Portable Colorimetric Hydrogel Test Kits and On-Mobile Digital Image Colorimetry for On-Site Determination of Nutrients in Water.

Portable colorimetric hydrogel test kits are newly developed for the on-site detection of nitrite, nitrate, and phosphate in water. Griess-doped hydrogel was prepared at the bottom of a 1.5 mL plastic tube for nitrite detection, a nitrate reduction film based on zinc powder was placed on the inner lid of a second 1.5 mL plastic tube for use in conjunction with the Griess-doped hydrogel for nitrate detection, and a molybdenum blue-based reagent was entrapped within a poly(vinyl alcohol) hydrogel matrix placed at the bottom of a third 1.5 mL plastic tube to detect phosphate. These test kits are usable with on-mobile digital image colorimetry (DIC) for the on-site determination of nutrients with good analytical performance. The detection limits were 0.02, 0.04, and 0.14 mg L−1 for nitrite, nitrate, and phosphate, respectively, with good accuracy (<4.8% relative error) and precision (<1.85% relative standard deviation). These test kits and on-mobile DIC were used for the on-site determination of nutrients in the Pak Bang and Bang Yai canals, the main canals in Phuket, Thailand. The concentrations of nitrite, nitrate, and phosphate were undetectable to 0.60 mg L−1, undetectable to 2.98 mg L−1, and undetectable to 0.52 mg L−1, respectively.

Griess-doped polyvinyl alcohol thin film for on-site simultaneous sample preparation and nitrite determination of processed meat products.

To facilitate on-site nitrite determination for processed meat products, Griess-doped polyvinyl alcohol film was synthesized in the bottom of a plastic tube for in-tube determination. The tube's aperture was used to control the sample dimensions. Each sample, cut into eight sectors, was subjected to nitrite extraction by water. Use of tap water or commercial drinking water vs. ultrapure water was associated with < 2% differences in nitrite levels. The use of film and digital image colorimetry showed a low limit of detection (12.6 ± 0.5 µg L-1), good precision (1.0%RSD, n = 5 days), and good accuracy (93.2 ± 3.5 to 108.5 ± 1.8%recovery). Using these methods, sodium nitrite concentrations in 700 processed meat products for sale in Phuket, Thailand, were found to range from 6.8 ± 0.2 to 113.6 ± 1.3 mg kg-1. These results showed no significant differences with the HPLC standard method (p > 0.05, n = 45).

Preparation and Characterization of Calcium Cross-Linked Starch Monolithic Cryogels and Their Application as Cost-Effective Green Filters.

Monolithic cryogels from starch were successfully synthesized and applied as alternative biodegradable filters for the first time. Rice flour was cross-linked with Ca2+ from limewater during gelatinization before being frozen and then thawed for three cycles. The resultant material was then soaked in ethanol for 3 h before incubation at 80 °C for 1 h, yielding monolithic material with interconnected pores in sizes of 51 ± 18 to 52 ± 15 µm without any need of freeze-drying. The cryogels possessed macroporous structure with specific surface areas from 1.1 to 4.3 m2g-1, they could adsorb water from 599 ± 27 to 635 ± 59% of their dry weight with low swelling ratios of 6.0 ± 0.3 to 6.4 ± 0.6 gwater/gcryogel, and could be applied as biofilters to remove suspended particles and reduce the light absorption of water sample from 25 ± 3 to 96 ± 5%. The prepared biofilters can be re-used up to three times, although they cost only USD 0.0004/piece. Complete weight loss resulted from burial in soil for 30 days, indicating environmentally friendly biodegradation and potential for environmental applications.

Greener Monolithic Solid Phase Extraction Biosorbent Based on Calcium Cross-Linked Starch Cryogel Composite Graphene Oxide Nanoparticles for Benzo(a)pyrene Analysis.

Benzo(a)pyrene (BaP) has been recognized as a marker for the detection of carcinogenic polycyclic aromatic hydrocarbons. In this work, a novel monolithic solid-phase extraction (SPE) sorbent based on graphene oxide nanoparticles (GO) in starch-based cryogel composite (GO-Cry) was successfully prepared for BaP analysis. Rice flour and tapioca starch (gel precursors) were gelatinized in limewater (cross-linker) under alkaline conditions before addition of GO (filler) that can increase the ability to extract BaP up to 2.6-fold. BaP analysis had a linear range of 10 to 1000 µgL-1 with good linearity (R2 = 0.9971) and high sensitivity (4.1 ± 0.1 a.u./(µgL-1)). The limit of detection and limit of quantification were 4.21 ± 0.06 and 14.04 ± 0.19 µgL-1, respectively, with excellent precision (0.17 to 2.45%RSD). The accuracy in terms of recovery from spiked samples was in the range of 84 to 110% with no significant difference to a C18 cartridge. GO-Cry can be reproducibly prepared with 2.8%RSD from 4 lots and can be reused at least 10 times, which not only helps reduce the analysis costs (~0.41USD per analysis), but also reduces the resultant waste to the environment.

Curcumin nanoparticle doped starch thin film as a green colorimetric sensor for detection of boron.

A tapioca starch film doped with curcumin nanoparticles was successfully fabricated and applied as a novel green colorimetric sensor for detection of boron in wastewater. Curcumin nanoparticles (curn, 30-90 nm) extracted from turmeric powder were used as a green probe, while tapioca starch was used as a natural support substrate. A yellow thin film (51 µm thick) fabricated on a used plastic spoon turned red-brown after immersion in boron solution (pH 9) for 15 min with excellent selectivity. The film costs only 0.0007 USD, while the cost of the sensor (curn-film on new plastic spoon) was 0.004 USD. After use the film could be completely washed from the plastic, it being biodegradable, while the used plastic spoon could be re-used to fabricate a new sensor at least 10 times. The good 1.52%RSD precision was obtained across three lots fabricated. When the curn-film was used in conjunction with digital image colorimetry (DIC), a simple and rapid quantification of boron was achieved. The green color layer in reflected light image of the red-brown product (IG) provided the highest sensitivity (64 ±â€¯1 a.u. L mg-1) and the lowest detection limit of 0.052 ±â€¯0.001 mg L-1. The intra-day testing (9 films) had 2.41 to 4.34%RSD, while the inter-day testing had 2.29 to 5.66%RSD (15 films, 5 days). Accuracy in terms of relative error for control samples (0.40 mg L-1) was +3.63%. Wastewater samples from Para-rubber wood processing plant were quantified by curn-film and DIC, giving 4248 ±â€¯391 mg L-1 boron concentration with no significant difference to ICP determination at 95% confidence level. The sensors after storage in a desiccator for a year gave readings changed by only +3.5% and -2.1% relative to freshly prepared sensors.