| Abstract: | 有關食米中總汞的分析方法,取食米(GBWCRM08508)乾粉樣品(70mg)放入7mL鐵氟龍瓶中,分別加入濃硝酸(700μL)和過氧化氫(50μL)做兩階段微波消化(80℃,10min)後,可將樣品基質溶解完全。以氫氧化鈉調整pH值至5.0-6.0,加入NaOAcbuffer(1mmol)和DMPS(400μL),使與Hg2+生成[DMPS-Hg]之複合物。預濃縮於兩支自製串聯之C18cartridge(100mg),再用甲醇沖洗出並定量至0.30mL,取出50μL注入GFAAS測定總汞的含量。本方法之偵測極限(MDL,3σ)為0.13ng(或1.9ng/g),線性可達3.00ng(或42.9ng/g)。測得GBW08508食米中總汞的準確度良好[三次平均的測值為(2.79±0.13)ngHg,可落在certifiedvalue(2.66±0.35)ngHg之範圍內],RSD(n=3)≦5%。有關食米中鈹的分析方法,取食米(GBWCRM08508)乾燥樣品(10mg)放入7mL鐵氟龍瓶中,加入濃硝酸(500μL)和過氧化氫(75μL)經微波消化(85℃,10min)後,用氨水調整pH值至5.0-6.0,加入NH4OAcbuffer(35mmol)和乙醯丙酮(acetylacetone,acac,50μL),使與Be2+生成[Be(acac)2]之螯合物。預濃縮於一支自製之Oasiscartridge(200mg),再用甲醇沖洗出並定量至1.00mL,取出20μL注入GFAAS測定鈹的含量。本方法之偵測極限(MDL,3σ)為0.014ng(或1.4ng/g),線性可達1.23ng(或123ng/g)。由於無certifiedvalue,使用標準添加法(0-1.20ngBe2+)測得食米(GBW08508)中鈹的含量為(0.036±0.005)ng。添加0.30-1.20ngBe2+於10mgGBW食米中,求得三次平均之回收率介於97.1-101%,RSD(n=3)≦6.8%。此外,也測得兩種台灣實際米樣中鈹的含量(苑裡米0.018ng,雲林濁水溪米0.037ng),兩次平均之回收率為99.6-101%,平均標準偏差(n=2)≦2.3%。有關中藥藥材中鈹分析方法,取10mg橄欖葉乾粉樣品(oliveleaves,BCRCRMNo.62)放入7mL鐵氟龍瓶中,分別加入濃硝酸(400μL)和過氧化氫(100μL)作兩階段微波消化(85℃,10min)後,將樣品基質分解完全。以氨水調整pH值至5.0-6.0,加入NH4OAcbuffer(15mmol)和acac(50μL),使與Be2+生成Be(acac)2之螯合物。預濃縮於兩支自製的Oasiscartridge(160mg),再用甲醇沖洗出並定量至1.00mL,取出20μL注入GFAAS測定Be的含量。本方法之偵測極限(MDL,3σ)為0.024ng(或2.4ng/g),線性可達5.49ng(或549ng/g)。由於無certifiedvalue,使用標準添加法(0-1.50ngBe2+)測得oliveleaves和2種中藥藥材(白芨和桂皮)中鈹的含量分別為0.49,0.59,和0.43ng。添加回收率介於97-104%之間,RSD(n=3)≦2.9%。
For methylmercury (Me-Hg) in rice sample. An amount (70 mg) of dried rice flour (GBW CRM 08508) was accurately weighed and placed in a 7-mL teflon microvessel. A microwave digestion procedure using 1.0mL of an alkaline solution [25% (w/v) KOH in MeOH ] was employed at 60.degree.C for 5 min. Me-Hg was extracted into the organic phase after adding HCl (4 M, 2.25 mL)/CH2Cl2 (6 mL), and shaking for 10 min. After removing the organic phase, another 6 mL of CH2CL2 was added in order to completely extract the Me-Hg. Two organic extracts were combined and pure water (30 mL) was added. After removing the CH2Cl2 by purging with N2, appropriate amounts of NaOAc buffer (1 mmol) and 2,3-dimercaptopropane-1-sulfonat e (DMPS, 400.mu.L) were added to form a complex of DMPS-CH3Hg.The complex was preconcentrated on two home-made C18 cartridges (100 mg) in series, and each cartridge was eluted with methanol and adjusted to 0.30 mL. A portion(50.mu.L) of methanol solution was introduced into a graphite tube and the amount of Me-Hg was measured by GFAAS. The method detection limit (MDL, 3 rho) was found to be 0.13 ng (or 1.9 ng/g); the calibration graph was linear up to 2.00 ng (or 28.6 ng/g). The amount of Me-Hg in GBW 08508 measured was below the MDL value and was reported as N.D. Since no CRM for Me-Hg in rice samples are available at present, spiked recoveries were used to evaluate the performance of the proposed method. Good recoveries (100%, n=2) were observed by spiking 1.00 ng of Me-Hg on GBW rice samples. |
