标准编号:	GB/T 12143-2008
中文名称:	饮料通用分析方法
英文名称:	General analytical methods for beverage
中标分类:	X50    饮料综合
行业分类:	GB    国家标准
ICS分类:	67.160.20 67.160.20    无酒精饮料 67.160.20
发布机构:	中华人民共和国国家质量监督检验检疫总局 中国家标准化管理委员会
发布日期:	2008-12-31
实施日期:	2009-5-1
标准状态:	valid
替代旧标准:	GB/T 12143.2-1989 果蔬汁饮料中氨基态氮的测定方法 甲醛值法 GB/T 16771-1997 橙、柑、桔汁及其饮料中果汁含量的测定 GB 12143.3-1989 果蔬汁饮料中L-抗坏血酸的测定方法 乙醚萃取法 GB/T 12143.4-1992 碳酸饮料中二氧化碳的测定方法 GB/T 12143.5-1992 浓缩果汁中乙醇的测定方法 GB 12143.1-1989 软饮料中可溶性固形物的测定方法 折光计法
翻译语言:	英文
文件格式:	PDF
中文字符数:	26000 字
翻译价格(元):	500.0
交付时间:	付款后 1 个工作日

Quality control system for heat treatment 1 Scope This standard specifies the requirements for the organizations to establish and implement a quality control system for heat treatment and the requirements for comprehensive quality control involving quality planning and continuous improvement, personnel, materials, equipment, technological materials, technology and process control, workplace, safety and health. This standard is applicable to the organizations' establishment of quality control system for heat treatment, preparation of heat treatment documents, management of heat treatment equipment and instrumentation, control of production process quality and implementation of technical transformation and planning and design, as well as the evaluation of the organizations' quality control system for heat treatment. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. GB/T 224 Determination of the depth of decarburization of steels GB/T 230.1 Metallic materials - Rockwell hardness test - Part 1: Test method (scales A, B, C, D, E, F, G, H, K, N, T) GB/T 231.1 Metallic materials - Brinell hardness test - Part 1: Test method GB/T 265 Petroleum products - Determination of kinematic viscosity and calculation of dynamic viscosity GB/T 268 Petroleum products - Determination of carbon residue - Conradson method GB 338 Methanol for industrial use GB 536 Liquefied anhydrous ammonia GB/T 3536 Petroleum products - Determination of flash and fire points - Cleveland open cup method GB/T 4340.1 Metallic materials - Vickers hardness test - Part 1: Test method GB/T 4989 Extension and compensating cables for thermocouples GB/T 4990 Alloy wires of extension and compensating cables for thermocouples GB/T 5617 Determination of effective depth of hardening after induction or flame hardening of steel GB 5959.3 Safety in electroheat installations - Part 3: Particular requirements for induction and conduction heating and induction melting installations GB/T 7232 Terminology of metal heat treatment GB/T 8121 The terminology of technological materials for heat treatment GB/T 8979 Pure nitrogen and high purity nitrogen and ultra pure nitrogen GB/T 9450 Steels - Determination and verification of the depth of carburized and hardened cases GB/T 9451 Determination of total or effective thickness of thin surface hardened layers of steel parts GB/T 9452 Testing method for working zone of heat treatment furnace GB/T 10066.1 Test methods for electroheat installations - Part 