TABLE V. Stability of human plasma samples of isoniazid under various storage conditions (n = 8).
| Stability | Measured concentration (ng/mL-1) | Fresh samplesa (ng/mL-1) | RSD (%) | Stability samplesa (ng/mL-1) | RSD (%) | Assay values (%) |
|---|---|---|---|---|---|---|
| Post-preparative stability (48 h, +7ºC) | 200 | 190.36 | 8.13 | 200.77b | 10.04 | -5.47 |
| 5,000 | 4.772.49 | 6.66 | 4.941.09b | 3.66 | 3.53 | |
| Long-term stability (63 days, -20ºC) | 200 | 199.42 | 11.13 | 191.09c | 8.57 | -4.18 |
| 5,000 | 4.807.86 | 3.77 | 4.556.39c | 2.66 | -5.23 | |
| Freeze-thaw stability (4 cycles/96 h, -20ºC) | 200 | 196.60 | 4.68 | 204.92d | 5.53 | 4.23 |
| 5,000 | 4.670.17 | 5.02 | 4.766.18d | 3.14 | 3.53 | |
| Short-term stability (6 h, room temperature) | 200 | 199.20 | 4.11 | 198.76e | 4.17 | -0.22 |
| 5,000 | 4.913.08 | 4.09 | 5.198.38e | 2.70 | 5.81 |
a: mean of eight replicates; b: after 48 h; c: after 1,512 h; d: after 96 h; e: after 6 h; RSD: relative standard deviation.