Nov 21, 2024
Method for the determination of PET Microplastics in Sediment
- 1Pontificia Universidad Católica de Valparaíso
- Laboratorio de Química Analítica y Ambiental
Protocol Citation: WALDO EMERZON QUIROZ VENEGAS 2024. Method for the determination of PET Microplastics in Sediment. protocols.io https://dx.doi.org/10.17504/protocols.io.5jyl82b77l2w/v1
License: This is an open access protocol distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited
Protocol status: Working
We use this protocol and it's working
Created: July 08, 2024
Last Modified: November 21, 2024
Protocol Integer ID: 103028
Keywords: microplastics, pet, fluorescence, sediment
Funders Acknowledgement:
ANID-FONDECYT
Grant ID: 1230585
Abstract
The methodology is based on a direct acid attack of HNO3/HCl 3:1 from the wet sediment sample, assisted by
microwaves digestion system. No drying, sieving or flotation procedures are neccesary. As a detection method we use induced fluorescence with a UV camera, Red Nile as a fluorophore and a cell phone camera.
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S1.docx
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Guidelines
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Materials
The reagents and solvents used were Scharlau HPLC grade acetone, Supelco suprapure hydrochloric acid,
Supelco suprapure nitric acid (65%), Milli-Q laboratory water, and Nile Red Sigma Aldrich.
Analytical-grade chitin and purified marine sand (both from Sigma Aldrich) and crude cellulose were used to simulate the sedimentary matrix.
The MPs used in the experiments represent the polymers most found in the marine environment: polyethylene terephthalate (PET), low-density polyethylene (LDPE), polystyrene (PS) and polypropylene (PP). MPs were made from virgin plastic resins of each type of polymer. A grinding system was implemented to ensure that the resin is free from contact with any other polymer. The grinding process
involves chopping at 5-second intervals with 10-second breaks to prevent heating and possible structural changes in each polymer. Subsequently, the material is screened through 1.0, 0.5 and 0.15 mm mesh, resulting in two working fractions (1-0.5 mm and <0.5-0.15 mm), which are stored in stainless steel containers.
Safety warnings
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Ethics statement
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Before start
Determination of PET in sediments
New methodology for the determination of PET microplastics in sediment, based on microwave-assisted acid digestion
New methodology for the determination of PET microplastics in sediment, based on microwave-assisted acid digestion
Sample Digestion:
1. Weigh 1g of wet sediment and place it in the
microwave digestion vial.
2. Add 20 ml of a 3:1 v/v HNO3/HCl mixture
to the sample in the microwave digestion vial. Seal and place it in the
microwave equipment.
3. Digest the sample for 1 hour at 60ºC.
4. Filter the digestion solution through a 0.45 µm
membrane filter. Quantitatively rinse all material from the digestion vial with
deionized water using a wash bottle. Before finishing the filtration, rinse
thoroughly with water to dislodge any digested material clinging to the
filtration vessel walls. Also, use circular motions with deionized water from a
wash bottle to ensure that the undigested solids are centered on the filtration
membrane.
5. Carefully transfer the membrane to a 100 mm
diameter Petri dish. Cover the Petri dish with aluminium foil and make small
holes in the top.
6. Place the dish in a drying oven or incubator at
60ºC for one hour. After this time, let the dish cool and proceed to the
staining stage.
Sample digestion
Staining step:
1. Prepare a Red Nile (RN) solution at a concentration
of 10 mg L-1 at 1% v/v in 99.5% v/v acetone.
2. Add 20 ml of the RN solution to the Petri dishes containing
the filtered solid and membrane. Cover the dish with its corresponding glass
lid.
3. Place the Petri dish in the incubator for 10
minutes at 50ºC.
4. After the incubation time, quickly cool the Petri
dish in an ice water bath. Let it stand for 20 minutes.
5. Filter the solution with abundant deionized water
through a 0.45 µm membrane filter.
6. Place the membrane with the stained material back
into the same Petri dish. Cover with aluminum foil and make holes.
7. Place in the incubator and dry at 60ºC for one
hour. After this time, let the dish cool and proceed to the stage of taking
photographs and counting particles.
Staining step
Photograph Taking and Particle Counting:
1. Uncover the dish and
carefully transfer the filters to the glass lid of the Petri dish. The dish
containing the solid material should be moved horizontally until a uniform
monolayer is obtained across the surface.
2. Insert each dish
separately into the UV chamber, verify that the excitation energy is at 254 nm,
and take the corresponding photograph.
3. For particle
counting, load the photograph into the ImageJ software.
4. Identify PET
particles by their characteristic color and manually count them in the software
as follows:
- Select the multipoint function from the
toolbar.
- Position the cursor over the particle and
right-click. As selections increase, the software will perform the count, and
each selected particle will be identified with its respective number.
Particle Counting
Protocol references
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