Determination of sorbic acid in urine by gas chromatography-mass spectrometry.

The average daily uptake of the common food preservative sorbic acid is estimated to range from 0.01 to 1.1 mg kg-1. Sorbic acid mainly is metabolised to carbon dioxide. Minor amounts are converted to trans,trans-muconic acid (ttMA) as well as excreted unchanged into the urine. Since urinary ttMA is a biomarker for the occupational and environmental exposure to benzene, there is an additional need for monitoring the uptake of sorbic acid, particularly at low, environmental benzene exposure levels. For this purpose, a simple, robust and rapid method for the determination of sorbic acid in urine at trace levels was developed. After addition of 10 ml of water and 5 ml of 8 M hydrochloric acid to 10 ml of the thawed urine, the sample was water steam distilled using an automated distillation device. A total of 100 ml of the distillate were solid-phase extracted. After washing, the sorbic acid was eluted with 4 ml methanol. The eluate was reduced under a stream of nitrogen to a volume of 300 microliters. After addition of 500 microliters boron trifluoride in methanol and incubation for 1 h at 60 degrees C, the resulting sorbic acid methyl ester was extracted three times with 1 ml heptane. To the combined heptane layers, sorbic acid ethyl ester was added as an internal standard. After reducing to a volume of 100 microliters in a stream of nitrogen, the final analysis was performed by GC-MS using the fragment ions m/z 126 for the analyte and m/z 140 for the internal standard. The limit of detection was 0.7 ng ml-1 urine and the R.S.D. of 69 duplicate determinations was 7.5%. In a controlled, experimental study and in a field study, we were able to show that urinary sorbic acid is a marker for the dietary uptake of sorbic acid and that sorbic acid is converted to ttMA. On average, 0.1% of the dietary sorbic acid is excreted unchanged into the urine. Excretion is complete within 24 h. We found that, on average, 0.23% of the oral dose of sorbic acid is excreted as urinary ttMA. There was a significant correlation between urinary excretions of sorbic acid and ttMA (r = 0.74, n = 69). We conclude that urinary sorbic acid can be used to correct the urinary ttMA level in order to determine the portion related to benzene exposure. This appears to be necessary particularly at low, environmental benzene levels.     

Simultaneous determination of benzoic acid and saccharin in soft drinks by using lanthanide-sensitized luminescence

A simple and fast approach is used for the first time to develop a time resolved lanthanide-sensitized luminescence method for the simultaneous determination of a preservative and a sweetener, namely benzoic acid (BZ) and saccharin (SC), respectively, in food samples. The method involves the formation of the corresponding ternary chelates with terbium(III) and trioctylphosphine oxide (TOPO) in the presence of Triton X-100, and the measurement of the initial rate and equilibrium signal of this system, which were obtained in 0.1 and 5 s, respectively. The dynamic ranges of the calibration graphs, obtained by using kinetic and equilibrium measurements, were 0.2-36 micrograms ml-1 and 0.15-30 micrograms ml-1, respectively, for BZ, and 3.3-24 micrograms ml-1 and 4-36 micrograms ml-1 for SC and the detection limits were 0.07 and 0.04 microgram ml-1, respectively, for BZ, and 1.1 and 1.2 micrograms ml-1, respectively, for sodium SC. The relative standard deviation ranged between 2.3 and 3.0%. Both compounds were determined simultaneously by using a system of two equations which were resolved by using the calibration data obtained individually for each analyte and by multiple linear regression. Mixtures of BZ and SC in ratios between 3:1 and 1:9 were satisfactorily resolved by using both approaches. The method was applied to the direct analysis of several soft drinks. Analytical recoveries ranged between 89.3 and 108.5%.     

Simultaneous determination of acetylsalicylic acid and its major metabolites in human serum by second-derivative synchronous fluorescence spectrometry.

A method is described for the simultaneous determination of acetylsalicylic, salicylic, gentisic and salicyluric acids (ASA, SA, GA and SU, respectively) in serum, based on their native fluorescence. The ASA-SA-GA-SU-containing serum samples are extracted with chloroform-1% acetic acid solution; ASA and SA are determined in the organic phase, and GA and SU in the aqueous phase, after removal of protein with trichloroacetic acid, at pH 5.0 and 11.6, respectively. The ASA-SA and GA-SU-SA mixtures are resolved using second-derivative fluorescence spectrometry and the appropriate empirical equations involving the effect of each acid on the signal of the other. Recoveries from sera spiked with ASA (1.0-10 micrograms ml-1), SA (25-50 micrograms ml-1), GA (0.05-0.2 micrograms ml-1) and SU (1.0-5.0 micrograms ml-1) ranged from 100 to 104% (mean 101%), from 93 to 99% (mean 97%), from 94 to 104% (mean 99%) and from 94 to 107% (mean 98%), respectively.     

