Application of diode array detectors for solute identification in toxicological analysis

Summary The possibilities and limitation of automated solute identification via UV/VIS spectroscopy in HPLC are demonstrated and applications in toxicologic analysis are described. A standard isocratic system is used. The influence of various chromatographic parameters on retention time is shown. A retention time window of ±15% is required. In addition to retention time, derived spectral data are calculated (minima and maxima of derivatives, area counts under standardized spectral ranges, absorption at various wavelength) and used for positive solute identification. It is possible to identify solutes with a high degree of certainty in urine and plasma if their concentration is at least 10 ppm.     

Determination of pheophytinatonickel(II) by reversed-phase highperformance liquid chromatography

Summary HPLC determination of pheophytinatonicke(II) (Pheo-Ni) prepared by the replacement of magnesium(II) in chlorophyll with nicke(II) is described. The good separation of PheoNi was obtained by using chemically bonded C₁₈ as the stationary phase and acetone-methanol (50∶50, vol/vol) as the mobile phase. Conventional spectrophotometric method was also used for the determination of PheoNi. For the synthetic samples prepared by mixing (pheophytinato a) nicke(II) [(Pheo-a) Ni] and (pheophytinato b) nicke(II) [(Pheo-b) Ni], analytical values obtained by the spectrophotometric method were very high compared to those obtained by HPLC. In the proposed HPLC method, (Pheo-a) Ni and (Pheo-b). Ni could be determined in the concentration range of 0.028–30μg/ml and 0.038–30μg/ml with relative standard deviations (n=10) of 3.1% and 0.8%, respectively.     

Fast LC analysis of the α-acid content of “fresh” and “aged” hops

Summary A quaternary mobile phase was optimized in conjunction with Fast LC techniques to separate α and β acids extracted from hops in less than 4 minutes. The method is proposed for automated analysis of large numbers of hop samples and its usefulness is demonstrated by comparing α-acid levels obtained by liquid chromatographic and conductometric techniques. Both assays provided similar values for “fresh” hops but in “aged” hops liquid chromatography showed a lower level of α-acids.     

Optimum performance of capillary GC columns as a function of tube diameter and film thickness under various operating conditions. Computer program for calculation of H-ū curves and minimum analysis times

The Golay-Giddings and Poiseuille equations are used to derive equations for the calculation of the maximum plate number and minimum time conditions for given columns at fixed, but selectable, outlet pressures. In addition, expressions are presented for the determination of minimum analysis times for separation problems requiring given plate numbers. In this instance, the optimum column length can be calculated as a function of outlet pressure. A Basic computer program, incorporating the equations for the various optima, together with the H-ū curves, is described. Input variables are either column length or desired plate number, column diameter, film thickness, capacity ratio of the solute, column outlet pressure, seperation temperature, and carrier gas. The carrier gas viscosity is automatically calculated in the case of hydrogen, helium, or nitrogen. For these gases, and if the solute is a n-alkane, the diffusivity of the solute in the mobile phase is calculated. In this case, the carbon number of the solute is needed in the computation. For high molecular weight polydimethylsilicone phases (e.g. SE-30), the program can approximate the diffusivity of n-alkanes in the stationary phase at the given temperature as a function of the carbon number. Of course, manually entered values of viscosity and diffusion coefficients can be included in the calculations.     

High-pressure synthesis of cyclic phenylacetylene oligomer

New conjugated oligomers were prepared by reacting phenylacetylene under high pressure of 0.11 to 0.92 GPa at 100–200°C for 0–5 h. The number-average molecular weight M?_n, the weight-average molecular weight M?_w, and the oligomer yield increased with pressure, tem-perature, and time. The average molecular weight of the oligomer showed the maximum value (M?_n: 830, M?_w: 2400) under 0.92 GPa, the maximum pressure, where phenylacetylene was oligomerized at a constant temperature. The structure of the oligomer was investigated from ESR, infrared, UV–VIS, field desorption mass (FDMS) spectra, and ¹³C NMR spec-trum. Analysis of the FDMS spectrum revealed that the molecular weight of the oligomer was multiple of the monomer. ¹³C NMR spectrum of the oligomer showed the absence of sp-carbon (? C?). We found that the oligomer had a cyclic structure. The cyclic oligomers of pentamer or more were new compounds. © 1995 John Wiley & Sons, Inc.     

