The 4 mm Millex syringe filter is available in both sterile and non-sterile versions for use when filtering sample volumes <1 ml. In order to maximize the use of samples, the syringe filter has been designed with a hold-up volume of <10 µl and a stepped outlet designed for use with smaller sample vials. These syringe filters are available with a variety of 0.22 µm and 0.45 µm membranes for use in a range of applications. The 4 mm syringe filter serves as a sample preparation tool when preparing samples for analysis using liquid chromatography/mass spectrometry (LC/MS). The small sample sizes that can be processed using the filter can lead to savings of limited samples and compounds.