene glycol dimethacrylate (EGDMA) as the crosslinker, dimethylformamide dispersed by GO as porogens, and then obtained by removing 1 cm wall from one end of the fused silica capillary tube. The fiber has large surface area (536 m2 g−1), pore capacity (0.694 cm3 g−1) good thermal stability (up to 320 ℃), long service life and good reproducibility (RSD ＜5% throughout 110 times) which facilitated for high throughput headspace solid phase microextraction (HS-SPME) coupled to gas chromatograph (GC) analysis. The HS-SPME/GC method using the new fiber was evaluated by the determination of five organophosphate esters (OPEs) in soil samples coupled to flame photometric detector (FPD). The proposed HS-SPME-GC/FPD method yielded satisfactory limits of quantification (0.03 ng g−1∼0.24 ng g−1); linearity (≥0.99), good intra- and inter-day precision expressed as relative standard deviations for a single fiber were in the range of 5.2–9.0% and 4.8–9.0%, respectively, and fiber-to-fiber reproducibility was in the range of 5.9–9.7%. The method was applied for the analysis of OPEs in environmental soil samples and the relative recoveries were found to be in the range from 80.1 to 105.6%. Based on these features, the new fiber has great potential for widespread use as a high throughput trace analysis tool.

A new sensitive photometric procedure for the determination of sulfate in fuel ethanol without sample preparation exploiting a flow-batch strategy

A simple, accurate, and fast flow-batch procedure employing photometric detection for the determination of sulfate in fuel ethanol was developed. After the formation of soluble barium sulfate in alcoholic medium, the remaining barium forms a product with dimethylsulfonazo III (DMS), the absorbance of which was monitored at 655 nm directly in the reaction chamber. The proposed procedure does not require any sample treatment such as dilution. Under the optimized conditions, the technique offers the advantages of low waste generation (<5 mL), sampling throughput of 35 h−1, linear response from 0.1–1.5 mg L−1 sulfate, and a limit of detection (95%) and coefficient of variation (n = 6) of 48 μg L−1 and 1%, respectively. The accuracy was assessed by comparison of results with those obtained by ion-chromatography; no significant difference was observed at the 95% confidence level.

3D Printing: The Second Dawn of Lab-On-Valve Fluidic Platforms for Automatic (Bio)Chemical Assays.

In this work, inexpensive manufacturing of unibody transparent mesofluidic platforms for pressure-driven Lab-On-a-Valve (LOV) methodologies is accomplished via rapid one-step 3D prototyping from digital models by user-friendly freeware. Multichannel architecture having 800-1800 μm cross-sectional features with unconventional 3D conduit structures and integrating optical and electrochemical detection facilities is for the first time reported. User-defined flow-programming capitalizing upon software control for automatic liquid handling is synergistically combined with additive manufacturing based on stereolithographic 3D printing so as to launch the so-called fourth generation of microflow analysis (3D-μFIA). Using an affordable consumer-grade 3D printer dedicated LOV platforms are 3D printed at will and prints are characterized in terms of solvent compatibility, optical and mechanical properties, and sorption of inorganic and organic species to prospect potentialities for the unfettered choice of chemistries. The unique versatility of the 3D-printed LOV device that is attached to a multiposition rotary valve as a central design unit is demonstrated by (i) online handling of biological materials followed by on-chip photometric detection, (ii) flow-through bioaccessibility tests in exposome studies of contaminated soils with miniaturized voltammetric detection, (iii) online phospholipid removal by TiO2-incorporated microextraction approaches using on-chip disposable sorbents, and (iv) automatic dynamic permeation tests mimicking transdermal measurements in Franz-cell configurations. A multipurpose LOV fluidic platform can be fabricated for less than 11 Euros.

The SAGE photometric survey: technical description

To investigate a huge sample of data related to the Stellar Abundance and Galactic Evolution (SAGE) survey in more detail, we are performing a northern sky photometric survey named SAGES with the SAGE photometric system. This system consists of eight filters: Strӧmgren-u, SAGE-v, SDSS g, r, i, DDO-51, Hαwide and Hαnarrow, including three Sloan broadband filters, three intermediate-band filters, two narrow-band filters and one newly-designed narrow-band filter. SAGES covers ∼12 000 square degrees of the northern sky with δ > −5°, excluding the Galactic disk (|b| < 10°) and the sky area 12 h < RA < 18 h. The photometric detection limit depth at signal-to-noise ratio 5σ can be as deep as V∼20 mag. SAGES will produce a photometric catalog with uniform depth for ∼500 million stars with atmospheric parameters including effective temperature Teff, surface gravity log g and metallicity [Fe/H], as well as interstellar extinction to each individual target. In this work, we will briefly introduce the SAGE photometric system, the SAGE survey and a preliminary test field of the open cluster NGC 6791 and its surroundings.

