GB/T 24750-2023Ethephon technical material (English PDF)

4.1 Appearance

White to light brown waxy solid.

4.2 Technical indicators

Ethephon technical material shall comply with the requirements specified in Table 1.

5.1 General

Unless otherwise specified, the reagents and water used in this document refer to analytically pure reagents and distilled water.

5.2 Sampling

The procedure shall be carried out in accordance with 5.3.1 of GB/T 1605-2001. The number of packages to be sampled shall be determined using a random number table.

The final sample quantity shall be no less than 100 g.

5.3 Identification test

5.3.1 Infrared spectroscopy

The infrared absorption spectra of the specimen and the ethephon reference standard in the range of 4000 cm^-1 ~ 400 cm^-1 should show no significant differences. The infrared spectrum of the ethephon reference standard is shown in Figure 1.

5.3.2 Ion chromatography

This identification test may be performed concurrently with the determination of the mass fraction of ethephon. Under identical chromatographic operating conditions, the relative difference between the retention time of a specific peak in the specimen solution and that of the ethephon peak in the standard solution shall not exceed 1.5%.

5.4 Appearance

Determine by visual inspection.

5.5 Mass fraction of ethephon, mass fraction of MEPHA

5.5.1 Determination of ethephon mass fraction and MEPHA mass fraction by ion chromatography (arbitration method for the determination of ethephon mass fraction)

5.5.1.1 Summary of method

The specimen is dissolved in water. A solution of sodium carbonate and sodium bicarbonate is used as the eluent. Ethephon and MEPHA in the specimen are separated by ion chromatography using an anion analysis column and a conductivity detector.

Quantification is performed using the external standard method. In this method, the limit of quantitation for the mass concentration of MEPHA is 0.002 mg/mL, and the limit of quantitation for the mass fraction of MEPHA in the sample is 0.002%.

5.5.1.2 Reagents and solutions

5.5.1.2.1 Sodium carbonate. guaranteed reagent.

5.5.1.2.2 Sodium bicarbonate. guaranteed reagent.

5.5.1.2.3 Water. ultrapure water.

5.5.1.2.4 Ethephon standard sample. known mass fraction, w >= 98.0%.

5.5.1.2.5 MEPHA standard sample. known mass fraction, w >= 95.0%.

5.5.1.3 Instruments

5.5.1.3.1 Ion chromatograph. equipped with a conductivity detector.

5.5.1.3.2 Chromatographic column. 250 mm × 4.0 mm (internal diameter) analytical column packed with alkanol-substituted quaternary ammonium salt, 5 µm packing material (or a column with equivalent performance).

5.5.1.3.3 Filter. membrane pore size is approximately 0.22 µm.

5.5.1.3.4 Ultrasonic cleaner.

5.5.1.4 Ion chromatography operating conditions

5.5.1.4.1 Eluent. mixed solution of sodium carbonate and sodium bicarbonate, c(Na2CO3) = 7.2 mmol/L, c(NaHCO3) = 9.0 mmol/L.

5.5.1.4.2 Flow rate. 1.0 mL/min.

5.5.1.4.3 Column temperature. 30°C.

5.5.1.4.4 Injection volume. 25 µL.

5.5.1.4.5 Suppressor current. 70 mA.

5.5.1.4.6 Retention time. approximately 11.1 min for ethephon, approximately 4.8 min for MEPHA.

5.5.1.4.7 The ion chromatography operating conditions specified in 5.5.1.4.1 ~ 5.5.1.4.6 are typical operating parameters. Appropriate adjustments to the specified operating parameters may be made based on the characteristics of different instruments to achieve optimal results. A typical ion chromatogram of ethephon technical material (for ethephon determination) is shown in Figure 2.A typical ion chromatogram of ethephon technical material (for MEPHA determination) is shown in Figure 3.

5.5.1.5 Determination procedure

Preparation of standard solution

The standard solution is prepared according to the following steps.

- Preparation of ethephon standard solution. Weigh 0.1 g (to the nearest 0.0001 g) of ethephon standard sample and place it in a 50 mL volumetric flask. Add water to dissolve and dilute to the mark. Mix well. Pipette 5 mL of the resulting solution into a 100 mL volumetric flask, dilute to the mark with water, and mix well.

- Preparation of MEPHA standard solution. Weigh 0.02 g (accurate to 0.0001 g) of the MEPHA standard sample and place it in a 50 mL volumetric flask. Dissolve with water and dilute to the mark. Mix well. Pipette 1 mL of the above solution into a 50 mL volumetric flask, dilute to the mark with water, and mix well. Filter through a membrane filter for use.

Preparation of specimen solution

Heat the specimen in a water bath or oven at 90°C~95°C until liquefied, then mix well.

Rapidly weigh 0.1 g of the specimen (to the nearest 0.0001 g) and place it in a 50 mL volumetric flask. Dissolve in water and dilute to the mark. Mix well (Solution I. This solution is used for the determination of MEPHA). Pipette 5 mL of the above solution into a 100 mL volumetric flask. Dilute to the mark with water and mix well (Solution II. This solution is used for the determination of ethephon).

5.5.1.6 Determination

5.5.1.6.1 Determination of ethephon mass fraction

Under the operating conditions specified in 5.5.1.4.1~5.5.1.4.6, and after the instrument has stabilized, continuously inject the ethephon standard solution until the relative variation in the ion peak areas of ethephon between two consecutive injections is less than 1.2%. Then, perform the measurements in the following order. ethephon standard solution, Solution II, Solution II, and ethephon standard solution.

5.5.1.6.2 Determination of MEPHA mass fraction

Under the operating conditions specified in 5.5.1.4.1~5.5.1.4.6, and after the instrument has stabilized, make successive injections of the MEPHA standard solution until the relative change in the MEPHA ion peak area between consecutive injections is less than 10%. Then, perform the measurements in the following order. MEPHA standard solution, Solution I, Solution I, and MEPHA standard solution.

5.5.1.7 Calculation

5.5.1.7.1 Calculation of ethephon mass fraction

Calculate the average peak areas of the ethephon ion for the two injections of the specimen solution and for the standard solution injections performed before and after the specimen. Calculate the mass fraction of ethephon in the specimen using formula (1).

Where, w1 - mass fraction of ethephon in the specimen, %;

A2 - average peak area of the ethephon ion in the ethephon specimen solution; m1 - mass of the ethephon standard, in grams (g); […]