NMR methods for endotoxin analysis
The invention features a method of monitoring a clotting process by measuring a signal characteristic of the NMR relaxation of water in a sample undergoing endotoxi-induced clotting to produce NMR relaxation data and determining from the NMR relaxation data a magnetic resonance parameter of water in the sample characteristic of the level of endotoxin present in the sample.
1. A method of measuring LAL gelation in a sample comprising an endotoxin, the method comprising the steps of:
(a) mixing said sample with LAL reagent to form a mixture in which the endotoxin produces coagulin, thereby resulting in LAL gelation;
(b) at a predetermined time following the mixing of step (a), measuring the NMR relaxation rate of water in the mixture, wherein the NMR relaxation rate is selected from the group consisting of T1, T2, T1/T2 hybrid, T 1rho , T 2rho , and T 2 * and corresponds to a level of LAL gelation in the mixture; and
(c) on the basis of said level of LAL gelation, determining a level of the endotoxin in said sample, wherein said method is capable of detecting 0.0001 EU/mL in said mixture.
2. The method of claim 1 , wherein step (b) is repeated and a change in said NMR relaxation rate is observed at two or more time points following step (a).
3. The method of claim 2 , further comprising calculating said change in said NMR relaxation rate, and, on the basis of said change, determining the endotoxin level in said sample.
4. The method of claim 1 , wherein step (c) further comprises comparing the NMR relaxation rate to a predetermined threshold value.
5. The method of claim 1 , wherein said endotoxin level is determined within 20 minutes of performing the mixing of step (a).
6. The method of claim 1 , wherein said mixture comprises from 10% to 50% of the amount of LAL reagent typically used in a turbidimetric assay.
7. The method of claim 1 , wherein said sample comprises a light scattering or light absorbing composition.
8. The method of claim 1 , further comprising determining from the NMR relaxation rate a magnetic resonance parameter value or set of values correlated to at least one population of water in said sample.
9. The method of claim 8 , comprising monitoring protons in water.
10. The method of claim 8 , comprising monitoring oxygen atoms in water.
11. The method of claim 1 , wherein said NMR relaxation rate measurements comprises a T2 measurement.
12. The method of claim 8 , wherein said magnetic resonance parameter value or set of values comprise a T2 parameter value.
13. The method of claim 8 , wherein said magnetic resonance parameter value or set of values comprise an amplitude parameter value.