New conductivity detection response equation for anions eluted with fully and partially ionised eluents in non-suppressed ion chromatography

A response equation for conductivity detection in ion chromatography has been derived. This equation is applicable to non-suppressed ion chromatography using both fully ionised and partially ionised eluents. A prime assumption of this equation is that when partially ionised eluents are used (such as benzoic acid), both the ionised and neutral components of the eluent species contribute to the detector response of anionic analytes. Experimental evidence is provided to support this assumption in that pH changes accompanying the elution of an analyte have been measured. These pH changes are proportional to the concentration of analyte injected onto the column, in accordance with predictions from the response equation. Furthermore, it is shown that protonated eluents (such as benzoic acid) give more sensitive detection than equivalent ionised eluents (such as potassium benzoate) and the signal enhancement achieved using a protonated eluent species is in accordance with theory.     

Application of self-organizing maps for the classification of chromatographic systems and prediction of values of chromatographic quantities

The separation of a complex mixture of inorganic and organic anions by ion chromatography–capillary electrophoresis using a cationic polymer added to the background electrolyte and indirect UV detection has been studied. The addition of unmodified polymer to an electrolyte suitable for indirect detection resulted in the appearance of a system peak due to the counter-anion on the polymer and while the position of the analytes relative to this system peak could be changed, this was found to be an unacceptable approach for mixtures of large numbers of analytes. Although conversion of the polymer to replace the counter-ion with the indirect UV detection probe ion simplified the system, this approach restricted the flexibility of the system because the probe and polymer concentration were necessarily linked. This limitation could be overcome by selecting the appropriate type of probe ion, with probes having a low ion-exchange selectivity coefficient providing greater retention of analytes than probes with a high ion-exchange selectivity coefficient. Three electrolyte systems with different probes (benzoate, chromate and phthalate) were modelled using a previously derived migration equation and this was used to optimise the electrolyte composition to enable the separation of a mixture of 24 inorganic and organic anions within 7 min. The electrolyte composition was then optimised for the analysis of anions in Bayer liquor with the final separation selectivity being substantially improved for selected key analytes.     

Evaluation of peroxyoxalate chemiluminescence postcolumn detection of fluphenazine in urine and blood plasma using high performance liquid chromatography

Peroxyoxalate chemiluminescence may be used for sensitive postcolumn detection of phenothiazine analytes separated by high performance liquid chromatography with appropriate optimization of measurement conditions such as solvent, pH and oxalate ester. Detectability of fluorescent analytes by chemical excitation varies greatly, but analytes with low oxidation potentials are generally more readily detected at low levels, as demonstrated for phenothiazines, an important class of fluorescent drugs. Some improvement in detection limits is observed for fluphenazine when chemiluminescence detection is compared to conventional fluorescence detection. Because of the specificity of chemical excitation, fewer interferences from fluorescent impurities in a urine matrix are observed.     

Simultaneous analysis of lead, mercury and selenium species by capillary electrophoresis with combined ethylenediaminetetraacetic acid complexation and field-amplified stacking injection.

In this study, speciation analysis was carried out for multispecies of lead, mercury and selenium by capillary electrophoresis (CE) with combined complexation and field-amplified stacking injection (FASI). Ethylenediaminetetraacetic acid (EDTA) was added to the sample mixture to form UV-absorbing complexes with the analytes, thus enabling direct UV detection. It was also used in the running electrolyte to improve resolution. Under optimal conditions, ten analytes were baseline-separated within 20 min. The influence of operational conditions (pH, EDTA concentration, sodium dodecyl sulfate concentration) on the electrophoretic behavior of the species was studied. The analyte-related parameters were calculated based on the migration equation. Enhancement of detection, up to 1700-fold, was achieved for the charged complexes with FASI, and sub-ng/mL detection limits were obtained. The performance of this method was compared with high-performance liquid chromatography, gas chromatography and other CE procedures.     

Recent advances in surface-enhanced Raman scattering detection technology for microfluidic chips

Microfluidic chip devices and their application to sensitive chemical and biological analyses have attracted significant attention over the past decade. The miniaturization of reaction systems offers practical advantages over conventional benchtop systems. In this case, however, a highly sensitive on-chip detection method is important for the monitoring of chemical reactions as well as for the detection of analytes inside the channel because the detection volume in a micrometer-size channel is extremely small. Recently, a surface-enhanced Raman scattering (SERS) technique is being regarded as a potential candidate for the highly sensitive detection of analytes in a microfluidic chip. This review provides a general survey and an in-depth look at recent developments in SERS techniques for the biological/environmental analysis of minute analytes in a microfluidic chip.     

