WATER SAMPLE COLLECTION AND FILTRATION PROTOCOLS

Below is a practical, ready-to-use set of protocols and SOP templates for water sampling and filtration covering common needs

(microbial, suspended solids, nutrients, metals, organics). Use only the parts that match your project/analyses and local regulations. I’ve included step-by-step procedures, materials, QA/QC, storage/preservation, safety notes, and a Chain-of-Custody + Sample Log template you can copy.

Definitions (quick)

• Grab sample — single-timepoint sample collected at one time/depth.
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• Composite sample — pooled over time or depth (time-weighted, flow-weighted, etc.).
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• Field filter — filtration performed at the sampling site.
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• Laboratory filtration — filtration in a controlled lab (laminar flow / clean bench).
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• Membrane filter pore sizes commonly used: 0.45 µm (dissolved/particulate boundary), 0.22 µm (sterile / bacteria removal), 0.7 µm GF/F (particulate / chlorophyll/TSS).

 Responsibilities

• Field technician: sample collection, labeling, chain-of-custody, in-field filtration (if applicable), initial storage (cooler/ice).
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• Lab analyst: final filtration (if done in lab), preservation, analysis, record retention.
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• QA officer: review sample log, check blanks/duplicates, ensure TIMELY processing.

Purpose & scope

• Provide consistent, contamination-minimized procedures for collecting, filtering, preserving, transporting, and documenting water samples for microbiological, particulate, nutrient, trace-metal and organic analyses.

 Materials & equipment (typical)

• Pre-cleaned sample bottles (HDPE for nutrients, polypropylene/amber glass for organics as required).
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• Sterile bottles for microbiological samples (sterile, sodium thiosulfate–dosed if disinfectant present).
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• Coolers with ice packs, temperature logger or thermometer.
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• Syringe filters (0.22 µm PTFE or PES for organics; nylon or PES for aqueous nutrients), disposable syringes.
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• Vacuum manifold and membranes (0.45 µm cellulose nitrate, mixed cellulose ester (MCE), or 0.45 µm PTFE depending on analyte).
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• Glass fiber filters (GF/F, 0.7 µm) for TSS and chlorophyll.
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• Sterile membrane filters (0.45 µm or 0.22 µm) for microbial concentration.
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• Portable peristaltic pump / filtration rig for field filtration (sterile tubing, in-line filter holders).
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• Field decontamination supplies (70% ethanol, 10% bleach solution, deionized water).
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• Preservatives: HNO₃ (trace metals), HCl, sulfuric acid (for certain analyses), NaOH (for alkalinity titration, if required), sodium thiosulfate (dechlorination).
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• Labels, permanent markers, sample bags, chain-of-custody forms.

 Grab sampling procedure (surface water)

1. Record GPS location, date/time, weather, water level and site conditions.
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3. Put on clean gloves; if near contaminants avoid touching bottle mouth or inside cap.
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5. Remove cap carefully; for surface samples, face upstream and reach 0.3–0.5 m below water surface (or as required) and fill bottle allowing overflow (for dissolved analytes rinse 3× with sample then fill). For deeper sampling use Van Dorn or bailer.
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7. For microbiology: use sterile bottle; fill leaving minimal headspace; if sample is chlorinated, collect into bottle containing sodium thiosulfate (pre-dosed).
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9. For dissolved metals and nutrients: filter (field or lab) through 0.45 µm and acidify to pH <2 with ultrapure HNO₃ (0.5–1% v/v final depending on guidance). Add acid AFTER filtration unless guidance says otherwise.
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11. For TSS: fill GF/F pre-weighed filter holders in lab or bring unfiltered sample kept cold; follow method requiring filtration on GF/F (0.7 µm).
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13. Cap, invert to mix preservative (if present), label and place in cooler at 4 ± 2 °C. Add chain-of-custody record.

 Laboratory filtration

• Work in a clean area or laminar-flow hood for low-concentration analyses.
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• Use disposable syringe filters for small volumes (≤100–250 mL) and vacuum manifold for larger volumes.
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• Sterilize reusable filter holders by autoclave between uses and rinse with sample water prior to filtration.
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• Document filter lot numbers, pore size, and membrane type in sample log.

Field filtration (when required)

Use field filtration to stabilize sample (e.g., metals, nutrients) when immediate lab access is >6–8 hours.

