I think ICP-MS

Since my sample is a liquid ( waste water) i was considering one of the chemical reduction techniques of CVAAS or CVAFS. I was wondering, which one of the two is better? Are there alternative methods?

Techiques more common for mercuy measured are Cold Vapor Atomic Absorption Spectroscopy (CVAAS) or Cold Vapor Atomic Fluorescence Spectroscopy (CVAFS). Both of these techniques are relatively straightforward to use and can accomplish the analytical requirements of detection limits in the low ppt range. The LOD with CVASF can be < 0.1 picograms of mercury. According the oficial normative to evaluation the exposure of mercury in human, this technique is adequate.

@ Hector, thank you so much for this insight

Hi, Jeremiah,

CVAFS or CVAAS sound like they will handle your needs, as Hector mentioned, is there a reason that ICP-MS would not work? We use that for monitoring waste-water for Hg as well and have also gotten down to the ppt level. The only real consideration is the inclusion of gold to stabilize it and help with washout times, but it sounds otherwise like a straight injection with ICP-MS.

Thanks!

Easy and cheap method is CV-AAS, than ICP-MS

The appropriate analytical method will be dictated by the complexity of your sample matrix. Each analytical system will have a subset of benefits and imitations. Halogens, hydrocarbons, and elevated concentrations of transition metals can interfere with the CVAFS or CVAAS methods depending on the molar ratio of reductant (stannous chloride) to chemically active compounds. Both referenced methods MAY be sufficient but dilution experiments must be applied to ensure the reaction to generate elemental mercury is not kinetically hindered. If you have an ICP-MS then pursuing FI-CV-ICP-MS would be most cost effective for you and it has much lower absolute detection limits than AAS or AFS. Great care must also be used when using inferior gold traps so proper quality control would necessitate integration of QC parameters or each trap during the amalgamation process if using CV-AAS and CVAFS. Historically, the QC for these approaches is less than optimal for monitoring trap failure. Feel free to check out my publication comparing the absolute detection limits for detectors.

@ Russell please forward the publication

@ James and Bedigama Thanks a lot

I have uploaded the article. If you have trouble seeing it on my profile please advise.

I recently came across the determination of Hg in water samples using sTRACE Gold electrode? Does anyone know how it works?

@ Hector, @ James, @ Russell , @ Bedigama and other colleagues, is there a better way to digest the waste water before doing the analysis?

I used ICP-MS for mercury determination in water, sediment and oysters. it is very sensitive

Please send literature if you do not mind!

The method of digestion depends on your data objectives. Preservation with bromine monochloride increases the relation to publications and many regulatory approaches but the performance is operationally defined. If you want to know the absolute mercury concentration a microwave or closed vessel bomb digestion would be more appropriate. Note, I did not present acidification with HNO3 as that may not have the oxidative capacity to stabilize inorganic mercury. Remember to use the appropriate collection vessels as well.

@Jeremiah,

For digestion, waste water, I followed following procedure

Take 45 mL sample add 5 mL conc. HNO3 and run microwave digestion progarm. You can tale microwave program from CEM web.

Thank you @ Bedigama

You can use Flame Atomic Absorption Spectrophotometer with a MVU(Hg vapor unit).

Atomic absorption spectrometry of cold vapors or

Thank you @ Asieba and @ Marina

I use a generator hydrides where the sample stabilized with potassium permanganate, is reacted with sodium borohydride and hydrochloric acid and then measured in AAS.

I used icp-ms for mercury determination in water and oysters

Iuliana, ICP-MS is an excellent tool, but too expensive for my availability .. with hydride generator i can still get good results without spending too much

Icp-ms is expensive indeed , but it's very sensitive. You can get your results in ppt or ppb at least. Good luck :)

I agree, for example ICP is indispensable when it comes to assess the suspected presence of contaminants in drinking water .. However, if the analysis is for waste water, as in this case, a good AAS is appropriate.

Thank you @ Sergio, @ Luliana and @ Najib i appreciate your contributions

Cold vapor is an excellent, inexpensive method. If you have a good UV source you don't need the full AAS system, as the digestion will eliminate the vast majority of your interferences present in WW.

