称取经冷冻干燥、粉碎的样品0.200 g，加入由0.1 mol·L^-1 Na₂EDTA-Mcllvaine缓冲溶液、乙腈、甲酸按体积比19.5∶80∶0.5混合而成的提取剂10 mL和100 μg·L^-1内标混合溶液50 μL，混匀后用甲酸（1+10）溶液调节pH至4.0~5.0，加入正己烷15 mL，超声提取15 min，振荡15 min，于4℃下，以8 000 r·min^-1离心5 min，取下层清液6 mL，用串联的SAX-HLB固相萃取柱净化，用1 mL乙腈（4+1）溶液淋洗，淋洗液于60℃经氮气吹干，用0.6 mL甲酸（0.5+99.5）溶液溶解残渣，溶液过0.22 μm微孔滤膜。滤液在BEH C₁₈色谱柱上分离，以乙腈-0.1%（体积分数）甲酸溶液为流动相进行梯度洗脱，质谱分析中采用电喷雾离子源和多反应监测模式。23种抗生素的质量浓度在一定范围内与其峰面积呈线性关系，检出限（3S/N）在0.2~3.3 μg·kg^-1之间。加标回收率在51.7%~102%之间，测定值的相对标准偏差（n=6）在3.5%~13%之间。方法用于分析北京郊区21家规模化畜禽养殖场的畜禽粪便中的抗生素残留，检出了多种抗生素。

10 mL of extractant composed of 0.1 mol·L^-1 Na₂EDTA-Mcllvaine buffer solution, acetonitrile and formic acid with the valume ratio of 19.5:80:0.5, and 50 μL of 100 μg·L^-1 mixed internal standard solution was added to 0.200 g of the freeze-dried, crushed sample. After being mixed well, the acidity of the mixture was adjusted to pH 4.0-5.0 with formic acid (1+10) solution, then 15 mL of n-hexane was added. After ultrasonic extraction for 15 min and oscillation for 15 min, the mixture was centrifuged at 8 000 r·min^-1 for 5 min at 4℃, and then 6 mL of the lower layer liquid was purified with a solid phase column composed with SAX column and HLB column in series, with 1 mL of acetonitrile (4+1) solution for elution. The eluent was dried at 60℃ by nitrogen blowing, and the residue was dissolved with 0.6 mL of formic acid (0.5+99.5) solution. After the solution was filtred through 0.22 μm microporous membrane, the filtrate was separated on a BEH C₁₈ column with acetonitrile-0.1% (φ) formic acid solution as the mobile phase for gradient elution. Electrospray ionization and multiple reaction monitoring were used for MS analysis. Linear relationships were found between peak areas and mass concentrations of 23 antibiotics within definite ranges, with detection limits (3S/N) in the range of 0.2-3.3 μg·kg^-1. Values of recovery obtained by standard addition method ranged from 51.7% to 102%, and RSDs (n=6) ranged from 3.5% to 13%. The proposed method was used to analyze the antibiotic residues in livestock manure of 21 large-scale livestock and poultry farms in the suburbs of Beijing, and many kinds of antibiotics were detected.