Metal organic frameworks-derived magnetic nanoporous carbon for preconcentration of organophosphorus pesticides from fruit samples followed by gas chromatography-flame photometric detection

In this work, magnetic nanoporous carbons (MNPCs) based on Zn/Co-MOFs was synthesized via a facial one-step carbonization method. The prepared MNPCs exhibited high specific surface areas, good chemical stability and high extraction efficiency for interest organophosphorus pesticides (OPPs). The good extraction performance of the MNPCs for interest OPPs can be primarily attributed to π-π interaction and hydrophobic interaction between MNPCs and OPPs. Based on it, MNPCs-based MSPE-GC-FPD method was established for the quantification of five OPPs in fruit samples. The main experimental conditions for MSPE of five target OPPs were investigated systematically and optimized, such as the desorption solvent and volume, extracted volume, ionic strength, extraction time and desorption time. Under the optimal conditions, the limits of detection (LODs, S/N = 3) were found to be in the range of 0.018 (ethion) -0.045 (malathion) μg/L. The linearity was 0.05-100 μg/L for phorate, diazinon, ethion and 0.1-100 μg/L for malathion, fenthion respectively. The reproducibility of the method was in the range of 3.5-9.7%. The recovery experiments were carried out by spiking target OPPs at three concentration levels to validate the accuracy of the proposed method, and the recoveries for target OPPs were 84-116%. The results show that the proposed method in this work can be successfully used to analyze OPPs residue in fruit sample.

Characterization of Odor-Active Volatiles in Hawthorn Puree Using Thermal Desorption System Coupled to Gas Chromatography-Mass Spectrometry-Olfactometry and GC-Flame Photometric Detector.

The volatile compounds in hawthorn puree obtained from three cultivars (Y1, Crataegus pinnatifida Bunge cv. "Waibahong", Y2, Crataegus pinnatifida Bunge cv. "Damianqiu", and Y3, Crataegus pinnatifida Bunge cv. "Dajinxing") were analyzed by the thermal desorption system coupled to gas chromatography-mass spectrometry-olfactometry and GC-flame photometric detector. In the samples of Y1, Y2, and Y3, 40, 42, and 42 odor-active compounds were, respectively, identified by olfactometry. Methyl 2-methylbutanoate, methyl hexanoate, hexyl isobutanoate, methional, heptanal, and ( Z)-3-hexenyl acetate contributed largely to the characteristic aroma of the three samples. Additionally, the odor activity value (OAV) was used to determine the main compounds and 3-mercaptohexyl acetate (OAV: 10-18), 3-mercapto-2-methylpentanal (OAV: 4-7), methyl 2-methylbutanoate (OAV: 9-21), methyl hexanoate (OAV: 8-16), and 2-pentyl acetate (OAV: 5-12) were considered as the important contributors to the aroma of hawthorn samples.

Design and implementation of high sensitivity micro spectrometer based on area array CCD

The area array CCD has the advantages of high sensitivity and wide dynamic range, which is suitable for fluorescence measurement, DNA sequencing, Raman spectroscopy and low photometric detection. Therefore, it is of great practical value to develop high sensitivity micro fiber spectrometer based on area array CCD. The optical resolution of 1 nm is obtained by using an optimized cross-asymmetric Czerny-Turner optical system structure. By combining the design methods of DC-DC and LDO, the complex power system with 6 voltage outputs is realized through USB power supply. The CCD drive timing design is achieved by Verilog HDL language and the signals are output through Altera's EPM7064 chip. After the CCD output video signal is converted by high-speed 16 bit AD chip AD9826, digital signals are stored in a separate static RAM, allowing dacquisition and reading of data to be separated. The sensitivity of designed micro-high sensitivity spectrometer is 11 times of that of spectrometer based on linear array CCD. Furthermore, it has a dynamic range of 20000: 1 and a signal-to-noise ratio of 500: 1. This work greatly improves the microfiber spectrometer performance.

