HEAT-ASSISTED ARGON ELECTROSPRAY INTERFACE FOR LOW-FLOW RATE LIQUID SAMPLE INTRODUCTION IN PLASMA SPECTROMETRY

 

Ryan G. Brennan, Savelas A. Rabb, Michael R. Winchester, and Gregory C. Turk

Affiliation: CSTL/Analytical Chemistry Division, NIST Gaithersburg , MD 20899

 

The demands for new or replacement reference materials having lower certified concentrations of trace elements is becoming quite common, e.g., for clinical materials and bioanalysis. These can pose significant certification measurement challenges where traditional analytical methods may no longer be appropriate. To address these challenges, new measurement approaches must be developed, such as the argon electrospray interface reported herein.

The aim of this work is to address key challenges in the analysis of biological samples by developing an innovative and efficient sample introduction approach for inductively coupled plasma (ICP) spectrometry that will enable analysis of samples of limited quantity at reduced sample flow rates while achieving maximum sensitivity. A heated (≈ 90 C) laminar flow interface has been designed to assist in the development of an argon electrospray sample introduction system to meet these requirements. Previously, the stability and robustness of the ICP were compromised by the entrainment of air, N2, or gas mixtures (e.g., Ar-N2) from the electrospray source. Also, more concentrated organic solvents (e.g., 50 % (v/v) methanol-water), typically introduced by electrospray, could generate carbon deposits that obstruct the entrance lens to an ICP optical emission spectrometer (ICP-OES) or the sampler/skimmer cone interface in an ICP mass spectrometer (ICP-MS), decreasing analyte sensitivity. With the new interface design, a stable spray of 5 % (v/v) methanol-water in a pure argon environment is achieved, eliminating the aforementioned problems. The turbulence and the consequent droplet loss caused by high gas velocity around the electrospray capillary are mitigated by using a laminar-flow gas with the aid of a flow diffuser. The argon electrospray interface is successfully installed on an ICP-OES and an ICP-MS for the first time.