Groundwater Arsenic Collection Containers and Preservation for ICP-MS Analysis

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I am working on my master's of water resources science research in hydrogeology and will be collecting samples from wells (agricultural, livestock, and residential) to analyze for TOTAL arsenic.  

I have conducted a thorough review of the literature and consulted two of the lab managers I will be working with, but I still do not have a clear answer to the proper collection procedures.  I will initially be screening the samples with a quick test kit and a colorimeter, then collect samples (60ml should be sufficient) to use for analysis in ICP-MS.  

My question is, is HDPE or polypropylene used to collect the samples?  Since I will only be preserving the samples for less than a week, does it matter which one I use?  Additionally, multiple methods refer to solely nitric acid as a rinse and preservation (ph

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8 Answers

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  2. Polypropylene bottles

    Hi there Lauren,

    Polypropylene bottles are suitable containers for samples collections in my opinion.

  4. I suggest using US EPA methods for a reference SW-846

    Lauren,

    Probably your easiest place to learn about analytical and preservation techniques is the on-line references to EPA's Solid Waste Method (includes water). http://www.epa.gov/wastes/hazard/testmethods/sw846/online/index.htm.

    Your assessment on containers is correct.  Almost any plastic is going to be fine.  I generally use HDPE because of regulatory compliance and shipping durability issues but have had no issues analytically with polypropylene.  Poly carbonate centrifuge tubes also work well, and are very inexpensive.  Perfect for research.

    For trace metals analysis on ICP-MS I suggest that you only use nitric acid, and make sure its trace metal grade or distill your own.  That applies for container washing too.  Don't use HCl for preservation or container washing using ICP-MS.  There are some papers out there that use 6M HCl to preserve arsenic species, but they don't use ICP-MS, and you are looking at total arsenic.  Chloride is a problem for arsenic analysis on ICP-MS but a skilled operator is usually able to get good results (ppb As), even with groundwater chloride as high as 100 ppm. 

    Cheers and good luck!

    Greg

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  5. Determination of As in biological samples by ICP-MS is difficult for two reasons: the formation of the molecular ion 40Ar35Cl, which overlaps with monoisotopic As at a mass-to-charge ratio (m/z) of 75 (causing spectral interference), and signal enhancement due to organic matrix (nonspectral interference). Available procedures were examined, including the application of different correction procedures using 40Ar37Cl and 16O35Cl molecular-ion formation Dr Abdelsalam Asweisi

  6. I agree with Walter and best way is to select analysis method and sampling together because one can interfere with other. Carefull sampling leaves you to a good conclusion avoiding time wasting because of mistake. Be carefull.

  7. I'd go with whatever the lab manager you're running the samples with says with respect to bottles and preservatives. Issues with interference will depend in part on your target reporting limits - at very low analytical limits interference is usually a bigger problem. Here's a link to a poster presentation I found discussing interference between Cl and As at low levels: http://www.cala.ca/nw_oct11_pt_challenge_moe_poster.pdf. Sample collection procedures are something to consider carefully. By total arsenic I assume you mean not filtered for dissolved fraction (as opposed to speciating for the valence state). If you are screening with field test kits, I assume you are not going for ultra-low detection limits so conventional sample collection with latex or nitrile gloves etc. should be fine. USEPA has developed procedures for low-level metals sampling, mostly related to aquatic-life standards and especially for mercury. You could look those up if you want to make sure your sampling protocol is appropriate. Finally, don't forget your quality assurance/quality control (QA/QC) samples. You'll want some duplicates and field blanks to convince yourself what you're measuring is reproducible and real. Also consider equipment rinse blanks for any re-usable equipment that has been decontaminated between samples. For laboratory QA/QC, you'll need some fraction of samples collected at double or triple volume to do matrix spike/matrix spike duplicates. Look up the USEPA Contract Laboratory Program procedures, and their SW-846 analytical protocols for more background.

  8. Hi Lauren, I would be surprised if the choice of bottle material had any impact on your results. I would personally take the cheapest one. You could always do a quick test with 2 bottles of each type, store them with an arsenic solution and analyse the the solution after a week. Regarding the acid, I would chose either HCl or nitric acid. Again, shouldn't have an impact on the results. Kind regards, Jorgen