酒类中微量甲醛的快速测定新方法

在FeCl3存在条件下,甲醛与自制蛋白液显色剂能生成紫色化合物,藉此可以定量测定微量甲醛。方法线性范围为1~10μg/10mL,线性相关系数r2=0.996,检出限为0.05μg/mL。用该法测定经活性炭脱色的啤酒和白酒中的甲醛含量,回收率为96.46%~103.32%,相对标准偏差为1.36%~2.09%(n=6)。     

A theoretical approach to substituent effects: Interaction between directly bonded groups in the isoelectronic series XNH3+, XCH3, and XBH3−

Ab initio molecular orbital theory including full geometry optimization at the 4-31G level is used to examine the interactions between substitutents X(X = Li, BeH, BH₂, CH₃, NH₂, OH and F) and substrates Y(Y = NH₃⁺, CH₃, BH₃^?) in the isoelectronic series XNH₃⁺, XCH₃ and XBH₃^?. The results indicate that the interaction energies are dominated by σ-effects. NH₃⁺ is found to interact favorably with the σ-donors (e.g. Li, BeH and BH₂) and unfavorably with the σ-acceptors (e.g. F, OH, NH₂). The reverse pattern a observed for XBH₃^?. The range of interaction energies for XCH₃ is considerably smaller than for XNH₃⁺ and XBH₃^?.     

测定啤酒和白葡萄酒中有机酸的离子排斥色谱法

研究了离子排斥色谱法分离测定啤酒和白葡萄酒中有机酸；选用常见的盐酸溶液作淋洗液，以四丁基氢氧化铵为再生液，考察了淋洗液浓度、流量等因素对分离和测定的影响，对啤酒和白葡萄酒中常见有机酸在阴离子排斥色谱柱上的保留行为进行了系统的研究；通过试验确定最佳的色谱条件为盐酸浓度1．10mmol/L，流量0．80mL/min；四丁基氢氧化铵浓度5.0mmol/L，流量1.10mL/min；并在该条件下，测定了啤酒和白葡萄酒中的有机酸。     

Beer Digestions for Metal Determination by Atomic Spectrometry and Residual Organic Matter

Many standard and official sample digestion procedures for trace metal determination are carried out in open vessels on hot plates. A new procedure for the determination of trace metals by flame atomic absorption spectrometry or inductively coupled plasmaatomic emission spectrometry in beer samples was developed to be performed in closed reactors assisted by microwaves. The results are compared with the ones obtained by other procedures by means of the analysis of the variance. The differences between the procedures are attributed to residual organic matter. Voltammetry, absorption molecular spectrophotometry and high pressure liquid chromatography with a photodiode array detector are used to study the nature of these residues. Nitrobenzoic acids, phenolic acids and other organic compounds are often present after digestion. The results obtained are related to the precision in metal determination by atomic spectrometry. The need for elaboration of certified reference materials for trace metals in beer is suggested.     

A theoretical approach to substituent effects: Stabilities and conformational preferences in β-substituted ethyl radicals

Ab initio molecular orbital theory is used to study substituent effects in a series of β-substituted Et radicals XCH₂CH₂. For X = BH₂ (plan.), CH₃, NH₂, OH and F, only slight conformational preferences and weak stabilizations are indicated. Such behaviour may be rationalized, using a PMO model, in terms of opposing changes, accompanying variation in X, in positive and negative hyperconjugation between the XCH₂ group and the CH₂ centre. On the other hand, for groups containing an appropriately oriented, low-lying vacant orbital, viz. X = Li, BeH and BH₂ (perp.), there is a pronounced preference for the perpendicular conformation of the radical. This is attributed to 1,3-interaction between the singly-occupied 2p(C) orbital and the vacant 2p(X) orbital.     

Simultaneous determination of hydride (Se) and non-hydride-forming (Ca,Mg, K,P, S and Zn) elements in various beverages (beer,coffee, and milk), with minimum sample preparation,by ICP–AES and use of a dual-mode sample-introduction system

A method has been developed enabling direct analysis (i.e. after dilution only) of beer, instant coffee, milk, and milk powder by ICP–AES. Analysis of the beverages after dilution with a low concentration of HNO₃ was used for accurate determination of essential minor and trace elements (Ca, Mg, K, P, S, and Zn). Selenium, introduced as the hydride, was determined simultaneously with the other non-hydride-forming elements using the commercial multi-mode sample-introduction system (MSIS). To obtain accurate results, however, some simple pre-treatment was needed. Analysis was also performed after microwave-assisted decomposition of the samples. Three different modes of sample-preparation, i.e. dilution only, partial decomposition (aqua regia treatment), and complete decomposition were compared. The results obtained by use of the three different sample-preparation methods were in very good agreement. Results from analysis of certified reference material (SRM 1459 non-fat milk powder) also verified the accuracy of the methods. The limit of detection obtained for Se using dual-mode sample introduction was 0.5 ng mL^–1, which corresponds to approximately 2 ng g^–1 in beer and approximately 4 ng g^–1 in coffee and milk when using the recommended procedure.     