离子交换色谱法同时测定啤酒中有机酸和无机阴离子

建立了用亲水性阴离子交换分离柱,KOH为淋洗液等浓度泵作梯度淋洗,电导检测,同时分离和检测16种无机阴离子和低分子量有机酸的离子色谱法。方法对所测无机阴离子和有机酸检出限在9．3～32μg/L之间;线性范围均在2个数量级以上;回收率在90．2％～107．2％之间。方法用于啤酒样品的分析,结果满意,样品的RSD小于5．3％(n=7)。     

Separation selectivity patterns of fully charged achiral compounds in capillary electrophoresis with a neutral cyclodextrin

Based on the separation selectivity equation, related to the dimensionless parameters for fully charged achiral analytes using a neutral CD, the separation selectivity can be classified into seven patterns. With respect to CZE without CD, the presence of CD in the buffer may improve, or reduce, the separation selectivity with this effect being accompanied by the same or reversed electrophoretic mobility order for charged analytes. This can depend on the separation selectivity of the two analytes in free solution, the binding selectivity, the separation selectivity of analyte–CD complexes and the ratio of electrophoretic mobility of the analytes in free, and complexed forms. Using positional isomers of benzoic acids and phenoxy acids as test analytes and α‐CD as a selector, the observed separation selectivity shapes were found to be in excellent agreement with the predicted separation selectivities.     

离子色谱法测定高氯、高钠油田回注水中的阴、阳离子及有机酸

建立了高氯、高钠油田回注水中痕量无机阴、阳离子和有机酸的离子色谱分析方法。对高钠基质中痕量阳离子的测定,选用IonPac CS12A分析柱、H2SO4溶液梯度淋洗、电导检测器检测;对高氯基质中阴离子及有机酸的测定,选用对OH-具有高选择性的高容量的IonPac AS11-HC柱、KOH梯度淋洗、电导检测器检测。在优化的梯度淋洗条件下,高氯或高钠的存在不影响痕量阴离子或阳离子的测定。该方法具有良好的线性(r=0.9926~0.9990)和精密度(测定组分峰面积的相对标准偏差(n=7)在8.0%以下),回收率     

N-Acylureido functionality as acceptor substituent in solvatochromic fluorescence probes: detection of carboxylic acids, alcohols, and fluoride ions

N,N'-Dicyclohexyl-N-(6'-methoxyanthryl-2-carbonyl)urea (1a) exhibits a strong solvatochromism with respect to its fluorescence properties. The emission maxima of 1a correlate well with the anion-stabilizing properties of the solvent. This feature allows the detection of analytes with high acceptor numbers, such as alcohols and carboxylic acids, and the detection of analytes such as fluoride ions which form strong hydrogen bonds with the amido hydrogen atom.     

金鸡纳生物碱电喷雾质谱裂解规律研究

利用电喷雾离子阱质谱（ES-ITMS）技术进行了金鸡纳中4种喹啉类生物碱（奎宁、奎尼定、辛可宁和辛可尼定）的电喷雾质谱研究。在优化的质谱条件下,正离子全扫描时,4种生物碱都易形成带一个质子的分子离子;进一步碰撞诱导解离四种母离子,二级质谱表明羟基丢失、奎宁环断裂及重排为其主要裂解方式。     

Headspace single drop microextraction combined with HPLC for the determination of trace polycyclic aromatic hydrocarbons in environmental samples

A new method by combining headspace single drop microextraction (HS-SDME) with HPLC fluorescence detection for the determination of trace polycyclic aromatic hydrocarbons (PAHs) in environmental samples was developed. Aqueous solution of saturated beta-cyclodextrin was used as extraction solvent and five PAHs were employed as target analytes. The factors affecting the extraction efficiency were studied in detail and the optimal extraction conditions were established. Beta-cyclodextrin was found to play two important roles, one is the improvement of extraction efficiency of target analytes and the other is the enhancement of their fluorescence intensities in HPLC fluorescence detection. The detection limits for the target analytes were found to be in the range of 0.004-0.247ng/ml and the relative standard deviations (R.S.D.s) of 5.1-7.1% were obtained. The proposed method was applied to the analysis of trace PAHs in environmental samples with satisfactory results.     

