Recent advances in supercritical fluid chromatography/mass spectrometry

A summary of the recent advances in SFC/MS is included in this review. Interface designs are described as well as the key control variables. Finally, future developments in SFC/MS are predicted.     

Open tubular column supercritical fluid chromatography/mass spectrometry on a benchtop mass spectrometer

A benchtop SFC/MS system is described which utilizes supercritical carbon dioxide in a 50 micron diameter open tubular column interfaced directly to an unchanged commercially available benchtop capillary GC/MS system equipped with a chemical ionization (CI) source. A small amount of methane reagent gas was admitted co-axially to a capillary restrictor at the exit of the capillary chromatographic column. This make-up gas served as the CI reagent gas and appeared to optimize the sensitivity of the system while providing abundant (M+1) ions for the analytes investigated in this study. Good chromatographic intergrity was obtained for the GC/MS test compound, decafluorotriphenylphosphine (DFTPP), but the capillary restrictor appeared to cause some tailing of the ion current profiles resulting from low nanogram levels of caffeine and some fatty acid esters. Improvements in the SFC/MS capillary restrictor interface and the pumping system of the benchtop GC/MS system should increase the capability of this system for future applications.     

Direct coupling of capillary supercritical fluid chromatography to high resolution mass spectrometry with minimum modification

Summary The coupling of a capillary supercritical fluid chromatograph with a high resolution double focusing mass spectrometer has been accomplished without any modifications to the pumping or ion source systems. The interface utilizes a direct insertion probe (DIP), which was originally designed for the direct analysis of solid samples, together with a trit restrictor as a decompression device. The DIP is placed opposite to the SFC restrictor, and it provides sufficient heat to prevent cluster formation and cooling resulting from the expansion of the supercritical fluid into the vacuum environment. Excellent mass spectra of standard polycyclic aromatic hydrocarbons under chemical-ionization (CI) conditions using methane as the reagent gas, and under charge-exchange (CE) conditions using CO₂ as the charge exchange medium were obtained.     

Simultaneous coupling of capillary supercritical fluid chromatography and high temperature glass capillary gas chromatography to a mass spectrometer

The coupling of glass capillary supercritical fluid chromatography to a high temperature GC/MS system via a micrometeradjustable glass capillary interface including an integrated pressure restrictor is described. With this coupling device, both complementary capillary chromatographic methods retain their full independence and flexibility. It is shown that in supercritical fluid chromatography glass fulfils all the requirements of a suitable support material. The preparation of narrow bore glass capillary columns (0.06 mm i.d.), coated with chemically bonded and crosslinked fluids with a film thickness of about 0.6 μm, which exploit the merits of OHterminated polysiloxanes as stationary phases is discussed. The application of glass capillary SFC is demonstrated and compared with examples given in the literature.     

Minimizing UV noise in supercritical fluid chromatography. I. Improving back pressure regulator pressure noise

Pressure fluctuations and resulting refractive index changes, induced by the back pressure regulator (BPR) can be a significant source of UV detector noise in supercritical fluid chromatography (SFC). The refractive index (RI) of pure carbon dioxide (CO(2)) changes ≈0.2%/bar at the most commonly used conditions in supercritical fluid chromatography (SFC) (40 °C and 100 bar), compared to 0.0045%/bar for water (CO(2) IS 44× worse). Changes in RI cause changes in the focal length of the detector cell which results in changes in UV intensity entering the detector. The change in RI (ΔRI/bar) of CO(2) decreases 8-fold at 200 bar, compared to 100 bar. A new back pressure regulator (BPR) design representing an order of magnitude improvement in the state of the art is shown to produce peak to peak pressure noise (PN(p-p)) as low as 0.1 bar, at 200 bar, and 20Hz, compared to older equipment that attempted to maintain PN(p-p)<1bar, at <5Hz. With this lower PN(p-p), changes in baseline UV offsets could be measured as a function of very small changes in pressure. A pressure change of ±1 bar at 100 bar, common with some older BPR's, produced a UV baseline offset >0.5 mAU. A pressure change of ±0.5 bar representing the previous state-of-the-art, resulted in a UV offset of 0.3m AU. Baseline noise <0.05 is required to validate methods for trace analysis. The new BPR, with a PN(p-p) of 0.1 bar, demonstrated UV peak to peak noise (N(p-p))<0.02 mAU with a >0.03 min (10Hz) electronic filter under some conditions. This new low noise level makes it possible to validate SFC methods for the first time.     

