Yang-Han Lee

Capillary electrophoretic determination of organic acids with indirect detection

Abstract Methods for the determination of several organic acids commonly found in foods and beverages, including oxalic, citric, acetic, tartaric, malic, succinic, lactic, carbonic, aspartic, glutamic, ascorbic and gluconic acids, by capillary electrophoresis (CE) with indirect absorbance detection were developed. Several absorbance providers, including chromate, p-hydroxybenzoate, phthalate, terephthalate, trimellitate and pyromellitate, were investigated for their suitability as background electrolytes (BGEs). CE was performed in the negative voltage (reverse polarity, detector towards anode) mode. The effects of pH and various additives on CE separations were evaluated. The BGE and pH each played a major role in affecting the selectivity and resolution of CE. All analytes except malate and succinate could be baseline resolved in one run by performing CE with 5 mM trimellitate (as the BGE)-1 mM tetradecyltrimethylammonium bromide at pH 9.0 in less than 10 min. On the other hand, the CE separation of the tri- and dicarboxylic acids and hydroxydicarboxylic acids (the first five) could best be obtained at pH 5.5 in 5 min. The precision of the method for most monoprotic analytes is typically less than 1% for the migration time and 1–4% for the peak area (n = 6). The detection limit for most analytes is of the order of 2.0·10−6 M. The new methods developed are rapid, sensitive and quantitative and can be readily applied to real food samples for quantitative analysis.

Capillary electrophoretic analysis of inorganic cations : role of complexing agent and buffer pH

Capillary electrophoresis for the determination of inorganic metal cations in the presence of various complexing agents was investigated. The complexing agents studied were acetic, glycolic, lactic, hydroxyisobutyric, oxalic, malonic, malic, tartaric, succinic and citric acid. They were all suitable as complexing agents for separating a mixture of six alkali and alkaline earth metal ions (lithium, sodium, potassium, magnesium, calcium and barium) using indirect UV detection with imidazole as a carrier buffer and background absorbance provider. The pH of the carrier buffer affected the electrophoretic separation in a complex but predictable way. The optimum pH for separating these ions in the presence of the complexing agent was around the pK1 of the acid. When di- and triprotic acids were used, electrophoresis carried out above the second acid dissociation constant resulted in a significant decrease in the mobility of divalent ions and a decrease in number of theoretical plates, N, due to complex formation. In most of the cases reported here one could obtain, typically, a migration time span from 1 to 2 min, a minimum and a maximum resolution of 1 and 15, respectively, and N from 16 000 to 750 000 per metre. Of the ten complexing agents studied, lactic, succinic, hydroxyisobutyric and malonic acid seemed to give the best overall performance.

Determination of metal cations by capillary electrophoresis effect of background carrier and completing agents

Abstract The determination of trace metals in aqueous samples can be readily accomplished by capillary electrophoresis (CE) via indirect absorbance detection. Methods for simultaneously determining alkali, alkaline earth and transition metal ions and Group IB, IIB and IVA metals ions were developed. Imidazole, benzylamine, ephedrine or pyridine was used as the carrier buffer and the background absorbance provider. Glycolic acid, α-hydroxy-isobutyric acid or succinic acid was used as the complexing agent. The elements determined were Li, Na, K, Cs, Mg, Ca, Sr, Ba, Cr, Mn, Fe, Co, Ni, Cu, Zn, Cd, Ag, Al and Pb. All ions could be separated in less than 15 min. In most instances reported here, more than a dozen ions could be separated in 5–10 min. All peaks were well separated and baseline resolved (i.e., no peaks overlapped), except Ag and Al, which required a separate and additional analysis. The detection limit was in the range 0.02 (Na)−208 ppb (Cr) with the electrokinetic injection mode (10 kV, 5 s). The reproducibility was 1% for the migration time and better than 5% for the peak height for most metal ions. The calibration graphs were linear for most ions in the concentration range 10−5−10−3M (R2 = 0.9995−0.9999) using the hydrodynamic injection mode. Concentrations lower than 10−5M can be determined using the electrokinetic injection mode, but the calibration graph is not linear. The methods developed here are well suited for determining metal ions in a variety of real samples.

Capillary electrophoretic determination of amino acids with indirect absorbance detection

Abstract Methods for the capillary electrophoretic (CE) analysis of a mixture of twenty common amino acids with indirect absorbance detection were developed. The suitability of nine background electrolytes (BGEs) was investigated. The effects on the CE separation of the analytes of the BGE, pH, and various additives were evaluated. Metal cations and cationic surfactants were used as buffer additives either to decrease or to reverse the electroosmotic flow in order to improve the resolution. p -Aminosalicylic acid and 4-(N,N-dimethyl)aminobenzoic acid are best suited as the carrier buffers and background absorbance providers as they have effective mobilities closer to the mobilities of most amino acids at alkaline pH. The CE separation of 17–19 amino acid peaks could be achieved in 20–40 min. The performance of CE in various BGEs and the influence of pH, divalent metal ions and cationic surfactants are discussed.

