Sample Preparation Guides

General Information

Occurrence – Germanium (Ge) is the third of the group 14 (IVA) elements and is between silicon (Si) and tin (Sn).  Ge is classified as a metalloid (both metallic and non-metallic properties) having some properties of the elements it is sandwiched between namely the non-metal Si and the metal Sn. Germanium powder metal is a light gray powder.  The fused metal resembles Sn.  Ge is 55^th in abundance with an average earth’s crust abundance of 1.6 ppm.¹ Ge occurs naturally as the sulfide and is always associated with other sulfide minerals. 

Properties as Related to Chemical Behavior and Stability – The group 14 elements have an electronic configuration that favors 2 and 4 valence states.  As you move to the higher atomic number elements in this group the 2-valence state comes more into play with Pb and to a lesser extent with Sn. In the case of Ge both the 2 and 4-valence states must be considered by the analyst. 

Ge is stable in HCl, HF, H₃PO₄, H₂SO₄, and HNO₃ as the [Ge (OH)_n(F)_6--n]^2-.  Avoid neutral to basic media because of Ge’s tendency to undergo hydrolysis.  Ge is unstable at ppm levels with metals that would pull F^-1 away.  You can mix Ge with Alkaline or Rare Earths, but this requires an experienced analyst. Ge is stable with most inorganic anions with a tendency to hydrolyze.  Fluorinated Ge solutions at the ppb levels are stable either alone or mixed with most other metals where the other elements are also at the ppb concentration level.  As the concentration increases from the low to mid to high ppm levels, Ge’s stability is best maintained either alone or mixed with elements that do not complex with fluoride.  destabilize the Ge by pulling away the F ligand, which will cause hydrolysis of the Ge.  A common matrix/container combination for achieving 1+ years of stability is 1- 5 % HNO₃ / 0.1% HF in a pre-HNO₃ leached LDPE container.  The objective here is to provide a moderate excess of HF that allows for dilutions into working matrices that will be stable.  We have found that 2-100 ppb Ge solutions mixed with over 60 of the common elements at the 2-100 ppb level are stable for 4+ years with no instability detected.  The order of additions of the components of these solutions is critical to achieving stability as well as the matrices of the single element “building block” solutions.

Uses- Up until the mid-20^th century Ge was of little use.  In a textbook written in the early 20^th century (1901) it states that ”there is practically no active market for the metal”.  The usefulness of Ge grew beginning in the 1950s and has been found very useful in the electronics industry, its use in optics, and as a polymerization catalyst. Many other uses in other industries such as medicine have been developed or are being explored. 

It is important to note that Ge is only useful to the electronics industry in the ultrapure state.  At Inorganic Ventures a key focus is in providing Certified Reference Materials (CRMs) that are highly pure.  This is especially true for Ge where the user may need to review the mass and emission spectral data obtained and archived by IV for every lot of product that is produced. 

Germanium Chemistry as Performed and Observed at IV

Inorganic Ventures uses elemental Ge° as the starting material. It resembles Si° in brittleness, high melting point and inertness to acids and bases, and tin in appearance.   However, the elemental pieces, as they are called, dissolve without having to be ground thereby avoiding contamination from the grinding apparatus.  It can be relatively easily acquired in high purity where it is claimed to be 99.999+% . As with all our starting materials it is carefully studied using ICP-MS and ICP-OES for impurities in the starting material vs. those introduced during manufacturing and handling.  We find that the handling of Ge° is not plagued by contamination that cannot be avoided during the grinding and sieving required to reduce neighboring Si° to a workable particle size. Therefore, we use Ge° in elemental form which dissolves in concentrated electronic grades HNO₃ and HF producing a 99.99+% solution free of metallic impurities for each lot (measured using ICP-MS and ICP-OES) and reported on the Certificate of Analysis. 

Sampling and Handling

Germanium will be found in minerals in the sulfide form mixed with other sulfides.  Its concentration in these minerals varies from a few ppm to ~ 5% and is recovered from processes that are intended to produce major amounts of other elements such as Zn in the USA.  It occurs only in the combined state in nature.  Prior to the development of ICP the analytical schemes involved the digestion of samples in HCl and HNO₃ or H₂O₂ and separating the Ge by distilling it as the GeCl₄. 

The use of ICP has greatly simplified the determination of Ge by not requiring separation of the Ge from the mineral/sample/preparation.  The sampling and handling of germanium materials is not generally a problem unless the metals present exist as sulfides. Sulfides are to be handled with the same care as cyanides.  Always handle with adequate ventilation, as in a fume hood, always wear safety glasses or goggles, wear nitrile or other resistant gloves, wear a long-sleeved, buttoned lab coat, long pants, and closed-toe shoes. Other PPE may be required, such as face shield, foot coverings, apron, etc.

Materials in which germanium exists as the metal or oxide (Ge°, GeO or GeO₂) are usually not hazardous and do not present sampling and handling problems.  However, many analytical measurement techniques require a solution of the sample and HF is most often required to stabilize Ge in solution.  Safety considerations appropriate to the use of HF will apply.  In materials where germanium is present in minor or trace amounts then sampling and handling considerations relative to the sample matrix will apply.

For details on sampling and sub-sampling see Chapter Three of our Trace Analysis Guide.

The Metal, Alloys, Oxides, Ores, Minerals, and Organics

Metal - Ge⁰ is insoluble in H₂O and HCl, soluble in Aqua Regia and H₂SO₄. It reacts with HNO₃ to form GeO₂ and combines directly with the halogens. It is insoluble in NaOH solution but dissolves with incandescence in fused alkalis. The metal is soluble in a mixture of 1:1:1 H₂O / HF / HNO₃.