A Rapid Analytical Method for the Selective Quenching-Free Determination of Thiols by GC-FPD

A rapid method is introduced, which facilitates the selective gas chromatography–flame photometric detection (GC–FPD) analysis of thiols. The method uses lead oxide particles or plumbite solution to complex thiols into a solid lead thiolate moiety that can be physically separated from complex sample matrices and then reconstituted as the original thiol in a simple replacement solvent for analysis. While both red or yellow forms of lead oxide are found to remove thiols from sample solutions, the latter does so about 10 times faster than the former. Comparatively, though, plumbite solution is most rapid in this regard and is still 10 fold faster than solid yellow lead oxide. For example, 98 ± 1% (n = 3) of a 1-butanethiol standard in hexane (600 ng µL− 1) was extracted after only 2 min of contact with a 0.06 M plumbite solution. The method allows thiols to be selectively isolated from co-eluting peaks and other sulfur species, which can simplify their determination. It also allows thiols to be removed from complex hydrocarbon matrices for analysis, which can greatly reduce interference from signal quenching when using a conventional FPD. For instance, analysis of a thiol standard in a commercial gasoline by this method showed that the FPD sulfur signal increased from 16 to 97% of its expected value by removing the quenching hydrocarbon interference. Accordingly, results indicate that this method could be a useful alternative approach for the selective analysis of such thiol-containing samples.

Determination of total and free ceftolozane and tazobactam in human plasma and interstitial fluid by HPLC-UV

Ceftolozane/tazobactam is a new cephalosporin/beta-lactamase inhibitor combination. An HPLC-UV method is described for the determination of total and free ceftolozane and tazobactam in human plasma and in microdialysate of subcutaneous tissue, respectively. Separation was performed using a reversed-phase column with phosphate buffer/acetonitrile as eluent and photometric detection at 260 nm (ceftolozane) or 220 nm (tazobactam). Linearity has been shown down to ceftolozane/tazobactam 0.1/0.05 mg/L in plasma and 0.03/0.015 mg/L in saline, respectively. The plasma protein binding of both drugs as determined by ultrafiltration was less than 10%. Temperature, pH or relative centrifugation force (up to 3000 x g) had no significant impact on the protein binding. The method was applied to the determination of ceftolozane and tazobactam in plasma and interstitial fluid of healthy volunteers following intravenous infusion of ceftolozane/tazobactam 1.0/0.5 g.

A feasibility study on the photometric detection of quiescent black hole X-ray binaries

We investigate the feasibility of detecting quiescent black hole X-ray binaries using optical photometric techniques. To test this we employ a combination of r-band and Halpha filters currently available at the Roque de los Muchachos Observatory. Photometric observations of four dynamical black holes (GRO J0422+320, A 0620-00, XTE J1118+480 and XTE J1859+226) at SNR>~35-50, supplemented with near simultaneous spectroscopic data, demonstrate that it is possible to recover the FWHM of the Halpha emission line to better than 10% for targets with a wide range of line EWs and down to magnitude r~22. We further explore the potential of our photometric system to disentangle other populations of compact stars and Halpha emitters. In particular, we show that HAWKs, a survey designed to unveil quiescent black holes, will also provide a detailed census of other Galactic populations, most notably short period (eclipsing) cataclysmic variables, neutron star X-ray binaries and ultra-compact binaries.

Characterization of the key aroma compounds in peach by gas chromatography–olfactometry, quantitative measurements and sensory analysis

The volatile compounds of peaches (Prunus persica L.) obtained from five cultivars (Chongyanghong, Y1; Ruiguang 19, Y2; Zaohongxia, Y3; Zaohong 2, Y4; and Wuyuehuo, Y5) were analyzed by gas chromatography–olfactometry (GC–O), gas chromatography–mass spectrometry (GC–MS) and GC–flame photometric detection (FPD). A total of 40 odor-active volatile compounds were observed in the GC–O experiments. Amongst those compounds, hexanal, (Z)-3-hexen-1-ol, (E)-2-hexenal, 3-mercaptohexanol, nonanal, γ-nonalactone, and γ-decalactone contributed greatly to aroma of peach. In addition, thirty-four quantified compounds were demonstrated as important odorants according to odor activity values (OAVs > 1). Amongst these compounds, hexanal (OAV: 28–89), pentanal (OAV: 9–16), (E)-2-heptenal (OAV: 19–60), (E)-2-hexenal (OAV: 26–86), (E)-2-octenal (OAV: 10–42), (E)-2-nonenal (OAV: 8–94), γ-decalactone (OAV: 13–34), δ-decalactone (OAV: 2–19), (R)-(−)-linalool (OAV: 29–76) and phenyl acetaldehyde (OAV: 4–59) were the most powerful compounds in five varieties of peach.