As my experience cold vapour AAS is good and enough to LOD for waster water analysis.

Thanks @ Krause and @ Jinadasa

I think ICP-MS

mercury is a very volatile metal .. the best method of determination is still that of the reduction of mercury with NaBH4 using a hydride generator that can be combined with different types of atomic absorption

The USEPA developed the 'cold vapour AAS' method for water back in the 1970's. As I recall the required 'method detection limit (MDL)' is 0.2 ppb (I think).

Cold vapor AA is easily done with minimal worries about matrix effects. Very high organics can sometimes interfere. Can be used with solid and liquid samples. Training requirements are minimal. The only downside is that a hood is required as you are working with aqua regia.

You can use CV-AAS or HG-ICP-OES because ICP-MS more expensive instrument

I see a lot of suggestions for ICP-MS. However, I worked as a hazardous waste water chemist for many years and I used a Hydra AF, (The Hydra AF is a fully automated, cold vapor atomic fluorescence analyzer ) for all of my Hg analysis. I found the recovery to be much more consistent and stable with the Hydra AF. However, ICP-MS is a widely used instrument, and most likely really accessible, however do take into account, the organic makeup of your samples the will cause interference If abundant enough.

EPA Method 245.1: Determination of Mercury in Water by Cold Vapor Atomic Absorption Spectrometry

Mercury in waste water can be determined by Flameless Atomic Absorption Spectroscopy. It is a cold vapour technique with very good sensitivity. The cold vapour unit can be attached to AAS and the analysis can be done easily.

The toxicity of Hg does depend on its chemical state. This can be probed by X-ray spectroscopy. The detection limit is much higher but it gives information on the ligand environment around Hg. See for example: Environmental Science & Technology 50, 10721–10729 and other papers by the authors.

It really depends on what reporting limit you are looking for and the sample matrix you are working with. I specialize in environmental analysis of trace metals in waste water using multiple analytical methods. Each type of instrumentation has it's pros and cons based on matrix, volume (in mL and in number of samples requiring analysis), laboratory capabilities, and required reporting limit.

In general, I would also recommend EPA method 245.1 or equivalent (SM-7470?, is 7470 an EPA method as well?) using cold vapor atomic absorption. In practice, my lab reports 245.1 to a reporting limit of 0.1 ug/L. The cold vapor mercury analyzers are crazy stable and don't require years of technical skill building like an ICP-MS does. I am generally comfortable setting a new analyst loose with this method after 2-3 weeks of training. The method stabilizes the volatility of mercury by oxidizing it to the stable water soluble for of Hg3+. But, you probably don't have a CVAA analyzer sitting around.

If you are looking for the lowest reporting limit possible, EPA method 1631E (Determination of Mercury using purge and trap atomic fluorescence) is report-able to 0.5 ng/L. Which is crazy low. This method also stabilizes mercury through oxidation. However, the method really doesn't work well for samples with solids or reducing agents. You also need access to a clean room and a touch more technical skill in sample/standard handling to eliminate cross contamination. You also probably don't have this instrument laying around either.

All said and done, you most likely have access to an ICP-MS. It is a solid methodology that is a rock start in some ways and has some severe limitations in others. I don't analyze mercury by ICP-MS because we use the other mercury methods. What I do know is that mercury is not sable at low concentrations for very long, and must be stabilized using hydrochloric acid. Mercury is also real volatile and is readly lost using open cup digestion methods. Mercury is a big ol' fat sticky element that exhibits high memory effects in the sample introduction system (carry over), and requires longer than usual rinse times between samples. This can be mitigated some by adding just a touch of gold to your rinse water. The gold complexes with the mercury in your sample introduction system and pulls the mercury out faster. The calibration standards should be kept to the lowest possible concentration (In practice, we run the CVAAa from 0.2 ug/L to 5.0 ug/L and rarely have a sample higher than 5.0 ug/L.). Mercury is only about 8% ionized in an argon plasma, which can lead to limited sensitivity.