Development of a paper strip test for colorimetric detection of urea in raw materials for animal feed.

Aiming at developing an easily implementable method for on-site analysis to detect urea adulteration in feed ingredients, a simple and inexpensive paper strip for urea detection via colorimetric assay is herein presented. The paper strip can be simply fabricated by immobilizing urease with bromothymol blue (BTB) as a pH indicator on cellulose fiber. Upon dipping the paper strip into the target sample, the release of ammonia during the reaction between urea in the sample and urease on the paper strip causes a pH change that results in the development of a blue color, thus indicating the presence of urea. A semiquantitative detection method was developed on the basis of the color change on the paper strip, which can be detected by naked eyes and compared with a color chart made by spiking urea at concentrations varying from 0.10% to 1.0% (w/w) in animal protein and fishmeal samples. Moreover, quantitative data were obtained by taking a picture with a smartphone camera and measuring the color intensity using ImageJ software. A comparison between BTB and phenol red as pH indicators revealed that the former afforded better results in terms of resolution. Under optimal conditions, good linear responses of blue intensity were obtained in a concentration range of 0.10%-1.0% (w/w). The recovery was determined to range between 98.1% and 118.3% with a relative standard deviation of <5%. The developed paper strip assay was applied to determine urea in animal protein and fishmeal, finding good agreement with the official AOAC method (No. 967.07). The present paper strip is rapid and requires neither sophisticated devices nor skilled personnel, allowing its use by quality controllers for the routine on-site detection of the urea adulteration of raw materials.

Alternative Patterning Methods for Paper-based Analytical Devices Using Nail Polish as a Hydrophobic Reagent.

A rapid, easy, and cost effective fabrication method for paper-based analytical devices (PADs) is described. This newly developed method is based on the use of nail polish as an alternative hydrophobic reagent, and the nail polish was resistant to basic and organic solvents. Three approaches for fabrication of paper-based analytical devices (PADs) were investigated, namely writing, stamping, and spraying. The writing approach was carried out by drawing the hydrophobic area of a pre-designed pattern on filter paper with a simple lab-made pen filled with nail polish as the hydrophobic agent. The stamping and spraying approaches required the use of a designed mask, which was made by laser cutting of the magnet rubber sheet. With laser cutting, two types of templates were made, i.e., positive and negative counterparts. The positive counterpart was the inside pattern and the negative counterpart was the outside pattern of the magnet sheets. For the stamping approach, the negative counterpart of the magnet rubber mask was attached onto a simple rubber stamper that was then stamped onto filter paper after loading with nail polish solution. With the spraying method, the positive counterpart was used to cover the hydrophilic area on the paper. Then, the nail polish solution was used with an air brush and sprayed on the paper covered with the magnet rubber mask. All approaches were cost effective and required neither extra equipment nor any pretreatment step. Among all three methods, however, the spraying method was found most suitable for mass production and provided the best resolution when compared with the other two approaches. With this approach, the actual channel widths obtained were similar to the designed widths, with the narrowest possible channel width of 650 µm. Furthermore, a nail polish-treated PAD was prepared by soaking the paper in the nail polish solution. The ability of the nail polish-treated PAD was examined for its resistance to a strong basic solution and an organic solvent (up to 30% ethanol and dichloromethane). The nail polish-treated paper also showed the potential to be used as an organic-aqueous separator.

Rapid characterization of trace aflatoxin B1 in groundnuts, wheat and maize by dispersive liquid-liquid microextraction followed by direct electrospray probe tandem mass spectrometry.

RATIONALE: Aflatoxins are poisonous and cancer-related chemical compounds commonly found in crops and plants. Aflatoxin B1 is the most toxic compound among aflatoxins and has been classified as group 1 carcinogenic to humans, especially in liver cancer. Herein, an ambient mass spectrometric method was developed for rapid characterization of trace aflatoxin B1 in peanuts. METHODS: Direct electrospray probe tandem mass spectrometry (DEP-MS/MS) was used to detect aflatoxin B1 in peanuts. To avoid the matrix effect, the aflatoxin B1 in the samples was extracted and concentrated by dispersive liquid-liquid microextraction. The mass spectrometer was operated in the positive ion mode to monitor the intact molecular ion (m/z 313, MH+ ) and product ion (m/z 241) of aflatoxin B1 using multiple reaction monitoring. RESULTS: Since no clean-up procedure of the sample was required, the sampling step and the subsequent mass spectrometric detection of the aflatoxin B1 was completed in less than 5 min. The limit of detection of aflatoxin B1 is at the sub-ppb level. The results obtained by DEP-MS/MS were also validated by liquid chromatography/tandem mass spectrometry (LC/MS/MS). Recovery of aflatoxin B1 in the sample was evaluated by analyzing spiked aflatoxin B1 with LC/MS/MS to be 85% and DEP-MS/MS to be 84%. CONCLUSIONS: DEP-MS/MS combined with a simple dispersive liquid-liquid microextraction procedure was successfully used for the quantitative analysis of AFB1 in nut samples. Due to its high efficiency, it is promising in providing important toxicological information for food safety in the real world. Copyright © 2017 John Wiley & Sons, Ltd.

A simple analytical platform based on thin-layer chromatography coupled with paper-based analytical device for determination of total capsaicinoids in chilli samples.

A new analytical platform based on the use of thin-layer chromatography (TLC) coupled with paper-based analytical device (PAD) was developed for the determination of total capsaicinoids in chilli samples. This newly developed TLC-PAD is simple and low-cost without any requirement of special instrument or skillful person. The analysis consisted of two steps, i.e., extraction of capsaicinoids from chilli samples by using ethanol as solvent and separation of capsaicinoids by thin-layer chromatography (TLC) and elution of capsaicinoids from the TLC plate with in situ colorimetric detection of capsaicinoids on the PAD. For colorimetric detection, Folin-Ciocalteu reagent was used to detect phenolic functional group of capsaicinoids yielding the blue color. The blue color on the PAD was imaged by a scanner followed by evaluation of its grayscale intensity value by ImageJ program. This newly developed TLC-PAD method provided a linear range from 50 to 1000mgL-1 capsaicinoids with the limit of detection as low as 50mgL-1 capsaicinoids. The proposed method was applied to determine capsaicinoids in dried chilli and seasoning powder samples and the results were in good agreement with those obtained by HPLC method.

Paper-based analytical device for sampling, on-site preconcentration and detection of ppb lead in water.

A simple and cost effectiveness procedure based on a paper based analytical device (PAD) for sampling, on-site preconcentration and determination of Pb(II) in water samples was developed. The inkjet printing method was used for patterning of PAD. Colorimetric assay was developed on a PAD for Pb(II) detection in µgL(-1) level. This µgL(-1) level detection limit was achieved by in situ- and on-site preconcentration of Pb(II) onto adsorption filter paper disc with a home-made holder before color development. Water sample was loaded onto a circular filter paper coated with zirconium silicate in 3% sodium carboxymethylcellulose for Pb(II) preconcentration. Subsequently, sodium rhodizonate in tartrate buffer solution (pH 2.8) was used as colorimetric reagent for direct Pb(II) detection on a PAD. Detection was achieved by measuring the pink color and recorded by scanner or digital camera. ImageJ software was used for measuring grey scale values. The calibration curve was linear in the range of 10µgL(-1) and 100µgL(-1), with a detection limit of 10µgL(-1). The developed method was successfully applied to the determination of Pb(II) in drinking water, tap water and surface water near electronic waste storage and the results were compared with those by graphite furnace atomic absorption spectroscopy (GF-AAS) with good agreement.