ntn bag sampling preparationnadp.slh.wisc.edu/lib/manuals/ntn_bag_sampling_v_1-13.pdfmicrosoft word...

NTN Bag Sampling Preparation SOP, 2012-06 Version 1.13

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NTN Bag Sampling Preparation

Items needed:

NTN bucket New, clean, NTN sample bag NTN circular weight Clean, non-talc laboratory gloves Bucket lids (2) Side-release buckle strap Insulated wire/twist-tie to secure bag to bucket Laboratory wipes Deionized water

Vacuum pump or other vacuum source Heavy duty tape

Instructions - Creating the NTN circular weight

Once completed, this step does not need to be repeated on a weekly basis. The circular weight is re-used. A site should have at least 2 circular weights. One with the deployed NTN bucket, and one for use with the NTN bucket for the upcoming week.

Fill tubing (provided) with lead shot or ball bearings to increase its weight. Sand can be used in the absence of other materials, but adds little weight to the tubing. Do not add liquid as the weighting material. Liquids may expand upon freezing and damage the tubing. A piece of Parafilm across the opening to the barbed fitting (provided with the tubing) may help when filling the tubing.

Connect ends of tubing with the barbed fitting to form circle. Parafilm can be left in place when completing this step.

Wrap connection with heavy duty tape (e.g., electrical tape) to prevent water from entering tubing.

Figure 1. NTN circular weight.

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3. The NTN sample bag has 2 sections: the top (longer) section for collecting the sample, and the bottom (shorter) section for securing the sample bag to the circular weight. Securing the sample bag to the circular weight helps keep the sample bag in the bucket throughout the sampling period (i.e., Tuesday to Tuesday).

Figure 3. NTN sample bag with upper section for sample, and lower section for NTN circular weight.

seam separating top and bottom sections of the NTN sample bag


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4. Insert the bottom (shorter) section of the NTN sample bag through the opening in the circular weight. Laboratory gloves do not need to be worn for steps 4 and 5.

Figure 4. Placement of NTN circular weight.

5. Open the bottom section of the NTN sample bag, wrapping the bag around the circular

weight. Do not place the circular weight inside the top (longer) section of the bag. This is the section of the sample bag that will be used to collect sample. Doing so will contaminate, and invalidate, the sample.

Figure 5. Wrap lower section of NTN sample bag around circular weight.


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6. Transfer the NTN sample bag to an NTN bucket such that the wrapped circular weight will be at the bottom of the bucket. The top (sample) portion of the bag should extend out of the bucket.

Figure 6. Wrapped circular weight at the bottom on an NTN bucket.

Put on a pair of clean, laboratory gloves. If laboratory gloves were worn to deploy the circular weight, they should be changed.

7. Open the NTN sample bag by starting at the top of the bag and working downward toward the seam.

Figure 7. Open the NTN sample bag starting at the top of the bag.


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8. Drape excess bag over the sides of the bucket. The bag should extend approximately 3 inches (7.5 cm) below the lip of the bucket. For a ringed bucket (see Figure 8) the bag will extend to the bottom ring.

Figure 8. Drape excess NTN sample bag over edge of NTN bucket.

9. Wrap the buckle strap around the sides of the NTN bucket to secure the sample bag to the

bucket. This helps prevent air leaks when the vacuum is applied in the next step. Cinch the strap to ensure a good seal. Avoid contact between the strap and the collection surface of the sample bag.

Figure 9. Wrap strap around NTN bucket to secure the NTN sample bag.


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Figure 10. Cinch the strap to secure the sampling bag to the NTN bucket.

10. Locate the vacuum hole in the side of the bucket. Apply a vacuum source to this opening

to form the sample bag to the walls of the NTN bucket. A laboratory vacuum line works well for this. A wet-dry vacuum (e.g., Shop-Vac1) may also be used if it is dedicated for this purpose. Exhaust from the wet-dry vacuum may contain dust which can contaminate the NTN sample bag. Direct the exhaust from the vacuum source away from the bucket and sample bag to avoid contaminating the bag.

Figure 11. Apply the vacuum to pull the sample bag to the walls of the NTN bucket.

1 Use of a trade or manufacturer’s name does not constitute an endorsement by the University of Illinois, the Illinois State Water Survey, the National Atmospheric Deposition Program, or project sponsors.


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11. Replace the buckle strap with a wire tie. The buckle strap provides a better seal than a wire tie when applying the vacuum. Unfortunately, the strap’s mesh will absorb water and will attract dust and dirt which can contaminate the precipitation sample. The wire tie is less likely to contaminate the sample, and will ensure that the sample bag remains in place throughout the sampling period.

Figure 12. Replace buckle strap with wire tie for field deployment.

Excess bag on the outside of the bucket should lie flat. Folds and pockets in the excess bag will trap water. This will cause the sample mass to be reported incorrectly, and may contaminate the sample when it is decanted to the shipping bottle. If necessary, re-apply the vacuum to remove folds and air pockets. Figure 13 illustrates the NTN bucket with the sample bag ready for deployment.


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Figure 13. NTN bucket and sample bag ready for deployment.

12. Cover the opening in the side of the NTN bucket with a piece of heavy duty tape to

prevent water from entering the bucket. Water between the sample bag and the walls of the bucket could damage the circular weight.

Figure 14. Cover hole in side of NTN bucket with heavy duty tape to prevent water from entering.


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13. Place the secured sample bag and bucket on a scale. Record the mass (pre-deployment) on the field form (FORF). Again, avoid leaning over the top of the bucket and touching the inside surface of the sample bag to avoid contaminating it.

Figure 15. Weigh NTN bucket, sample bag, and wire tie.

14. Place a clean, unused lid on the bucket to protect the sample bag. Again, avoid leaning

over the open sample bag. Do not touch the inside surfaces of the sample bag or the lid. The NTN bucket and sample bag are now ready to be transported to the field for deployment.

Figure 16. Place lid on NTN bucket to protect NTN sample bag.


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Figure 17. Secure lid to NTN bucket.

15. Carry a second clean lid to the field to use when collecting the deployed sample from the

collector. Lids should not be re-used. Doing so may contaminate the sample bag and/or the sample.

ntn bag sampling preparationnadp.slh.wisc.edu/lib/manuals/ntn_bag_sampling_v_1-13.pdfmicrosoft word...

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