Improvement of the capabilities of inductively coupled plasma optical emission spectrometry by replacing the desolvation system of an ultrasonic nebulization system with a pre-evaporation tube

The effect of replacing the desolvation system (i.e., heater/condenser (HC) and membrane desolvator (MD)) of an ultrasonic nebulizer (USN) system with a pre-evaporation tube (PET) that is heated to about 400 °C on the analytical capabilities of inductively coupled plasma optical emission spectrometry (ICP–OES) was investigated. A multivariate optimisation was conducted in each case to find operating conditions maximizing plasma robustness. Under optimum conditions, the analytical performance of ICP–OES was significantly improved (i.e., better sensitivity, detection limit and plasma robustness) with USN–PET compared to that achieved with both the commercially-available USN–HC–MD and a conventional pneumatic nebulizer/spray chamber sample introduction system. However, only the USN–PET approach allows the determination of Hg, which appears to otherwise be lost in the heater/condenser system. Using a simple external calibration, without any matrix matching, and using an argon emission line for internal standardization, the results obtained for the determination of trace elements in certified soil reference materials (SRM 2710 and 2711) by USN–PET were in good agreement with certified values. This is unlike with conventional sample introduction systems where internal standardization using an Ar line is unusual, as it does not compensate for physical interferences, and either internal standardization (with internal standards added to the sample and standard solutions) or matrix-matched calibration is required.     

Use of evaporative light scattering detection for the quality control of drug substances: Influence of different liquid chromatographic and evaporative light scattering detector parameters on the appearance of spike peaks

High performance liquid chromatography (HPLC) with evaporative light scattering detection (ELSD) is a versatile, easy to use and inexpensive alternative when it comes to the analysis of substances lacking a chromophor for UV detection. However, in pharmaceutical analysis injection of highly concentrated test solutions are normally required to control impurities at low levels. Under these conditions spike peaks were observed in the chromatograms of the test solutions making a proper evaluation of the impurity profile impossible. The influence of different eluent and ELSD parameters such as eluent composition, eluent flow-rate, ELSD scavenger gas flow-rate and evaporation temperature on the appearance of spike peaks was investigated. It could be shown that spike peaks can be avoided when selecting elevated eluent flow-rates and ESLD scavenger gas flow-rates. Moreover, eluents containing high amounts of organic modifier seem to foster the appearance of spike peaks.     

Preparative isolation and purification of ginsenosides Rf,Re, Rd and Rb1 from the roots of Panax ginseng with a salt/containing solvent system and flow step-gradient by high performance counter-current chromatography coupled with an evaporative light scattering detector

Ginseng is a popular herb worldwide and has had varied uses in traditional Asian medicine for thousands of years. There are several different species of the herb, but all share the same constituents. Ginsenosides, the most extensively studied chemical components of ginseng, are generally considered to be one of the most important active ingredients of the plant. In this study, we have developed fast and efficient methodology for isolation of four known ginsenosides Rf, Rd, Re and Rb1 from Ginseng by high performance counter-current chromatography (HPCCC) coupled with evaporative light scattering detection (ELSD). The crude sample for HPCCC was purified firstly from a ginseng extraction using macroporous resin. The enriched saponin fraction (480 mg) was separated by using methylene chloride–methanol–5 mM aqueous ammonium acetate–isopropanol (6:2:4:3, v/v,) as the two-phase solvent system and yielded 10.7 mg of Rf, 11.0 mg of Rd, 13.4 mg of Re and 13.9 mg of Rb1. The purity of these ginsenosides was 99.2%, 88.3%, 93.7% and 91.8%, respectively assessed by HPLC-DAD-ELSD, and their structures were characterized by electrospray ionization mass spectrometry (ESI-MS) and compared with standards. Ammonium acetate was used to shorten the separation time and eliminate emulsification together with a flow step-gradient. The salt can be removed by re-dissolving the sample using acetone.     

Abnormal composition of commerical waxes revealed by supercritical fluid chromatography

Summary The analysis of natural waxes is a complicated process because they occur as complex mixtures. A study using supercritical fluid chromatography with packed columns made it possible to observe the behavior of each family of hydrocarbons, fatty esters, alcohols, acids and triglycerides. The latter were then separated according to their function type and alkyl chain lengths using octadecyl silica as stationary phase. With a polar modifier added to the supercritical fluid, it was possible to analyse certain waxes. Composition anomalies were observed which related to an overabundance of certain compounds which, in excess, are harmful to the quality of waxes intended for use in cosmetics.     