The dependence of reduced plate height on reduced velocity in carbon dioxide supercritical fluid chromatography with packed columns

Summary The relation is proposed for the dependence of reduced plate height, h, on reduced velocity in carbon dioxide, supercritical fluid chromatography with packed columns. The classical Knox model does not take into account the density drop in the column which produces a peak-broadening. A supplementary coefficient with a parabolic dependence on velocity must be added and then a good fit between experimental results and theory is observed. Finally, the influence of other parameters such as pressure, capacity factor and solute molecular area is discussed.     

Design and application of Hadamard-injectors coupled with gas and supercritical fluid sample collection systems in Hadamard transform-gas chromatography/mass spectrometry

A novel Hadamard transform-gas chromatography/mass spectrometry (HT-GC/MS) system equipped with on-line sample collection systems is described. A Hadamard-injector was successfully designed and then coupled with an on-line adsorption/desorption system for detecting volatile organic compounds (VOCs) and a supercritical fluid extraction (SFE) system, respectively, by HT-GC/MS. Six VOCs and three pesticides were used as model compounds. In the former case, an activated-charcoal trap was used to trap VOCs from the indoor air. After 10 L of indoor air had passed through the trap, the condensed components were heated and simultaneously injected into the GC column through the Hadamard-injector, based on Hadamard codes. In a second experiment, a sample of rice was spiked with three types of pesticides and the sample then extracted using a commercially available supercritical fluid extractor. After extraction, the extracted components were transferred to a holding tank and simultaneously injected into the GC column also using the Hadamard-injector. The findings show that, in both cases, the combination of on-line sample collection methods and the use of the Hadamard transform resulted in improved sensitivity and detection. Compared to the single injection used in most GC/MS systems, the signal-to-noise (S/N) ratios were substantially improved after inverse Hadamard transformation of the encoded chromatogram.     

固相萃取-超临界流体色谱-质谱联用同时快速测定中成药和保健食品中的12种抗过敏化学药物

建立了固相萃取-超临界流体色谱-质谱联用（SPE-SFC-MS/MS）快速检测中成药和保健食品中12种抗过敏化学药物的分析方法。样品经甲醇超声提取,Oasis MCX固相萃取柱净化。采用Waters Trefoil CEL1色谱柱（150 mm×3.0 mm,2.5 μ m）,以CO₂为流动相A,甲醇-氨水（100：0.1,v/v）为流动相B,进行梯度洗脱。流速为1.2 mL/min,柱温和背压分别为45℃和12.4×10⁶ Pa。12种抗过敏化学药物以电喷雾离子源在正离子或负离子模式下用多反应监测（MRM）方式进行监测,整个分析过程在10 min内完成。结果表明,12种化学药物在5~250 μ g/L范围内线性关系良好,相关系数（r）均≥ 0.998,检出限（LOD）为0.141~0.262 μ g/L,定量限（LOQ）为0.703~1.308 μ g/L。3种加标水平（10、20和100 μ g/L）下,12种化学药物的平均回收率为76.1%~112.5%,相对标准偏差（RSD）为1.1%~8.3%。该法简便,灵敏性高,实用性强,可用于抗过敏类中成药和保健食品中非法添加抗过敏化学药物的检测。     

Headspace solid phase microextraction in-situ supercritical fluid extraction coupled to gas chromatography-tandem mass spectrometry for simultaneous determination of perfluorocarboxylic acids in sediments