Simultaneous determination of sugars and picrosides in Picrorhiza species using ultrasonic extraction and high-performance liquid chromatography with evaporative light scattering detection

Sugars play a critical role in regulating overall cellular metabolism in high altitude growing plants. These plants are shown to have high levels of sugars to enhance their tolerance to abiotic stresses such as drought and freezing temperature. In the present study, a simple, sensitive, selective and reliable HPLC method based on ultrasonic extraction and evaporative light scattering detection (ELSD) has been developed and validated for the simultaneous determination of important sugars (xylose, xylitol, mannitol, glucose and sucrose) and picrosides (picroside-I and picroside-II) in two species Picrorhiza kurroa and P. scrophulariiflora. The analysis was carried out on a Zorbax amino column (250 mm x 4.6 mm i.d., 5 microm) with isocratic elution of acetonitrile:water (78:22, v/v). The method was validated for accuracy, precision, limit of detection and quantification according to International Conference on Harmonization (ICH) guidelines. The drift tube temperature of the ELSD system was set to 81 degrees C and nitrogen flow rate was 2.0 standard liter per minute (SLM). The regression equation revealed a good linear relationship (r(2)=0.9997+/-0.0012) within test ranges. The limit of detection and quantification for seven analytes in ELSD were less than 0.98 and 2.95 microg, respectively. The method showed good reproducibility for the quantification of seven analytes in Picrorhiza species with intra- and inter-day variation of less than 2.0%.     

梯度洗脱优化-离子色谱-脉冲安培法分析婴幼儿配方乳粉中的糖和糖醇

建立了梯度洗脱优化-离子色谱-脉冲安培检测技术分析婴幼儿配方乳粉中麦芽糖醇、半乳糖、葡萄糖、蔗糖、果糖、乳糖6种与代谢疾病紧密相关的糖和糖醇的方法。该方法对样品的前处理、色谱柱的选择、淋洗液的梯度等色谱条件进行了优化,重点研究了淋洗液梯度对各组分分离效果的影响。将梯度洗脱程序分解为弱保留组分分离、乳糖分离、基质消除、系统平衡4个子程序,并分别对其进行了条件优化,实现了6种组分的完全分离,并有效解决了弱保留组分色谱峰易重叠、乳糖色谱峰易拖尾等现象。6种组分的线性范围为0.5~100 mg/L,相关系数（r）>0.99,方法的检出限（S/N=3）为0.06~0.40 mg/L。该方法具有分离度好、灵敏度高等优点,可满足例行分析的要求,同时也为淋洗液的梯度优化提供了可借鉴的方法。     

Modeling the effects of type and concentration of organic modifiers, column type and chemical structure of analytes on the retention in reversed phase liquid chromatography using a single model

A previously proposed model for representing the retention factor (k) of an analyte in mixed solvent mobile phases was extended to calculate the k of different analytes with respect to the nature of analyte, organic modifier, its concentration and type of the stationary phase. The accuracy of the proposed method was evaluated by calculating mean percentage deviation (MPD) as accuracy criterion. The predicted vs. observed plots were also provided as goodness of fit criteria. The developed model prediction capability compared with a number of previous models (i.e. LSER, general LSER and Oscik equation) through MPD and fitting plots. The proposed method provided acceptable predictions with the advantage of modeling the effects of organic modifiers, mobile phase compositions, columns and analytes using a single equation. The accuracy of developed model was checked using the one column and one analyte out cross validation analyses and the results showed that the developed model was able to predict the unknown analyte retention and the analytes retentions on unknown column accurately.     

Assay of protein drug substances present in solution mixtures by fluorescamine derivatization and capillary electrophoresis.

A method is described to enhance the resolution and detection sensitivity of proteins, peptides, and amino acids in capillary electrophoretic analysis of solution mixtures. The method consists of derivatizing the analytes with fluorescamine, which is normally used as a fluorogenic reagent for compounds containing a reactive primary amine functional group, and then using the derivative as an ultraviolet chromophore to enhance detection sensitivity (measured at 280 nm) in capillary electrophoresis. The results demonstrated a significant improvement in the separation and detection sensitivity of the derivatized analytes as compared to their underivatized counterparts. The use of chromophores, such as fluorescamine, in capillary electrophoresis facilitates the analysis of components of solution mixtures, such as pharmaceutical formulations, that could not be resolved and/or detected by conventional capillary electrophoresis procedures.     