1: General GB/T 10066.4 Test methods for electroheat installations - Part 4: Indirect resistances furnaces GB/T 10066.31 Test methods for electroheat installations - Part 31: High-frequency induction heating installation - Test methods for the determination of power output of the generator GB/T 10067.1 Basic specifications for electroheat installations - Part 1: General GB/T 10067.3 Basic specifications for electroheat installations - Part 3: Induction electroheat installations GB/T 10067.4 Basic specifications for electroheat installations - Part 4: Indirect resistance furnaces GB/T 10067.41 Basic specifications for electroheat installations - Part 41: Mesh belt resistance heating unit GB/T 10067.42 Basic specifications for electroheat installations - Part 42: Pusher resistance heating unit GB/T 10067.43 Basic specifications for electroheat installations - Part 43: Forced convection pit resistance furnaces GB/T 10067.44 Basic specifications for electroheat installations - Part 44: Box-type resistance furnaces GB/T 10067.45 Basic specifications for electroheat installations - Part 45: Vacuum quenching furnace GB/T 10561 Steel - Determination of content of nonmetallic inclusions - Micrographic method using standards diagrams GB/T 11133 Liquid petroleum products - Determination of water - Karl Fischer reagent method GB/T 11354 Determination of nitrided case depth and metallographic microstructure examination for steel and iron parts GB/T 13298 Inspection methods of microstructure for metals GB/T 13299 Steel - Determination of microstructure GB/T 13324 Terminology of heat treatment equipment GB 13690 General rule for classification and hazard communication of chemicals GB 15603 Rule for storage of chemical dangers GB 15735 Requirements for the safety and health in production process of metal heat treatment GB/T 16923 Normalizing and annealing of steel parts GB/T 16924 Quenching and tempering of steel parts GB/T 17394.1 Metallic materials - Leeb hardness test - Part 1: Test method GB/T 18177 Gas nitriding of steel parts GB/T 18404 Mineral insulated metal-sheathed thermocouple cables and thermocouples GB/T 19000 Quality management systems - Fundamentals and vocabulary GB/T 19001 Quality management systems - Requirements GB/T 22560 Gas nitrocarburizing of iron and steel parts GB/T 22561 Vacuum heat treatment GB/T 25744 Metallographic examination for carburizing quenching and tempering of steel parts GB/T 25745 Heat treatment of cast aluminium alloys GB/T 27946 Limited value of hazardous substance in the air of heat treatment working place GB/T 30822 Environmental protection technical requirements for heat treatment industry GB/T 30823 Nickel-alloy probe test method for determination cooling characteristics of industrial quenching oil GB/T 30825 Pyrometry for heat treatment GB/T 50087 Code for design of noise control of industrial enterprises JB/T 3999 Carburizing or carbonitriding, post-quenching and tempering of steel part JB/T 4392 Test method of polymer quenchants