Collecting Samples

[Alan Garrett]

I want to collect a couple of small water and sediment samples from a cave tomorrow for microscopic examination and was wondering if anyone could advise how best to do it. I only need maybe 100ml max from two or three locations in the cave. I was toying with the idea of filling a few sterile medicine bottles with distilled water, or maybe a solution of water and potassium metabisulfite, then purging them with gas from my regulator just prior to taking the samples. I know that if I don't pre-fill them with something I'll never be able to open them at depth, but I want to avoid as much contamination as possible. Any better ideas?

[jason]

I make my own water sampling tubes using PVC pipe. The problem with using bottles is that it is impossible to get an undisturbed water sample - by using PVC pipe with two end caps that you can screw on you can slide the tube through the water and cap it at both ends. Prefilling bottles and purging them with exhaust could result in a sample diluted by unexpelled distilled water and if diver exhaust stays in the bottle it will change the PCO2. It is also important to sample during the initial descent if you are expecting depth-dependent water chemistry variations. If you don't want to spend the time to make your own water sampler with PVC - OMS sells an acrylic tube that unscrews at either end. Is there any reason that you can't just sample the spring boil?

Jason

[jason]

You can also use large syringes sans needles.

[Jerry]

Alot of your decision depends upon what you are analyzing for. Simple nalgene screw top bottles will work; cubitainers are used alot; some analytes require glass. The nalgene or cubis will suffice since this probably isn't an EPA or State job(is it?). edit__DON'T get narrow mouth jars!!! They are nearly impossible to purge.

You will be able to open the containers at depth if not filled with water; the bottles will be horribly distorted (yes, that is the voice of experience). I would worry more about integrity of the seal being compromised and contaminating the container.

I have done just what you suggested many times and it works just fine; use distilled (and deionized; if you can) your octo/backup and use fresh gas from your tank to purge, repeat to ensure total removal of distilled water. Some term this "precontamination" By very slowly tilting the container you can fill the container very slowly and gently. I have used this for collecting several sets of samples for State jobs with no ill results.

Jerry

[Alan Garrett]

I'm really wanting to get both water and sediment from different penetration distances. I'm trying to get some idea how the microcritters differ as you get farther back from the spring vent. There's a place maybe p500' where some catfish are digging some deep pits in the sediment, apparently feeding off something, but I've seldom seen that kind of thing going on much farther back than that.

[REastman]

Alan,

We have collected samples in the past for water analysis. We used the following procedure.

1) Prepare the container(s) by washing it with sterile water sevearl times. We used empty two liter bottles for larger collections, and smaller 16 or 12 ounce plastic coke bottles for smaller needs. Make sure you use distilled water. Pour the water in, swich it around, pour it out, repeat 5 times. Some collections before have required even more using special checmicals to make sure the container was completely clean, but this is sufficient for most stuff. We prepare three containers for each collection using this method.

2) Fill the bottles completely with distilled water before capping. Screw the caps down tight in order to prevernt unwanted contamination.

3) Once at the desired collection location uncap the first bottle. Hold the bottle upside down and purge the water with air from one of your regulators until the bottle is completely filled with air. Turn the bottle back up, and work the air out and let the water in. Repeat this two more times for the same bottle.

4) Repeat step three for the two remaining bottles.

[Alan Garrett]

Sounds like I might not be too far off the mark already. I was thinking of using the potassium metabisulfite to make sure the bottles are sterile and keeping them that way until the moment the sample is collected. You may already know this, but potassium metabisulfite ("meta" for short) is used to prevent spoilage in wine, and in higher concentrations is used to sterilize the bottles and equipment prior to making and bottling the wine. It promptly kills bacteria and is safe to mess with. Since I already make my own wines at home, the meta is already on hand. Just thought it might be a prudent extra step to ensure the purity of the samples.

[OutlawCaver]

Wingman & I used some large syringes without needles. Perfect for slurping sediment and/or water.

[Alan Garrett]

I might pick some up next time, but I don't have any on hand and I have to do the deed tomorrow. I'll bet one of those big turkey injector syringes would be ideal!

[skip]

I might pick some up next time, but I don't have any on hand and I have to do the deed tomorrow. I'll bet one of those big turkey injector syringes would be ideal!

if you need a smaller amount of water, try West Marine, or any boating place with fiberglass repair supplies. large syringes and not too much cost (used for filling with epoxy). I have used the smaller ones (10 ml or so), but they do make larger ones.

-skip