Procedure (sterile technique):

1. Assemble sterile filtration setup: peristaltic pump or syringe + in-line filter (0.45 µm for dissolved metals/nutrients; 0.22 µm when sterility needed). Pre-rinse filter with sample water (discard first 50–100 mL) using the same sample to avoid bias.
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3. Filter desired volume (see analyte-dependent volumes below). Use low pressure; avoid heating sample.
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5. Collect filtrate into pre-rinsed, pre-labeled bottles. For metals: acidify filtrate to pH <2 with trace-metal grade HNO₃ (specify amount to reach pH <2). For nutrients: keep refrigerated and analyze or freeze as per method.
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7. Preserve and store at 4 °C unless freezing is required.

• Notes: pre-rinsing and discarding first filtrate reduces adsorption artifacts. For organics, use solvent-rinsed glassware and PTFE-lined caps.

Volumes & holding times (typical guidance)

• Microbiology (bacteria): sample ≤6 hours to lab, hold at 4 °C; process within 6–24 hours depending on standard method.
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• Metals (filtered & acidified): hold up to 6 months for many metals (check method).
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• Nutrients: analyze within 48 hours (some can be frozen for longer).
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• TSS: analyze within 7 days; immediate filtration recommended.
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• Organics (pesticides/VOCs): many have short hold times (VOCs: 14 days for some analyses; check method).
• Always check the specific reference method (EPA, APHA, ISO) for exact holding times and volumes required by that method and your accrediting body.

 Decontamination of reusable equipment

• Rinse with tap water → soak 10% Decon/10% bleach (if compatible) → rinse with copious DI water → rinse with 10% HCl for trace metal work → rinse with DI water → dry or store in clean area. For microbiology, autoclave or use 70% ethanol and flame when appropriate.

FILtration specifics by analyte

Microbial analysis (bacteria/coliform/E. coli):

• Typical filter: 0.45 µm mixed cellulose ester or 0.45 µm nitrocellulose.
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• Volume: depends on expected bacteria load — 100 mL is common; if low bacteria expected, filter 500–1000 mL.
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• After filtration, place membrane onto selective growth medium (m-Endo, m-FC, etc.) or extract for qPCR. Process within 6 hours ideally. Keep at 4 °C during transport.

Viruses:

• Use electronegative filters or ultrafiltration methods; large volumes (5–100 L) often required and concentration steps are necessary. Follow specialized viral concentration SOPs.

Total Suspended Solids (TSS) / Particulates:

• Pre-weighed GF/F (0.7 µm) or GF/C filters.
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• Filter known volume (e.g., 500 mL to several L as required), dry at 103–105 °C, cool in desiccator, weigh to compute TSS.

Dissolved metals:

• Filter through 0.45 µm (or 0.2 µm if required), then acidify to pH <2 with ultra-pure nitric acid, store at 4 °C. Use trace-metal clean bottles.

Nutrients (NO₃, NO₂, NH₄, PO₄, SiO₂):

• Filter through 0.45 µm (0.7 µm GF for chlorophyll/particulate nutrients as specified). Keep at 4 °C and analyze within specified holding times (commonly 24–48 hours; if longer, freeze or follow method guidance).

Organic compounds (pesticides, VOCs, pharmaceuticals):

• Use amber glass bottles with PTFE-lined caps for semi-volatiles; HCl or NaHCO₃ preservation only when method calls for it. For VOCs, collect with zero-headspace glass vials, preserve with acid if required, transport chilled. Use appropriate SPE cartridges for concentration; filter through 0.7 µm GF/F prior to SPE in some protocols.

Troubleshooting & tips

• If filter clogs quickly: reduce turbidity by pre-filtering with a larger pore (e.g., 1–5 µm) or reduce sample volume, or use larger filter surface area.
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• If analyte adsorption suspected (metals/nutrients): pre-rinse filters with sample and use appropriate membrane chemistry (PTFE or cellulose acetate depending on analyte).
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• For low-concentration organics: minimize plastics, use glass with PTFE cap liners, pre-rinse glass with methanol for organics if SOP allows.
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• For microbial viability: avoid temperature fluctuations; keep cool and avoid freezing unless method says so.
• nitrate
• nitrate nitrogen
• nitrate in water
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• nitrate analysI

• NITRATE CHROMATOGRAM PEAK IDENTIFICATION IN ION CHROMATOGRAPHY.LAXMI ENTERPRISE.VADODRA,GUJARAT,