スギ樹幹に含まれる微量元素の各種抽出操作による移動性

Abstract

スギ (Cryptomeria japonica D. Don) の樹幹に含まれる微量元素のうち, 含有率が高く, 分析精度の高いK, MgおよびCaについて, 数種の簡単な抽出操作によって抽出される元素量を定量し, その抽出の難易から存在状態について考察した。試験片を圧搾して樹液を採取した後, ミクロトームにより100μmの木口切片とし, 冷水 (30℃), 冷メタノール (30℃), 熱水 (沸点), アルコール・ベンゼン混合溶液 (沸点) などによる抽出を行った。得られた樹液, 抽出液, 抽出後の切片に含まれる元素を原子吸光法あるいはフレーム分光法により分析した。樹幹全体に含まれる元素量のうち樹液中に存在する各元素の割合はK＞Mg＞Caの順で、あり, またいずれの元素も辺材の方が心材よりも樹液中の存在割合が小さかった。樹液圧搾後に樹幹中に残存するKは冷水抽出によってほとんどすべて取り出された。また冷メタノールによる抽出速度は冷水抽出に比べるとかなり遅かった。MgとCaは冷水での抽出量は少なかったが, 引き続いて行った熱水抽出によりほとんどすべてが抽出された。冷メタノールによる抽出量は冷水抽出に比べると少ないが, 初期段階で抽出されるMg, Caの割合は水抽出のそれよりも大きいことから, メタノールによって容易に抽出される部分があることが示唆された。またこれらの元素は心材の方が, 辺材よりもいずれの抽出法によっても抽出されにくかった。この一因として, 心材成分による固定あるいはブロックが予想されたが, アルコール・ベンゼン抽出を行った場合も, その後の水抽出による抽出量が増大することはなく, 心材成分によるこれらの元素の抽出阻害の可能性は低い。これらの元素はナトリウムぞ含む各種水溶液でイオン交換により容易に抽出されることが判明した。

Among many trace elements are found in stem of sugi (Cryptomeria Japonica D. Don), potassium (K), magnesium (Mg) and calcium (Ca), which present in a rather high quantity, can be quantitatively determined with accuracy. Therefore, these elements were extracted by some simple procedures and analyzed. From easiness of the extraction their existing state in the stem was discussed. After the wood specimen was squeezed out by a vise to collect the sap, wood blocks were sliced to cross sections of 100 μm in thickness. Subsequently, the sections were extracted with water and methanol both at 30℃, boiling water and boiling alcohol-benzene mixture and so on. The squeezed sap, the extracts and the extracted wood sections were then analyzed by atomic absorption spectrophotometry or flame emission spectrophotometry. As a result, proportion of their quantity present in the sap to that in whole stem decreased in the order of K›Mg›Ca. Additionally, all three elements were found to be lower in the heartwood than sapwood for their proportion in the sap. Besause the sum of K element squeezed out and extracted with cold water was comparable to its content for the whole stem, it can be concluded that most of the K element was extracted before the hot water extraction. The extraction rate of K element with cold methanol was rather smaller than with cold water. Though only small amounts of Mg and Ca were extracted with subsequent hot water treatment. In methanol extraction, smaller amounts of these elements were extracted compared with cold water. However, in the initial extraction stage, larger amounts of Mg and Ca were extracted with methanol than with cold water. This suggests that a part of these elements is more accessible to methanol than water. From the fact that these two elements resisted against extraction in greater extent in the heartwood than the sapwood, we first speculated that a blocking or a fixing of these took place by some nonpolar heartwood extractive components. However, since alcohol-benzene extraction did not show any difference in the extraction amount of Mg and Ca with cold water, this is not the case. Since the extraction rate of Mg and Ca was accelerated by hot water, a chemical bonding of these elements with pectic substances is conceivable. However, since the effect of the buffer solution which attacks the pectic substances was far predominant to the enzyme, the effect of the enzyme treatment could not be clarified. It is apparent that K, Mg and Ca could be easily extracted by an ion exchange in any solution which contains sodium ion.