Dear trieuvan,
Thật sự thì mình không biết trên thế giới xảy ra bao nhiêu vụ tai nạn AAS, nhưng mình chỉ biết Flashbacks trong AAS là hiện tượng như sau, không biết đúng không nhỉ?:
Flashbacks:
If the flowrate of gases through the burner is reduced below the rate of flame
propogation, the flame can flash back into the spray chamber, and a small
explosion will result. A red hot particle falling through the burner into the spray
chamber could produce a similar effect.
Should a flashback occur, the fuel gas must be turned off as quickly as possible.
The spray chamber must be removed, dismantled and examined for damage. It is
probable that all need to be replaced.
Dear all,
Bên dưới là những chú ý đối với người sử dụng khi dùng AAS các bạn tham khảo nhé:
Safety Precautions:
1 Some of the chemicals used in Atomic Absorption Spectrometry are corrosive,
and/or flammable and samples may be radioactive, toxic or potentially
infective. Care should be taken to follow normal laboratory procedures for
handling chemicals.
2 The UV radiation from a deuterium lamp and some hollow cathode lamps can
be harmful to the skin and eyes. Always view the lamp through protective
glasses/goggles that will absorb the UV radiation and avoid looking directly at
the deuterium discharge. Do not expose the skin to direct or reflected UV
radiation.
3 Fumes produced by Atomic Absorption Spectrometry can be toxic and highly
dangerous. Ensure, therefore, that the fume extraction equipment is switched
on and operating before using the spectrometer. Do not use a fume cupboard.
4 Exhaust gases from the burner or fumes from the Furnace Head must be
extracted through stainless steel ducting fitted with a hood and fan.
5 The intensity of the light emitted by a heated graphite cuvette can harm the
eyes. Although the operator is protected from direct glare, radiation escapes
through the side windows and the gas exit hole in the Furnace Head cover.
Do not look down over the Furnace Head Cover; in addition to harmful
radiation, noxious gases may be present which could be inhaled.
6 Allow the Furnace Head to cool before opening the hinged cover and touching
internal components.
-
It is strongly recommended that flashback arrestors are fitted at the regulator
outlets of acetylene and hydrogen cylinders.
-
It is essential that the gas lines, fittings, etc., are free from contamination by oil
or grease. Otherwise gas flow rates could be reduced or the cuvette
contaminated and measurement precision could be impaired.
-
It has been shown that aspiration of perchloric acid and metal perchlorates
into a nitrous oxide/acetylene flame in AAS can significantly increase the risk
of an explosion or flashback into the spray chamber.
Consequently, we do not recommend the use of perchloric acid in sample
preparation for nitrous oxide/acetylene flame determinations unless it is
absolutely necessary. If perchloric acid must be used, then its final
concentration in the sample solution must be reduced to the minimum level
that can be tolerated before aspiration is attempted. An air/acetylene flame
should be used wherever practical and care must be taken to minimise the
risk by following these accepted safety precautions:
(a) Make sure that burners are kept clean at all times, inside and out, and do
not allow carbon residues to build up on the burner slot.
(b) Aspirate perchloric acid solutions for the shortest time possible and make
sure that sufficient distilled water is used to flush the spray chamber and
burner between each sample and at the end of the analysis.
(c) Never allow the spray chamber/burner system to run dry because dry
perchlorate salts can explode spontaneously with heating.
(d) Perchloric acid solutions should never be allowed to come into contact
with organic solvents during aspiration. Organic solvent extractions from
solutions involving perchloric acid should be avoided if at all possible.
If organic solvents have previously been aspirated through the spray
chamber, the organic residues should be completely removed from the
spray chamber and drain system before attempting to aspirate perchloric
acid solutions. The spray chamber must be thoroughly dry of all traces of
organic solvents before aspiration of the acid solution commences.
(e) It is dangerous to allow acetone, carried over with the acetylene from the
gas cylinder, to come into contact with perchloric acid solutions. It is
imperative, therefore, that all safety recommendations regarding cylinder
storage and replacement are followed explicitly. Do not store cylinders on
their sides and never use a cylinder showing less than 6.9 bar pressure on the gauge.
(f) Always ensure that the protective door and chimney enclosing the burner
and spray chamber are in place and firmly latched.
-
Non-alloyed copper or silver must NOT be used in the construction of any
acetylene supply systems as they can combine with acetylene to form a
highly explosive compound.
-
Normal brass fittings contain less than 50% copper and may be used. It is
essential to check the copper content of any fitting prior to use with acetylene.
-
Certain elements in group 1a (Ag, Au and Cu) can combine with acetylene to
form unstable acetylides which considerably increased the risk of an
explosion or flashback in the spray chamber.
When analysing solutions containing these elements the final concentration in
the sample solutions must be reduced to the minimum level that can be
tolerated before aspiration. Care must be taken to mimimise the risk by
following these accepted safety precautions:
(a) Make sure that the burner and spray chamber are kept clean at all times,
inside and out, and do not allow residues to build up on the burner slot.
(b) After each sample, flush the spray chamber and burner by aspirating with
de-ionised water for 60 seconds.
(c) Never allow the spray chamber/burner system to run dry because dry
acetylides of copper, silver and gold can explode spontaneously.
(d) At the end of each analytical session thoroughly flush the spray chamber/
burner system by aspirating de-ionised water for 15 minutes.
13.It is strongly recommended that flashback arrestors are fitted at the regulator
outlets of acetylene cylinders.
-
When cleaning the surface of the burner care must be taken
to avoid hot particles entering the spray chamber, as they
may cause a flashback.
-
Cleaning the surface of the burner whilst in operation must
never be attempted when using a nitrous oxide based flame.
16.When cleaning the surface of the burner care must be taken
to avoid hot particles entering the spray chamber, as they
may cause a flashback
Mong được trao đổi để học hỏi thêm.
Thân chào.
PS: ah, trieuvan oi, nếu với số lượng mẫu lớn đo As, Hg thì mình chỉ khuyên là nên dùng những thiết bị chuyên dụng khác như IC hay IC-MS chẳng hạng, và không nên dùng bộ hóa hơi còn tại sao thì nếu bạn dùng nhiều thì bạn sẽ biết mà, mình chỉ khuyên vậy thôi, 