Selecting the correct autosampler vial and insert to improve reproducibility and accuracy in mass spectrometry analyses

Acquiring accurate and reproducible data is crucial for analytical chemists, however, sample storage and manipulation play a large role in achieving high-quality results. Autosampler vials and small-volume inserts are used for sample preparation and storage prior to mass spectrometry analyses, however, the utility, design, and material of these vary greatly. Here, we assessed differences in data reproducibility, sample loss, and physical differences among vials and inserts made of glass and polypropylene for combinations (vial/insert): glass/glass (GG), glass/polypropylene (GP), polypropylene/glass (PG), and polypropylene/polypropylene (PP). Six per- and polyfluoroalkyl substances (PFAS) were evaluated in 40:60 methanol:water with 3 mM ammonium acetate for 32 days to determine peak area reproducibility over time since PFAS do not degrade, therefore changes would most likely be due to adhesion and evaporation. On Day 1, the measured average peaks areas for the 6 PFAS were not statistically significant between any combinations, however, PP was the least reproducible (relative standard deviation > 10 %). All samples were then recapped and stored for one month at −20 °C and reanalyzed to compare the peak areas between Day 1 to Day 32. All combinations showed >10 % differences in peak area for at least 4 PFAS and both evaporation and adhesion were observed. While the greatest effects due to adhesion occurred in the glass inserts, the glass vials showed the least volume loss to evaporation. Thus, when adhesion and evaporation are considered together, the GP combination is recommended for PFAS analyses as the glass vial reduces evaporation rates, and the polypropylene insert minimizes adhesion.