醋酸的多用途，除了常被當作化學用劑外，也是食醋與葡萄酒製品中重要的成份，因此能即時偵測醋酸濃度於排放廢棄物或食品品管中是相當重要的。然而目前被開發的醋酸感測器，多以生化酵素間接依耗氧量來推算醋酸濃度；或是以傳統方式來量測，其中包括酸鹼滴定法、氣相層析法、光聲光譜與近紅外線吸收光譜，用傳統方法偵測樣品的醋酸濃度不僅耗時，且需耗費額外的儀器操作。故能以電化學原理發展出一個能精確、價廉與應答快速的感測器，作為現場監控樣品中醋酸濃度是相當重要的。
本研究嘗試以常被運用在有機電化學合成中的氧化還原媒子來間接催化醋酸而得到應答電流。在初步工作電極選擇方面，是將電極置於感測系統環境，在溫度300K下含 0.005M的V2O5電解液，以循環伏安法測試該電極在原始溶液pH值(2.85)時是否有穩定的表現，如不與電解質起反應或電位窗向正方向偏移等，在測試白金、石墨、鉛與鎳等電極後，發現只有鎳電極能在該感測環境下，作為與電解液間穩定轉移電子的介面。
在靜置傳統三極式電極系統中，發現媒子濃度與電解液pH對於感測的影響是最直接的，而溫度與攪拌速率對於感測結果則會相互影響，實驗結果在300K下，pH值為2.85與0.005M的V2O5電解液，維持攪拌速率在600 rpm時有最好的感測表現，當施加電位在-1.1 V(vs. Ag/AgCl)，可得到應答電流與醋酸濃度的校正曲線i(uA)=-0.006359[HAc(ppm)]-0.482，靈敏度則為6.359 uA/ppm*cm2，線性係數0.992，偵測醋酸極限1800 ppm，應答時間33秒。
在電極微小化方面，以真空濺鍍方式製作濺鍍電極，並嘗試改變濺鍍因素來討論感測表現，結果發現真空度60 W、濺鍍功率 0.25torr及濺鍍時間20分鐘下，能得到均勻的濺鍍鎳層，而感測的結果也較好；相反的，高真空度、高濺鍍功率及短濺鍍時間下，會得到大鎳顆粒表面的薄膜或鍍層過薄，因此感測的結果也較差。
在靜置微小化電極系統中，在300K下pH值為2.85與0.005M的V2O5電解液，維持攪拌速率在60 rpm時能獲得最佳感測表現，即當施加電位在-1.8 V(vs. Ag/AgCl)，可得到應答電流與醋酸濃度的校正曲線i(uA)=-0.32[HAc(ppm)]-15.041，靈敏度則為1.28 uA/ppm*cm2，線性係數0.983，偵測醋酸極限600 ppm，應答時間7秒。
在反應控制系統中，對於鎳工作電極，由理論求得應答電流與醋酸濃度的關係式為:
r2=I2/nFA
=[k2K'1CV2O5*(CH+^2)/CH2O+K'1(CH+)^2]CHAc-(Ι-1)
其中，k2、K'1 、[V2O5] 、 [H2O]與 [H+]為常數，則應答電流與醋酸濃度成現性關係，因此理論與實際實驗結果幾乎相符；在擴散控制系統方面，由理論可推導出感測電流與醋酸濃度關係式。
i(t)=[nFA(Do^1/2)/(pi*t)^0.5]Co (Ι-2)
若上式中的n、F、A、Do與t均為常數，可由 i(t)與Co 一次方線性關係求得擴散係數Do。

Acetic acid is very useful, not only chemical agent but also the most important ingredient in vinegar and red wine. Hence, it is essential to detect acetic acid concentration immediately in discharged waste water or during quality control process in food industry. Up to now, the majority of the developed acetic acid sensors are enzyme-based. The enzyme-based sensors take advantage of indirect oxygen-consumed concentration to count acetic acid content un this study. The others are traditional methods including titration, gas chromatography, photoacoustic spectroscopy and near-infrared absorption spectroscopy. But the traditional methods are time-consuming and need extra expensive instruments. Therefore, it is very important to develop an exact, low-cost and fast-responding electrochemical sensor which can be in situ applied in the processes related to acetic acid concentration.

In this study, the concept of redox mediators is applied to catalyze acetic acid reduction indirectly. About initial choice of the working electrodes, the electrodes are set in a batch system as figure 3-3 shown. The sensing solution contained0.005MV2O5at 300K. During cyclic voltammogram test, nickel foil is much more stable interface for electron transference between sensing solution (pH=2.85) and electrode than platinum, carbon and lead.

In the three-electrode batch system, the optimal sensing conditions are as following: temperature at 300K, stirred rate at 600 rpm, pH 2.85 and0.005M V2O5 supporting electrolyte. When the applied potential set at -1.1V (vs. Ag/AgCl), the relationship between acetic acid concentration and response current was plotted resulting a straight line, i(uA)=-0.006359[HAc(ppm)]-0.482. The sensitivity of this system is 6.359 uA/ppm*cm2, the linear coefficient is 0.992, the detecting concentration range is from 0 to 1800ppm and the response time is 33 seconds.

The sputtered electrodes for sensing acetic acid were prepared at the conditions: degree of vacuum, sputtered power and sputtered time set at 0.25 torr, 60 W and 20 minutes, respectively. At this preparing condition, the optimal sensing conditions of a sputtered Ni electrode can be gained. As the optimal electrode test in a batch system was carried out resulting a straight line, i(uA)=-0.32[HAc(ppm)]-15.041. The sensitivity is 1.28 uA/ppm*cm2, the linear coefficient is 0.983, the detecting concentration range is from 0 to 600ppm and the response time is 7 seconds.

In kinetic control system, the relationship between response current and acetic acid concentration was derived theoretically as shown in equation (I-1) for Ni foil working electrode.
r2=I2/nFA
=[k2K'1CV2O5*(CH+^2)/CH2O+K'1(CH+)^2]CHAc-(Ι-1)
Where,k2 is, K'1is, [V2O5] is, [H2O] is, and [H+] is. Almost these parameters were constant. The relationship between response current and acetic acid concentration is linear. Experimental results are nearly fitting the theoretically analysis. In this case, when the diffusion was the rate determining step, the relationship between response current and acetic acid concentration was simplified to equation (I-2),
i(t)=[nFA(Do^1/2)/(pi*t)^0.5]Co (Ι-2)
Where, the constants, n is, F is, A is, Do is, and t is. Based on equation (I-2) and experimental data of a linear relationship between i(t) and the diffusion coefficient, Do, was obtained.

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