⚗️ Dry residue, residue on ignition and loss on ignition in water and wastewater — gravimetric method (105 °C / 550 °C)

Physicochemistry PN-78/C-04541

Overview

Status of the standard: PN-C-04541:1978 (formerly designated PN-78/C-04541) has been withdrawn, but the method remains in laboratory practice.

PN-78/C-04541 "Woda i ścieki — Oznaczanie suchej pozostałości, pozostałości po prażeniu, straty przy prażeniu oraz substancji rozpuszczonych, substancji rozpuszczonych mineralnych i substancji rozpuszczonych lotnych" [Water and waste water — Determination of dry residue, residue on ignition, loss on ignition, dissolved solids, dissolved mineral solids and dissolved volatile solids] is a withdrawn standard (with no successor indicated in the PKN catalogue), but laboratories still quote it in their scopes of accreditation for this group of gravimetric determinations. The content of this entry is based on the PWr (Wrocław University of Science and Technology) textbook "Chemia wody" [Water chemistry] and on the PWr laboratory manual "Chemia wody i powietrza — metody analityczne" [Water and air chemistry — analytical methods], which describe this classical gravimetric methodology.

The dry residue is the sum of the substances dissolved and suspended in the water; it is determined by evaporating the sample and drying it at 105 °C. To determine the dissolved solids the sample is filtered (a filter with 0.45 µm pores gives the dissolved fraction, 1.2 µm — the fraction with colloids), evaporated and dried at 105 °C. Ignition at 550 °C gives the residue on ignition — the amount of mineral dissolved and suspended substances; filtration allows the dissolved mineral substances to be determined. The difference between the dry residue and the residue on ignition is the loss on ignition, that is the content of volatile (organic) substances. Range of determination: 5.0–200 mg in the sample. Samples are taken into clean glass or plastic bottles and determined without delay; if that is not possible, they are preserved with 2 cm³ of chloroform per 1 dm³ and stored at about 4 °C, the determination being made within 24 h.

THE CHOICE OF THE WRITING CONVENTION AND THE SCALE OF CITATIONS (23.09.2026). This standard appears in the accreditation scopes in TWO conventions of the same designation: the old one, with the year in the prefix ("PN-78/C-04541"), and the new one, with the year after the colon ("PN-C-04541:1978"). The distribution is unambiguous — the old one occurs 36 times in bare form plus four times with an added clause or procedure number, the new one twice. The key of this entry pointed to the NEW convention and gave 2 entries at 2 laboratories; after it was switched to the old one, the "Laboratories" tab shows 40 entries at 25 laboratories. The choice can neither be avoided nor "corrected": one prefix does not cover both generations of the record, so the two records in the new convention remain outside the matching.

Method principle

Dry residue: evaporation and drying to constant mass of a defined volume of the sample; dissolved solids: filtration, evaporation and drying to constant mass of a defined volume of the sample; residue on ignition: ignition of the dry residue at 550 °C and weighing. Clean, labelled crystallising dishes are dried for 2 h at 105 °C to constant mass (the difference between weighings ≤ 0.5 mg). For the determination 100 cm³ of a very thoroughly mixed sample is measured out (or 100 cm³ of filtrate through a paper filter for the dissolved solids), evaporated on a water bath, dried for 2 h at 105 °C to constant mass, cooled in a desiccator to room temperature and weighed; the dish with the residue is ignited for about 1 h in a muffle furnace at 550 °C (in the laboratory manual: drying at 105 °C for 60 min, ignition at 550 °C for 30 min), cooled in a desiccator and weighed. Calculations: dry residue X_og = (m₂ − m₁)·1000/V, dissolved solids X_m = (m₂ − m₁)·1000/V (m₁ — mass of the dried clean dish, m₂ — with the residue or the evaporated filtrate, in mg; V — volume of the sample, in cm³), residue on ignition X_pp = (m₂ − m₁)·1000/V with the masses after ignition, loss on ignition X_sp = X_og − X_pp; results in mg/dm³ rounded to 1.

Applications

• Surface water and groundwater — overall mineralisation (dry residue, dissolved mineral solids)
• Raw and treated wastewater — the share of volatile (organic) substances in the dry residue
• Boiler, cooling and process waters — control of salinity and of deposits
• Completion of the balance: dry residue = dissolved solids + total suspended solids
• Gravimetric laboratories — simple equipment: water bath, drying oven, muffle furnace, analytical balance

Key parameters

Standard

Standard number

PN-C-04541:1978

Title (PL)

Woda i ścieki — Oznaczanie suchej pozostałości, pozostałości po prażeniu, straty przy prażeniu oraz substancji rozpuszczonych, substancji rozpuszczonych mineralnych i substancji rozpuszczonych lotnych

Title (EN)

Water and waste water — Determination of dry residue, residue on ignition, loss on ignition, dissolved solids, dissolved mineral solids and dissolved volatile solids

Step-by-step procedure

1. Sample

   Take the sample into a clean glass or plastic bottle; determine it without delay, and if that is not possible — preserve it with 2 cm³ of chloroform per 1 dm³, store at about 4 °C and determine within 24 h.

2. Preparation of the dishes

   Dry clean, labelled crystallising dishes for 2 h at 105 °C (for ignition — ignite them at 550 °C) to constant mass (difference between weighings ≤ 0.5 mg); cool in a desiccator and weigh (m₁).

3. Dry residue

   Measure 100 cm³ of the very thoroughly mixed sample into the dish, evaporate on a water bath, dry for 2 h at 105 °C to constant mass, cool in a desiccator and weigh (m₂).

4. Dissolved solids

   Mix the sample thoroughly, filter it through a paper filter (or a 0.45 µm membrane filter), measure out 100 cm³ of the filtrate and proceed as in step 3.

5. Residue on ignition

   Ignite the dish with the residue from the determination of the dry residue (or of the dissolved solids) for about 1 h in a muffle furnace at 550 °C, cool in a desiccator to room temperature and weigh.

6. Calculations

   X = (m₂ − m₁)·1000/V [mg/dm³] for the dry residue, the dissolved solids and the residue on ignition respectively (with the masses after ignition); loss on ignition = dry residue − residue on ignition. Round to 1 mg/dm³.

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• Muffle furnace at 550 °C and drying oven at 105 °C — tongs, heat-resistant gloves, careful removal of the dishes
• Chloroform (preservation) — toxic; dispense in a fume hood
• Wastewater — possible pathogens; gloves, disinfection

Frequently asked questions