Spectrophotometric determination of tannins in tea and beer samples with iron(III) and 1,10-phenanthroline as reagents

A simple and accurate spectrophotometric method is proposed for the determination of tannins in tea and beer samples based on the reduction of iron(III) to iron(II) by tannins at 80 degrees C for 20 min. The iron(II) was then reacted with 1,10-phenanthroline at pH 4.4 to form a coloured complex. Background correction could be effected by precipitating the tannins in the sample solution twice with gelatin and kaolin. Absorbance measurements were made at 540 nm and the calibration graph was linear from 0 to 5.5 micrograms ml-1 of tannic acid with a slope of 0.213 A p.p.m.-1. The precision for the determination of tannins in a tea sample containing 9.45% of tannins was 1.8%. Most of the ingredients commonly found in tea and beer samples do not interfere with the determination. Several tea and beer samples were analysed for their tannin content using the proposed method.     

Simultaneous determination of ascorbic acid, caffeine and paracetamol in drug formulations by differential-pulse voltammetry using a glassy carbon electrode

A simple, rapid and accurate method for the simultaneous determination of ascorbic acid, caffeine and paracetamol in drug formulations has been developed. Peak currents were measured with a glassy carbon electrode at +0.350, +0.618 and +1.425 V versus a saturated calomel electrode for ascorbic acid, paracetamol and caffeine, respectively. Perchloric acid (0.1 M) - methanol (1 + 1) was used both as a solvent and supporting electrolyte. The optimum modulation amplitude, pulse repeat time and scan rate of the polarographic analyser were found to be 50 mV, 0.5 s and 5 mV s-1, respectively and the linear calibration ranges for ascorbic acid, caffeine and paracetamol were 0-35, 0-50, and 0-55 micrograms ml-1, respectively. The relative standard deviations for 9.30 micrograms ml-1 of ascorbic acid, 8.50 micrograms ml-1 of caffeine and 7.30 micrograms ml-1 of paracetamol were 1.3, 2.5 and 0.7%, respectively. Results are reported for several commercially available drugs.     

毛细管气相色谱法测定速冻食品中的山梨酸和苯甲酸

建立了速冻食品中山梨酸和苯甲酸的毛细管气相色谱检测方法。样品用石油醚-乙醚高速匀浆的方法提取后,通过改变酸度而改变其在有机相和水相中分配比的方法,去除脂肪等杂质的干扰,用FFAP毛细管色谱柱FID检测器进行检测。该方法测定结果的相对标准偏差为1.4%~6.6%,回收率为90.5%~96.9%,检出限为1mg/kg。     

Polarographic determination of sorbic acid in fruit juices and soft drinks

A simple differential-pulse polarographic method using a laboratory-built hanging mercury drop electrode as the working electrode was developed for the determination of sorbic acid in fruit juices and soft drinks. Sorbic acid was extracted from the samples with diethyl ether. After reduction of the ethereal solution to a small volume by direct evaporation, the residual ether was dissolved in the supporting electrolyte (25 ml of acetonitrile + 1 ml of 0.06 M acetic acid + 0.8 g of tetraethylammonium bromide). Peak current was measured at -1.7 V. The working range of the method, without dilution or pre-concentration of the samples, was from 4 to 229 p.p.m. for the original juice and drink samples. The validity of the method was confirmed by parallel determinations using the method of the Association of Official Analytical Chemists and by recovery tests on a large variety of juice samples. Satisfactory recoveries and agreement in results from the two methods were obtained. The recovery and precision (relative standard deviation) of the method were 97 +/- 4 and 100 +/- 3%, respectively, for blackcurrant juice for five determinations.     

Spectrophotometric determination of taurine in food samples with phenol and sodium hypochlorite as reagents and an ion-exchange clean-up

A simple and accurate spectrophotometric method is proposed for the determination of taurine in food samples using phenol and sodium hypochlorite as reagents, which form a blue colour with taurine at room temperature and pH 10.35. Ion exchange was used to improve the selectivity of the method. Absorbance measurements were made at 630 nm and the calibration graph was linear from 0 to 180 micrograms ml-1 of taurine with a slope of 0.00242 A (p.p.m.)-1. The precision for the determination of taurine (156 micrograms ml-1) was 0.8% (n = 10). The method was applied successfully to the determination of taurine in milk products and energy drinks.     