Alloys - The earlier (before 1970) sample preparation methods for Ge metal and its alloys involved dissolution in a HNO₃ / H₂SO₄ mixture. HNO₃/HCl was used when separation of Ge from complex mixtures was considered necessary due to interelement interferences. Separation was accomplished by distillation of the tetrachloride (boiling point 86° C) from a hydrochloric acid solution (1:1).  HF could not be used in wet chemical methods due to an interference with titrimetric, colorimetric, and gravimetric methods.  Titrimetric chelates do react stoichiometrically with the Ge fluoride complex, colorimetric reagents do not react with the Ge fluoride and gravimetric reagents do not react stoichiometrically.

The development of ICP has greatly simplified the sample preparation of Ge metal and alloy samples to:

• Take 0.1 to 1.0 grams of sample and dissolve with 10 ml conc HNO₃ + 10 ml conc HF + 10 ml conc H₂SO₄ +25 ml H₂O (W. W. White, Anal. Chem, 38, 512 (1966).  
• The presence of HF will not cause interference.  However, it does require the use of HF resistant sample introduction.

One of the great advantages of ICP is the freedom to use HF in the preparation of Ge as well as Ti, Zr, Hf, Nb, Ta, W, Sn, Si, Sb, and Te where the use of HF greatly simplifies the preparation.

Oxides - Germanium forms two oxides, GeO and GeO₂ with the dioxide being the more stable and common.  Germanium I oxide (GeO) is readily soluble in HCl or NaOH.  Germanium II oxide (GeO₂) is not soluble in water or dilute acids or NaOH.  However, fused with sodium carbonate converts it to a water soluble germanate [GeO(OH)₃]¯.  The following is a general procedure covering a wide range of sample types:

• Weigh the sample into a Pt dish or crucible capable of holding 30 to 50 ml of liquid.
• Add sodium carbonate (2 g / 0.5 grams sample). And place in a muffle furnace.
• Slowly bring the temperature up to 1000 °C and hold for 15 minutes.
• Remove from muffle allowing to cool.  The ash can be dissolved in dilute nitric or nitric plus HF.  Avoid HF if matrix levels of alkaline or rare earths are present.
• Although I tend to use HF ‘just in case’ it can be problematic and dilute nitric will work just as well for most matrices.
  
  

Ores & Minerals - In those alloys in which titanium exists as the base metal then methods of dissolution can be employed as given for the metal, usually some combination of acids including hydrofluoric. For alloys where Ti is one of the lesser constituents the use of concentrated nitric acid, Aqua Regia or a mixture of acids suitable to dissolution of the base metals is used. Geological Samples may be fused in Pt⁰ crucibles with Na₂CO₃ followed by HCl solution of the fuseate. After the sample is dissolved make certain to keep the acid content of the final solution sufficiently high to avoid hydrolysis. 

Organics - This includes a wide variety of materials including petroleum matrices, coal, organic plant material, biological material, synthetic organics, etc. Organic Matrices can undergo dry ashing at 450⁰C in Pt⁰ crucibles and be dissolved by gently warming with 1:1:1 H₂O / HF / H₂SO₄ (or fuse the ash with Na₂CO₃ and dissolve the fuseate with HCl / H₂O). Samples can also be digested with nitric/perchloric.  For more detailed information about acid digestions of organics please see Chapter Twelve of our Trace Analysis Guide.

Testing Methods

Testing Ge by ICP-OES is relatively trouble free if your samples and standards are properly stabilized with HF. You can expect the best performance from the 164.919 nm emission line if your instrument has an optical system that can view low UV lines. Lines 219.871 nm and 265.117 nm will also have good detection limits, down to 20 – 60 ppb or lower, when running clean samples. However, these lines have more potential interferences than 164.919 nm. Line 219.871 nm can have a significant spectral interference from tungsten. This W interference should be specifically noted since HF elements like Ge and W are often placed in the same stock standard by CRM manufacturers. Line 265.117 nm may have a spectral interference from Be on the left shoulder of the Ge peak. To correct for this Be interference you may need to change your background to use the right-hand set point only.

Analysis of Ge by ICP-MS is more susceptible to polyatomic interferences because of the mass range of the Ge isotopes. Oxides from Fe and Ni may fall on each isotope of Ge. Interferences from argon (³⁶Ar₂) may also increase the background concentration of ⁷²Ge. If your matrix contains HCl then you may also see interferences from ³⁵Cl₂ and ³⁵Cl³⁷Cl. The presence of sulfur or potassium may also introduce interferences on ⁷²Ge (from ⁴⁰Ar³²S) & ⁷⁴Ge (from ³⁹K³⁵Cl). Finally, you may also experience doubly-charged interferences from Ce, Nd, and/or Sm. When analyzing samples in HNO₃ matrices you should expect to achieve 1-5 ppb detection limits easily with a single quadrupole ICP-MS in a normal operating mode. We would recommend using a He KED mode if you wish to eliminate background polyatomic interferences. Using a KED can help achieve detection limits to sub-ppb concentrations, however your will lose overall intensity which may increase your measurement % RSDs (thus decreasing measurement precision).

Ge may also be used as an internal standard for ICP-MS to correct for potential signal suppression from varying levels of total dissolved solids in your samples. However, your samples will need to be free of any potential interferences described above to accurately apply correction factors to your results. See Chapter Eleven of our ICP Operations Guide for more information about using internal standards.

1. National Research Council (US) Committee on Medical and Biological Effects of Environmental Pollutants. Arsenic: Medical and Biologic Effects of Environmental Pollutants. Washington (DC): National Academies Press (US); 1977. 3, Distribution of Arsenic in the Environment. Available from: https://www.ncbi.nlm.nih.gov/books/NBK231016/