Figure 1.
The biosynthesis of taurine from cysteine (a) and illustrative scheme of derivatization process of taurine using AccQ•Tag Ultra reagent (b).
Table 1.
UHPLC gradient program for the separation of taurine.
| Time (min) | Flow (mL/min) | Mobile phase A (%) | Mobile phase B (%) |
|---|---|---|---|
| Initial | 0.5 | 99 | 1 |
| 0.7 | 0.5 | 99 | 1 |
| 1.3 | 0.5 | 87 | 13 |
| 3.7 | 0.5 | 85 | 15 |
| 7 | 0.5 | 60 | 40 |
| 8 | 0.5 | 5 | 95 |
| 9 | 0.5 | 5 | 95 |
| 9.8 | 0.5 | 99 | 1 |
| 10.5 | 0.5 | 99 | 1 |
Table 2.
Overview of several selected operation and validation parameters of the UHPLC-MS method.
| Taurine | |
|---|---|
| tR (min) | 1.96 |
| a (counts) | 0.00642644 |
| RSDa (%), n = 6 | 9.7 |
| b (counts × μmol−1 × L) | 0.00801683 |
| RSDb (%), n = 6 | 4.8 |
| r2 | 0.9982 |
| Linear range (μmol/L) | 10–500 |
| LOD (μmol/L) | 4.29 |
| LOQ (μmol/L) | 10 |
| N | 93,340 |
[i] Separation efficiency (N) was calculated according to the equation N = 5.545*(tR/w1/2)2, where tR is the retention time and w1/2 is the full width at half maximum of the peak. The calibration curve is expressed by the equation y = b.x + a. All calculations and results were obtained from the measurements of samples at LOQ concentration level (i.e., 10 μmol/L).
Table 3.
Evaluation of accuracy parameters of taurine tested at three concentration levels (10, 100, and 500 μmol/L).
| Nominal (μmol/L) | Found (μmol/L) | RSD (%) | RE (%) | |
|---|---|---|---|---|
| Intra-day, n = 5 | 10 | 10.92 | 2.62 | 9.2 |
| 100 | 90.99 | 0.10 | −9.0 | |
| 500 | 533.94 | 0.72 | 6.8 | |
| Inter-day, n = 10 | 10 | 10.95 | 3.95 | 9.5 |
| 100 | 92.31 | 0.57 | −7.7 | |
| 500 | 535.30 | 1.41 | 7.1 |
[i] RE – relative error, RSD – relative standard deviation
Table 4.
Recovery of taurine tested at three concentration levels (10, 100, and 500 μmol/L).
| Taurine | |||
|---|---|---|---|
| Added (μmol/L) | 10 | 100 | 500 |
| Found (μmol/L) | 10.80 | 91.50 | 532.70 |
| RSD (%), n = 5 | 0.8 | 2.7 | 0.6 |
| Recovery (%) | 108.0 | 91.5 | 106.5 |
Table 5.
Determined concentration of taurine in four tested commercial available energy drinks.
| Beverage | Parameters | |||
|---|---|---|---|---|
| Found ± SD (mg/mL) | RSD (%), n = 3 | Declared (mg/mL) | % of declared content | |
| Red Bull | 2.80 ± 0.07 | 2.6 | 4 | 70.0 |
| Hell | 3.77 ± 0.05 | 1.4 | 4 | 94.5 |
| Tiger | 3.78 ± 0.01 | 0.1 | 4 | 91.8 |
| Maxx | 3.67 ± 0.03 | 0.9 | 4 | 94.3 |
Figure 2.
Illustrative chromatograms of taurine and the IS obtained from the analysis of four energy drinks: a) Red Bull, b) Hell, c) Tiger, d) Maxx. For separation and detection conditions, see Section 2.1.