There are a multitude of tubing and sampling tip materials available to the practitioner. Section 3.2.2, pages 11 and 12 of the ASGI states: "To minimize purge volume, use small diameter (1/8 to 1/4 inch) sampling tubing from the vapor probe tip to the ground surface, made of material which will not react or interact with site contaminants. The probe tip, probe and probe connectors should all have the same diameter to provide a good seal between the formation and the sampling assembly.” Additionally, bullet number 3 of the same section and page 12 states “Metal tubes should not be used to collect hydrogen sulfide samples.  Nylaflow®, polyetheretherketone (PEEK), and Teflon® are recommended for soil vapor sampling. Low-density polyethylene (L-D PE) should not be used due to decreased performance relative to other tubing types in both off-gassing of VOCs inherent in the tubing structure (contribution to background) and for decreased contaminant recovery (reactivity). Reduced recovery of naphthalene was observed when using Nylaflow® tubing with small sample sizes. For additional information, see Appendix B". Soil gas sampling tips come in a variety of styles depending on the application. Tips should allow subsurface vapors to enter the sampling system with little or no restriction. Prior to sampling, an assembled soil gas probe, tip and tubing should be blank tested at a frequency of one analysis per new batch of tubing or material used (see ASGI Section 3.2.3, bullet 4 a, b, and c and question 7 below).