Instrumax CAD Performance Evaluation

Objective

Evaluate the performance of the Instrumax CAD detector using glucose.

Experimental conditions

Instruments: INSTRUMAX Charged Aerosol Detector (CADetector a1), INSTRUMAX Nitrogen Generator g15, Agilent HPLC-1200 liquid chromatograph, Ohaus AR1530 balance (0.001 g), Finnpipette F1 20-200 μL pipette.

Column: Alltech Chrom H+ hydrogen-form sugar column, 300 mm × 7.8 mm, 8 μm. Reagent: distilled water. Sample: D-Glucose (CHEM SERVICE, purity 99.5%). Mobile phase: pure water.

1. Experimental procedure

Column temperature: 60 °C. Flow rate: 1 mL/min. Sample concentration for method evaluation: glucose 5 μg/mL.

CAD conditions: drift tube temperature 40 °C, nebulizing gas flow 3 L/min, charging gas flow 1 L/min, charging current 1 μA, Gain 0.05, RF 2.0.

Sample preparation: 0.100 g glucose was dissolved and diluted to 10 mL to obtain 10 mg/mL stock solution, then serially diluted to mg/mL and μg/mL working solutions down to 0.1 μg/mL.

3.2 Experimental results

3.2.1 Baseline noise and baseline drift

Baseline noise (ASTM): 9.997 fA. Baseline drift: 25.27 fA.

3.2.2 Minimum detectable concentration

Sample: 5.0 μg/mL glucose, injection 10 μL. Minimum detectable concentration: 4.48×10⁻⁸ g/mL.

3.2.3 Linear range

Standard-curve levels: 100 μg/mL, 200 μg/mL, 300 μg/mL, 400 μg/mL and 500 μg/mL. Peak heights: 48.808, 109.756, 172.952, 243.223 and 308.256 pA.

Upper concentration CH = 3.00×10⁻³ g/mL. Lower concentration CL = 4.48×10⁻⁸ g/mL. Linear range CH/CL = 6.69×10⁴.

3.2.4 Instrument performance: qualitative and quantitative repeatability

For 100 μg/mL glucose at 5 μL injection, retention-time RSD was 0.109% and peak-area RSD was 0.981%. For 5 μg/mL glucose at 10 μL injection, RSD values were 0.171% and 1.441%. For 5 μg/mL glucose at 20 μL injection, RSD values were 0.106% and 1.371%.