GB/T 8088-2025Raw natural rubber and natural rubber latex - Determination of nitrogen content (English PDF)

Foreword

This document is in accordance with the provisions of GB/T 1.1-2020 "Guidelines for standardization work Part 1: Structure and drafting rules for standardization documents" Drafting.

This document replaces GB/T 8088-2008 "Natural rubber and natural rubber latex - Determination of nitrogen content".

In addition to structural adjustments and editorial changes, the main technical changes are as follows.

a) Added "When there is a dispute over the use of the semi-micro method, the glass apparatus method shall be the preferred method" (see Chapter 1);

b) Deleted catalyst solution (see 4.1.1.2 of the 2008 edition);

c) Added titanium dioxide catalyst mixture (see 5.1.1.1, 5.4.1, 6.1.1.1 and 6.4.1);

d) Added the normative reference document GB/T 601 as the calibration method for sulfuric acid standard solution and sodium hydroxide standard solution.

Method (see 5.1.3, 5.1.4, 6.1.3 and 6.1.4);

e) The sample weight of solid boric acid for preparing boric acid solution has been changed (see 5.1.6 and 6.1.6, 4.1.6 and 5.1.6 of the 2008 edition);

f) Change the mixed indicator solution to mixed indicator solution A (see 5.1.7 and 6.1.7.1, 4.1.7 and 6.1.7.1 of the 2008 edition) 5.1.7), and added mixed indicator solution B (see 6.1.7.2);

g) Change the total solids content of latex in the constant method from "2g" to "10g" (see 5.3, 4.3 of the 2008 edition);

h) The precise value of sample weighing has been changed (see 5.4.1, 4.4.1 of the 2008 edition);

i) The expression and calculation formula of nitrogen content have been changed (see 5.6 and 6.6, 4.6 and 5.6 of the 2008 edition);

j) The concentrations of sodium hydroxide standard titrant and sulfuric acid standard titrant are increased to three significant figures (see 5.6 and 6.6);

k) Added automatic digestion module (see 6.2.2);

l) The automatic and semi-automatic Kjeldahl nitrogen analyzer methods are added to the semi-micro method (see 6.2.5 and 6.4.2.2);

m) Change the length of the condenser from 250mm to 300mm (see Figure 8, Figure 7 of the 2008 edition), and change the length of the condenser outlet pipe to the height is changed from 500mm to 600mm (see Figure 10, Figure 9 of the 2008 edition);

n) Change the total solid amount of latex in the semi-micro method from "0.1g" to "5g" (see 6.3, 5.3 of the 2008 edition);

o) The precision was changed from a requirement to informative and its basis and data were changed (see Chapter 7, Chapter 6 of the 2008 edition).

This document is modified to adopt ISO 1656:2019 "Natural rubber and natural rubber latex — Determination of nitrogen content".

This document has the following structural adjustments compared to ISO 1656:2019.

--- Deleted 5.1.3, 6.1.3 and 6.2.1 of ISO 1656:2019;

---6.1.3~6.1.6 correspond to 6.1.4~6.1.7 of ISO 1656:2019, of which 6.1.7.1 corresponds to 6.1.8;

---6.2.1 and 6.2.2 correspond to 6.2.1.1 and 6.2.1.2 of ISO 1656:2019, and 6.2.3 and 6.2.4 correspond to 6.2.2 and 6.2.3 of ISO 1656:2019;

---Added 6.2.5;

---Separate 6.4.2 of ISO 1656:2019 into 6.4.2.1 "Glass apparatus method" and 6.4.2.2 "Automatic and semi-automatic Kjeldahl apparatus" Two articles of the Law.

The technical differences between this document and ISO 1656:2019 and their reasons are as follows.

--- Changed the scope (see Chapter 1) and increased the applicable limits of the document to adapt to the provisions of GB/T 1.1-2020;

--- The requirements for disodium tetraborate solution (see 5.1.3 of ISO 1656:2019) have been deleted and implemented in accordance with GB/T 601 to adapt to my country's Provisions for the calibration of standard titration solutions;

--- Changed the calibration of sulfuric acid standard solution and sodium hydroxide standard solution to be carried out in accordance with GB/T 601 (see 5.1.3, 5.1.4, 6.1.3 and 6.1.4, ISO 1656:2019 5.1.3, 5.1.4, 6.1.3 and 6.1.4), to adapt to the standard titration solution in my country provisions;

--- Replaced ISO 123 with the normative reference GB/T 8290, replaced ISO 124 with the normative reference GB/T 8298, replaced ISO 125 with the normative reference GB/T 8299, replaced ISO 126 with the normative reference GB/T 8291 the normative reference GB/T 15340 replaces ISO 1795 (see 5.3 and 6.3, 5.3 and 6.3 of ISO 1656:2019), with Adapt to my country's regulations on latex and natural rubber;

--- Changed the amount of water and sulfuric acid standard titration solution in the test steps of the constant method (see 5.4.2, ISO 1656:2019 5.4.2) to meet the test conditions;

--- Changed the expression and calculation formula of nitrogen content (see 5.6 and 6.6, 5.6 and 6.6 of ISO 1656:2019) to adapt GB/T 20001.4-2015 regulations;

--- Added a mixed indicator solution (see 6.1.7.2) to meet the needs of the newly added "automatic and semi-automatic Kjeldahl nitrogen determination instrument method";

--- Change the notes in Figures 1 to 7, 9 and 10 to segments in the figures (Figures 1 to 7, 9 and 10, ISO 1656:2019 Figures 1 to 7, 9, and 10), because they contain licensed content;

--- Automatic and semi-automatic Kjeldahl nitrogen determination instrumental methods (see 6.2.5 and 6.4.2.2) have been added to the semi-micro method to provide new test methods;

--- Changed the amount of sulfuric acid standard titration solution and sodium hydroxide solution in the semi-micro method test steps (see 6.4.2.1, ISO 1656.

