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Sample preservation and holding time

Test Parameters Preservative Maximum Holding Time
Alkalinity Ice 14 days
Ammonia, Ammonia Nitrogen Ice, sulfuric acid (H2SO4) to pH≈<2 28 days
Arsenic Ice, nitric acid (HNO3) to pH ≈2 6 months
BOD (biochemical oxygen demand) Ice 48 hours
Boron Ice 28 days
Bromide None required 28 days
Calcium Ice, nitric acid (HNO3) to pH≈2 6 months
Chloride None required 28 days
Chlorine, Total Residual None required Analysis immediately
Chromium, Hexavalent (VI) Ice 24 hours
COD (chemical oxygen demand) Ice, sulfuric acid (H2SO4) to pH≈2 28 days
Coliform, fecal Ice, 0.008% sodium thiosulfate (Na2S2O3 ● 5HOH) if residual chlorine is present 6 hours
Color Ice 48 hours
Cyanide, Total Ice, sodium hydroxide (NaOH) to pH >12 14 days BUT maximum holding time is 24 hours if sulfide is present
DO (dissolved oxygen) None Analyze immediately
Fluoride Ice 28 days
Hardness Ice, nitric acid (HNO3) to pH ≈2 6 months
Hydrocarbons, Aromatic Volatile Organic Ice, hydrochloric acid (HCI) to pH <2 14 days
Mercury Ice, nitric acid (HNO3) to pH≈2 28 days
Metals, except those specifically listed Ice, nitric acid (HNO3) to pH ≈2 6 months
Nitrate Ice 48 hours
Nitrate-Nitrite Ice, sulfuric acid (H2SO4) to pH≈2 28 days
Nitrite Ice 48 hours
Nitrogen, organic Ice, sulfuric acid (H2SO4) to pH≈2 28 days
Nitrogen, total kjeldahl Ice, sulfuric acid (H2SO4) to pH≈2 28 days
Oil & Grease Ice, hydrochloric acid (HCI) to pH <2 28 days
Organics, Other Ice, 0.008% sodium thiosulfate (Na2S2O3 ● 5HOH) 7 days until extraction; 40 days following extraction
Orthophosphate Filter immediately, ice 48 hours
Pesticides Ice immediately 7 days until extraction; 40 days following extraction
Petroleum hydrocarbons, total recoverable Ice, hydrochloric acid (HCI) to pH≈2 28 days
pH None required Analyze immediately
Phenols Ice, sulfuric acid (H2SO4) to pH≈2 24 hours
Phosphorus, total Ice, sulfuric acid (H2SO4) to pH≈2 48 hours
Sodium Ice, nitric acid (HNO3) to pH≈2 6 months
Specific Conductance None required Analyze immediately
Sulfate Ice 28 days
Sulfide Ice, zinc acetate plus sodium hydroxide (NaOII) to pII>9 7 days
Sulfite Ice Analyze immediately
Temperature None required Analyze immediately
Total Dissolved Solids Ice 7 days
Total Settleable Solids Ice 48 hours
Total Suspended Solids Ice 7 days
Turbidity None required Analyze immediately
Volatile Organic Aromatics (VOA) None required  
Volatile Organic, Halogenated Ice, 0.008% sodium thiosulfate (Na2S2O3 ● 5HOH) 14 days
Volatile Organic, Non- halogenated Ice, 0.008% sodium thiosulfate (Na2S2O3 ● 5HOH)  


Acidification Guidelines Table for sample pH ≈ 2
(Provided by the Water Quality Division Laboratory)
Acid name 250 ml sample (8 oz. plastic container) add ml acid 500 ml sample (16 oz. plastic container) add ml acid 1000 ml sample (1L) (32 oz. plastic container) add ml acid 2000 ml sample (2L) (64 oz. plastic container) add ml acid
1: 1 Nitric 0.7 1.3 1.7 3.0
Hydrochloric 0.9 1.3 2.4 4.5
Sulfuric 0.3 0.5 1.1 1.9


Method Reference: United States Environmental Protection Agency Methods for Chemicals Analysis of Water and Wastes, EPA - 600 / 4-79-020; Standard Method for the Examination of Water and Wastewater,18th edition, 1992; Water Quality Division Laboratory

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