JB/T 4393 Polyvinyl alcohol of quenching media JB/T 5069 Metallographic examination method of diffusion metallized layer of steel parts JB/T 6050 Generalization of hardness test for heat treated iron and steel parts JB/T 6955 The specification of quenching medium for heat treatment JB/T 6956 Iron nitriding for iron and steel parts JB/T 7530 General technical requirements for argon, nitrogen and hydrogen gases used in heat treatment JB/T 7710 Determination of microstructure for the thin layer carbonitriding or carburizing elements JB/T 9201 Induction hardening and tempering of iron and steel parts JB/T 9202 Salts for heat treatment JB/T 9204 Metallographic examination of induction hardened steel parts JB/T 9205 Metallographic examination of pearlitic graphite cast iron parts induction hardened JB/T 9209 Technical requirement of medium for thermo-chemical treatment JB/T 10312 Steel-foil method for determination of carbon-potential of carburizing atmosphere JB/T 10457 Technological requirements of liquid quenching apparatus SH 0553 Industrial propane and butane 3 Terms and definitions For the purposes of this document, the terms and definitions given in GB/T 7232, GB/T 8121, GB/T 13324 and GB/T 19000 and the following apply. 3.1 organization system or group that consists of a number of elements linked together in a certain way and based on certain purposes and goals, which is internal organization or independent commercial organization that provides heat treatment service 3.2 furnace monitoring system system for monitoring the operation of heat treatment furnace 3.3 control plan documented description of the systems and processes required to control the product, which is prepared internally by the organization to describe the important characteristics and engineering requirements of the product 3.4 responsibility matrix detailed description of assignment of responsible persons (including primary and secondary responsible persons) for key functions of heat treatment to correspond to the related responsibilities 3.5 shop travelers record prepared and issued by the organization for the condition of each batch of processed parts, defining the technological route and process through which the parts flow 3.6 special characteristic product characteristic or manufacturing process parameter that may affect the safety or regulatory compliance, fit, function, performance or subsequent processes of product 3.7 process table table in quality control of heat treatment that lists the process controls required for the heat treatment process and includes the minimum (minimal) requirements 3.8 energy monitor electronic monitor that measures and displays the actual energy [in kilowatt-seconds (kW·s)] transmitted to the induction heater 3.9 maximum adjustment maximum allowable adjustment value that allows the temperature reading of the temperature control system to be consistent with the temperature reading of the calibrated test instrument system if the temperature control