Selenium speciation in enriched and natural samples by HPLC-ICP-MS and HPLC-ESI-MS with perfluorinated carboxylic acid ion-pairing agents

Selenium-enriched plants, such as hyperaccumulative phytoremediation plants (Astragalus praleongus, 517 micrograms g-1 Se, and Brassica juncea, 138 micrograms g-1 Se in dry sample), yeast (1200, 1922 and 2100, micrograms g-1 Se in dry sample), ramp (Allium tricoccum, 48, 77, 230, 252, 405 and 524 micrograms g-1 Se in dry sample), onion (Allium cepa, 96 and 140 micrograms g-1 Se in dry sample) and garlic (Allium sativum, 68, 112, 135, 296, 1355 micrograms g-1 Se in dry sample) were analyzed by HPLC-ICP-MS for their selenium content and speciation after hot water and enzymatic extractions. Reference samples with natural selenium levels, such as onion and garlic controls, cooking garlic powder, baking yeast powder and a commercial garlic supplement were also analyzed. Selected samples were also examined by HPLC-electrospray ionization (ESI)-MS. HPLC was mostly carried out with 0.1% heptafluorobutanoic acid (HFBA) as ion-pairing agent in 1 + 99 v/v methanol-water solution, but 0.1% trifluoroacetic acid (TFA) in 1 + 99 v/v methanol-water solution was also utilized to permit chromatography for compounds that did not elute with HFBA. More than 75% of the total eluting selenium compounds, based upon element specific detection, were identified from retention time data and standard spiking experiments, and between 60 and 85% of compounds were identified by MS, with up to 25% of the total eluting molecular selenium species being unidentified as yet. Limits of quantification (LOQ, defined as the concentration giving an S/N of 10) for HPLC-ICP-MS were in the range 2-50 ng mL-1 Se in the injected extracts for the selenium-enriched samples and 2-10 ng mL-1 Se for the natural selenium level samples. LOQ values for HPLC-ESI-MS were ca. 100 times higher than those measured by HPLC-ICP-MS.     

Continuous flow molecular emission cavity analysis of cephalosporins by alkaline degradation to sulphide

A continuous flow method for the determination of some cephalosporins (cephradine, cephalexin, cephalosporin C, cefadroxil, cephapirin and cephalothin) in the general range 10.0-250.0 micrograms ml-1 is described. The sample is mixed with sodium hydroxide and remains for 20 min at 90 degrees C in the delay coil of an air-segmented system. The solution is then mixed with an excess of orthophosphoric acid, and the hydrogen sulphide evolved is continuously transferred into the cavity for generation of the S2 molecular emission. The analysis is automated, requires no sample pre-treatment and samples can be analysed at a rate of 30 per hour with a relative error of 1-2%. The method was evaluated by carrying out recovery experiments and by the analysis of commercial formulations. Results agreed well with those obtained by the standard methods.     

A simple and rapid method for simultaneous determination of benzoic and sorbic acids in food using in-tube solid-phase microextraction coupled with high-performance liquid chromatography

A simple, rapid and sensitive on-line method for the simultaneous determination of benzoic and sorbic acids in food was developed by coupling in-tube solid-phase microextraction (SPME) to high-performance liquid chromatography (HPLC) with UV detection. The diethylamine-modified poly(glycidyl methacrylate-co-ethylene dimethacrylate) monolithic capillary selected as the extraction medium exhibited a high extraction capability towards benzoic and sorbic acids. To obtain optimum extraction performance, several in-tube SPME parameters were investigated, including pH value, inorganic salt, and the organic solvent content of the sample matrix. After simple dilution with 0.02 mol/L phosphate solution (pH 4.0), carbonated drink, juice drink, sauce and jam samples could be directly injected for extraction. For succade samples, a small amount of acetonitrile was required to extract analytes prior to dilution and subsequent extraction. The linearity of the method was investigated over a concentration range of 5–20000 ng/mL for both analytes, and the correlation coefficients (R ² values) were higher than 0.999. The detection limits for benzoic and sorbic acids were 1.2 and 0.9 ng/mL, respectively. The method reproducibility was tested by evaluating the intra- and interday precisions; relative standard deviations of less than 4.4 and 9.9%, respectively, were obtained. Recoveries of compounds from spiked food samples ranged from 84.4 to 106%. The developed method was shown to be suitable for the routine monitoring of benzoic and sorbic acids in various types of food samples.     

