Abstract
Filtration is commonly used to separate liquids from solid materials before the determination of trace element concentrations in aqueous solutions. Therefore, it is important to determine how much elemental content is extracted from the filter itself or lost via absorption into the filter. In this study, we investigated three types of disposable syringe filters (polyvinylidene difluoride, PVDF; polytetrafluoroethylene, PTFE; PTFE with glass microfiber prefiltration media, GD/X) and their acid-cleaned versions using ammonium nitrate (NH4NO3) and acetic acid (HOAc) solutions. The concentrations of most trace elements (Li, Al, Cr, Mn, Co, Ni, Cu, Zn, Rb, Sr, Mo, Cd, Cs, Ba, Pb, and U) were higher in filtrates that had passed through acid-cleaned filters than those that had passed through uncleaned filters. In filtrates from PVDF and PTFE filters, many trace elements were below the detection limit. However, regardless of the filter type and acid cleaning, Li, Cu, Zn, Mo, and Ba concentrations in filtrates of NH4NO3 solutions, and Al, Cr, Mn, Cu, Zn, and Ba concentrations in filtrates of HOAc solutions were much higher than those of other trace elements. These differences were particularly noticeable in filtrates from GD/X filters containing glass microfiber layers. These data indicate that certain trace elements can be released from membrane materials by reacting with acid in the filtered solution. Furthermore, the amounts of each trace element were associated with the membrane type. These findings suggest that filter type should be carefully selected to obtain the required accuracy, in consideration of the target elements and whether an acid-cleaned filter is needed.
Highlights
Filtration is a common procedure used in the field and in laboratory settings to separate dissolved ions from suspended materials
Filtrate solutions were passed through three syringe filter types (PVDF, PTFE, and GD/X) with and without prior acid-cleaning
Considering the trace element concentrations in the primary HOAc solution, as well as those in the polyvinylidene difluoride (PVDF) and PTFE filtrates, these results indicate that large amounts of material are extracted from glass microfiber (GMF)-layered membranes
Summary
Filtration is a common procedure used in the field and in laboratory settings to separate dissolved ions from suspended materials. Filter paper and syringe filters are the most commonly used filtration media. The use of filter paper is labor-intensive and often more time-consuming than that of syringe filters. Filtration through syringe filters requires relatively low sample volumes. These advantages have led to the widespread use of syringe filters, the type of syringe filter should be carefully selected because some of the raw materials used to manufacture filtration membranes can leach analytes into the filtrate [1]. The chemical compatibilities of these membranes differ among acids and bases, so it is important to select a filter that is compatible with the system to avoid an effect
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