Spring 2008
Gravimetric Measurement of Total Suspended Solids (TSS)
Introduction
The amount of total suspended solids may be quantified (mg/L, mg/m3) by vacuum filtration of a known
volume of sample through a pre-weighed (tared) membrane (Millipore) filter. The filter is rinsed of salts, dried
and re-weighed. The difference of the weight is due to filtered material and it has thus been measured
gravimetrically.
Vacuum Filtration
Equipment
Millipore vacuum filter apparatus, Millipore filters, distilled water, forceps (flat bladed, non-serrated),
desiccator, analytical balance, aluminum foil, drying oven, water sample.
Procedure
Filter Preparation:
NOTE: Steps 1 and 2 of Filter Preparation have already been completed for you. Each group will be
analyzing 3 water samples: Greenfield Lake, Cape Fear River, and Leland Retention pond. You will need 3
filters per sample, as well as 2 blank filters, for a total of 11 filters.
1. Soak the filters for about 5 minutes in distilled water. Gently shake dry and lay them out on a strip of
aluminum foil (pre-crumpled & reflattened helps to prevent sticking).
2. Dry the filters (on the foil) for 60 minutes at 75°C. Remove and let cool in a desiccator if unable to get
to a balance immediately.
3. Do NOT touch the filters with your fingers. Use the forceps to handle the filters. Use a ball point pen
(or non-water soluble marker) to number the filters along their edges. Place each filter in a small petri
dish.
4. Weigh each filter and record this weight, in mg, as the TARE WEIGHT. Use an analytical balance
recording the value in the proper desired units (mg).
Filter Use:
1. Place a filter on the membrane filter set-up and filter the sample. MIX the water sample by inversion
before filtering. Use 15 inches of mercury (in. of Hg) of vacuum. Record the sample's number, filter
number, and volume filtered (in liters).
2. Use two distilled water rinses of about 3 to 5 mL each to wash residual salts off the solids and through
the filter. Turn the suction off while adding the rinse water. Finish rinsing by removing the filtration
apparatus top and rinsing the filter edge by adding water to the edge while the suction is on.
3. Remove the wet filter with the forceps, place it on foil, re-dry (60 minutes at 75°C)** and reweigh.
Record this second weight, in mg, as the GROSS WEIGHT.
**While you are waiting for your filters to dry, prepare your Lab Notebook write-up.
Blank Determination:
Since the filters are hygroscopic (readily absorb water from the atmosphere) a Blank Correction must be
calculated and applied. This is done by keeping some (2 or 3) prepared filters unused and then re-weighing
them with the rest of the sampled filters. Any change in weight from the TARE value is due to interaction with
the atmosphere and must be corrected for: an average decrease must be added back for all the sampled
filters' Net Weight; an average increase must be subtracted from all the sampled filters' Net Weight. The Blank
Correction should correct for the average weight change of your Blanks.
Spring 2008
Results & Calculations
SPM in mg/L = W2 - W1 ± X
V
Where:
W2 = GROSS WEIGHT (in mg)
W1 = TARE WEIGHT (in mg)
X = BLANK CORRECTION (in mg)
(+ or - as appropriate)
V = VOLUME (in Liters)
Note: W2 – W1 ± X is the CORRECTED NET!
Include any sources of error in your Discussion/Conclusion section of your Lab Notebook.
Imhoff Cone
In addition to the vacuum filtration procedure, settleable solids will be measured using Imhoff cones. The
settleable solids test is the measurement of the volume of solids in one liter of sample that will settle to the
bottom of an Imhoff cone during a specific time period. The test indicates the volume of solids removed by
settling in sedimentation tanks, clarifiers or ponds.
Equipment
Imhoff cone and rack, stirring rod and timer
Procedure
1. Fill an Imhoff cone to the one-liter mark with a well mixed sample.
2. Allow sample to settle in the Imhoff cone for 45 minutes.
3. Gently stir the sample with a glass stirring rod to release the suspended matter clinging to the sides of
the Imhoff cone. Do not disturb the settled solids at the bottom of the cone!
4. Let sample settle for an additional 15 minutes.
5. At this point, one hour has passed. Record the volume of settleable solids (in milliliters) in the Imhoff
cone.
**Note: Do not include any floating solids as settleable matter.
Results & Calculations
The following must be recorded in your Lab Notebook:
 Sample identification (source, name and date(s) of collection
 Analyst(s)
 Raw data/final results with correct units (reported to nearest mL/L)
 Description of unusual sample characteristics
No calculations are necessary to determine the settleable solids. The data obtained after the one hour test is
the result.