Simultaneous determination of acetylsalicylic and salicylic acids in human serum and aspirin formulations by second-derivative synchronous fluorescence spectrometry

A second-derivative synchronous scanning spectrofluorimetric method for the simultaneous determination of acetylsalicylic acid (ASA) and salicylic acid (SA) is described. The method is based on the native fluorescence of both acids in a 1% acetic acid-chloroform solution. Both ASA and SA can be determined within the concentration ranges 0.2-70 and 0.03-10 micrograms ml-1, respectively. The effect of each acid on the signal of the other has been studied in detail. Empirical equations have been used to overcome this effect, thus allowing the accurate determination of both acids in binary mixtures, without a separation step. The method has been applied to the determination of ASA and SA in blood serum and to the determination of SA impurities in aspirin formulations. Recoveries from sera spiked with both ASA (2.5-50 micrograms ml-1) and SA (100-160 micrograms ml-1) varied from 99.5 to 106.7% (mean = 102.6%) and from 93.0 to 98.0% (mean = 95.8%), respectively. Recoveries of SA from spiked aspirin solutions (0.25-1.5 mg g-1 of aspirin) varied from 98.0 to 102.0% (mean = 100.3%).     

Solid-phase extraction method for patulin in apple juice and unfiltered apple juice.

Patulin, a mold metabolite, is commonly found in rotting apples. Some countries regulate patulin at levels ranging from 30 to 50 micrograms/L. Most analytical methods for patulin in apple juice include liquid-liquid partitions. A solid-phase extraction method has been developed for apple juice and unfiltered apple juice in the United States. A portion of the test sample (5 mL) was passed through a macroporous copolymer cartridge and was washed with 1 mL 1% sodium bicarbonate and then with 1 mL 1% acetic acid. Patulin was eluted with 3 mL 2% acetonitrile in anhydrous ethyl ether and was determined by reversed-phase liquid chromatography with UV detection at 276 nm. Recoveries ranged from 93 to 104% in test samples spiked at 20-100 micrograms/L.     

Spectrophotometric determination of vanadium(V) in minerals, steels, soil and biological samples using phenothiazine derivatives.

Two simple, rapid and sensitive spectrophotometric methods have been proposed for the determination of vanadium(V) using butaperazine dimaleate (BPD) and propionyl promazine phosphate (PPP). These methods are based on the formation of red-colored radical cations on reaction with vanadium(V) in phosphoric acid medium, with their absorbance maxima at 513 nm. Beer's law is valid over the concentration range of 0.25-5.0 micrograms ml-1 and 0.2-4.0 micrograms ml-1, with Sandell's sensitivity values of 6.1 ng cm-2 and 6.0 ng cm-2 for BPD and PPP respectively. The proposed methods have been successfully applied to the analysis of vanadium steels, minerals, biological samples and soil samples.     

Solid-phase reactors as high stability reagent sources in flow analysis: selective flow injection spectrophotometric determination of cysteine in pharmaceutical formulations

The flow injection spectrophotometric determination of cysteine was carried out by reaction with cobalt(II) ions entrapped in a polymeric material and filling a packed-bed reactor; the released cobalt(II) complexed with the amino acid was monitored at 360 nm. The method worked with a high repeatability, even with independent reactors, days and solutions. Selectivity of the procedure was tested with twenty different foreign compounds found in pharmaceutical formulations containing cysteine, parent amino acids included; no serious interferences were observed. The calibration graph for cysteine was linear over the range 1-90 micrograms ml-1 with a relative standard deviation of 0.8% at 60 micrograms ml-1 (n = 158). The calculated sample throughput was 90 h-1. The method was applied to determine the content of cysteine in pharmaceutical formulations.     

