A cost-effective mini-CNC and negative-pressure approach for automated sample handling, low-volume sample introduction, and eluent delivery in open tubular capillary ion chromatography.

A novel cost-effective and resource-efficient sample introduction system was developed by combining mini-computer numerical control (mini-CNC) with a negative pressure (NP) approach to enable automated sample manipulation, low-volume sample introduction, and eluent delivery for operation in a low pressure open tubular capillary ion chromatography (OTIC). The developed OTIC system was applied for the separation of water-soluble inorganic anions (Cl-, NO2-, Br-, and NO3-) on AS-18-coated fused silica capillary (25 or 50 μm i.d.) with a capacitively coupled contactless conductivity detector (C4D) to improve accessibility to ion analysis in low-resource settings. A single line micro-flow injection analysis (μ-FIA) format was used to evaluate the basic injection system, and provided a signal repeatability of 4.3% RSD (n = 19) as a proof-of-concept. The repeatability of the entire process, including sample solution introduction and ion separation, was 5.6% RSD (n = 9). A sample loading volume of 20 μL in a small vial was sufficient for multiple injections with an injected volume of <10 nL per injection, reducing reagent use and analytical waste. The linear calibration for quantification of the four anions was achieved in the range of 0.1 - 10 mg L-1. The novel mini-CNC-NP system coupled with OTIC was applied for the determination of water-soluble small inorganic anions in PM2.5 extracted solution samples. The accuracy of the device was validated by comparing the analytical results with a standard packed column ion chromatograph (IC); a statistical t-test showed acceptable agreement. The recoveries of samples spiked with standard anions ranged from 90.9% to 102.5%. The novel mini-CNC-NP system could benefit automated sample manipulation/injection in other capillary scale separation systems.