system under test has exceeded the allowable deviation and needs to be corrected 3.10 operation instruction document describing the contents, methods and requirements of operations such as loading, inspection and heat treatment operation involved in the heat treatment process 3.11 advanced product quality planning; APQP structured approach to identify and develop the steps required to ensure that the heat treatment satisfies the customers, with the goal of facilitating contact with everyone involved to ensure that the required steps are completed on time 3.12 process failure modes and effects analysis; PFMEA analysis technique used by the quality planning team to ensure quality by ensuring to the maximum extent that various potential failure modes in the heat treatment process and their associated causes and mechanisms have been adequately considered and discussed 3.13 work zone working space in a heat treatment furnace determined by temperature survey to meet the specified temperature and temperature uniformity of the heat treatment technology 3.14 system accuracy test; SAT test in which the temperature of the temperature control system of heat treatment equipment after reasonable compensation is compared in situ with the temperature of a calibrated and deviation-corrected measurement system to determine whether the temperature deviation of the temperature control system meets the requirements 3.15 temperature uniformity survey; TUS a series of measurements of the deviation between the temperature of each area in the work zone of the furnace and the temperature specified in the technology using a calibrated temperature tester, thermocouple, and compensating cable after the heat treatment furnace has been thermally stabilized 3.16 process capability magnitude of statistical quality variation with the heat treatment process in a stable control state 4 Quality planning and continuous improvement 4.1 General requirements The organization must be certified by GB/T 19001 Quality Management System or the quality management system specified by the customer, and must be within the validity period of certification. The organization shall ensure that the system requirements developed are effectively implemented and continuously improved. 4.2 Quality planning 4.2.1 Establishment of quality planning team The organization shall establish a quality planning team to be responsible for the quality planning and control of the heat treatment process. 4.2.2 Management of customer requirements and related heat treatment standards and specifications 4.2.2.1 The organization shall document clear procedures and regulations to ensure that the customer requirements and related heat treatment standards and specifications are identified, understood and, where appropriate, referenced, reviewed, issued and implemented in a process that shall not exceed two working weeks. 4.2.2.2 The organization shall ensure that the customer requirements and related heat treatment standards and specifications are the latest versions available. 4.2.2.3 The organization shall ensure that the customer requirements and related heat treatment standards and specifications are implemented step by step to the production site, users and the specific departments and posts that carry them out.

