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1.Reagents and Solutions

  Ethyl acetate: analytical pure

2. Instruments

Gas chromatograph: with FID detector

chromatographic column: 30m×ø0.25mm(id), SE-30 capillary column with film thickness of 0.5µM

Microinjector: 10µL

Chromatographic data processor

3.Operating conditions of gas chromatography

Column temperature: 240℃; Vaporization room: 300℃; Detector room: 300℃.

Split injection: split ratio 1:50

Injection volume: 0.4 μL

Retention time: 18-Crown-6 about 7min

   The above chromatographic conditions are typical operating parameters. The operating parameters can  be adjusted appropriately according to the operating characteristics of different instruments in order to obtain the best effect. A typical gas chromatogram is shown in Figure 1

  Figure1 gas chromatogram of 18-crown-6

4.Determination steps

4.1 Preparation of sample solution: Weigh 0.5g of the sample and dissolve it with 5 ml of ethyl acetate

    4.2 Determination: Under the above operating conditions, after the instrument baseline is stable, inject several needles of sample repeatedly, and calculate the content when the change of relative response value of two adjacent needles is less than 0.5%.

4.3 Calculation

Assay of 18-Crown-6 Xi (%), calculate as formula:

In formula:

               Xi: Percentage content of 18-Crown-6;

               Ai: Peak area of 18-crown-6;

               ∑Ai: Sum of chromatographic peak areas in sample solution.

4.4 Allowable difference

The difference between the two parallel determinations results should not exceed 0.50%, taking the arithmetic mean as the determination result.