Quantitative analysis of small molecules by desorption electrospray ionization mass spectrometry from polytetrafluoroethylene surfaces

Abstract

Desorption electrospray ionization mass spectrometry (DESI-MS) is an emerging technique for ambient analysis. However, its application to routine quantitation has not been explored extensively and this is undertaken here. We present studies that utilize a particularly suitable surface, porous polytetrafluoroethylene (porous PTFE), which shows less cross contamination between samples and improved sensitivity and signal stability compared to other surfaces. Quantitative experiments for 1 microL spotted solutions of the beta-blocker propranolol, using isotopically labeled propranolol as internal standard, showed a good linear correlation (r2 > 0.996) over the range 0.01-100 microM. The inter-day precision, based on the relative standard deviation, for replicates analyzed on three different days was 13% for 0.01 microM and better than 7% for the remainder of the calibration points. The inter-day accuracy, expressed as relative error, was better than +/-7% for all calibration points along the curve. These day-to-day measurements suggest that DESI-MS can be successfully employed for routine quantitative analysis. The use of the analog atenolol as an internal standard and further considerations that should improve quantitation by DESI-MS are also presented.

High-throughput quantitative analysis by desorption electrospray ionization mass spectrometry

“…DESI analysis was performed on four types of samples in a 96-sample array in the course of a single experiment: two sample types were free of any chemical background, one was made in a 10% urine solution, and one in 250 ng/ L brain total lipid extract. Isotopically labeled standards were selected to minimize complicating effects that might arise from the use of chemically similar but distinct standards [18]. The total analysis time per sample (including analysis time and the time required to move between samples) was 1.5 s for background-free samples and 2.5 s for the samples in a biological milieu, allowing the entire 96 sample plate to be analyzed in just over 3 min.…”

“…To explore this application, we procured custom-made PTFE printed glass slides in a 96-sample format (Figure 1). This PTFE printed glass substrate has been shown to be an effective and versatile surface for DESI that gives strong, stable signal for a wide array of analytes [18,20]. This system offers several advantages.…”

“…Isotopically labeled standards were selected to minimize complicating effects that might arise from the use of chemically similar but distinct standards [18]. The total analysis time per sample (including analysis time and the time required to move between samples) was 1.5 s for background-free samples and 2.5 s for the samples in a biological milieu, allowing the entire 96 sample plate to be analyzed in just over 3 min.…”

“…The slides were 124 mm ϫ 83 mm and were printed with 96 dots using a hydrophobic ink containing PTFE [17,18]. The dots were 3.2 mm in diameter and 9 mm apart in a regular 12 ϫ 8 grid.…”

“…The two background-free calibration curves were PRN with PRN-d 7 One L of each sample was deposited on a custommade glass slide with a "96 well" type of format, except that the "wells" were small raised spots ( Figure 1). The slides were 124 mm ϫ 83 mm and were printed with 96 dots using a hydrophobic ink containing PTFE [17,18]. The dots were 3.2 mm in diameter and 9 mm apart in a regular 12 ϫ 8 grid.…”