Table 5: Accuracy of TPH determination by reflectance spectroscopy and three commercial laboratories.

Lab Spectroscopy A B C TPH level (calculated) AVG delta AVG deviation Max delta Max deviation AVG delta AVG deviation Max delta Max deviation AVG delta AVG deviation Max delta Max deviation AVG delta AVG deviation Max delta Max deviation Low (400–600) 325 68% 747 143% 349 68% 500 93% 192 42% 356 84% 283 57% 508 97% Medium (2500–6000) 2055 47% 4360 74% 1956 51% 2795 92% 1010 30% 2532 78% 2590 60% 4781 97% High (9000–12000) 6187 61% 11494 83% 4392 49% 6150 81% 1827 26% 4210 73% 4413 50% 5859 95%