Headspace solid phase microextraction (HS-SPME) in-situ supercritical fluid extraction (SFE) was investigated for the determination of trace amounts of perfluorocarboxylic acids (PFCAs) in sediments. Quantitation was performed by using gas chromatography coupled to negative chemical ionization-tandem mass spectrometry (GC-NCI-MS/MS). The optimum conditions of HS-SPME following SFE were obtained using 500 μL n-butanol as a derivatization reagent in supercritical carbon dioxide with static extraction for 10 min, then dynamic extraction for 20 min at 30 MPa and 70 °C and simultaneous collected with 100 μm film thickness PDMS fiber. The linear range of proposed method was from 5 to 5000 ng g(-1), with limit of detection ranging from 0.39 to 0.54 ng g(-1) and limit of quantitation ranging from 1.30 to 1.80 ng g(-1). The developed method was successfully applied to analyze PFCAs in sediments from rivers and beach near industrial areas. The concentrations of PFCAs determined are from 282 to 4473 ng g(-1).     

固相萃取-气相色谱-负化学源质谱法测定人血清中的多溴联苯醚

采用OasisHLB固相萃取柱萃取血清中的多溴联苯醚(PBDEs),经浓硫酸柱上除脂后,利用气相色谱-负化学源质谱法测定BDE-17、28、47、66、99、100、153、154、183和209共10种PBDEs组分。BDE-209的测定采用DB-5 ms色谱柱(15 m×0.25 mm×0.1 μm),其他组分采用VF-5 ms色谱柱(30 m×0.25 mm×0.25 μm)。对样品中蛋白质的去除溶剂和固相萃取条件(如洗脱溶剂及其用量)进行了优化。胎牛血清中的加标回收试验结果显示,各PBDEs单体相对于内标的平均回收率为78.5%～109.7%,日内测定的相对标准偏差(RSD)为0.3%～7.4%,日间测定的RSD为1.4%～14.1%。胎牛血清中三溴～七溴联苯醚的检出限(信噪比为3)为0.10～0.27 ng/L;定量限(信噪比为10)除了BDE-209为7.91 ng/L外,其他PBDEs为0.35～0.91 ng/L。采用本方法测定标准参考物质SRM1957和SRM1958,结果在参考值范围内。实验结果表明,本方法灵敏度高、准确度和精密度好,简便快速,溶剂消耗量少,适用于人体血清中三至十位溴取代联苯醚的测定。     

Rapid and selective determination of UV filters in seawater by liquid chromatography-tandem mass spectrometry combined with stir bar sorptive extraction

Fast liquid chromatography coupled to triple-quadrupole tandem mass spectrometry was employed for the determination of six UV filters in seawater. The separation of the analytes was achieved in less than 5 min; polarity switching was used as four of the analytes were ionized in positive mode and the remaining two in negative mode. Two ionization sources were employed and compared: atmospheric pressure chemical ionization (APCI) gave better results than electrospray ionization (ESI) for all analytes, with higher reproducibility and lower detection limits. Therefore APCI was chosen for the determination of the analytes in seawater samples using stir bar sorptive extraction-liquid desorption (SBSE-LD).Quantitative analysis was performed in multiple reaction monitoring (MRM) mode; fragmentation pathways of the analytes with regard to the formation of the MRM ions were also proposed.For the analysis of seawater samples, calibration curves were drawn using SBSE in spiked seawater. All figures of merit of the method were satisfactory; limits of detection were particularly low for the four analytes ionized in positive mode, being in the range 8-31 ng/L. The method was applied to the determination of the six UV filters in seawater samples from Liguria, Italy. Only benzophenone-3 (BP-3) and ethylhexyl methoxycinnamate (EHMC) were measured in the analyzed samples; some of the remaining analytes were also detected but always below the limit of quantitation.     

