I want to complete nutrient analyses on the filtrate from dry cell weight analysis. Thus I will be using a 0.45 micron membrane filter. However, it occurs to me that standard filters used to filter samples for N, P & COD are GF/Cs. Thus due to the larger pore size of the GF/C if I used membrane filters instead of GF/Cs for nutrient analyses then it may not be representative as more nutrients may be removed?
If I understood well, you want to analyse the dry mass on the filter, right?
If it is the case, I assume it would be better to use 0.45 micron membrane filter, otherwise you might loose a significant No. of cells.
Hi Tim. You can use filtrate from 0.45 um filters. Note that smallest algal cell is around 10 um. Nonoplankton is described as algae passing through 50 um filter opening. Any filter with opening less than 10 um should be OK.
Just pay attention on cyanobacterial cells. I don't know if you included them, or need them in your analyses, but every waste water is followed by their presence. Cyanobacterial cells range in size from 0.5-1 μm to 40 μm in diameter.
Good luck!
I guess you will have to make your own observations, Although I feel that GF/C filters are perfectly adequate for most purposes.. For microalgae cultures and/or nutrient analysis in natural samples I have always (less some cruises back in the 1960s and early 70s) used GF/C filters. In my personal experience and from Coulter coounter counts, I have never found differences between the particle numbers present in the GF/C or Whatman 0.45 μm filtrates.
you might find of interest the following titles (all available on the net)
Hickel, W. 1984. Seston retention by Whatman GF/C glass-fiber filters. MEPS 16: 185-191.http://www.int-res.com/articles/meps/16/m016p185.pdf
Sheldon 1972. Size separation of marine seston by membrane and glass-fiber filters. Limnol Oceanogr. 17(3), 494-498 http://www.aslo.org/lo/toc/vol_17/issue_3/0494.pdf
However, in the following it was found that between 22 to 38 % of the total bacterial biomass (>0.8 μm) . was contained in the filtrate
Lee S et al. 1995. Imperfect retention of natural bacterioplankton cells by glass fiber filters. MEPS 119: 285-290, http://www.int-res.com/articles/meps/119/m119p285.pdf
If I understand correctly your question, you also feel that there might be some retention of nutrients by the filter. To all practical purposes, given the volumes of water filtered, I feel that this is groundless.
This should be fine. Typically when I filter I use either GF/C's or GF/F's (0.7 micron) depending on the algal size for dry cell weights. I have also used 0.2 micron filters for nutrient analysis. I have never noticed any difference except that dense cultures and smaller cells take significantly longer with smaller pore size.
Hi Tim, you're right filtering the samples alters the original amount of dissolved inorganic forms of nitrogen. If your interest is addressed to the amount of nutrients independently of the living portion, the solution could be very simple: collect additional water sample to determine nitrogen only. Best.
I think it also depends on the method you use to determine nitrogen and phosphorus. Some devices (e.g. Dionex) are very sensitive and require that the sample is passed through a finer filter (0,45 µm), while when you use the spectrophotometer engaged the FIA system may be used filter of 0.7 µm (GF/F) and if you use only spectrophotometer even 1.2 µm (GF-C)may be used. You should also consider that if the filter used is too thin you will have difficulty in filtering all the material, which may compromise the initial volume.
I study macroalgal communities from continental water and according to the chemicals that make the analysis of nutrients and metals will be necessary to make an acid digestion before analyze the ions present in the sample. If this is your case - check the nitrogen and phosphorus in the algae which are the sample, you should check that equipment analysis will be performed and then check if there is a limitation to the filter being used.
I think when you filter your sample you will introduce an error , but if the concentration of nitrogen and Phosphorus (especially in waste water) are high and also the turbidity, the filtration help to remove particles; but in this cas , you will loose phosphorus adsorbed in the particlesand experimental errors ; in my opinion it is better to have a large volume of water and after sedimentation take the upper part for analysis.
The is not an ideal method, the important thing is to do the same for all samples in a manner that you can compare your results.
Good luck
GF/Cs or GF/Fs filters are probably the best compromise, depending on your species size. Some membrane filters leach ammonium, nitrate, and/or phosphate, depending on their composition and the presence of "wetting agents" that help filtration but are actually detergents. Filtering on GF filters will overestimate ammonium at low ambient concentrations and undersetimate ammonium at high ambient concentrations. For dissolved organic carbon, use GF filters ashed at 450°C for a few hours to remove any organic carbon.
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