Rapid analysis of free medium-chain fatty acids and related ethyl esters in beer using SPE and HRGC

A modification of a procedure by Hage [1] is proposed for the gas chromatographic evaluation of the content of free medium-chain fatty acids and related ethyl esters in beer. The method involves extraction of free fatty acids and ethyl esters by SPE using C₁₈ bonded phase columns, derivatization of free fatty acids and related ethyl esters with diazomethane, and GC analysis using an SP-2340 capillary column. The results obtained have shown the method to be rapid and highly reproducible. The technique has been compared with other methods used for determination of free fatty acids.     

Discrimination of Beers by Cyclic Voltammetry Using a Single Carbon Screen-printed Electrode

A fast, simple and costless methodology without sample pre-treatment is proposed for the discrimination of beers. It is based on cyclic voltammetry (CV) using commercial carbon screen-printed electrodes (SPCE) and includes a correction of the signals measured with different SPCE units. Data are submitted to partial least squares discriminant analysis (PLS−DA) and support vector machine discriminant analysis (SVM−DA), which allow a reasonable classification of the beers. Also, CV data from beers can be used to predict their alcoholic degree by partial least squares (PLS) and artificial neural networks (ANN). In general, non-linear methods provide better results than linear ones.     

Determination of trace iron in beer using flow injection systems with in-valve column and bead injection

Three flow injection (FI) systems were investigated for the determination of trace iron in beer: an FI-in-valve column-flame atomic absorption spectrophotometry (FI-FAAS) system, a spectrophotometric FI system with a column placed at the detection point, and an FI-spectrophotometric system with bead injection (FI-BI). Cationic exchange resin Dowex 50W X8 and iminodiacetate chelating resin, Chelex-100, were employed for the FI-spectrophotometric and FI-FAAS systems, respectively. The FI-in-valve column, packed with the resin, enhances the FAAS performance. The spectrophotometric FI system with a column (packed with Chelex-100) placed at the detection point (in a cell holder of a spectrophotometer) is based on the formation of iron (II)–1,10-phenanthroline complex sorbed onto the resin. No eluent has been found to be suitable. The FI-BI for renewable microcolumn has been proven to be an alternative. The FI-FAAS and FI-BI procedures provide online sample preseparation and preconcentration for the determination of iron in beer. Both are simple, rapid, and economical. The procedures also involve sample preparation (decarbonation and suppression of tannin interference by adding ascorbic acid) and standard addition. The results obtained by FI-FAAS and FI-BI agree with those of AOAC spectrophotometric method.     

Picomole‐level Formaldehyde Determination in Gaseous and Beer Samples Using Flow Injection Chemiluminescence Analysis

Based on the linear enhancement of formaldehyde (FA) within 7.0 ～ 1000 pmol l^?1 on luminol—bovine serum albumin (BSA) chemiluminescence (CL) system, FA determination in air and beer samples using CL with flow injection (FI) was proposed. The detection limit was 2.5 pmol l^?1 (3σ) and the relative standard deviations were less than 4.5% (n = 7). At a flow rate of 2.0 mL min^?1, a whole analysis from sampling to washing only needed 32 s, offering a sample throughput of 112 h^?1. This proposed method was successfully utilized to determine FA vapor pressure in liquid (121.8 ± 3.8 Pa), FA content in real air sample (8.93 ± 0.03 mg m^?3), and FA levels in beer (199.5 ± 5.6 ～ 225.2 ± 3.5 mg l^?1), giving determination recoveries from 90.7% to 109.3%. The mechanism of BSA—FA interaction was also investigated, showing FA binding to BSA was a spontaneous process mainly through hydrogen bonding and van der Waals force by FI‐CL, with binding constant K of 1.89 × 10⁶ l mol^?1 and the number of binding sites n of 0.86. Molecular docking analysis further revealed FA could enter into the pocket at subdomain IIA of BSA, with K of 1.71 × 10⁵ l mol^?1 and ΔG of ‐29.68 kJ mol^?1.