Development and validation of a novel HPLC/ELSD method for the direct determination of tobramycin in pharmaceuticals,plasma, and urine

A novel method for the direct determination of the aminoglycoside tobramycin was developed and validated based on reversed-phase high-performance liquid chromatography (RP-HPLC) with evaporative light scattering detector (ELSD). Using a Waters ODS-2 C18 Spherisorb column with an evaporation temperature of 45°C and nitrogen pressure of 3.5 bar, the selected mobile phase consisted of water/acetonitrile 55:45 containing 1.5 mL L^–1 HFBA (11.6 mM) in an isocratic mode at a rate of 1.0 mL min^–1. Tobramycins retention time was 4.3 min with an asymmetry factor of 1.7. A logarithmic calibration curve was obtained from 1 to 38 g mL^–1 (r > 0.9998). LOD was 0.3 g mL^–1; within-day %RSD was 1.0 (n = 3, 4.7 g mL^–1) and between-day %RSD was 1.1 (3 days within a week). The developed method was applied to the determination of tobramycin in a pharmaceutical crude substance and formulations (eye drops and ointments). Dilution experiments revealed the absence of interference from excipients (no constant and proportional errors); recovery from spiked samples was 99–103% with %RSD < 2.2 (n = 3×3). The developed HPLC/ELSD method was also found to be applicable in the determination of tobramycin in human plasma (0.6–12.5 g mL^–1) and urine (1.5–12.5 g mL^–1) after solid-phase extraction using carboxylate cartridges followed by solvent evaporation (×2 preconcentration). A mean recovery of 86% for plasma and 91% for urine was obtained.     

High performance liquid chromatography of raw sugars and polyols using bonded silica gels

Summary Bonded silica columns have been evaluated for their ability to separate carbohydrates and polyols. Mobile phases consisting of dichloromethane/methanol produced the best separations in comparison with the acetonitrile/water mixtures commonly used with amino columns. Of all the bonded phases tested, LiChrospher Diol silica provided the best separations, and selectivities were not very different from those obtained on the most popular system using an amino bonded phase and acetonitrile/water as eluent. In addition, diol columns with a dichloromethane/methanol eluent offer excellent stability with no Schiffs base formation of reducing sugars. Using an evaporative light scattering detector, low limit detection is obtainable (20 ng of glucose from a column) and gradient elution is quite feasible.     

Applications of HPLC with evaporative light scattering detection in fat and carbohydrate chemistry

Summary The advantages of an evaporative light scattering detector in HPLC are demonstrated using the separation of α, ω-dicarboxylic and hydroxycarboxylic acids, alkyl glucosides and mono-, di- and triglycerides as examples. By using this detector reversed phase as well as normal phase gradient HPLC becomes possible for substances with no UV absorption. Presented at the 17th International Symposium on Chromatography, September 25–30, 1988, Vienna, Austria.     

Analysis of mixtures containing free fatty acids and mono-, di- and triglycerides by high-performance liquid chromatography coupled with evaporative light-scattering detection

Commercial monostearates of glycerol, generally used as antistatic agents for thermoplastic polymers, consist of a complex mixture of mono-, di- and trisubstituted glycerides and the corresponding fatty acids. Thus far, the glycerides and the fatty acids have been analyzed separately by high-performance liquid chromatography (HPLC). In fact, the simultaneous analysis of glycerides and fatty acids requires esterification of the acids in order to avoid overlapping of the chromatographic peaks. This paper describes an HPLC method which allows the direct separation and identification, simultaneously and in a single run, of the variously substituted glycerides, and also the corresponding saturated fatty acids that are found as by-products in commercial glycerol monostearates. The procedure is based on the use of a ternary gradient HPLC instrument equipped with an evaporative light-scattering detector; the stationary phase was a reversed-phase RP-8 end-capped (Merck) column; the mobile phase was two consecutive binary gradients consisting of acetonitile-water plus acetic acid (0.1%, v/v) and acetonitrile-methylene chloride. The method is fast and shows high sensitivity and selectivity, being able to separate also the positional isomers of mono- and digycerides in addition to the mixed di- and triglycerides.     

高效液相色谱-蒸发光散射检测器测定食品中胆固醇含量

建立了可满足各类食品（包括动物性食品、动植物混合食品）中胆固醇的HPLC—ELSD快速测定方法。样品经50％（w）KQH直接皂化和石油醚萃取后进行色谱分析。色i普柱为ODS柱,流动相为乙醇和乙脯,通过优化梯度洗脱条件,在20min内实现了胆固醇与干扰物质（如植物甾醇）的有效分离,分离度月大于1．5。胆固醇色谱峰面积的自然对数与浓度的自然对数呈良好的线性关系（r〉0．9996）,检出限（LOD）为0.20μg（S／N=3）,定量下限（LOQ）为0．56μg（S／N=10）,回收率为93％-96％（n=6）,重复性RSD〈3．0％（n=6）。     

电化学方法研究氯气冷凝器的腐蚀

冷凝器的腐蚀在氯碱工业中极为严重,并可酿成致命事故.常压冷凝器制造通常采用的钢材为16MnR和10#,焊接材料为J507.本文研究了上述3种材料在29.9%(by mass)的氯化钙溶液中的电化学行为,分析其腐蚀电流密度icorr和电化学阻抗参数变化规律.结果表明,在16MnR、10#和焊接材料的三相区,焊接材料腐蚀较快,为整体结构的薄弱点,因此氯气冷凝器需要定期检测和修复.