Different chemical methods to dissolve a sample completely

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Sample dissolution

2. One of the most important steps when
carrying out any type of analysis is the
Sample Preparation
Introduction
• Time consuming • Complexity

3. Timing in the analytical processes
Sampling
Sample preparation
Analysis
Data processing
61%

4. • Homogenisation
• Reduction of the size particles (crushing)
• Homogenisation
• Drying
• Removal of the moisture in the sample
• Milling
• Finishing of the sample for analysis
(200μm / 100μm/ <100μm)
Sample preparation

5. Sample dissolution
To dissolve a sample completely, each insoluble component
must be converted into a soluble form.
Dissolution
Insoluble
sample
Soluble
sample
Solvent
Solvent
Chemical digestion

6. • Decomposition of solids involves a series of reactions,
which transform the original substance and produce
quantitatively new phases.
• The decomposition usually results in the formation of
solutions or melts.
• Several different chemical methods may need to be
employed to dissolve a sample completely.
Chemical digestion

7. Techniques for sample dissolution
• Acid Digestion
• Microwave Digestion
• Fusion Digestion
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8. Acid digestion
 Different acids are used either alone or in combination to
decompose specific compounds.
 The digestion can be particularly challenging and many
inorganic matrices such as oxides, silicates, nitrides, carbides,
and borides can be difficult to dissolve completely.
 Many decomposition procedures use acid digestion to
dissolve the major portion of the sample. The remaining
residue may require additional treatment (by wet ashing or
fusion), depending on.

9. Microwave digestion
 It is considered faster, cleaner, more reproducible, and more
accurate than hot-plate digestion
 High pressures on the order of 10 MPa can be needed.
 However, microwave dissolution requires the aqueous acid
media to get the sample digestion.

10. Fusion digestion
Fusionis a general name for all kinds of chemical attacks on
solid samples to transform them into compounds that are
easily transformed into a solution.
These compounds are an intermediate step between the
original sample and the solution that is used later in an
analytical process.
J. P. Willis, Glass beads by borate fusion in: XRF Sample preparation, 2010, PANalytical B.V., The Netherlands.

11. Fusion digestion
 Acid digestion requires numerous manipulations of
concentrated acids (HClO4 is explosive and HF is extremely
dangerous for human health).
 The traditional methods or the sample digestion are tedious
and time-demanding.
 A fusion with an alkali flux (lithium borate, hydroxide, sodium
peroxide and carbonate mixture) is well known to be effective
for the decomposition of the refractory minerals and alloys.
 Sodium peroxide is undoubtedly the most effective alkaline
fusion agent.

12. Fusion: oxidation
Elements easily oxidized
by solids
Moderately hard to
oxidize by solids
Compounds hard to
oxidize by solids
Fe, Cu
Cr, Mn, Pb, Mg, Co, Zr, Cd,
sulphides, (FeS, PbS, ZnS…)
slags
Nb, Si, Zn, W, Ti, Al, Ni,
PGMs, ferroalloys (FeMn,
FeTi, FeNi…), alloys,
carbides
Weak oxidizers Medium oxidizers
Strong
oxidizers
NH4NO3, NaNO3, KNO3, carbonates
(Li2CO3, K2CO3…)
LiNO3, Sr(NO3)2, Li2O2 LiOH, Na2O2
*Claisse, F.; Blanchette, J.S. Physics and chemistry of borate fusion, 3th Edition,
Ed. Bouchard, B.; Boivin, M.; LeMay, P.E. Katanax Inc. Québec QC Canada.

13. ICP Analysis
Fusion: dissolution, sample preparation
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 Oxidation
 Fusion
 Homogenization
Wet process

14. Fusion procedure
 The mixture is heated to a temperature above the melting
point of the salt and sample is then allowed to react in the
molten mixture.
 For a fusion to be successful, the sample must contain
chemically bound oxygen as in oxides, carbonates, and
silicates.
 Samples that contain no chemically bound oxygen, such as
sulfides, metals, and organics, must be oxidized before the
fusion process.
 When the reaction is completed, the fused sample is then
dissolved, and the analysis is continued.

15. Metal(sample) + Na2O2 metal oxide + Na2O
Mix
Sample
+ Acid media
Na2O2
Δ 500ᵒC
Zr crucible
Fusion
process
Na2O2 Fusion

16. Sodium peroxide fusion:
 Is quick
 Allows total sample dissolution
 Eliminates dangerous acids
 Demonstrates good accuracy, precision and recovery.
, s
Controlled temperature
ramp to avoid
explosive
reaction
Start shaking
Peroxide fusion and homogenization
Cooling process
Na2O2 Fusion