Certification and uncertainty evaluation of the certified reference materials of poly(ethylene glycol) for molecular mass fractions by using supercritical fluid chromatography

Poly(ethylene glycol) (PEG) is a useful water-soluble polymer that has attracted considerable interest in medical and biological science applications as well as in polymer physics. Through the use of a well-calibrated evaporative light-scattering detector coupled with high performance supercritical fluid chromatography, we are able to determine exactly not only the average mass but also all of the molecular mass fractions of PEG samples needed for certified reference materials issued by the National Metrology Institute of Japan. In addition, experimental uncertainty was determined in accordance with the Guide to the expression of uncertainty in measurement (GUM). This reference material can be used to calibrate measuring instruments, to control measurement precision, and to confirm the validity of measurement methods when determining molecular mass distributions and average molecular masses. Especially, it is suitable for calibration against both masses and intensities for matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Figure Comparison between the molecular mass fractions of PEG 1000 before calibration (si) (○) and after calibration (wi) (⧫). The error bar shows the expanded uncertainty of k = 2 of each mass fraction     

固相微萃取-气相色谱/质谱法测定果汁及茶饮料中的10种光引发剂

建立了用固相微萃取结合气相色谱/质谱（GC/MS）检测13种果汁饮料和3种茶饮料中10种光引发剂的方法。通过正交试验筛选对萃取过程影响较大的因素,再通过单因素试验进一步优化,确定最佳的操作条件。样品经萃取后,在GC/MS进样口解吸3 min,经HP-5MS色谱柱分离,以选择离子方式监测,外标法定量。为消除基质的干扰,以样品基质加标做工作曲线,线性范围为0.3~60 μg/L,检出限为3~16 ng/L。分别对4个不同加标水平的样品平行测定5次,相对标准偏差均小于14.5%。对不同品牌、不同种类的16种盒装饮料进行了测定,所有样品中全部检出二苯甲酮,部分样品中检出对二甲氨基苯甲酸异辛酯、2-异丙基硫杂蒽酮、4-甲基二苯甲酮、1-羟基环己基苯基甲酮、2-氯噻吨酮。该方法操作简单、灵敏度高、无污染,可对10种光引发剂同时测定。该研究结果为从包装材料迁移至饮料中的光引发剂的测定提供了参考。     

Direct determination of melamine in dairy products by gas chromatography/mass spectrometry with coupled column separation

A coupled capillary column system was developed for the qualitative and quantitative determination of melamine with isotope internal standard in dairy products by gas chromatography/mass spectrometry (GC/MS) without derivatization. A 30 m of DB-5ms ((5%-phenyl)-methylpolysiloxane, 0.25 mm i.d., 0.25 μm df) coupled with a 1.5 m of Innowax (polyethylene glycol, 0.32 mm i.d., 0.25 μm df) by a quartz capillary column connector was introduced as separation column. Three advantages were discussed for the coupled system. The sample was fortified with a ring-labeled ¹³C₃¹⁵N₃-melamine as an isotope internal standard and extracted by 1% of trichloroacetic acid aqueous solution. 2.2% of lead acetate solution was then added to deposit protein in the sample matrix. After purification by cation exchange cartridge, the sample solution was directly injected and detected by GC/MS. A six-point calibration curve ranging from 0.05 to 2 mg kg⁻¹ of melamine in sample was used to establish instrument response. The recovery was 93.9-102% with relative standard deviation from 3.1 to 8.7% when isotope internal standard used. The calculated method detection limit was 0.01 mg kg⁻¹.     

超快速液相色谱-四极杆/线性离子阱质谱同时检测猪组织中9种β-受体阻断剂残留

建立了同时检测猪组织中9种β-受体阻断剂(BBs)残留的超快速液相色谱-四极杆/线性离子阱质谱方法。均质试样经β-葡糖醛苷酶/芳基硫酸酯酶水解,乙腈提取,硅藻土与BondElut分散固相萃取填料双重快速净化,以0.1%(v/v)甲酸水溶液-甲醇为流动相使用KinetexTMC18-XB色谱柱(150 mm×2.1 mm,2.6μm)超快速液相色谱分离,优化多反应监测(MRM)离子对后,采用预设定多反应监测(sMRM)-信息依赖性采集(IDA)-增强子离子扫描(EPI)模式检测,在线EPI谱库定性分析,内标法定量。结果表明,9种BBs在线性范围内的线性关系良好(r≥0.995);定量限(LOQ,S/N≥10)均达到0.5μg/kg;3个添加水平(0.5、1.0和5.0μg/kg)下的回收率为87.5%~111.8%;RSD为4.0%~12.5%。该方法快速、准确、灵敏,可有效用于猪组织样品中多种BBs残留的同时测定。     

