💧 Free, bound and total cyanides in water and waste water — the withdrawn PN-C-04603 series

Water and waste water PN-C-04603-01

Overview

THE SCOPE OF SHEET 01 FROM THE PKN CATALOGUE CARD, IN FULL: "The method is used for the determination of free, bound and total cyanides in the concentration range 0.005 to 1.0 mg/l. The method is not used for the determination of bound and total cyanides if the test sample contains acrylonitrile, calcium cyanamide, thiourea, urotropine or formalin. The method consists in separating the cyanides from the sample by distillation, reducing the free cyanides with chlorine (from chloramine), reaction with pyridine, condensation with barbituric acid and the formation of a red-violet polymethylene dye. The intensity of the colour of the dye formed is proportional to the cyanide content of the test sample and is measured photometrically or assessed visually. Reagents and solutions, apparatus and instruments, preparation of samples for testing, preparation of the set of standard solutions, drawing up the calibration curve, carrying out the distillation, carrying out the test, calculation of the result, and the final result of the determination are given".

FIVE SUBSTANCES THAT RULE THE METHOD OUT — THE MOST IMPORTANT SENTENCE OF THIS SCOPE. The card names them expressly: acrylonitrile, calcium cyanamide, thiourea, urotropine and formalin. In their presence the method MUST NOT be used for bound and total cyanides — the restriction not extending to free cyanides. It is a rare case of a catalogue card stating exclusion conditions outright; usually such restrictions sit in the text of the standard. For a laboratory accepting a commission on industrial waste water this is the first question: does any of these five substances occur in the stream.

THREE FORMS OF CYANIDE — AND WHY THEY ARE NOT THE SAME. Free cyanides are the cyanide ion and hydrogen cyanide — the most toxic form and the one most readily released. Bound cyanides occur in complexes with metals, of widely varying stability. Total cyanides are the sum of both. Limit values in regulations are sometimes set separately for free and for total cyanides, so the report must state which form was determined — the name "cyanides" alone is incomplete. This distinction is in any case the subject of a separate entry in this knowledge base, based on the standard ISO 6703.

DISTILLATION AS THE DECIDING STAGE. The method separates the cyanides from the sample by distillation — and it is the conditions of distillation that decide which complexes will decompose, and hence what is actually measured. The colour reaction with pyridine and barbituric acid is common to all three forms; what differentiates them is the way the sample is prepared before distillation.

THE SERIES AND ITS SHEETS. The card of sheet 00 ("General provisions and scope of the standard", 1 page) gives in its scope: "The subject and thematic scope of the standard are given, including the list of the sheets of the standard". Sheet 00 was withdrawn on 31-12-2002, sheet 01 on 07-11-2011. The catalogue also holds sheets 02, 03 and 04 from the years 1980–1986. A reference to "PN-80/C-04603" without the sheet number does not settle which method is meant — the same class of ambiguity as with the PN-Z-04030 series, described in a separate entry of this knowledge base.

BOTH SHEETS CHECKED ARE WITHDRAWN. The cards retrieved on 16 September 2026 carry the heading "Withdrawn" consistent with the "Date of withdrawal" row. Neither contains a "Superseded by" field — the catalogue names no successor. In this knowledge base the current practice is described by entries based on ISO standards: the determination of cyanides to ISO 6703 and flow analysis to PN-EN ISO 14403-2. The present entry serves the recognition of older references, not the application of the method.

WHAT WE DO NOT GIVE. We do not have the texts of the sheets — PKN supplies them for a fee (sheet 01 has 4 pages, KT 121 — the PKN technical committee for Water Quality, Chemical Testing, Inorganic Substances). Apart from the concentration range and the list of five substances, which the card itself gives, WE GIVE NEITHER the concentrations of reagents, NOR the conditions of distillation, NOR the measurement wavelength, NOR the way of calculating the result.

Method principle

The cyanides are separated from the sample by distillation, after which the free cyanides are treated with chlorine derived from chloramine — the card calls this stage a reduction — then reacted with pyridine and condensed with barbituric acid. A red-violet polymethylene dye is formed, the intensity of whose colour is proportional to the cyanide content; it is measured photometrically or assessed visually. It is the conditions of sample preparation and distillation that decide whether the result concerns free, bound or total cyanides.

Applications

• Recognising references to the PN-C-04603 series met with in older procedures and accreditation scopes
• Distinguishing whether a report concerns free, bound or total cyanides
• Judging whether the method was admissible for a given sample — five substances rule it out
• Historical context for the current methods of determining cyanides based on ISO standards

Key parameters

Standard

Standard number

PN-C-04603-01:1980 (wersja polska)

Title (PL)

Woda i ścieki -- Badania zawartości cyjanków -- Oznaczanie cyjanków wolnych, związanych i ogólnych metodą kolorymetryczną

Title (EN)

Water and waste water — Tests for cyanide content — Determination of free, bound and total cyanides by the colorimetric method

Step-by-step procedure

1. Check whether the document is still in force

   Sheet 01 has been WITHDRAWN since 07-11-2011. A procedure invoking this series requires updating; the current practice is described by entries based on ISO standards.

2. Check for the substances that rule the method out

   Acrylonitrile, calcium cyanamide, thiourea, urotropine, formalin. Their presence rules out the method for bound and total cyanides.

3. Establish the form to be determined

   Free, bound or total. The preparation of the sample depends on it, and so does the limit value the result will be compared with.

4. Distillation

   Separation of the cyanides from the sample. WE DO NOT GIVE THE CONDITIONS — they are in the text of the sheet.

5. Colour reaction and measurement

   Reduction with chlorine, reaction with pyridine, condensation with barbituric acid; photometric measurement or visual assessment.

6. Record in the report

   Give the form of cyanide determined and the FULL designation with the sheet number — "PN-80/C-04603" alone does not identify a method.

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• Cyanides are extremely toxic substances — the lethal dose is counted in milligrams; work only under a sound fume hood, with access to a rescue kit
• ACIDIFYING A SAMPLE CONTAINING CYANIDES RELEASES HYDROGEN CYANIDE — a lethally poisonous gas with a faint odour that part of the population cannot detect; the distillation is carried out in a closed system
• Pyridine is a flammable, harmful liquid with a penetrating odour that lingers in the room and on clothing
• The waste from the determination contains cyanides — it requires disposal and must not be discharged to the sewer

Frequently asked questions