The low soil method relies on a hermetically sealed sample vial that remains sealed from collection through analysis. Closure performance can directly affect VOC retention, as it directly affects the ability to prevent VOC loss during transport and handling. ILT’s SURE Clean caps are designed with a protective overlay cap to help maintain sample cleanliness from the collection point through laboratory analysis.
Method 5035 is suitable for volatile organic compounds with boiling points below 200°C and low water solubility. It can include water-soluble compounds, though quantitation limits are typically higher due to reduced purging efficiency.
When paired with Method 8015 (GC/FID), Method 5035 supports analysis of aliphatic hydrocarbons such as gasoline fractions. For aromatic compounds like BTEX, Method 8021 (GC/PID) is commonly used. These methods can be used together for broader hydrocarbon analysis.
To prevent contamination of purge-and-trap systems, samples should be screened before analysis. Because sealed containers cannot be opened without compromising integrity, collecting multiple aliquots is recommended for screening and reanalysis.
2. Summary of Method
One approach involves collecting a bulk sample without preservative and preparing it in the laboratory using a water-miscible solvent. This process requires opening the container, which may lead to loss of volatile compounds.
A second approach involves collecting approximately 5 g of sample directly into a pre-weighed vial containing a water-miscible solvent such as methanol, sealed with a lined screw cap. ILT screw caps with bonded liners are commonly used in these workflows to support consistent sealing and sample protection during transport and analysis.
3. Interferences
Contamination may arise from purge gas impurities or organic compounds released from system components. Analytical systems should be verified using method blanks to ensure clean baseline conditions.
Materials used in the purge-and-trap system can contribute to background interference. Components that are not PTFE-based, including certain plastics, sealants, and rubber elements, may out-gas and affect results. Closure materials also play a role. Septa with PTFE-faced surfaces are commonly used to reduce bleed and minimize interference during analysis.
Laboratory environments must be controlled to prevent solvent contamination. Methylene chloride is a known source of background interference and should be isolated from analytical and storage areas.
4. Apparatus & Materials
Sample container requirements depend on the purge-and-trap system being used. In many cases, glass vials capable of holding at least 5 g of sample and 10 mL of liquid are required, along with screw caps fitted with PTFE-faced silicone septa.
System manufacturers may specify compatible vial and closure configurations. Selecting closures that align with method requirements is critical for maintaining seal integrity and consistent analytical performance. Typically, in the United States, a 40mL VOA vial is used with a 24mm open top cap lined with silicone/PTFE. ILT offers a full range of 24mm caps for VOA analysis.
5. Quality Control
Laboratories must demonstrate proficiency in both sample preparation and determinative methods, producing accurate and reproducible data for target analytes.
Additional quality assurance practices should be implemented based on sample type and laboratory protocols. This may include analysis of reference materials and participation in performance evaluation programs.