Kováts' coefficients for predicting polarities in silicone stationary phases and their mixtures

Summary A correlation between the retention polarity and the Kováts' coefficient has been found for a number of commercial stationary phases used in gas chromatography. The correlation has been used to predict the polarity of a few mixed stationary phase columns prepared as binary mixtures of OV-101 with OV-25, DC-550 or Carbowax 20M, and also mixtures of OV-225 with SP-2340. A linear relationship was found between polarity and mixture composition. The temperature dependence of the Kováts' coefficient was investigated and found to increase linearly with temperature, the rate of increase depending on the polarity of the stationary phase, with greater increases for more polar stationary phases.     

Headspace-gas chromatography: The influence of sample volume on analytical results

Summary The role of the volume of the sample and the sample vial in equilibrium headspace-gas chromatography is discussed. A new term, thesample phase fraction (_S) is introduced. It is shown that if the value of _S is kept constant, the vial's volume has no influence on the sensitivity of the headspace analysis (which is proportional to the concentration of the analyte in the headspace). In a given headspace sampling system, concentration of the compound of interest in the headspace (c _G ^* ) at equilibrium is related to the value of _S: a higher _S will increase c _G ^* . However, the influence is important only in the case of low distribution coefficients: in the case of higher distribution coefficients this influence is negligible. This conclusion is also true for small changes in the sample volume in duplicate analyses: exact reproducibility of the sample volume is important only in the case of low distribution coefficient values.     

High performance liquid chromatography assay for alanine amino transferase

Summary An improved method of alanine-amino transferase determination is proposed. The reaction is carried out with alanine and 2-oxoglutarate as substrates and analysis is by HPLC on a reversed-phase chromatographic system using a C₁₈ column and tetrabutylammonium phosphate in phosphate buffer (pH 7.0)-acetonitrile as mobile phase. The enzyme activity was determined by directly following the formation of pyruvic acid without employing any secondary reaction, which is necessary in the spectrophotometric method. The detection limit of pyruvic acid is 10 pmole l^–1 and the standard deviation for the enzymatic activity of standard solutions is 5.4%. Furthermore under the chromatographic conditions selected it is possible to detect the presence of some intermediate species.Work supported by National Research Council of Italy. Presented in part at the First International Symposium on Applications of HPLC in Enzyme Chemistry, Verona, September 1990.     

SDS/苯甲醇/H2O体系的相行为与结构

SDS／苯甲醇／H2O体系能生成胶束、微乳液、层状液晶、六角状液晶等分子有序组合作，它们之间转换关系可以从凝聚能理论得到解释．来甲酸在O／W微乳液中的分配系数K＝168，表明绝大多数苯甲醇被增溶于SDS胶束相内．随重量比本甲醇／SDS增加，层状液晶中的do值几乎不变，溶剂渗透率略有增加，六角状液晶中圆柱缔合体的半径r值几乎不变，溶剂渗透率增加．     

Fractionation and purification of antioxidant peptides from Chinese sturgeon (Acipenser sinensis) protein hydrolysates prepared using papain and alcalase 2.4L

Protein hydrolysates have the potential to be natural and safer sources of bioactive peptides. In this study, two proteases were used to hydrolyze Chinese sturgeon (Acipenser sinensis) protein, and the hydrolysates were then purified to yield antioxidant peptides. The degree of hydrolysis of 23.56 % and 18.14 % was obtained using papain and alcalase 2.4L, respectivly, and hydrolysates had 96.80 % and 87.24 % total amino acid content, respectivly. The papain hydrolysate (PH) and alcalase 2.4L hydrolysate (AH) showed good antioxidant activity against DPPH^? (IC₅₀ of 3.64 and 3.15 mg/mL) and ABTS^?+ (IC₅₀ of 1.92 and 1.58 mg/mL), respectively. The low-molecular-weight (<1000 Da) fraction of both hydrolysates demonstrated the highest antiradical activity (IC₅₀ of 2.59 and 2.31 mg/mL, DPPH) and (IC₅₀ of 1.54 and 1.36 mg/mL, ABTS), respectively. Nine peptides were separated from both hydrolysates using reverse phase high performance liquid chromatography (RP-HPLC). The IC₅₀ for ABTS^?+ scavenging activity of peptide P5 with valine, glycine and asparagine (MW of 282.13 Da) from PH, and peptide P3 with histidine, glycine and alanine (MW of 302.74 Da) from AH was 0.89 and 0.72 mg/mL, respectively. The fractions and purified peptides obtained from Chinese sturgeon hydrolysates could be utilized as natural antioxidant substitutes in pharmaceuticals and food products.