Combining Results of Two GC Separations Partly Achieves Determination of All <Emphasis Type="Italic">cis</Emphasis> and <Emphasis Type="Italic">trans</Emphasis> 16:1, 18:1, 18:2 and 18:3 Except CLA Isomers of Milk Fat as Demonstrated Using Ag-Ion SPE Fractionation

Milk fat is a complex mixture of geometric and positional isomers of monounsaturated and polyunsaturated, including short-, long- and branch-chain fatty acids (FAs). There has been partial success to resolve this mixture of FAs using different GC temperature programs, or a combination of GC isothermal and temperature programs. To overcome the problem associated with overlapping isomers prior silver-ion separation was recommended. However, this procedure is time consuming and not practical for routine analysis. In addition, previous methods focused mainly on the trans and cis isomers of 18:1. The present method takes advantage of differences in the relative elution times between different types of FAs. The method involved analyzing each milk fat using the same highly polar 100-m capillary column and GC instrument, and conducting two separations using temperature programs that plateau at 175 and 150 °C. The relative shift among the geometric and positional isomers at these two temperature settings was enough to permit identification of most of the trans and cis 16:1, 18:1 and 20:1, the c/t-18:2 and the c/c/t-18:3 isomers found in milk fat. The identity of these FAs was confirmed by prior separation of the total fatty acid methyl esters (FAMEs) of milk fat using Ag⁺-SPE columns, and comparing the fractions to the total milk fat. The Ag⁺-SPE technique was modified to obtain pure saturated, trans- and cis-monounsaturated and diunsaturated FAMEs. By combining the results from these two separate GC analyses, knowing the elution order, it was possible to determine most of the geometric and positional isomers of 16:1, 18:1, 20:1, 18:2 and 18:3 without a prior silver-ion separation. Only few minor FAs could not be resolved, notable the conjugated linoleic acid isomers that still required the complimentary Ag⁺-HPLC separation. The two GC temperature programs have been successfully used to routinely analyze most FA isomers in total milk and beef fats in about 200 min without the use of prior silver-ion separations.     

中性氧化铝固相萃取柱在柴油分析中应用

使用中性氧化铝固相萃取柱(SPE)对柴油中的饱和烃和芳烃组分进行了有效的分离,并用气相色谱-质谱联用仪分析了加入内标液的饱和烃、芳烃组分,数据显示该柱可以满足柴油组成的现场实验,符合测试标准的SPE柱分离效率小于5%要求。     

Development and validation of multi-residue analysis for tetracycline antibiotics in feed by high performance liquid chromatography coupled to mass spectrometry

ABSTRACT

A new multi-residue method for the analysis of the tetracycline antibiotics oxytetracycline, tetracycline, chlortetracycline, and doxycycline was developed and validated for animal feed. After extraction with 0.1M Na₂EDTA-McIlvaine buffer (pH 4), the samples were centrifuged, purified by SPE (Strata-X-CW cartridges) and analysed by HPLC-MS. Validation of the method was performed according to the guidelines indicated in European Commission Decision 2002/657/EC. The procedure was validated by spiking feed samples at three different levels (300, 1000, and 5000 µg/kg). Average recoveries for tetracyclines were in the range 79.70–98.8%, with RSD for repeatability and reproducibility in the ranges of 5.0–9.5% and 6.5–11.0%, respectively. The method was successfully validated and proved to be efficient, precise, and useful for quantification of tetracyclines in animal feed. The validated method was successfully applied to 65 suspect feed samples collected from different regions of Poland in 2015–16 and obtained from farms and feed manufactures. Of these 65 purportedly non-medicated feeds, eight (12.3%) were positive for the presence of doxycycline or chlortetracycline.     