Foreword I Introduction II 1 Scope 2 Normative references 3 Terms and definitions 4 Quality planning and continuous improvement 5 Personnel 6 Materials 7 Equipment 8 Technological materials 9 Technology and process control 10 Workplace and personnel safety/health

饮料通用分析方法 1 范围 本标准规定了饮料通用分析方法的总则和具体分析方法。 本标准适用于饮料中特定组分的分析。 2 规范性引用文件 下列文件中的条款通过本标准的引用而成为本标准的条款。凡是注日期的引用文件，其随后所有的修改单(不包括勘误的内容)或修订版均不适用于本标准，然而，鼓励根据本标准达成协议的各方研究是否可使用这些文件的最新版本。凡是不注日期的引用文件，其最新版本适用于本标准。 GB/T 601 化学试剂 标准滴定溶液的制备 GB/T 6682 分析实验室用水规格和试验方法(GB/T 6682—2008，ISO 3696：1987，MOD) GB 10789 饮料通则 3 总则 3.1 本标准中所采用的名词术语、计量单位应符合国家相关标准的规定。 3.2 本标准中的“仪器”为分析中所必备的仪器，一般实验室常用仪器、设备等不逐项列出。 3.3 本标准中所用的水，在未注明其他要求时，应符合GB/T 6682中三级以上(含三级)水的规格。所用试剂，在未注明其他规格时，均指分析纯。 3.4 本标准中的“溶液”，除另有说明外，均指水溶液。 4 饮料中可溶性固形物的测定方法(折光计法) 4.1 方法适用范围 本方法适用于透明液体、半粘稠、含悬浮物的饮料制品。 4.2 方法原理 在20℃用折光计测量待测样液的折光率，并用表A.1查得或从折光计上直接读出可溶性固形物含量。 4.3 仪器 实验室常用仪器以及下列仪器： 4.3.1 阿贝折光计或其他折光计：测量范围0％～80％，精确度±0.1％。 4.3.2 组织捣碎机。 4.4 试液的制备 4.4.1 透明液体制品 将试样充分混匀，直接测定。 4.4.2 半粘稠制品(果浆、菜浆类) 将试样充分混匀，用四层纱布挤出滤液，弃去最初几滴，收集滤液供测试用。 4.4.3 含悬浮物制品(果粒果汁类饮料) 将待测样品置于组织捣碎机中捣碎，用四层纱布挤出滤液，弃去最初几滴，收集滤液供测试用。 4.5 分析步骤 4。5.1 测定前按说明书校正折光计，以阿贝折光计为例，其他折光计按说明书操作。 4.5.2 分开折光计两面棱镜，用脱脂棉蘸乙醚或乙醇擦净。 4.5.3 用末端熔圆之玻璃棒蘸取试液2滴～3滴，滴于折光计棱镜面中央(注意勿使玻璃棒触及镜面)。 4.5.4 迅速闭合棱镜，静置1 min，使试液均匀无气泡，并充满视野。 4.5.5 对准光源，通过目镜观察接物镜。调节指示规，使视野分成明暗两部，再旋转微调螺旋，使明暗界限清晰，并使其分界线恰在接物镜的十字交叉点上。读取目镜视野中的百分数或折光率，并记录棱镜温度。 4.5.6 如目镜读数标尺刻度为百分数，即为可溶性固形物含量(％)；如目镜读数标尺为折光率，可按附录A换算为可溶性固形物含量(％)。 将上述百分含量按附录B换算为20℃时可溶性固形物含量(％)。 4.6 允许差 同一样品两次测定值之差，不应大于0.5％。取两次测定的算术平均值作为结果，精确到小数点后一位。 5 果蔬汁饮料中氨基态氮的测定方法(甲醛值法) 5.1 方法适用范围 本方法适用于果汁和蔬菜汁类饮料。 5.2 方法原理 氨基酸为两性电解质。在接近中性的水溶液中，全部解离为双极离子。当甲醛溶液加入后，与中性的氨基酸中的非解离型氨基反应，生成单羟甲基和二羟甲基诱导体，此反应完全定量进行。此时放出氢离子可用标准碱液滴定，根据碱液的消耗量，计算出氨基态氮的含量。其离子反应式如下： 5.3 试剂 5.3.1 30％过氧化氢。 5.3.2 中性甲醛溶液：量取200 mL甲醛溶液于400 mL烧杯中，置于电磁搅拌器上，边搅拌边用0.05 mol/L氢氧化钠溶液调至pH8.1。 5.3.3 氢氧化钠标准溶液：0.1 mol/L，按GB/T 601配制与标定。 5.3.4 氢氧化钠标准滴定溶液：0.05 mol/L，用0.1 mol/L的氢氧化钠标准溶液当天稀释。 5.3.5 pH6.8缓冲溶液。 5.4 仪器 5.4.1 酸度计：测量范围0～14pH，精度±0.1pH。 5.4.2 电磁搅拌器。 5.4.3 玻璃电极和甘汞电极。 5.5 试样液的制备 5.5.1 浓缩果蔬汁 在浓缩果蔬汁中加入与在浓缩过程中失去的天然水分等量的水，使其成为果汁，并充分混匀，供测试用。 5.5.2 果蔬汁及果蔬汁饮料 将试样充分混匀，直接测定。 5.5.3 含有碳酸气的果蔬汁饮料 称取500 g试样，在沸水浴上加热15 min，不断搅拌，使二氧化碳气体尽可能排除。冷却后，用水补充至原质量，充分混匀，供测试用。 5.5.4 果蔬汁固体饮料 称取约125 g(精确至0.001 g)试样，溶解于蒸馏水中，将其全部转移到250 mL容量瓶中，用蒸馏水稀释至刻度。充分混匀，供测试用。 5.6 分析步骤 5.6.1 将酸度计接通电源，预热30 min后，用pH6.8的缓冲溶液校正酸度计。 5.6.2 吸取适量试样液(氨基态氮的含量为1 mg～5 mg)于烧杯中，加5滴30％过氧化氢。将烧杯置于电磁搅拌器上，电极插入烧杯内试样中适当位置。如需要加适量蒸馏水。 5.6.3 开动电磁搅拌器，先用0.1 mol/L氢氧化钠标准溶液慢慢中和试样中的有机酸。当pH达到7.5左右时，再用0.05 mol/L氢氧化钠标准滴定溶液调至pH8.1，并保持1 min不变。然后慢慢加入10 mL～15 mL中性甲醛溶液。1 min后用0.05 mol/L氢氧化钠标准滴定溶液滴定至pH8.1。记录消耗0.05 mol/L氢氧化钠标准滴定溶液的毫升数。 5.7 结果计算 试样中氨基态氮含量按式(1)计算： (1) 式中： X——每100 g(或100 mL)试样中氨基态氮的毫克数，单位为毫克每百克或毫克每百毫升(mg/100 g或mg/100 mL)； c——氢氧化钠标准滴定溶液的浓度，单位为摩尔每升(mol/L)； V——加入中性甲醛溶液后，滴定试样消耗0.05 mol/L氢氧化钠标准滴定溶液的体积，单位为毫升(mL)； K——稀释倍数； 14——1 mL 1 mol/L氢氧化钠标准滴定溶液相当于氮的毫克数； m——试样的质量或体积，单位为克或毫升(g或mL)。 