COD Digestion Vials. Minimize handling of corrosive and toxic chemicals and eliminate pipetting hazardous reagents. 16 mm Test ’N Tube for Hach DR 6000™ and DR 3900™ Spectrophotometers. Ultra-low Range — 0.7-40.0 mg/L with 150 tests. Low Range — 3-150 mg/L with 150 tests, EPA compliant.