2019, 6.4.2.1), to meet the test conditions;

--- Changed "results and their units" to "test results" (see Chapter 8, Chapter 8 of ISO 1656:2019), because the results are only There are numerical values but no units.

The following editorial changes have been made to this document.

--- Changed the introduction and added instructions on semi-micro automatic and semi-automatic Kjeldahl nitrogen determination instrumental methods;

--- Change the description of boric acid in the principle to a note (see Chapter 4) because it does not belong to the content of the principle;

--- Added the CAS number of the reagent (see 5.1 and 6.1);

--- Change the mixed indicator solution to mixed indicator solution A (see 5.1.7 and 6.1.7.1, 5.1.8 and 6.1.8);

---Change "c(H2SO4)" to "c(1/2H2SO4)";

--- Changed Appendix A (informative).

Introduction

The purpose of this document is to determine the nitrogen content of natural rubber by the Kjeldahl method using a non-toxic catalyst (catalyst that does not contain selenium).

The method is simple, safe, and environmentally friendly, and does not require additional analytical instruments.

The method presented in the previous version of this document has the advantages of being simple, accurate, using conventional instrumentation, and being low-cost.

Selenium or selenium salts are harmful to the environment and people.

In the Rubber Products Working Group (RPBWG/ACCSQ) of the Advisory Committee on Standards and Quality Activities of the Association of Southeast Asian Nations (ASEN), Vietnam has studied the above situation and finally found a suitable catalyst mixture to replace selenium.

It is the best catalyst mixture to replace the original Se/CuSO4/K2SO4.The test results of the new method have high accuracy and are consistent with the previous method.

In comparison, it is safer and easier to operate for both technicians and the environment.

In addition, the total cost of using the new catalyst is much lower than the previous cost (about 50% of the cost of using the selenium mixture catalyst).

Statistical data have been obtained from laboratories in ASEAN member countries to prove the reliability and good reproducibility of this method.

ITP. This ITP is organized by the Malaysian Rubber Board (MRB) with the permission of the ASEAN Secretariat.

The results of using selenium catalyst and alternative catalysts were reported, and the stability of the method was also demonstrated.

At present, more and more laboratories are equipped with automatic and semi-automatic Kjeldahl nitrogen analyzers to more conveniently and efficiently determine the nitrogen content of natural rubber and natural rubber.

In order to determine the nitrogen content of natural latex, this revision has added automatic and semi-automatic Kjeldahl instrumental methods.

Determination of nitrogen content of natural rubber and natural rubber latex Warning. People who use this document need to have practical experience in regular laboratory work. This document does not address all possible safety issues.

The user is responsible for taking appropriate safety and health measures and ensuring that the conditions stipulated by relevant national laws and regulations are met.

1 Scope

This document describes the macro and semi-micro methods for the determination of nitrogen content in raw natural rubber and natural rubber latex by the Kjeldahl method.

This document is applicable to the determination of nitrogen content in natural raw rubber and natural rubber latex.

When there is controversy over the use of the semi-micro method, the glass apparatus method is the preferred method.

Note. The determination of nitrogen content in natural rubber is often used to estimate the protein content in rubber. However, natural rubber also contains a small amount of non-protein nitrogen.

These non-protein nitrogen-containing components account for a considerable proportion of the total nitrogen content in dry solids obtained from natural rubber latex.

2 Normative references

The contents of the following documents constitute the essential clauses of this document through normative references in this document.

For referenced documents without a date, only the version corresponding to that date applies to this document; for referenced documents without a date, the latest version (including all amendments) applies to this document.

GB/T 601 Preparation of standard titration solutions for chemical reagents GB/T 8290 Latex Sampling (GB/T 8290-2021, ISO 123:2001, MOD) GB/T 8298 Latex—Determination of Total Solids Content (GB/T 8298-2017, ISO 124:2014, MOD) GB/T 15340 Sampling and preparation of natural and synthetic rubber (GB/T 15340-2025, ISO 1795:2017, IDT)

3 Terms and Definitions

There are no terms or definitions that require definition in this document.

4 Principles

After a known amount of sample is digested with a mixture of concentrated sulfuric acid and a catalyst, the nitrogen-containing compounds in the sample are decomposed and converted into ammonia, which is then mixed with the solution.

The sulfuric acid combines to form ammonium bisulfate, which is then heated under alkaline conditions to distill off the ammonia.

The distilled ammonia is absorbed with sulfuric acid standard titration solution, and then the excess acid is titrated with alkaline standard titration solution; or it is absorbed with boric acid solution.

The excess acid was then titrated with a standard acid solution.

Note. Boric acid is a weak acid and has no effect on the indicator used during titration.

5 Constant Method