Analysis by Atomic Absorption Spectroscopy requires collection, storage and at times transportation of samples. Containers can pose a contamination risk of Atomic Absorption Spectroscopy samples and the extent of contamination will be significant over extended storage periods.
Container materials in common use are made from
In this article we shall cover the properties of such materials that make them desirable for collection and storage of AAS samples.
It goes without saying that the container should be inert with least possibilities of leaching or adsorption. New containers require pre-treatment. Glass containers should be soaked overnight in 1:1 concentrated at \(HNO_3\) or HCl prior to use. The pre-treatment minimizes the alkaline character of glassware. Plastics should be soaked in 1:1 nitric acid for a week followed by a week in HCl and finally a week in deionised water.
Used containers should be washed serially with a non-phosphate detergent, deionised water, acidified potassium dichromate and finally with deionised distilled water.
Some solvents and acids gradually dissolve glass and get contaminated with elements such as Si, K, Na, Ca, Mg and Al.
- Most commonly used
- Resistant to most acids except HF and boiling \(H_3PO_4\)
- Not suitable for heating or storage of hot alkaline solutions
- Should not be heated to temperatures above 500°C
Quartz exists in opaque and transparent forms. Opaque form has higher trace element concentration and is not suitable for trace metal analysis. Containers made from transparent parts are used for sampling for trace metals AAS analysis.
- Borosilicate glass parts also attacked by HF and boiling \(H_3PO_4\)
- Suitable for strong alkaline solutions
- Can be heated up to 1100°C
Plastic containers have their own advantages and disadvantages. However, availability of different chemically modified plastic materials do limit some of the disadvantages.
- Preferred for trace metal analysis due to greater inertness
- Heating not possible
- Cannot be used with organic solvents
The commonly used plastic container materials are:
- Polytetrafluoroethylene (PTFE or Teflon)
- Fluorinatedethylenepropylene (FEP)
- Perfluoroalkoxy (PFA)
- HDPE (high-density polyethylene)
- LDPE (low-density polyethylene)
PFA has some excellent desirable properties such as acid digestions upto 250°C using acids such as HF, HNO3, HCl, H2SO4 and H3PO4. It is also used for making microwave digestions vessels
LDPE and HDPE bottles are typically used for extended storage of solutions with upto 10% \(HNO_3.\)
The choice of container material will depend on a number of considerations such as:
- Required level of detection
- Inertness of container
- Ability to handle hot boiling acids
- Storage period prior to analysis.
As a good practice samples should be analysed at the earliest opportunity post preparation or collection.
Please share your experiences and views on different container materials and your comments.