Table 2. Drug residues in nonsaleable raw milk detected and quantified by liquid chromatography-tandem mass spectrometry (LC-MS/MS).
| Drug residue | Distribution1 (%) (n = 28) | Mean2 (μg/mL) | SE3 | LOQ4 (μg/mL) | Tolerance5 (μg/mL) |
|---|---|---|---|---|---|
| β-Lactams6 | 50 | ||||
| Ampicillin | 7.1 | 0.472 (n = 2) | 0.438 | <0.01 | 0.01 |
| Cephapirin | 3.5 | 0.033 (n = 1) | — | <0.01 | 0.02 |
| Ceftiofur | 39.2 | 0.151 (n = 11) | 0.042 | <0.01 | 0.1 |
| Cloxacillin | 3.5 | 0.055 (n = 1) | — | <0.01 | 0.01 |
| Penicillin G | 14.2 | 0.008 (n = 4) | 0.001 | <0.005 | 0 |
| Sulfonamide | |||||
| Sulfadimethoxine | 3.5 | 1.00 (n = 1) | — | <0.002 | 0.01 |
| Tetracycline | |||||
| Oxytetracycline | 3.5 | 0.01 (n = 1) | — | <0.01 | 0.3 |
| Nonsteroidal antiinflammatory | |||||
| 5-Hydroxyflunixin | 3.5 | 0.003 (n = 1) | — | <0.002 | 0.002 |
1
Percent of milk samples with drug residues at concentrations above the limit of quantification (LOQ) for LC-MS/MS for each individual drug or drug class described.
2
Mean concentration of drug residues in nonsaleable raw milk samples collected from dairy farms and quantified by LC-MS/MS. Number of samples with drug residues within the limit of detection in parentheses.
3
Standard error of drug residues quantified by LC-MS/MS.
4
LOQ of LC-MS/MS for each drug tested.
5
Food and Drug Administration (FDA) tolerance for drug residues in raw milk.
6
Samples with detectable concentrations of one or more β-lactam drug residues measured by LC-MS/MS.