5.8 允许差 同一样品以两次测定结果的算术平均值作为结果，精确到小数点后第一位。 同一样品的两次测定结果之差： 氨基态氮≥10 mg/100 g(或10 mg/100 mL)，不得大于2％； 氨基态氮＜10 mg/100 g(或10 mg/100 mL)，不得大于5％。 6 果蔬汁饮料中L-抗坏血酸的测定方法(乙醚萃取法) 6.1 方法适用范围 本方法适用于果汁和蔬菜汁类饮料中L-抗坏血酸的测定，但不适用于脱氢抗坏血酸的测定。 6.2 方法原理 本方法根据氧化还原反应原理，2，6-二氯靛酚能被L-抗坏血酸还原为无色体，微过量的2，6-二氯靛酚用乙醚提取，然后由醚层中的玫瑰红色来确定滴定终点。 6.3 试剂 6.3.1 丙酮。 6.3.2 乙醚。 6.3.3 硫酸铜溶液：10％，称取10 g硫酸铜(CuSO4·5H2O)溶解于水，并稀释至100 mL。 6.3.4 草酸溶液：2％，称取20 g草酸(C2H2O4·2H2O)溶解于水，并稀释至1 L。 6.3.5 碘标准滴定溶液 ：按GB/T 601配制与标定，贮存于棕色瓶中。 6.3.6 碘标准滴定溶液 ]：将0.11 mol/ 碘标准滴定溶液在使用时稀释V25 mL→V250 mL，浓度以c1表示。 6.3.7 0.88 mg/mL抗坏血酸标准溶液：称取0.22 g抗坏血酸，用草酸溶液(6.3.4)溶解并稀释到250 mL。 标定：吸取抗坏血酸标准溶液20.00 mL，加1 mL淀粉指示液(6.3.10)，用0.01 mol/L碘标准滴定溶液(6.3.6)滴定至呈微蓝色为止。 L-抗坏血酸的浓度按式(2)计算： (2) 式中： c2——L-抗坏血酸溶液的浓度，单位为毫克每毫升(mg/mL)； c1——碘标准滴定溶液的浓度，单位为摩尔每升(mol/L)； V1——标定时所用碘标准滴定溶液的体积，单位为毫升(mL)； 88——1 mL 1 mol/ 碘标准滴定溶液相当于L-抗坏血酸的毫克数。 6.3.8 0.088 mg/mL L-抗坏血酸标准溶液：吸取25.00 mL 0.88 mg/mL L-抗坏血酸标准溶液(6.3.7)，用草酸溶液(6.3.4)稀释，V25 mL→V250 mL。 注：6.3.7和6.3.8的L-抗坏血酸溶液在使用时配制。 6.3.9 2，6-二氯靛酚标准滴定溶液：称取200 mg 2，6-二氯靛酚，用少量热的重蒸馏水湿润，然后再慢慢加入热的重蒸水，搅拌溶解，过滤。冷却后，滤液用重蒸馏水稀释到1 L，保存于冰箱中。一星期至少标定一次。 标定：吸取10.00 mL L-抗坏血酸标准溶液(6.3.8)置于50 mL比色管中，按测定样品的步骤标定2，6-二氯靛酚溶液的滴定度。 2，6-二氯靛酚溶液的滴定度按式(3)计算： (3) 式中： F——2，6-二氯靛酚溶液的滴定度，即1 mL 2，6-二氯靛酚溶液相当于L-抗坏血酸的毫克数，单位为毫克每毫升(mg/mL)； m1——10 mL L-抗坏血酸标准溶液中含抗坏血酸的量，单位为毫克(mg)； V2——标定时所用2，6-二氯靛酚溶液的体积，单位为毫升(mL)。 6.3.10 淀粉指示液：5 g/L，称取0.5 g可溶性淀粉，用5 mL冷水调匀，将所得乳浊液在搅拌下徐徐注入100 mL沸腾着的水中，再煮沸2 min～3 min，使溶液透明。加0.1 g碘化汞作保存剂。 6.4 仪器 6.4.1 微量滴定管：10 mL。 6.4.2 比色管：50 mL和100mL。 6.4.3 分液漏斗：125 mL。 6.5 试液的制备 6.5.1 浓缩汁 在浓缩汁中加入与在浓缩过程中失去的天然水分等量的水，使成为原汁。然后同原汁一样取一定量样品，稀释、混匀供测。 6.5.2 原汁 称取含抗坏血酸4 mg～10 mg有代表性的样品(精确到0.001 g)，用2％草酸溶液稀释到200 mL，混匀供测。 6.5.3 果蔬汁饮料 6.5.3.1 抗坏血酸含量在0.05 mg/mL以下的样品，混匀后直接取样测定。 6.5.3.2 抗坏血酸含量在0.05 mg/mL以上的样品，称取含抗坏血酸4 mg～10 mg有代表性的样品(精确到0.001 g)，用2％草酸溶液稀释到200 mL，混匀供测。 6.5.4 果蔬汁碳酸饮料 先将样品旋摇到基本无气泡后，按6.5.3制备。 6.5.5 固体饮料 称取含抗坏血酸4 mg～10 mg有代表性的样品(精确到0.001 g)，用2％草酸溶液溶解并稀释至200 mL，混匀供测。 6.5.6 乙醚抽提处理 对于高度乳化或样液色泽较深且易被乙醚抽提的样品，取样后置分液漏斗中。加30 mL乙醚，充分振摇但勿使之乳化。待分层后将下层祥液放入200 mL容量瓶中，分液漏斗中加入20 mL 2％草酸溶液。适当振摇，待分层后，将下层水溶液放入上面的200 mL容量瓶中。如此反复操作四次，将每次的下层水溶液均放入200 mL容量瓶内，然后用2％草酸溶液稀释至刻度。 6.5.7 空白试液的制备 按试液制备中所确定的取样量称取同一样品(精确到0.001 g)，置于250 mL锥形瓶中，加20 mL10％硫酸铜溶液，加水使总体积约为100 mL，置于垫有石棉网的电炉上，小心加热至沸并保持微沸15 min，然后用流动水冷却到室温。将此溶液转移到200 mL容量瓶中，用水稀释至刻度，摇匀，供空白测定。 6.6 分析步骤 6.6.1 试液的测定 取10支～15支50 mL比色管，在每支比色管中加入10.00 mL按6.5制备好的试液，各加2.5 mL丙酮。放置3 min后，在第一支比色管中加入1 mL 2，6-二氯靛酚溶液(6.3.9)，充分混匀，精确控制40 s后，加入2 mL乙醚，充分振摇，放置几分钟，待乙醚与水溶液分层后，观察醚层有无出现玫瑰红色。当出现淡玫瑰红色时，则表明已达到测定的暂定终点。如果2，6-二氯靛酚全部被抗坏血酸还原，乙醚层保持无色，则在第二支比色管中加入1.5 mL 2，6-二氯靛酚溶液。如还不显红色，再逐一按2.0 mL、2.5 mL、3.0 mL、3.5 mL、4.0 mL、4.5 mL、5.0 mL的量加入2，6-二氯靛酚溶液，直到乙醚层出现玫瑰红色达到暂定终点为止。这时所加的2，6-二氯靛酚的量常常是过量的，所以需进一步试验，确定精确的终点。 如果加到3.0 mL 2，6-二氯靛酚溶液时出现玫瑰红色，则从第六支加有试液的比色管中开始分别加入2.6 mL、2.7 mL、2.8 mL、2.9 mL 2，6-二氯靛酚溶液，直至呈现淡玫瑰红色为止。如在2.9 mL刚呈红色，则2.9 mL为精确终点。如加到2.9 mL 2，6-二氯靛酚溶液仍不显玫瑰红色，则上面的3.0 mL就是精确终点。所用2，6-二氯靛酚溶液为Va。 对于抗坏血酸含量低于2 mg/100 g的样品，用100 mL比色管直接加倍取样测定。丙酮与乙醚的加量也相应加倍，操作同上。 对于同一个被测样液需平行测定三次。 6.6.2 空白试液的测定