Powered by Google www.ChineseStandard.net Database: 189759 (9 Jun 2024)

GB/T 7729-2021 PDF in English


GB/T 7729-2021 (GB/T7729-2021, GBT 7729-2021, GBT7729-2021)
Standard IDContents [version]USDSTEP2[PDF] delivered inName of Chinese StandardStatus
GB/T 7729-2021English230 Add to Cart 0-9 seconds. Auto-delivery. Chemical analysis of metallurgical products -- General rule for spectrophotometric methods Valid


Standards related to: GB/T 7729-2021

GB/T 7729-2021: PDF in English (GBT 7729-2021)

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 shall be energy-related quantities such as transmittance,
reflectance, and absorbance, or set according to the instrument's operating manual.
7.2.2 Selection and setting of measurement wavelength
Wavelength can also be replaced by units such as wave number (cm-1), energy (eV),
frequency (Hz).
Plot the molecular absorption spectra of the color developer and light absorbing
substance, so as to determine the absorption wavelength and optimal contrast. Generally,
the selected wavelength is within the maximum absorption peak range of the absorption
curve. In some cases, for example, the maximum absorption peak is very sharp, or there
is interference from other light-absorbing substances in the maximum absorption peak
range, do not work at the maximum absorption peak of the absorption curve. Select
additional absorption peaks or other flat portions of the absorption curve.
7.2.3 Selection of absorption dish
According to the optimum range of the spectrophotometer used, select the appropriate
size of the absorption dish.
7.3 Measurement preparation
Measurement preparation shall be carried out as follows:
a) Confirm whether the device is running stably;
b) Place (or activate) a light shield in the sample beam path for the two-beam method
and the beam path for the single beam method to cut off the beam path. Adjust the
indication value of transmittance to 0;
c) Remove (or close) the light shield. Adjust the indication value of transmittance to
100;
d) Repeat the operations shown in b) and c). Confirm that there is no fluctuation in
the indication value.
If the device has the function of automatically implementing the operations of a) ~ d),
operate according to the device manual. In the case of devices using photodiode
detectors, some devices require an output zero correction.
7.4 Measurement methods
7.4.1 Doable-beam measurement method
The measurement by doable-beam measurement method shall be performed as follows:
a) Place two reference samples in the sample light path and the reference light path,
respectively. Adjust the transmittance to 100 or the absorbance to 0. This can also
be done without a reference sample. Equivalent results can be obtained by data
manipulation;
b) Put the testing sample and the reference sample into the sample optical path and
the reference optical path, respectively. Read the transmittance or the absorbance.
When operating without a reference sample, the equivalent transmittance or
absorbance can be obtained through data processing;
c) If necessary, calibrate the blank value of the absorption dish.
7.4.2 Single-beam measurement method
The measurement by single-beam measurement method shall be performed as follows:
a) Place the reference sample in the light path. Adjust the transmittance to 100 or the
absorbance to 0;
b) Place the target sample in the light path. Measure the transmittance or the
absorbance;
c) Repeat the operations shown in a) and b) above if necessary. Confirm that the
readings are less scattered;
d) If necessary, calibrate the blank value of the absorption dish.
7.4.3 Measurement of the blank value of the absorption dish
In the measurement wavelength range, the sample absorption dish and the reference
absorption dish preferably have the same optical characteristics. In the case where the
optical eigenvalues are not exactly the same, but the difference is small, it needs to
measure the blank absorption value of the absorption dish. Then calibrate it. If the
device has a baseline calibration function, it is not necessary to calibrate the cuvette
blank value.
Put the same solution in the sample absorption dish and the reference absorption dish
(the absorption value at the measurement wavelength is smaller) as the testing sample
and the reference sample, respectively. Operate as in 7.4.1 or 7.4.2.
When the measurement result is transmittance, convert it to absorbance.
Take the obtained value as the blank absorbance value of the sample absorption dish to
the reference absorption dish. When the blank value of the absorption dish is determined,
it shall use the same absorption dish to combine in the same set of data.
c) The calibration curve within the straight line range is preferred;
d) When preparing the calibration curve, the concentration of the testing sample shall
be between the concentrations of the solution drawn by the calibration curve;
e) When the sample is suspended, there is light attenuation due to scattering in
addition to the sample absorbance. In this case, apply the absorption value at the
wavelength where the sample absorption and scattering absorption coexist minus
the absorption value at the wavelength where only the scattering absorption is
present. Use the difference of the two absorption values to draw a calibration curve.
This will use two wavelengths;
f) In the photometric determination, although the interference can be eliminated by
certain analysis steps, the obtained photometric reading still includes the
background absorption and the photometric reading of the reagent blank, which is
usually called "reagent blank". When analyzing the specimen and drawing the
calibration curve, a blank test shall be done along with the operation steps. If a
solvent is used as the reference solution, the photometric reading of the blank test
solution shall be deducted from the photometric reading of the test solution.
9.2 Calibration addition method
Pipette four or more samples of the same volume from the same testing sample solution.
Except for one sample, add a known concentration of the analyte solution to the
remaining solutions. Make a concentration gradient in several solutions. The
concentration of the analyte added shall be equivalent to or of the same order of
magnitude as the concentration of the analyte in the sample solution. Colorize these
solutions. Then set volume to the same volume. Measure its absorbance. Take the
increase in the concentration of the analyte after adding the standard solution as the
abscissa, and the absorbance as the ordinate to draw a correlation curve. The
intersection of the correlation curve and the abscissa gives the concentration or amount
of the analyte. The calibration addition method is only applicable if the relationship
curve is linear. The values that draw the calibration curve correct the blank test values
via the absorbance at origin. An example of the calibration addition method is shown
in Figure 2.
......
 
Source: Above contents are excerpted from the PDF -- translated/reviewed by: www.chinesestandard.net / Wayne Zheng et al.