Capillary electrophoretic determination of amino acids improvement by cyclodextrin additives

Abstract Previously, we have developed methods for the capillary electrophoretic determination (without derivatization) of twenty common amino acids with indirect absorbance detection [Y.-H. Lee and T.I. Lin, J. Chromatogr. A, 680 (1994) 287]. Here, we report a further improvement in the resolution, resulting from the use of various cyclodextrin (CD) additives. Capillary electrophoresis (CE) was performed at pH 11.0 with either p-aminosalicylic acid (PAS) or 4-(N,N′-dimethylamino)-benzoic acid (DMAB) as the background electrolyte (BGE). The effects on the CE separation brought about by various CD additives, e.g. α- and β-cyclodextrins, methyl-, hydroxypropyl-2 2,6-dimethyl-, and 2,3,6-trimethyl-β-cyclodextrins were investigated. These CD additives form inclusion complexes with the BGE and also with amino acids, altering the migration behavior of the analytes. For some amino acids which have previously proved difficult or impossible to separate, an improvement in the separation selectivity has been attained. Association constants of BGEs for cyclodextrins were determined on the basis of the CE mobility changes caused by the CD additive. The concentration of CD additive needed to achieve a suitable separation was calculated and optimized experimentally. Using 10 mM PAS or DMAB, in the presence of 20 mM α-cyclodextrin at pH 11.0, eighteen amino acid peaks were baseline-resolved in under 35 min. Leu and Ile could also be separated in the presence of 15–20 mM β-CD under similar CE conditions. The performance of CE in separating amino acids in the presence of various CD additives is discussed.

Measurement of RF PCB Dielectric Properties and Losses

This paper presents the calculations of transmission line loss factor by extracting from the Q-factor measurement of the quarterwavelength open stub resonators over the designed frequency and other resonant frequencies. A comparison of the loss factor of the design frequency with other resonant frequencies of each of the stub’s quarter-wave resonances is provided in this paper. The radiation and discontinuity losses are undesirably included in the unloaded Q-factor measurement and it shows that the unloaded Q-factor is not repeatable at different designed frequency. The implementation of the loss factor measurement by quarter-wavelength open stub resonators is becoming more and more important to be considered with the increase of using the electronic circuits operating at high frequencies. † This author is also with Department of Electronic Engineering, Tam Kang University, 151 Ying-chuan Road, Tamsui, Taipei County, Taiwan 25137, R.O.C.

Providing multiple data rates in infrastructure wireless networks

In this paper, we will discuss how to provide multiple-data-rate transmissions in a contemporary IEEE 802.11 infrastructure wireless network. According to the characteristics of modulation schemes, the highest data rate between a pair of mobile stations will be inversely proportional with the transmission distance. Therefore, a moving mobile station is requested to dynamically adjust its modulation scheme to achieve maximal network throughput as well as to keep the connection alive. In this paper, we propose a hybrid handshake protocol with a simple broadcasting protocol to help mobile stations to obtain the necessary location information. The critical fairness problem of multi-rate wireless networks is also discussed and solved in this paper.

The impact of laser phase noise on the coherent subcarrier multiplexing system

In coherent optical subcarrier multiplexing (CSCM) systems, the laser phase noise may cause signal spectrum broadening and hence, causes significant deterioration in the system performance. The impact of phase noise on the CSCM system is analyzed in terms of carrier-to-noise ratio, intermodulation distortion, and adjacent channel crosstalk. The optimal modulation index and carrier to noise ratio are also presented. Some numerical results are outlined. >

The Measurement and Analysis of WiMAX Base Station Signal Coverage

This paper presents the fleld trial measurement data of WiMAX base station; it includes the system coverage, signal strength and available transmission rate. Data consisting of real time images, VoIP internet telephone are transmitted through Skype software by using WiMAX, HSDPA (3.5G) and EDGE (2G) transmission techniques, and these data are connected to centrally equipped wireless monitoring servers to perform data monitoring and analysis. Finally, we make comparisons, analysis and discussions of these three transmission techniques from the measured and characterized data.

Design of a self-routing frequency division multiple access (SR-FDMA) network using an optical ring filter with or without gain as a router

Self-routing frequency division multiple access (SR-FDMA) network with ASK coherent detection and dual ring topology is proposed. The router, which employs the optical ring filter, is used as a means for selecting the desired channel carrier and at the same time as a bypass of the other channel carriers. The channel capacity and the carrier-to-noise ratio are investigated with the consideration of cross talk and power budget penalty. We find that there exists an optimum coupling coefficient of the transceiver coupler and a trade-off in selecting channel number and data rate. The results show that the router with gain can suppress the cross talk, compensate the power budget penalty, and largely increase the channel number. Therefore, with this router, a self-routing, high-density FDMA network is feasible.