吸收光谱法同时检测食品中的苯甲酸钠与山梨酸钾

利用苯甲酸钠和山梨酸钾的紫外吸收光谱特性,设计了正交试验,结合偏最小二乘变量筛选法,获得变量数少、相关系数高、预报准确性好、能同时对苯甲酸钠和山梨酸钾进行浓度预报的模型,并应用于饮料、蜜饯、糕点和调色酒样品中苯甲酸钠和山梨酸钾的检测。样品平行测定结果的相对标准偏差均小于10%,方法的加标回收率为82%～107%,苯甲酸钠和山梨酸钾的检测范围分别为0.1～16.0 mg.L-1和0.1～6.0 mg.L-1,检出限分别为0.05 mg.L-1和0.01 mg.L-1。样品的检测结果与国标法的检测结果相吻合。     

Determination of nucleic acids with crystal violet by a resonance light-scattering technique

For the first time, Crystal Violet (CV) was used to determine nucleic acid concentrations using the resonance light-scattering (RLS) technique. Based on the enhancement of the RLS of CV by nucleic acids, a new quantitative determination method for nucleic acids in aqueous solutions has been developed. At pH 5.03 and ionic strength 0.005 mol kg-1, the interaction of CV with nucleic acids results in three characteristic RLS peaks at 344.0, 483.0 and 666.0 nm. With 4.0 x 10(-5) mol l-1 of CV, linear relationships were found between the enhanced intensity of RLS at 666.0 nm and the concentration of nucleic acids in the range 0-2.5 micrograms ml-1 for herring sperm DNA, 0-4.0 micrograms ml-1 for calf thymus DNA and 0-4.5 micrograms ml-1 for yeast RNA. The limits of determination were 13.8 ng ml-1 for herring sperm DNA, 36.8 ng ml-1 for calf thymus DNA and 69.0 ng ml-1 for yeast RNA. The assay is convenient, rapid, inexpensive and simple.     

Determination of trace selenium by solid substrate-room temperature phosphorescence enhancing method based on potassium chlorate oxidizing phenyl hydrazine-1,2-dihydroxynaphthalene-3,6-disulfonic acid system

A new method for the determination of trace selenium based on solid substrate-room temperature phosphorimetry (SS-RTP) has been established. This method was based on the fact that in HCl-KCl buffer solution, potassium chlorate could oxidize phenyl hydrazine to form chloridize diazo-ion after being heated at 100 degrees C for 20 min, and then the diazo-ion reacted with 1,2-dihydroxynaphthalene-3,6-disulfonic acid to form red azo-compound which could emit strong room temperature phosphorescence (RTP) signal on filter paper. Selenium could catalyze potassium chlorate oxidizing the reaction between phenyl hydrazine and 1,2-dihydroxynaphthalene-3,6-disulfonic acid, which caused the sharp enhancement of SS-RTP. Under the optimum condition, the relationship between the phosphorescence emission intensity (DeltaIp) and the content of selenium obeyed Beer's law when the concentration of selenium is within the range of 1.60-320 fg spot-1 (or 0.0040-0.80 ng ml-1 with a sample volume of 0.4 microl). The regression equation of working curve can be expressed as DeltaIp=13.12+0.4839CSe(IV) (fg spot-1) (n=6), with correlation coefficient r=0.9991 and a detection limit of 0.28 fg spot-1 (corresponding to a concentration range of 7.0x10(-13) g ml-1 Se(IV), n=11). After 11-fold measurement, R.S.D. were 2.8 and 3.5% for the samples containing 0.0040 and 0.80 ng ml-1 of Se(IV), respectively. This accurate and sensitive method with good repeatability has been successfully applied to the determination of trace selenium in Chinese wolfberry and egg yolk with satisfactory results. The mechanism of the enhancement of phosphorescence was also discussed.     

Determination of sorbic acid with sodium chlorite

A new method for the determination of sorbic acid is proposed, using sodium chlorite in hydrochloric add medium as reagent. In these conditions the hydrochloric acid is oxidized to chlorine which adds on to the double bonds of the sorbic acid. The addition is rapid (30-90 sec) and for this reason the determination is more rapid then others similar to it. Sorbic acid has been determined in foods by this method, after a preliminary solvent extraction or steam-distillation.     

反相高效液相色谱法同时快速测定食品中常见的8种食品添加剂

 采用反相高效液相色谱法测定食品中常见的 8种食品添加剂 :糖精、甜味素、苯甲酸、山梨酸、香兰素、咖啡因、胭脂红和日落黄。实验采用Shim packCLC ODS分析柱 ,以甲醇 乙酸铵 (pH 7 0 ) (体积比为 44∶5 6 )为流动相 ,在UV 2 2 0nm处检测。样品经Carrez试剂处理去除杂质后直接进样 ,一次进样分析仅需 8min。平均回收率为 91 9%～ 10 8 5 % ,相对标准偏差小于 4% (n =5 )。