毛细管区带电泳法分析绿茶中的痕量成份

采用毛细管电泳/安培检测法(CE/AD)同时分离测定了绿茶中的芦丁、没食子酸、槲皮素、绿原酸等生物活性成分的含量, 考察了运行缓冲液酸度、浓度、分离电压、氧化电位和进样时间等实验参数对分离、检测的影响。在最优化条件下, 以300 μm碳圆盘电极为检测电极, 检测电位为+ 950 mV (vs. SCE) , 60 mmol/L硼酸盐运行缓冲液(pH 8.7)中, 上述各组分在20 min内可实现基线分离。各组分浓度与峰电流在3个数量级范围内呈良好线性, 检出限(S/N=3)在1.0×10^-7到1.0×10^-4g^.mL^-1范围,四种标样7次平行进样的相对标准偏差(RSD)小于3.0 %。该方法已成功地应用于绿茶中生物活性成分的测定, 结果令人满意。     

Determination of small phosphorus-containing compounds by capillary electrophoresis

The review focuses on the analysis of small phosphorus-containing compounds by capillary electrophoresis (CE) with different detection modes including UV absorption, laser-induced fluorescence, conductometry, amperometry, atomic spectrometry, and mass spectrometry. Determinations of phosphates, organophosphate, and chemical warfare agents in environmental samples such as water, soil and grains are emphasized. To achieve better sensitivity, high-resolving power, and reproducibility, the optimum separation conditions for various analytes (samples) are different. We compare the merits and demerits of the different detection modes for the detection of the analytes. Although the present methods are successful in many cases, there is still a need to develop high-throughput CE techniques for screening numerous environmental samples and sample stacking techniques in CE for the analysis of trace analytes.     

AT-column, a novel concentrating technique for large-volume injections in gas chromatography

Nowadays, large-volume injection is widely used for the GC determination of trace analytes, specifically to improve detectability. The most popular injectors for large-volume injections are the programmable temperature vaporisation (PTV) injector and the cold on-column (COC) injector, where each device has its own advantages and limitations. The novel AT-column concentrating technique combines features of two other injection techniques, loop-type large-volume and vapour overflow. AT-column injection is based on solvent evaporation in an empty liner with solvent vapour discharge via the split line. Little or no optimisation is required. The only relevant parameter is the injection temperature which can easily be calculated using the equation of Antoine. As an application, AT-column injection is combined with GC-MS for the trace-level determination of labile analytes and with GC-flame ionisation detection for the analysis of high molecular weight polymer additives. In summary, AT-column is an injection technique that combines the inertness of the COC, and the flexibility and robustness of the PTV large-volume technique.     

Electrochemical strategies for the label-free detection of amino acids, peptides and proteins

Electrochemical methods for the detection of amino acids, peptides, and proteins in a variety of media are reviewed. Label-free strategies in which the detection is based on the inherent electrochemical properties of the analyte are discussed. Various processes such as direct or mediated (in solution or immobilised) redox processes and interfacial ion transfers have been employed for the electrochemical detection and determination of the target analytes. The various methods covered encompass voltammetry at uncoated and modified electrodes and at immiscible liquid-liquid interfaces, potentiometry at polymer membrane electrodes and electrochemical impedance spectroscopy. The determination of the target analytes in complex biological matrices is discussed. The various approaches highlighted here illustrate the rich capabilities of electrochemical methods as simple, low-cost, sensitive tools for the determination of these important biological analytes at trace and ultra-trace levels.     

Luminol-type chemiluminescence derivatization reagents for liquid chromatography and capillary electrophoresis

The present paper provides the principles for chemiluminescence of luminol-type compounds and their wide and powerful application to the detection system in liquid chromatography and capillary electrophoresis as derivatization reagents. The reagents can be classified into two types, chemiluminescence labeling and chemiluminogenic reagents. The former reagents are highly chemiluminescent themselves and used for tagging their intense chemiluminophores to analytes, whereas the latter are weakly chemiluminescent but generate intense chemiluminescence by reaction with analytes. The liquid chromatographic methods utilizing chemiluminescence derivatizing reactions with luminol-type reagents allow the analytes to be detected at pmol–sub-fmol levels. Furthermore, the chemiluminogenic reactions show high selectivity owing to their selective reaction against the analytes permitting facile and reproducible detection.