主题：【求助】样品分析遇到问题，怎么解决？

苯丁酸钠杂质c顶空气相线性应该怎么做
各位老师，新手求助。我正要做苯丁酸钠杂质C气相方法，参考EP上的方法，方法如下：
pH (2.2.3) : 6.5 to 7.5.
Dissolve 0.20 g in carbon dioxide-free water R and dilute to
10 mL with the same solvent.
Impurity C. Gas chromatography (2.2.28).
Silylation solution. To 2 mL of N,O-bis(trimethylsilyl)trifluoroacetamide
R add 0.04 mL of chlorotrimethylsilane R
and mix.
Test solution. Dissolve 50.0 mg of the substance to be examined
in 3 mL of water R and add 0.5 mL of hydrochloric acid R.
Extract with 2 quantities, each of 5 mL, ofmethylene chloride R.
Evaporate the combined methylene chloride extracts to dryness
in a vial with a screw cap and add 0.5 mL of the silylation
solution. Seal the vial and heat at 70 ± 5 °C for 20 min.
Reference solution (a). Dissolve 5.0mg of sodium
phenylbutyrate impurity C CRS in methylene chloride R and
dilute to 10.0 mL with the same solvent.
Reference solution (b). Dilute 1.0 mL of reference solution (a)
to 10.0 mL with methylene chloride R. Place 1.0 mL of this
solution in a vial with a screw cap, evaporate to dryness and
add 0.5 mL of the silylation solution. Seal the vial and heat at
70 ± 5 °C for 20 min.
Reference solution (c). Dissolve 10 mg of the substance to be
examined in 25 mL of water R. To 3 mL of this solution add
0.1 mL of hydrochloric acid R. Extract with 2 quantities, each
of 5 mL, of methylene chloride R. Combine the methylene
chloride extracts in a vial with a screw cap and add 2 mL of
reference solution (a). Evaporate to dryness and add 0.5 mL of
the silylation solution. Seal the vial and heat at 70 ± 5 °C for
20 min.
Column:
— material: fused silica;
— size: l = 25 m, Ø = 0.25 mm;
— stationary phase: poly(dimethyl)(diphenyl)siloxane R (film
thickness 1.0 μm).
Carrier gas: helium for chromatography R.
Flow rate: 0.9 mL/min.
Split ratio : 1:100.
Temperature :
Time
(min)
Temperature
(°C)
Column 0 - 5 50
5 - 27 50 → 270
27 - 32 270
Injection port 270
Detector 270
Detection: flame ionisation.
Injection: 1 μL.
Relative retention with reference to phenylbutyrate (retention
time = about 20 min): impurity C = about 0.98.
System suitability : reference solution (c) :
— resolution: minimum 3.0 between the peaks due to
impurity C and phenylbutyrate.
Limit:
— impurity C: not more than the area of the corresponding
peak in the chromatogram obtained with reference
solution (b) (0.1 per cent).

样品前处理比较麻烦，先用二氯甲烷萃取后再蒸干，然后再硅烷化后顶空进样。我的疑问是杂质C常温下是液态，萃取后如何蒸干二氯甲烷？