ISO 8968-2-2001 PDF

Full title and description

ISO 8968-2:2001 — Milk — Determination of nitrogen content — Part 2: Block-digestion method (Macro method). This part of ISO 8968/IDF 20 specifies a macro block-digestion (Kjeldahl-style) analytical procedure for the determination of total nitrogen in liquid milk (whole or skimmed) to allow calculation of crude protein content.

Abstract

ISO 8968-2:2001 defines a block-digestion procedure (macro method) based on the Kjeldahl principle for mineralizing milk samples, followed by distillation and titration to determine nitrogen content. The standard gives required reagents, apparatus, sampling and sample preparation, the stepwise procedure, blank and recovery checks, calculation methods for nitrogen and crude protein, and precision data (repeatability and reproducibility) for routine dairy laboratory use.

General information

• Status: Withdrawn / superseded (see details below).
• Publication date: 15 December 2001 (Edition 1).
• Publisher: International Organization for Standardization (ISO) — also published as IDF 20-2.
• ICS / categories: 67.100.10 (Milk and milk products).
• Edition / version: Edition 1, 2001.
• Number of pages: 9 (typical published length for this part).

Scope

This part applies to the determination of total nitrogen in liquid milk (whole or skimmed) using a block-digestion (macro) Kjeldahl procedure. It covers sampling, reagents and apparatus, digestion, distillation and titration steps, blank and recovery tests, calculation of nitrogen and conversion to crude protein, and gives precision statements. It is intended for routine and reference testing of milk; it does not cover products outside the stated sample types or alternative nitrogen-determination techniques.

Key topics and requirements

• Principle: block digestion (sulfuric acid + catalyst) to convert organic nitrogen to ammonium, followed by alkaline distillation and acid titration (Kjeldahl approach).
• Specified reagents, digestion catalysts and recommended concentrations for reproducible digestion.
• Required apparatus: digestion block or comparable equipment, distillation unit, titration setup, sample containers and volumetric glassware.
• Sampling and sample preparation guidance for liquid milk (homogenization, representative test portion sizes for the macro method).
• Step-by-step procedure: test portion selection, digestion conditions, distillation, titration and blank determinations.
• Calculation methods to report nitrogen content and to convert nitrogen to crude protein using the appropriate factor.
• Quality checks: blank tests, recovery tests (spikes), and handling of interfering substances.
• Precision statements: repeatability and reproducibility criteria based on interlaboratory trials reported in the standard.

Typical use and users

Used by dairy industry quality-control and R&D laboratories, independent food-testing laboratories, regulatory and inspection bodies, and standards organizations for routine testing and contract analyses of milk. It is suitable where a macro Kjeldahl digestion workflow (moderate sample size, conventional digestion block) is preferred over semi-micro or automated rapid methods.

Related standards

ISO 8968 is a multipart series; related items include ISO 8968-1 (Kjeldahl principle and crude protein calculation — later consolidated and updated in ISO 8968-1:2014), ISO 8968-3 (block-digestion semi-micro rapid routine method), IDF 20 series equivalents, and earlier reference methods such as ISO 5549 (withdrawn). Many national and regional adoptions exist as EN ISO 8968-2:2001 and equivalent national standards.

Keywords

milk, nitrogen determination, Kjeldahl, block digestion, macro method, crude protein, IDF 20-2, ISO 8968, dairy analysis, repeatability, reproducibility

FAQ

Q: What is this standard?

A: ISO 8968-2:2001 is the part of the ISO 8968 series that specified a block-digestion (macro Kjeldahl) method for determining total nitrogen in liquid milk and for calculating crude protein.

Q: What does it cover?

A: It covers reagents, apparatus, sampling, digestion, distillation and titration steps, blank and recovery checks, calculation of nitrogen and crude protein, and precision (repeatability and reproducibility) for the macro digestion method applied to whole and skimmed milk.

Q: Who typically uses it?

A: Dairy industry QC and R&D labs, independent food testing laboratories, regulators and anyone performing routine or contract analysis of milk for nitrogen/protein content who prefers a macro Kjeldahl digestion workflow.

Q: Is it current or superseded?

A: ISO 8968-2:2001 has been superseded and is no longer the current active part for many applications. The ISO 8968 series was consolidated and updated in later publications (notably ISO 8968-1:2014 for the Kjeldahl principle and crude protein calculation). The 2001 Part 2 text is considered withdrawn/superseded in favor of the updated series parts; users should refer to ISO 8968-1:2014 and current parts for the presently recommended methods and any updated scope or precision statements.

Q: Is it part of a series?

A: Yes — ISO 8968 is a multipart series on determination of nitrogen content in milk and milk products (Parts 1, 2, 3, etc.), published jointly with IDF (IDF 20 series). Part 2 (this document) addressed the macro block-digestion method; other parts address the Kjeldahl principle, semi-micro methods and related techniques.

Q: What are the key keywords?

A: Milk, nitrogen, Kjeldahl, block digestion, macro method, crude protein, IDF 20-2, ISO 8968, dairy analysis.