5 replies to this topic

[Jaymz]

Hi

i was wondering if someone could help me with some information regarding chlorates. I'm currently performing some tests on chlorates, and i'm encountering some problems to detect it. I'm trying to extract it from aerosol dust samples. I already have established an accurate method using visible spectrophotometry to detect the concentration of chlorate in standard solutions. However i seem to be unable to detect any in dust. Anyone knows if dust actually modifies the chlorate in some way?! or tends to adsorb it rather strongly?! I'm simply trying to extract chlorates from the dust with water and heating. Then finally i centrifuge,and test the supernate for chlorates using my validated method. I know the extraction process is rather simple, however chlorates are highly soluble in water, so i assumed this process should have been enough.

Any help would be greatly appreciated.

[BrightStar]

Hi and welcome to the forum.

It seems unlikely that the dust would physically adsorb the chlorates to the extent that they couldn't be washed out in solution. Is it possible that you're inadvertently reducing the chlorates by heating in solution with other contaminants in the dust?

There seems to be quite a bit of literature on the analysis of pollutants in dust that might give some experimental tips:

Pollutants in house dust as indicators of indoor contamination

[Jaymz]

Thx glad to be part of it. I did consider that the chlorates are actually being modified in some way. Chlorates are strong oxidizers so it is highly possible that they're interacting with some form of chemical species in the dust. I did do quite a bit of background reading, however i couldn't find anything directly linked to chlorates in dust! Chlorates are sensitive to the presence of some metals as far as i know, however heating to 100^oC shouldn't induce a reaction. Thx for the link, i will read it once i get hold of the full article. I'm currently sick, so i haven't been able to perfrom further tests. I was thinking of trying some form of acid extraction. However i'm worrying that this will extract other chemical species which aren't soluble in water, which will make matters worse.

The funny thing is that my collegue is using a very similar method for perchlorates and it's working fine.

Once again any ideas to what the problem might be would be greatly appreciated as i'm kind of lost

[Arthur Brown]

If our test method is as good as you say you have proved, then is it possible that the test sample has less chlorate than your method's detection threshold.

Take the contents of a typical vacuum cleaner bag (or no bag!) then weigh out samples. To the samples add a weak solution of chlorate quantitatively then do your test method. "Typical dust" with quantitatively certain chlorate should test your analytical skills and the method used.
Once you have a proven quantitatively detectable dust as reference then you can look for method errors possibly caused by non-typical dust and redox in the vaguely damp powder.

Try using an air pump to pull dusty air through a GFA or GFB filter circle then after a known amount of air has passed analyse the dry circle.

Dust is always going to be variable and usually very slight in the contaminants present so minimum dilutions are called for to minimise below threshold detection failures. House dust is a big % dead skin! Workshop dust can be oil bound or dry metal powder or metal oxides No one dust is typical No one reaction set is uniquely correct.

[Jaymz]

My first reaction to getting no readings at all for chlorates was that the chlorate levels in the dust were very low. However i performed the following test to check on this:

1) spiked the dust sample with a 10ppm standard solution (of chlorate obviously) - this is well within my detection limits
2) evaporated the dust sample to dryness (gentle heating)
3) then i performed the usual 'extraction' with 5mL of deionized water and vigorous shaking
4) then i perform my usual test for chlorates and somehow all the chlorates have vanished hehe

So the problem seems to be in the extraction method, which is quite crude in my opinion and should definitely be improved. The question is how? Because the best solvent for chlorates seems to be water, and with acid too many species will dissolve. However simply adding water seems to be inadequate

Btw. I'm working on aerial dustfall, so i'm collecting dust from the rooftops of buildings over a 30 day period using an appropriate sampling device. So it's not purely an aerosol study as precipiataion (just rain, no snow or ice or anything) was quite frequent during my sampling period

[Arthur Brown]

OK so "dust" may be reacting with the chlorate. Take some "Dust" spike it with say 100ppm chlorate solution then divide it and do extractions after 0, 1, 2 etc minutes and hours. The sample before extraction had 100ppm so if there is a reaction the rate should leave a decaying chlorate content which should show up.

Can you make an enlightened guess as to the nature of the dust in your experimental area?