對胺基苯甲酸的測定方法之研究   全文下載

Comparison of Methods for Determination of para-Aminobenzoic Acid (PABA)

對胺基苯甲酸（PABA）是許多細菌製造葉酸的必須成分，因它對紫外光具有良好的吸收能力，被廣泛用於防曬軟乳液的製備。PABA有溫和的抗發炎且在無毛小鼠中能保護皮膚組織免受光照所引起的皮膚癌；然而，迄今少有文獻報導PABA在食品及動、植物組織中含量之測定。本研究室發現PABA在中性水溶液中具有螢光性質（λex = 280 nm，λem= 340 nm），利用此一性質作為食物（主要是穀類）、動物組織（大鼠肝及血液）及含PABA的綜合維生素中定量之用，並與呈色法及高效液相層析法（HPLC／uv）比較。本實驗的結果是利用計算標準偏差（S.D.）及變異係數（C.V.）以比較各方法之重覆性與再現性，來評估其精密度。此外，亦由回收實驗結果作為比較各方法之準確度的一個準則。就各分析方法對綜合維他命中PABA的定量作比較，呈色法不僅重覆性（0.2%-0.7%）及再現性（2.6%-6.1%）皆比其他方法好，而且回收率（78.5%）亦較另二種方法高。對穀類的定量而言，螢光測定法的檢測效果不佳，因干擾而無法測定出穀物類中微量之PABA；另外，呈色法的再現性（2.2% - 12.8%）較HPLC／uv （10.8% - 19.4%）為佳，且回收率（96.1% - 100.8%）亦最高。在血液測定方面， PABA在血液中的含量很低，只有呈色法可測得，其值為1.52 ± 0.22 μg／ml血液。在大鼠肝臟之PABA含量測定方面，呈色法測得5.92 ± 0.10 μg／g 肝，HPLC／uv則為1.23 ± 0.09 μg／g 肝，但螢光法卻因受到干擾而無法定量。本研究藉以多種型式樣品之測試說明了這三種分析方法之優劣，以確定其實用性。一般而言，呈色法之實驗程序既簡單又成本便宜，其精密度及準確度皆佳，況且它的偵測限度（detection limit）與另二種分析方法之間差異不大；然而，動物肝臟及血液之檢測則以HPLC／uv較優，因其干擾最少；同時，本法易於改進以適用於其它樣品之檢測。

para-Aminobenzoic acid (PABA) is a precursor of folate in certain bacteria and is commonly used in sun-blocking creams because of its UV-absorbing property. It has mild anti-inflammatory activity and protects against photocarcinogenesis in hairless mice. However, there have been very few reports on the quantitative determination of PABA in foods, plants and animal tissues. In this study we utilized the fluorescent property of PABA in neutral solution (excitation at 280 nm, emission at 340 nm) to quantify PABA in multivitamin preparations, cereals, rat liver and blood, and compared with a colorimetric method and a HPLC/uv method. In addition to the assessment of PABA, we compared the precision (standard deviation, S.D., coefficient variation, C.V.) and recovery (as a criterion of accuracy) between the three methods. lntercomparison of the methods in multi-vitamin products showed that the colorimetric method was superior in reproducibility (i.e., within- run C.V., 0.2-0.7 %; run-to-run C.V., 2.6-6.1 %) compared to the other methods. The recovery (78.5 %) was also higher for the colorimetric method compared to the other methods. For cereals, the fluorimetric method was not applicable because of interferences and colorimetric method was found superior to HPLC/uv in both precision (2.2- 12.8 vs. 10.8-19.4 %) and recovery (96.1- 100.8 vs. 53.4-69.9 %). In rat blood, PABA was detected exclusively by the colorimetric method (1.52 ± 0.22 µg / ml of blood), although each method produced nearly 100 % recovery . For rat liver, PABA was detected by colorimetric (5.92 ± 0.10 µg / g liver) and HPLC/uv ( 1.23 ± 0.09 µg / g liver) while the fluorimetric method was not useful due to interferences. This research demonstrates the comparative applicability, quality and problems of the three methods assessing 3 varieties of samples. In general, the colorimetric method is simple and economical with satisfactory precision and accuracy. In addtion, the detection limit (0.3µM) was comparable to that of fluorimetric method (0.2µM) and HPLC/uv (0.2µM). However, in animal tissues, the HPLC/uv method is superior due to avoidance of interferences, and may be readily improved to apply to other types of samples.