Labware made of Fluoroplastic PFA
Today, trace analysis operates with concentrations in the range of ng/g (ppb) and pg/g (ppt). Thus, all modern processes require a corresponding trace analytical laboratory hygiene. However, the analytical accuracy of the measurement depends not only on the accuracy of the analytical instrument, but also directly on the judicious selection of container materials and the preparation of the samples themselves. Under these conditions, the fluoroplastic PFA truly shows its worth.
Labware made from polyolefins, such as polypropylene (PP) or polyethylene (PE), has found broad application in modern laboratories. Since catalysts (e.g., Ziegler-Natta or Philipps) are used during the manufacturing process, the constituent elements (frequently Al, Cr, Mg, Si, Ti or Zn) can still be detected in the ultra-trace range, and thus might affect the analysis results. In direct comparison to these manufacturing processes, PFA is especially suitable for trace element analysis because it is manufactured without the use of additives, and therefore cannot become contaminated by the additive components.
In addition to this advantage, PFA has other remarkable properties. PFA can be used for a broad range of applications by virtue of its resistance to almost all organic and inorganic compounds. PFA is one of the most resistant materials after platinum, and is practically chemically inert. Moreover, PFA stands apart with extraordinarily high thermal stability, making it possible to operate in the temperature range of -200 to +260 °C.
For all PFA products, VITLAB uses only high-purity PFA, which is particularly well-suited for trace analysis. For less critical uses, e.g. if the main requirement is a high chemical resistance, VITLAB offers bottles of “economy grade” PFA, which are partly made of recycled PFA. These are favourably priced and also environmentally friendly.
PFA evaporating dish
Pictures of the surface structure of PTFE, PFA, and PE-HD with a scanning electron microscope (8000 times magnification).
VITLAB’s PFA vessels have unique, extremely smooth, liquid- repellent surfaces that are made possible through modern manufacturing processes and acknowledged expertise (see pictures on “Surface Structure”). This is especially significant in the illustrative comparison. The pictures taken in a scanning electron microscope show uneven and irregular surfaces for PE-HD and PTFE, and deep pores and concavities can be identified in the PTFE surface. In contrast to the uneven surfaces, PFA evaporating dishes had to be marked (X) and exhibit a completely smooth, even and uniform surface structure.
Due to this characteristic, all PFA labware is particularly easy to clean and presents hardly any interactions with samples as compared to conventional container materials. With these advantages combined with the minimal water absorption by PFA (< 0.03%), even samples at very low concentration can be stored for long periods of time in PFA containers without changes in their concentration (see the application example on Mercury Standards).
Cleaning after contamination
The valuable properties of PFA, primarily the near absence of memory effects, ensure the reliability of trace analytical results. In comparison with a commercially available glass flask, the simple cleaning after contamination with lead (Pb) solution at a concentration of 1000 ppb (ng/g) is a telling example (see the section on Cleaning of Volumetric Flasks). The cleaning of the glass and PFA volumetric flasks was conducted by shaking with 65% HNO3 *Suprapur® (Pb < 0.005 ppm) at room temperature. With PFA volumetric flasks, the minimum concentration of 0.003 ppb is reached after three rinses, while substantially higher lead concentrations can be measured in glass flasks even after four rinses. The experiment also shows that PFA labware does not require the usual time-consuming boiling.
*Suprapur® is a trademark of Merck KGaA.
Application Example – Mercury Standards: Storage of an Hg standard in high-purity PFA containers (concentration 2 ppb (ng/g) each). Source: GIT Laboratory Trade Magazine 1/95
Cleaning of glass and PFA volumetric flasks after contamination. Source: Kali-Forschungsinstitut, K. Mangold