GB/T 1600-2021 English PDF (GBT1600-2021)

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GB/T 1600-2021: Testing method of water for pesticides
GB/T 1600-2021
GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 65.100
CCS G 23
Replacing GB/T 1600-2001
Testing method of water for pesticides
ISSUED ON: DECEMBER 31, 2021
IMPLEMENTED ON: JULY 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 Test method ... 4
Testing method of water for pesticides
1 Scope
This document describes testing methods of water for pesticides by the Karl Fischer
method and the azeotropic distillation method.
This document applies to the determination of water for pesticides and their processed
preparations.
2 Normative references
The following documents are referred to in the text in such a way that some or all of
their content constitutes requirements of this document. For dated references, only the
version corresponding to that date is applicable to this document; for undated references,
the latest version (including all amendments) is applicable to this document.
GB/T 8170-2008, Rules of rounding off for numerical values and expression and
judgment of limiting values
3 Terms and definitions
No terms and definitions need to be defined in this document.
4 Test method
Warning – Personnel using this document shall have practical experience in
laboratory work. This document does not address all safety concerns.
It is the user’s responsibility to take appropriate safety and health
measures.
4.1 General provisions
The reagents and water used in this document refer to analytical reagents and distilled
water unless other requirements are noted.
4.2 Karl Fischer method
4.2.1 Karl Fischer chemical titration method
4.2.1.1 Method summary
Disperse the sample in methanol; use a standard Karl Fischer reagent of known water
equivalent for titration.
4.2.1.2 Reagents and solutions
4.2.1.2.1 Anhydrous methanol: The mass fraction of water shall not be greater than
0.03%. Take 5 g ~ 6 g of magnesium (or magnesium strips) with a smooth surface and
0.5 g of iodine; place them in a round-bottomed flask; add 70 mL ~ 80 mL of methanol;
heat and reflux on a water bath until all the magnesium forms flocculent magnesium
methoxide; then, add 900 mL of methanol; continue to reflux for 30 minutes; then, carry
out fractionation, and collect anhydrous methanol at 64.5 ℃ ~ 65 ℃. The instrument
used shall be dried in advance, and the part connected to the atmosphere shall be
connected to a drying tube filled with calcium chloride or silica gel.
4.2.1.2.2 Anhydrous pyridine: The mass fraction of water shall not be greater than 0.1%.
Pyridine passes through a glass tube filled with granular potassium hydroxide. The
length of the tube is 40 cm ~ 50 cm, the diameter is 1.5 cm ~ 2 cm, and the height of
the potassium hydroxide is about 30 cm. After treatment, carry out fractionation and
collect the fractions at 114 °C ~ 116 °C.
4.2.1.2.3 Iodine: sublimate again and place it in a sulfuric acid desiccator for 48 hours
before use.
4.2.1.2.4 Silica gel: containing color change indicator.
4.2.1.2.5 Sulfur dioxide: Add concentrated sulfuric acid dropwise into a branch flask
containing a paste aqueous solution of sodium sulfite (or sodium bisulfite); cool the
generated sulfur dioxide (as shown in Figure 1) to a liquid state by cold hydrazine (add
dry ice and ethanol or ice and salt mixed outside of the cold hydrazine). Before use,
place the cold hydrazine containing liquid sulfur dioxide in the air for vaporization; dry
in a concentrated sulfuric acid and calcium chloride drying tower.
Key:
A – 10 mL automatic burette;
B – reagent bottle;
C – drying tube;
D – titration bottle;
E – galvanometer or galvo;
F – variable resistor;
G – switch;
H – 1.5 V ~ 2.0 V battery pack.
Figure 2 – Titration device
4.2.1.3.2 Reagent bottle: 250 mL, equipped with a 10 mL automatic burette. Use a
suction ball to press the Karl Fischer reagent into the burette. Place an appropriate
drying tube to prevent moisture absorption.
4.2.1.3.3 Reaction bottle: about 60 mL, equipped with two platinum electrodes, a
stopper to adjust the burette tip, and a vent tube protected by desiccant. Pass the sample
to be titrated through the inlet tube or add through the side-port with an open-and-close
ground stopper; use electromagnetic stirring during the titration process.
4.2.1.3.4 1.5 V or 2.0 V battery pack: connected in parallel with a variable resistor of
about 2 000 Ω. A microammeter is connected in series with the platinum electrode.
When 0.2 mL excess Karl Fischer reagent flows through the platinum electrode, adjust
the variable resistor so that the initial current does not exceed 20 mA. Each time Karl
Fischer reagent is added, the ammeter pointer deflects once, but quickly returns to its
original position. When the titration reaches the end point, the deflection time lasts
longer.
Ammeter: full-scale deflection is not greater than 100 μA.
4.2.1.4 Reference materials calibrated by Karl Fischer reagent
4.2.1.4.1 Sodium tartrate dihydrate as reference material
Add 20 mL of methanol to the titration container, use Karl Fischer reagent to titrate to
the end point; quickly add 0.15 g ~ 0.20 g (accurate to 0.1 mg) of sodium tartrate; stir
until it is completely dissolved (about 3 min); then, continue to add Karl Fischer reagent
dropwise at a speed of 1 mL/min to the end point.
The water equivalent of Karl Fischer reagent is calculated according to Formula (1):
Where:
w1 – mass fraction of water, expressed as percentage (%);
Vt – volume of Karl Fischer reagent consumed by the titration reagent, in milliliters
(mL);
cE – water equivalent of Karl Fischer reagent, in milligrams per milliliter (mg/mL);
ms – mass of the sample, in grams (g).
4.2.1.6 Tolerance
When the mass fraction of water is greater than 1%, the relative difference between two
parallel measurements shall not be greater than 5%; when the mass fraction of water is
0.1% ~ 1%, the relative difference between two parallel measurements shall not be
greater than 10%; when the mass of water is less than 0.1%, the relative difference
between two parallel measurements shall not be greater than 20%. Respectively take
the arithmetic mean value as the measurement result.
4.2.2 Karl Fischer volumetric method
4.2.2.1 Method summary
The Karl Fischer volumetric method is often used to determine sample with a water
content greater than 0.1%. Place the sample in the titration cell; use titrant for titration;
let the water in the sample reacts with the titrant; detect the titration end point by a
potentiometer. The optimal environment for titration shall be pH 5 to pH 7. If the pH
value of the sample solution exceeds this range, buffer solution shall be added or acid
or alkali shall be used for neutralization.
4.2.2.2 Reagents
4.2.2.2.1 Single-component system reagents:
a) Solvent: suitable alcohols, such as methanol;
b) Titrant: an alcoholic solution of known water equivalents of sulfur dioxide,
iodine and a base (such as imidazole).
4.2.2.2.2 Two-component system reagents:
a) Solvent: alcohol solution containing sulfur dioxide, alkali (such as imidazole);
b) Titrant: an alcoholic solution containing iodine of a known water equivalent.
4.2.2.3 Instruments
Karl Fischer automatic titration system: a drying tube filled with fr...