GB/T 26568-2011Magnesium sulfate for agricultural use (English PDF)

4.3 Requirements for raw material sulfuric acid

If it uses sulfuric acid as raw material, it shall comply with requirements of GB/T 534.

5.1 Determination of water-soluble magnesium content -

Disodium ethylenediaminetetraacetic acid volumetric method

5.1.1 Method summary

Cover iron and aluminum ions with triethanolamine; cover calcium ion with EGTA; titrate magnesium ion with EDTA complex.

5.1.2 Reagents and solutions

5.1.2.6 Acid chrome blue K-naphthol green B mixed indicator (referred to as K-B indicator).

5.1.2.5 Ammonia-ammonium chloride buffer solution (pH = 10)

5.1.3 Apparatus

General laboratory instruments.

5.1.4 Determination procedures

Carry out parallel determination of two samples.

5.1.4.1 Preparation of sample solution

5.1.4.3 Determination

Accurately pipet 25.00 mL of sample solution. Place it in a 500 mL Erlenmeyer flask. Add 100 mL of water, 5 mL of triethanolamine solution. Add into EGTA solution according to the amount of EGTA added as specified in 5.1.4.2. Add 15 mL of ammonia-ammonium chloride buffer solution. Add about 0.1 g of K-B indicator. Use EDTA standard titration solution to titrate into the solution till purple turns pure blue. It shall be the end if it does not fade within 30 s. Carry out the blank test simultaneously.

5.1.4.5 Tolerance

5.2 Determination of water soluble sulfur content - Drying method

The preparation of sample solution shall be carried out according to 5.1.4.1.

The analysis results shall be expressed in water soluble sulfur content (in S).

The rest shall be performed in accordance with the provisions of 3.5 in GB/T 19203-2003.

5.7 Determination of pH value - Acidity meter method

5.7.1 Principle

Add water into sample. Dissolve it at room temperature. Use pH meter to determine.

5.7.2 Reagents and solutions

5.7.3 Apparatus

5.7.3.1 General laboratory instruments.

5.7.3.2 pH meter. sensitivity is 0.01 pH units.

5.7.4 Determination

5.7.6 Tolerance

The absolute tolerance of parallel measurement results shall not exceed 0.1 pH.

5.8 Appearance

Visually inspect.

6.1 Inspection categories and inspection items

Product inspection consists of exit-factory inspection and type inspection. Table 2 lists all exit-factory inspection items. Items in 4.2 in Table 2 are type inspection.

6.2 Batch

The products shall be inspected in batch. A batch refers to the output of one day or two days. The maximum is 500 t.

6.3 Sampling program

6.5 Results of determination

6.5.1 The qualification determination of product quality indicator in this

Standard uses "Comparison of Revised Value" in GB/T 8170-2008.

6.5.2 The manufacturer shall carry out the exit-factory inspection and type inspection according to the requirements of this Standard. When all items of exit-factory inspection and type inspection comply with requirements of this Standard, this batch of products shall be qualified. Each batch of qualified products shall be attached with quality certificate of which the content shall include manufacturer's name, address, product name, category, batch number or date of production, net weight, water-soluble magnesium, water soluble sulfur content, chloride ion content and reference to this Standard.