AOAC Official Method 2000_aoac44.1.25a
|
ID： |
8B9424538B474DEB9795542284167E89 |
|
文件大小(MB)： |
0.04 |
|
页数： |
4 |
|
文件格式： |
|
|
日期： |
2024-7-30 |
|
购买： |
文本摘录（文本识别可能有误，但文件阅览显示及打印正常，pdf文件可进行文字搜索定位）：
44.1.25A,AOAC Official Method 2000.17,Determination of Trace Glucose and Fructose,in Raw Cane Sugar,High-Performance Anion-Exchange Chromatography,First Action 2000,[Applicable to the determination of glucose and fructose,(0.080–0.25%) in raw cane sugar].,See Tables 2000.17A and 2000.17B for the results of the,interlaboratory study supporting acceptance of the method.,A. Principle,Test portion and internal standard are dissolved in water and filtered,through a 0.45 μm membrane filter. The filtered solution is injected,onto a liquid chromatographic (LC) system. Carbohydrates,are separated on a pellicular anion-exchange column and measured,by pulsed amperometric detection (PAD). Carbohydrates are identified,and quantified (peak height response) by comparison with standard,solutions. The separation mechanism of these columns relies on,the fact that carbohydrates are weak acids that are ionic at high pH.,With an eluant at the appropriate pH, many sugars can be separated,rapidly by high-performance ion chromatography. The pellicular,nature of the packing allows rapid equilibration, and because the,ionization of sugars is pH sensitive, these columns are notably more,selective than gel-based cation-exchange columns. The CarboPac,columns can tolerate overloading from sugars that are not being,quantified (in this case sucrose). The separated carbohydrates are,measured by the electrical current generated by their oxidation at the,surface of a gold electrode at optimum pH of about 13. A repeating,sequence of 3 applied potentials for specific durations ensures that the,surface of the gold electrode remains in good condition even after prolonged,use. PAD is more sensitive and specific than refractive index,detection. Lactose is added as the internal standard. Calibration standards,are prepared to bracket the expected concentration range. Peak,heights are estimated by using an electronic integration system.,B. Apparatus,(a) Liquid chromatograph.—Able to withstand 250mM NaOH,and consisting of the following: (1) high-pressure pump; (2),autosampler or manual injection valve; (3) HPAEC column packed,with a strong basic quaternary amine anion exchanger on a 10 μm,polystyrene-divinylbenzene (5% cross-linked) pellicular substrate,e.g., CarboPac PA1 (Dionex Corp., PO Box 3603, Sunnyvale, CA,94088-4603, USA), 250 ′ 4 mm id; protected by a guard column,such as CarboPac Guard PA (Dionex), 25 ′ 3 mm; maintained at,constant temperature (27°C); and operated at a flow rate of,1 mL/min; (4) pulsed amperometric detector with gold working,electrode, i.e., Dionex PAD-2, Dionex PED-2, ESA Coulochem II,(ESA, Inc., 22 Alpha Rd, Chelmsford, MA 01824, USA), Waters,464 (Waters Corp., 34 Maple St, Milford, MA 01757, USA), or,equivalent. Settings provided by the manufacturer or optimized by,the user should be used. The sensitivity (and thus the selected measuring,range) is affected by the area of the gold electrode. Typical diameters,available are 1.4 or 3 mm; a measuring range of 1 μA is,suitable for the former and 5 μA for the latter. Typical settings for 2,commonly used detectors are listed in Table 2000.17C.,(b) Column and detector heater.—Controlled by thermostat set,at ca 27°C.,(c) Integrator.—Electronic integrator (e.g., HP 3396, Agilent,Technologies, 2850 Centerville Rd, Wilmington, DE 19808, USA),or a PC with suitable software (e.g., Ezchrom for Windows), operated,in the peak height mode. Note: The peak width, threshold settings,and other integration options should be chosen to ensure that,the same type of integration is used for the sugar peaks in,chromatograms of both the test samples and standards. Peak height,quantification has greater freedom from interference by adjacent,peaks, but the baseline selection must be carefully controlled to ensure,uniformity between the standards and the analytes, and repeatable,retention times are essential.,(d) Analytical balance.—Readable to 0.1 mg.,(e) Glassware.—Beakers, volumetric flasks, pipets, vials, etc.,(Scrupulous cleanliness is essential.),(f) Membrane filters.—Cellulose acetate (or similar material),with 0.45 μm pore size and 25 and 47 mm diameter.,(g) Membrane filter holders and syringes.,(h) Vacuum filtering system.,(i) Magnetic stirrer.,(j) Vacuum oven.—Operated at 40°C.,C. Reagents,(a) Glucose.—Analytical reagent grade, BDH (BDH Laboratory,Supplies, Poole, Dorset BH151TD, UK, export@bdh.com) Product,No. 10117, or equivalent. Dry under vacuum overnight at 40°C over,P2O5, and store in a desiccator.,(b) Fructose.—Analytical reagent grade, BDH Product No.,10367, or equivalent. Dry under vacuum overnight at 40°C over,P2O5, and store in a desiccator.,(c) Lact……
……