17. Na2O2 Fusion: ICP-OES analysis of FeCr alloys
Chady, S. Application note, 2011. ICP-OES Analysis of FeCr Alloys Prepared by Sodium
Peroxide Fusion. Perkin Elmer, Inc. Waltham, Ma, USA. www.perkinelmer.com
Instrument: Optima 8300 ICP-OES
Nebulizer SeaSpray
Spray Chamber Baffled cyclonic
Torch Single slot quartz torch
Injector 2.0 mm alumina
Power (W) 1500
Plasma Gas (L/min) 10
Aux Gas (L/min) 0.3
Neb Gas (L/min) 0.65
Sample Rate (mL/min) 1.5
Internal Standard 5 ppm yttrium + 10 ppmcesium
(as an ionization buffer)
Analyte Certified Measured Recovery
(%)
Al --- 658 ---
Ca --- 295 --
Co 510 520 102
Cr 680000 655000 96.3
Cu 50 < MDL ---
Fe 249800 260000 104
K --- 4.20 ---
Mg --- 23120 ---
Mn 1600 1650 103
Mo --- 165 ---
Ni 4300 4050 94.2
P 200 191 95.6
S 670 731 109
Si 12200 11450 93.9
Ti 200 205 102
V 1500 1587 106
Zn --- < MDL ---
Sample preparation:
 Zirconium Crucible
 0.2 g of finely ground sample
 3 g of sodium peroxide
 0.5 g of sodium carbonate

18. Na2O2 Fusion: traces of precious metals
Balcerzak, M. Anal. Sci., 2002, 18(7), 737-750. Sample digestion methods for
the determination of traces of precious metals by spectrometric techniques.
Sample (weight)
Element
determined
Flux Temp. (time)
Detection
technique
Concentration
Geological (0.5 g) Pt, Pd, Ru and Ir Na2O2
200°C (15 min)
490°C (1 h)
ICP-MS
0.15(Ir) – 3792(Pt)
ng g-1
Silicate rocks SARM-7
(0.5 g)
Pt, Pd and Au Na2O2 550 – 600°C (1 h) GFAAS µg g-1
Geological
(1 – 20 g)
Ru, Rh, Pd, Ir, Pt
and Au
Na2O2 700°C (10 min) ICP-MS ng g-1
Impact breccias
Ru, Rh, Pd, Ir and
Pt.
Na2O2 650°C (30 min) ICP-MS ng g-1
Secondary raw
materials Au-Ag-Cu
(0.1 – 0.5 g)
Au Na2O2 800°C (20 min) ICP-OES 58.80%
Manual sample preparation:
 Silver or nickel crucible in a muffle
 0.1 – 20 g of finely ground sample
 Flux sodium peroxide
 Sodium carbonate

19. Na2O2 Fusion: Rare earth elements by ICP-OES and ICP-MS
Application note, 2018. Analysis of Rare Earth Elements by ICP-OES and ICP-MS Potentials and Limitations.
Analytik Jena AG, an Endress+Hauser Company. Jena Germany. www.analytik-jena.com
Sample preparation:
 Porcelain crucible (30 x 30 mm) in a muffle
 100 mg of ground sample 200- mesh
 600 mg sodium peroxide
 480 ± 10ᵒC, 30 min
 Dissolved in a aqueous HCl + HNO3
Element
CRM GBW 7103
(GSR-1) Granite
powder [mg/kg]
Measured
[mg/kg]
Recovery
[%]
MDL
[mg/kg]
La 54 ± 4 53.4 99 0.14
Ce 108 ± 7 112 112 0.85
Pr 12.7 ± 0.8 12.2 96 1.55
Nd 47 ± 4 48.6 106 0.34
Sm 9.7 ± 0.8 9.23 95 0.65
Eu 0.85 ± 0.07 0.71 84 0.04
Gd 9.3 ± 0.7 10.3 111 0.36
Dy 10.2 ± 0.4 10.6 104 0.32
Er 6.5 ± 0.3 7.0 108 0.15
Ho 2.05 ± 0.17 2.22 108 0.11
Yb 7.4 ± 0.5 7.67 104 0.34
Lu 1.15 ± 0.09 1.11 97 0.19
Instrument: HR ICP-OES PlasmaQuant®
PQ 9000 Elite
Nebulizer Parallel path, PFA
Spray Chamber PTFE cyclonic, 50 mL
Torch Single slot quartz torch
Injector 2.0 mm alumina
Plasma Gas (L/min) 15
Aux Gas (L/min) 1.0
Neb Gas (L/min) 0. 5
Sample Rate (mL/min) 1.5
Plasma view axial

20. Conclusions
 The effect of the sample-preparation steps on the quality of
analytical results is universally recognized. Na2O2 fusion
allow to get accurate and precise results.
 The acid digestion procedures are time-consuming and may
not provide total dissolution of the sample. With Na2O2
fusion complete sample digestion in minutes is reached.
 The digestion procedure with automatic fluxer is more simple
compared to other sample dissolution recipes.
 No HF or other hazardous acids are needed.