Total Suspended Solids (TSS) and Total Dissolved Solids (TDS)
1 Purpose
This SOP describes the gravimetric determination of Total Suspended Solids (TSS) and Total Dissolved Solids (TDS) in environmental water samples (e.g., surface water, groundwater, runoff). TSS represents the portion of solids retained by a glass fiber filter, while TDS represents the portion that passes through the filter and is dried to constant weight in a vessel (APHA et al., 2012).
2 Scope
- Applies to: Environmental water samples analyzed for TSS and TDS by gravimetric methods.
- Does not apply to: Settleable solids, volatile suspended solids, or non-aqueous matrices.
- Location: Environmental analysis laboratories.
3 Responsibilities
| Role | Responsibility |
|---|---|
| Lab PI | Approve SOP, ensure training compliance |
| Trained Personnel | Follow this SOP, report deviations |
| New Students | Complete training before independent use |
4 Definitions
- Constant mass: Successive weighings (after additional drying cycles of at least 1 hour) agree within ±0.5 mg; the criterion confirming complete desiccation.
- Detection limit (MDL): The minimum concentration that can be reliably distinguished from a blank; for gravimetric TSS/TDS, the practical lower limit is approximately 5 mg/L, set by the precision of the analytical balance and filter tare variability (APHA et al., 2012).
- Fixed residue: The fraction of total solids remaining after ignition at 550 °C; equivalent to inorganic (mineral) solids.
- Relative percent difference (RPD): A measure of duplicate precision: RPD (%) = |A - B| / ((A + B) / 2) × 100; acceptance criterion for TSS/TDS duplicates is ≤ 10%.
- Total dissolved solids (TDS): The mass of material passing through a 0.45 µm filter per unit volume of sample, determined gravimetrically after evaporation at 180 °C; expressed in mg/L (APHA et al., 2012, Method 2540 C).
- Total solids (TS): The residue remaining after evaporation of a sample at 103–105 °C; TS = TSS + TDS.
- Total suspended solids (TSS): The mass of material retained on a pre-weighed glass fiber filter per unit volume of sample; expressed in mg/L (APHA et al., 2012, Method 2540 D).
- Volatile suspended solids (VSS): The fraction of TSS lost on ignition at 550 °C; approximates the organic content of suspended solids (APHA et al., 2012).
5 Safety and Hazards
- Thermal: Drying ovens (103–180 °C) and muffle furnaces can cause severe thermal burns. Always use heat-resistant crucible tongs and thermal gloves when handling hot apparatus.
- Vacuum/Implosion: Vacuum filtration assemblies operate under reduced pressure. Ensure filtration flasks are borosilicate glass and free of visible cracks to eliminate implosion risks.
5.1 Required PPE
5.2 Emergency Procedures
In case of burn or equipment failure, refer to SOP-L002 Laboratory Safety or call campus safety.
6 Equipment and Materials
6.1 Equipment
| Item | Notes |
|---|---|
| Vacuum filtration apparatus | Buchner funnel, flask, and vacuum pump |
| Analytical balance | Capable of weighing to ±0.1 mg |
| Drying oven | Regulated at 103–105 °C (TSS) and 180 ±2 °C (TDS) |
| Desiccator | With active color-indicating silica gel |
| Blunt forceps | For filter handling |
| Graduated cylinder | For measuring sample volume |
6.2 Consumables
| Item | Notes |
|---|---|
| Glass microfiber filter disks | e.g., Whatman 934-AH, 1.5 µm nominal pore size (APHA et al., 2012) |
| Evaporating dishes | Porcelain or high-silica glass |
| Aluminum weigh pans | For filter drying |
| Deionized (DI) water | For filter washing and volume adjustment |
7 Procedure
7.1 Filter and Dish Preparation
TSS filter prep: Place a glass fiber filter on the filtration apparatus. Apply vacuum and wash with three successive 20 mL volumes of DI water. Continue vacuum until all trace water is removed. Transfer the filter to an aluminum weigh pan and dry in an oven at 103–105 °C for 1 hour. Cool in a desiccator to room temperature and weigh to determine the tare mass (\(B_{\text{TSS}}\)) (APHA et al., 2012).
TDS dish prep: Clean an evaporating dish and heat in an oven at 180 ±2 °C for 1 hour. Cool completely in a desiccator and record the stable tare mass (\(B_{\text{TDS}}\)).
7.2 Filtration and Sample Analysis
Assemble the pre-weighed filter pad into the filtration funnel and wet with a small volume of DI water to seal it against the porous plate. Turn on the vacuum.
Shake the sample bottle vigorously to achieve homogeneous particle distribution. Measure a known sample volume (\(V\), typically 100 mL to 500 mL depending on turbidity) using a graduated cylinder.
Pour the measured sample into the filter funnel. Wash the cylinder and funnel walls with three successive 10 mL aliquots of DI water, allowing total drainage between washings.
For TSS: Carefully remove the filter pad from the funnel using blunt forceps. Place it back in its aluminum pan and dry in the oven at 103–105 °C for at least 1 hour. Cool in the desiccator and weigh to constant mass (\(A_{\text{TSS}}\)).
For TDS: Transfer the entire filtrate volume from the filter flask quantitatively into the pre-weighed evaporating dish. Place the dish into the drying oven at 180 ±2 °C until all liquid evaporates completely. Dry for at least an additional hour, cool inside the desiccator, and weigh to find the final mass (\(A_{\text{TDS}}\)).
“Constant mass” means that successive weighings (after additional drying cycles of at least 1 hour) agree within ±0.5 mg (APHA et al., 2012).
7.3 Shutdown and Cleanup
- Discard used filters in solid waste.
- Rinse filtration apparatus thoroughly with DI water.
- Return evaporating dishes and tongs to storage after cooling.
- Turn off the vacuum pump and drying oven if no other users need them.
8 Calculations
\[ \text{TSS (mg/L)} = \frac{(A_{\text{TSS}} - B_{\text{TSS}}) \times 1{,}000{,}000}{V \text{ (mL)}} \]
\[ \text{TDS (mg/L)} = \frac{(A_{\text{TDS}} - B_{\text{TDS}}) \times 1{,}000{,}000}{V \text{ (mL)}} \]
Where:
- \(A\) = weight of dry filter or dish plus residue (g)
- \(B\) = tare weight of clean filter or dish (g)
- \(V\) = sample volume (mL)
If the calculated TSS residue mass is less than 2.5 mg, increase the sample volume and repeat (APHA et al., 2012).
9 Quality Control and Acceptance Criteria
- Run a method blank (DI water through the full procedure) with each batch. The blank result must be less than the method detection limit (APHA et al., 2012).
- Duplicate samples should agree within ±10% RPD.
- If the measured residue mass is less than 2.5 mg, use a larger sample volume.
10 Waste Disposal
| Waste Type | Container | Disposal Method |
|---|---|---|
| Used glass fiber filters | Solid waste bin | Standard solid waste |
| Filtered water samples | Drain | If no hazardous analytes |
11 References
- APHA et al. (2012)
- SOP-L002 Laboratory Safety
- SOP-L114 Vacuum Filtration
13 Training Record
Training is documented in the lab training log. Before working independently, personnel must:
- Read this SOP in full
- Observe a trained operator perform the procedure
- Perform the procedure under supervision
- Be signed off by the PI or designated trainer