Milestone ultraWAVE 3 - Page 58

Milestone Srl MA245-003 – ultraWAVE 3 – User Manual
56
related to the ability of HNO
3
to dissolve most metals to form soluble nitrates. Such oxidant
action can be further enhanced by the addition of other acids or H
2
O
2
.
H
2
SO
4
Concentrated sulfuric acid (98%) can carbonize organic substances, its boiling temperature
is 338 °C. It is a strong dehydrating agent and commonly used in combination with HNO
3
or H
2
O
2
.
HClO
4
Perchloric acid presents an oxidant power directly related to its concentration and reaction
temperature. It presents a strongly trend to react violently with organic matter under
heating, but its mixture with HNO
3
decreases the reaction rate. HClO
4
is thermally
decomposed at 245 °C, which releases higher amounts of gaseous by-products, leading to
high excess of pressure.
H
2
O
2
Hydrogen peroxide is normally used in concentrations ranging from 30 to 50%. Higher
concentration can react explosively with some organic compounds. It is frequently used in
combination with HNO
3
and H
2
SO
4
in wet digestions.
HCl
Hydrochloric acid is a non-oxidizing agent that exhibits weak reducing properties. HCl
readily dissolves many metal carbonates, peroxides, and alkali hydroxides. Despite a major
part of metals form soluble chlorides, some elements can form insoluble compounds as
AgCl, TiCl and PbCl
2
. While HCl reacts with most metals, it is normally combined with HNO
3
to form Aqua regia, which is able to dissolve even noble metals.
HF
Hydrofluoric acid presents a strong complexing nature. It is most commonly used for
inorganic matrices because it is one of the few acids that can dissolve silicates. Glass or
quartz reactors can not be used for sample digestion. In some cases its removal before
analysis is mandatory in order to prevent equipment damages. In this case, usually, boric
acid is often added to neutralize active HF, being necessary to filter the sample solution at
the end of the digestion. Its use prevents the formation of sparingly soluble products of
groups 4, 5, 13 and 14 of the periodic table, increasing the solubility and stability of Si, Sn,
Ti, Zr, Hf, Nb, Ta, Pa, etc.
Aqua
Regia
A mixture of concentrated HCl and concentrated HNO3 (volumes 3:1) is commonly called
as “aqua regia”. This reagent has an additional oxidizing effect by formation of NOCl with
a subsequent formation of nascent chlorine. The main feature of this mixture is the ability
for dissolution of noble metals, such as gold, silver, palladium and so on.
Milestone suggests following the above guidelines or the Milestone Application
Book.
ultraWAVE 3 can be used only with methods / procedures agreed with Milestone
Application Specialist.