From Mark.Mattson@state.ma.us Thu Mar 23 12:02:33 2000 Date: Mon, 28 Jun 1999 7:25:49 EDT From: "Mattson-EQE, Mark" To: lakes-l@badger.state.wi.us Subject: Total Phosphorus storage replies "For Use in Intra-Agency Policy Deliberations" Here is a summary of replies to my question on acidification and freezing of total P samples. There were many requests to post replies to the list. In summary no one seems to have any published data to either support or object to both acidifiying and freezing samples. Most people seemed to think both would be ok and that is my feeling as well. One potential problem with acidifying that we have noted is a higher limit of detection. The best procedure is probably the one provided by Milt Ostrofsky, (see Below) who suggests collecting right in the tube used for digestion, and presumably storing right on the shelf with no further additions. The digestion will take care of any sorbtion. The only drawback would seem to be breaking the glass tubes in the field. For us, as it turns out, there was a reorganization of the sampling plan and now all samples can be done without storage. Replies: Mark: I don't have a firm answer to your question, but I am interested in hearing what others have to say. I'd appreciate it if you forward the responses to me or post them on-line. My personal feelings are that (1) there is no scientific basis (i.e. no experimental data) for the 28-day limitation in Std. Methods other than some vague feeling that samples should be analyzed in a "timely" fashion, and (2) acidifying and refrigerating may be slightly better than freezing because of the possibility of precipitating some P into forms that may be difficult to get back into solution (or reasonably uniform suspension) upon thawing. If a sample is acidified and refrigerated, there shouldn't be any biological activity (growth on bottle walls) aand there shouldn't be any chemical precipitation of soluble forms. Again, these thoughts are not based on experimental data, and I'd be interested in hearing what others have to say. Regards, Pat Patrick L. Brezonik ---------------------------- We once tried splitting samples with a few of our volunteers. Both samples were acidified, the original was analyzed within 28 days and the split put in the volunteer's freezer where it sat until we met with them again 4 months later. We did not get good standard deviations between the splits. (Unfortunately, the experiment never got written up and the person who did it is gone so I can't give you the numbers.) If you have the time, you might consider testing this out for yourself. I've been meaning to revisit this issue one day. Could you let me know (or post to Lakes-l) any useful comments you get? Dave Hallock ----------------- >Mark; > >About 20 years ago I was working in a remote area and I needed to store >water samples taken for total phosphorus analysis until I could return to a >laboratory. It seemed to me that most of the concern about holding samples >was P sorption onto the container wall, and subsequent loss from the stored >water. Here is how I solved that problem. The procedure worked so well >that I use it to this day, even though I am usually able to begin analysis >within hours of sampling. > >I collect samples in 25 x 200 mm screw top culture tubes (Fisher). I throw >away the bakelite caps that come with the tubes and use 24mm solid >polypropylene caps (also Fisher). I calibrate tubes in advance with a ring >of masking tape at 50 mL. Tubes can be filled directly from streams or >lake surfaces, or from a kemmerer sampling bottle. A couple of flicks of >the wrist will adjust the volume to the 50 mL mark at the top of the tape. >Once the samples are taken and capped, no further precaution is necessary >for indefinate storage because P is analyzed in the tubes. > >When I get back to the lab, I add potassium persulfate with a calibrated >scoop (~0.4 g). Hach makes a variety of scoops although I had my own >machined in our shop. Persulfated samples are recapped tightly, then >autoclaved to convert all P species to PO4. Again, samples may be stored >indefinately after autoclaving. > >To analyze, I add 5 mL of mixed reagent (Strickland and Parsons) directly >to the tube, invert to mix, then read color at 885 nm after 60 min. Any P >that sorbs to the container wall will be oxidized by the persulfate, and >will react with the mixed reagent. Sample handling is minimized. There >are no transfers from container to container. Replicate samples (in their >own tubes) show very low variance. > >The procedure is given in Ostrofsky and Rigler (1987, CJFAS 44:775-781). I >used the tubes first in Labrador, then brought the technique with me to >Rigler's lab for work around Yellowknife, NWT. Most folks working in the >lab at the time have used it with good result (Rob Peters, Ellie Prepas, >and their subsequent students). > >The only limitation is that if you are analyzing several parameters, you >will need a separate, designated set of tube for P only, and a set of other >containers for the other parameters. But, the P storage problem is solved. > >Good luck, > >Milt Ostrofsky >Biology Dept. >Allegheny College >Meadville, PA, 16335 >mostrofs@alleg.edu --------------- Mark - Our experience suggests that acidifying (< pH 2, with H2SO4) and refrigerating gives the longest stability. We have seen good stability for at least 3 months, but have not tested a year. Sooner is always better. On the other hand, we have observed substantial loss with freezing - perhaps accelerating adsorption to container walls? Good luck, John Wehr ----------- Hi Mark - I love to see someone else with a research background struggling through this sort of morass. I am a true believer in not adding anything to a sample unless absolutely necessary. In particular for Total-P, the act of preservation seems to be to prevent wall growth of a bioslime that could tie up some of the total when you decant. Freezing prevents this as well as poisoning organisms. For some assays, such as nitrate, if you are using a hydrazine method and the water has a relatively high sulfate content, freezing will precipitate salt (probably gypsum and some carbonate) that won't necessarily go back into solution when thawed without bringing the pH down (~2) . We had to refilter even filtered samples that were frozen from lake Mead (EC ~` 800-900 umhos/cm) to avoid particulate interferences with our nitrate assay. We did a lot of tests re phosphate at low levels (TP<~`10 ug/L, SRP : ~0 to 2) So I say FREEZE 'em. Frankly I can't see how 10 years in storage would matter since there's no gas phase to lose. However, if we don't run them within 1 - 2 months, chances are we'll lose the samples themselves - even worse than getting high LOD data. "Richard Axler" ------------------------ In my experience, total phosphorus is a fairly forgiving parameter. Freezing for multiple months (we used to do that at Oneida Lake to push the work load toward the fall) or acidification to pH<2 (typical for storage at labs in MA for up to the 28 day limit) are reasonable. Loss issues relate mainly to bacteria uptake and attachment to container walls, so either freezing or acidification are reasonable alternatives (although nothing beats immediate analysis, as you can well imagine). I have never heard of both approaches being used at once, but there is no reason I know of that this would be a problem for total P. The time limits for each are somewhat arbitrary as far as I can tell. It a whole different story for other forms of P, but that's not what you were asking for. -Ken Wagner With Regards, Dr. Mark D. Mattson Massachusetts Dept. Environmental Protection Division of Watershed Management 627 Main St. 2nd Floor Worcester, MA 01608 email mark.mattson@state.ma.us phone (508) 767-2868 fax (508) 791-4131