Instrumax CAD Performance Evaluation

Experimental Purpose

Evaluate the performance of the Instrumax Charged Aerosol Detector (CAD) using hydrocortisone as the test compound.

Experimental Conditions

Instrument: Instrumax CADetector a1 Charged Aerosol Detector; Instrumax Nitrogen Generator g15; Agilent HPLC-1200 liquid chromatograph; Finnpipette F1 20-200 μL pipette.

Column: InfinityLab Poroshell 120 EC-C18 3.0 × 100 mm, 2.7 μm. Reagents: Watsons distilled water and Merck HPLC-grade acetonitrile. Sample: hydrocortisone (5 mL:25 mg).

1. Experimental Procedure

3.1 Experimental Conditions

Mobile phase: acetonitrile/water = 35:65. Column temperature: 35 °C. Flow rate: 0.4 mL/min. Diluent: acetonitrile/water = 50:50.

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

The hydrocortisone stock solution concentration was 5 mg/mL. It was serially diluted with diluent to 3 mg/mL, 2 mg/mL, 1 mg/mL, 500 μg/mL, 400 μg/mL, 300 μg/mL, 200 μg/mL, 100 μg/mL, 1 μg/mL and 0.01 μg/mL.

3.2 Experimental Results

3.2.1 Baseline Noise and Baseline Drift

Noise (ASTM): 11.84 fA. Drift: 5.526 fA.

3.2.2 Minimum Detection Concentration

Sample: 0.01 μg/mL hydrocortisone, 10 μL injection. Minimum detection concentration: 9.17 × 10^-10 g/mL.

3.2.3 Linear Range

Samples: 100 μg/mL, 200 μg/mL, 300 μg/mL, 400 μg/mL, 500 μg/mL, 1 mg/mL, 2 mg/mL, 3 mg/mL and 5 mg/mL.

A standard curve was prepared from concentration and response. The upper detection concentration CH was 2.00 × 10^-3 g/mL and the lower detection concentration CL was 9.17 × 10^-10 g/mL. Linear range = CH/CL = 2.18 × 10^6.

3.2.4 Overall Instrument Performance

Samples: 10 μg/mL and 100 μg/mL hydrocortisone, 5 μL injection for each. After baseline stabilization, hydrocortisone standard solution was injected six consecutive times and retention time and peak area were recorded.

Results: qualitative repeatability RSD values were 0.440% and 0.403%; quantitative repeatability RSD values were 1.102% and 1.486%.

2. Summary and Discussion

Baseline noise 11.84 fA met the ≤40 fA reference requirement. Baseline drift 5.526 fA met the ≤40 fA/20 min requirement. The minimum detection concentration 9.17 × 10^-10 g/mL met the ≤5 × 10^-6 g/mL reference requirement. The linear range 2.18 × 10^6 was better than 10^3. Qualitative repeatability 0.403% at 100 μg/mL met ≤1.5%, and quantitative repeatability 1.486% at 100 μg/mL met ≤4.0%.

These results show that the Instrumax CAD detector has high sensitivity, a wide linear range, good repeatability and strong overall performance.

3. References

GB/T 26792-2019 Liquid chromatograph. JJG 705-2014 High-performance liquid chromatograph.