高效液相色谱-电喷雾串联质谱法测定饲料中的N-氨基甲酰-L-谷氨酸

建立了高效液相色谱-电喷雾串联质谱(HPLC-ESI-MS/MS)测定饲料中N-氨基甲酰-L-谷氨酸(NCG)含量的方法。饲料样品经甲醇提取、混合型强阴离子交换反相固相萃取(PXA)柱净化、HPLC分离后,采用ESI-MS/MS在正离子多反应监测(MRM)模式下进行检测,以碎片离子m/z 148.0和m/z 84.0进行定性,以碎片离子m/z 130.0进行定量。NCG的检出限(S/N >3)为24 μg/kg,定量限(S/N >10)为80 μg/kg,在20~1000 μg/L的质量浓度范围内峰面积与含量的线性关系良好,相关系数为0.9999。对饲料中NCG在80、200、500 mg/kg等3个添加水平下的回收率进行了测定,分别为104.0%、103.5%、95.3%,相对标准偏差分别为7.5%、6.3%、5.8%。结果表明,该方法操作简单,净化效果好,快速,灵敏度和准确度高,符合对饲料样品中NCG检测分析的要求。     

凝胶渗透色谱结合气相色谱-负化学源质谱法分析鱼肉及鱼油中的多溴联苯醚和得克隆阻燃剂

建立了凝胶渗透色谱(GPC)结合气相色谱-负化学源质谱(GC-NCI/MS)检测鱼肉及鱼油中8种多溴联苯醚(PBDEs)同系物及2种得克隆阻燃剂(DP)的分析方法。试样中加入内标物BDE-77和13C12-BDE-209后进行索氏提取,提取液经自动GPC系统除脂,多层硅胶层析柱净化后,在15 m长的毛细管气相色谱柱上分离,NCI/MS以选择离子监测方式检测目标化合物。以鱼肉样品为基质,当PBDEs的加标水平为0.2 ng/g和2 ng/g、BDE-209和DP的加标水平相应提高10倍时,其平均加标回收率为71.1%～121.4%,相对标准偏差为2.96%～13.31%(n=5);以信噪比(S/N)为3计算方法的检出限(LOD)为2.2～39.8 ng/kg。用该方法检测市售鱼肉及鱼油样品,其中多溴联苯醚总含量为2.18～15.93 ng/g,以BDE-209、BDE-47为主,两种DP均未检出。该方法准确、灵敏度高,能够满足富含脂质的动物性样品中痕量DP和PBDEs残留的分析要求。     

Analysis of polybrominated diphenyl ethers (PBDEs) by liquid chromatography with negative-ion atmospheric pressure photoionization tandem mass spectrometry (LC/NI-APPI/MS/MS): application to house dust

Eight polybrominated diphenyl ether (PBDE) congeners of primary interest to the US EPA were separated using reverse-phase liquid chromatography on an octadecylsilane column. BDE-28, BDE-47, BDE-99, BDE-100, BDE-153, BDE-154, BDE-183, and BDE-209 were baseline-resolved under isocratic conditions in 92:8 methanol/water (v/v). Negative-ion atmospheric pressure photoionization (NI-APPI) with a toluene dopant produced precursor ions corresponding to [M–Br+O]^– for the eight congeners studied. Each congener was quantified by tandem mass spectrometry through a unique multiple reaction monitoring (MRM) transition. On-column limits of detection were between 2.4 and 27.8 pg for the eight congeners studied, with an intra-day method precision of 9%. The LC/NI-APPI/MS/MS method was validated for the analysis of the eight PBDE congeners in NIST SRM 2585 (Organics in House Dust). Pressurized liquid extraction (PLE) with subsequent LC/NI-APPI/MS/MS analysis afforded quantitative recovery for all eight PBDE congeners with recoveries ranging from 92.7 to 113%. The liquid-phase separation of the LC/NI-APPI/MS/MS method is not prone to the thermal degradation issues that plague splitless GC based analyses of highly brominated PBDEs such as BDE-209.