GB/T 7729-2021 English PDF (GBT7729-2021)

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GB/T 7729-2021: Chemical analysis of metallurgical products -- General rule for spectrophotometric methods
GB/T 7729-2021
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 77.080
CCS H 04
Replacing GB/T 7729-1987
Chemical analysis of metallurgical products - General rule
for spectrophotometric methods
ISSUED ON: AUGUST 20, 2021
IMPLEMENTED ON: MARCH 01, 2022
Issued by: State Administration for Market Regulation;
Standardization Administration of the People's Republic of China.
Table of Contents
Foreword ... 3
1 Scope ... 4
2 Normative references ... 4
3 Terms and definitions ... 4
4 Principle ... 5
5 Reagents and materials ... 5
6 Instruments and equipment ... 5
7 Instrument operation methods ... 8
8 Preparation of testing sample ... 11
9 Measurement ... 12
10 Precision ... 14
Annex A (informative) Basic laws for spectrophotometric method ... 15
Chemical analysis of metallurgical products - General rule
for spectrophotometric methods
1 Scope
This document specifies the principle, reagents and materials, instruments and
equipment, instrument operation methods, preparation of testing samples, measurement
and precision of spectrophotometric method that is used for chemical analysis of
metallurgical products (hereinafter referred to as the photometric method).
This document applies to the application, research and personnel training of the
photometric method for chemical analysis of metallurgical products.
2 Normative references
The following referenced documents are indispensable for the application of this
document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
GB/T 6379.1, Accuracy (trueness and precision) of measurement methods and
results - Part 1: General principles and definitions
GB/T 6379.2, Measurement methods and results - Accuracy (trueness and precision)
- Part 2: Determine the standard methods of measurement repeatability and
reproducibility of the basic method
GB/T 6682, Water for analytical laboratory use - Specification and test methods
GB/T 8322, Molecular absorption spectrometry - Terminology
GB/T 26798, Single beam UV/VIS spectrophotometer
GB/T 26810, Visible spectrophotometer
GB/T 26813, Doable beam UV/VIS spectrophotometer
3 Terms and definitions
For the purposes of this document, the terms and definitions defined in GB/T 8322
apply.
UV spectrophotometer is usually tungsten lamp and deuterium lamp (wavelength range
is about 180nm~1000nm).
The light source shall have good stability.
Tungsten lamps shall be checked frequently to maintain the stability of the spectral
composition.
6.2.2 Wavelength selector
A wavelength selector is a device that can separate a certain wavelength range from the
optical radiation energy spectrum. It can select the wavelength band as needed.
There are two types of wavelength selectors: fixed wavelength selectors and
continuously changing wavelength selectors.
Fixed wavelength selectors are often called light filters. In the optical path, placing an
appropriate light filter can achieve wavelength selection. The most commonly used are
glass filters, which have good stability to light and heat.
Continuously changing wavelength selectors: The light beam passes through the
dispersive element and realizes the continuous change and selection of the wavelength
by means of the adjusting mechanism. Commonly used dispersive elements are prisms
and gratings. Gratings are linearly dispersive. The dispersion rate of a prism varies with
wavelength. But it is easier to eliminate diffuse scattering of optical radiation. Quartz
prisms are suitable for use in the ultraviolet, visible and near-infrared regions. In the
visible light region, the dispersion rate of glass prisms is greater than that of quartz
prisms, so glass prisms are often used in the visible light region.
The exit slit of the wavelength selector is generally adjustable. Usually adjust to the
same width as the inlet slit. The width of the slit is one of the parameters of the
spectrophotometer.
6.2.3 Absorption dish
Commonly used absorption dishes are glass absorption dishes and quartz absorption
dishes. Glass absorption dishes are used in the visible and near-infrared regions. Quartz
absorption dishes are suitable for near-ultraviolet, visible and near-infrared regions
(wavelength range is 180nm~1000nm). The two walls of the absorption dish through
which the light radiation passes shall be parallel to each other.
Commonly used spectrophotometers can use several sizes of absorption dishes. When
using several absorption dishes for photometric determination, the length of the dishes
shall be corrected. When calibrating, inject a solution with an absorbance of about 0.4
into a calibration dish and a standard dish with an accurate optical path length. Measure
the absorbance. Take the absorbance of the standard dish as 1.0. Calculate the correction
factor for the absorbance of the calibration dish relative to the standard dish. When the
calibration dish is used for measurement, the actual absorbance of the measured
solution is the product of the measured absorbance value and the calibration coefficient.
6.2.4 Detector
A detector is the component that detects the light intensity after passing through the
solution and converts it into an electrical signal. It is often composed of photocells,
photomultiplier tubes or photodiodes and their circuits.
6.2.5 Monitor
Commonly used spectrophotometers: The electrical signal output by the detector is
indicated on the display head as absorbance (A) or transmittance (T), or both at the
same time. Some spectrophotometer monitors give analytical results or other
information directly in terms of concentration.
6.3 Main instrument types
6.3.1 Doable beam spectrophotometer
The photometric reading displayed by such instruments is the ratio of the intensity of
light transmitted through the sample solution to the intensity of light transmitted
through the reference solution at the same time. So, use two beams of light for the
measurement at the same time. Usually, two beams of light split from the same light
source are projected onto two symmetrical detectors, respectively; or both are projected
onto one detector. When a detector is used, the detector receives two beams of light
energy alternately. For this system, the frequency of alternation is quite high. It can be
considered that the comparison of the two beams of light energy is carried out
simultaneously.
6.3.2 Single beam spectrophotometer
The photometric reading displayed by the instrument is obtained by successively
measuring the light intensity transmitted through the sample solution and the light
intensity transmitted through the reference solution.
6.4 Instrument performance indicators
Instrument performance indicators include:
a) Wavelength accuracy: The deviation BETWEEN the wavelength at the maximum
absorbance of the absorption curve of the optical filter or the wavelength at the
maximum intensity of the emission line of a low-pressure mercury or deuterium
lamp AND the given standard wavelength.
b) Repeatability of wavelength settings: The variance of measured wavelength
values when repeated measurements are taken from the emission line of a low-
pressure mercury or deuterium lamp, or the absorption curve of an optical filter.
7.2 Establishment of instrument operation conditions
7.2.1 Selection and setting of measurement mode
The measured values sha...