Occurrence of melamine contamination in powder and liquid milk in market of Iran

Melamine contamination is known as a significant health risk and seriously considered by scientists worldwide. Cyanuric acid is one of the melamine by-products that contribute to its renal toxicity via the formation of melamine cyanurate crystals in the kidney. Therefore, co-determination of melamine and cyanuric acid in both powder and liquid milk samples has grown significantly throughout the world. High-performance LC with ultraviolet detection has been used as a simple and rapid method for the determination of melamine and cyanuric acid in powder and liquid milk samples and the results confirmed by using LC-MS/MS. In this study, nine powder milk and five liquid milk samples from different brands available in Iranian markets were chosen randomly and analysed. SPE column was used to clean up the samples. The results showed that except one brand of milk powder and liquid milk, all other samples were contaminated with melamine in the range of 1.50–30.32?μg/g for milk powder and 0.11–1.48?μg/mL for liquid milk. No cyanuric acid was detected in milk powder or liquid milk samples, which reduces the risk of melamine toxicity for consumers.     

固相萃取-高效液相色谱-二极管阵列检测法同时测定饮料中10种合成着色剂

本文建立了固相萃取-高效液相色谱-二极管阵列检测法（SPE-HPLC-PDA）同时测定饮料中10种合成着色剂（新红、柠檬黄、苋菜红、靛蓝、胭脂红、日落黄、诱惑红、亮蓝、赤藓红、酸性橙Ⅱ）的含量。样品经Waters Oasis WAX固相萃取柱净化,采用Aglient TC-C18色谱柱（5 μm,4.6 mm×250 mm）,以甲醇和0.02 mol/L的乙酸铵溶液为流动相,梯度洗脱,PDA检测波长为210 nm~650 nm。以保留时间结合待测物的紫外吸收光谱进行定性分析,采用外标法进行定量分析。10种合成色素线性范围为1~20 μg/mL(r>0.999);方法检出限为0.01~0.02 mg/kg;加标回收率为90.2~100.6%,RSDs为0.44~2.48%（n=6）。该方法简单、准确、灵敏,适用于饮料中合成着色剂的测定。     

分子印迹材料的制备与应用

分子印迹技术(molecularly imprinted technique,MIT)来源于免疫学、生物化学,是模拟生物体内抗体与抗原、酶与底物等分子之间的识别过程,是合成对某一种分子具有专一识别性的聚合物的方法。本文对分子印迹材料的合成方法——共价法、非共价法和半共价法等进行了综述,并介绍了分子印迹材料与技术在分析化学与生物领域的应用。     

SPE-GC-MS方法检验全血中多虑平

目的:建立人全血中多虑平的固相萃取-气相质谱联用仪检测方法。方法全血中的多虑平以SKF525A为内标,应用waters HLB固相萃取小柱提取净化,应用气相质谱联用仪SIM方法进行定性定量检验。结果多虑平检出限为1.0 ng/mL,多虑平质量浓度在0.01~10μg/mL范围内线性良好(r≥0.998),平均萃取回收率为62.8%~71.6%,日内、日间精密度RSD≤6.42%(n=5)。结论该方法专属性强,去干扰能力好,灵敏及准确。     

固相萃取—气相色谱/质谱法测定水中7种农药

采用全自动固相萃取法提取水中7种农药,并采用气相色谱/质谱法检测,以保留时间和选择离子定性分析、菲-D10为内标物进行定量分析。结果表明:气相色谱/质谱法检测水中有机磷农药的最低检出限在1.0～2.4μg/L之间,全自动固相萃取测定有机磷农药的相对标准偏差是1.7%～7.2%,回收率在82.6%～92.0%之间。     

Monitoring the enrichment of virgin olive oil with natural antioxidants by using a new capillary electrophoresis method

The enrichment of virgin olive oil (VOO) with natural antioxidants contained in various herbs (rosemary, thyme and oregano) was studied. Three different enrichment procedures were used for the solid–liquid extraction of antioxidants present in the herbs to VOO. One involved simply bringing the herbs into contact with the VOO for 190 days; another keeping the herb–VOO mixture under stirring at room temperature (25 °C) for 11 days; and the third stirring at temperatures above room level (35–40 °C). The efficiency of each procedure was assessed by using a reproducible, efficient, reliable analytical capillary zone electrophoresis (CZE) method to separate and determine selected phenolic compounds (rosmarinic and caffeic acid) in the oil. Prior to electrophoretic separation, the studied antioxidants were isolated from the VOO matrix by using an optimised preconcentration procedure based on solid phase extraction (SPE). The CZE method was optimised and validated.