標準編號:	GB/T 12143-2008
中文名稱:	飲料通用分析方法
英文名稱:	General analytical methods for beverage
中標分類:	X50    飲料綜合
行業分類:	GB    國家標準
ICS分類:	67.160.20 67.160.20    無酒精飲料 67.160.20
發布機構:	中華人民共和國國家質量監督檢驗檢疫總局 中國家標準化管理委員會
發布日期:	2008-12-31
實施日期:	2009-5-1
標準狀態:	valid
替代舊標準:	GB/T 12143.2-1989 果蔬汁飲料中氨基態氮的測定方法 甲醛值法 GB/T 16771-1997 橙、柑、桔汁及其飲料中果汁含量的測定 GB 12143.3-1989 果蔬汁飲料中L-抗壞血酸的測定方法 乙醚萃取法 GB/T 12143.4-1992 碳酸飲料中二氧化碳的測定方法 GB/T 12143.5-1992 濃縮果汁中乙醇的測定方法 GB 12143.1-1989 軟飲料中可溶性固形物的測定方法 折光計法
翻譯語言:	英文
文件格式:	PDF
中文字符數:	26000 字
翻譯價格(元):	500.0
交付時間:	付款后 1 個工作日

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

飲料通用分析方法 1 范圍 本標準規定了飲料通用分析方法的總則和具體分析方法。 本標準適用于飲料中特定組分的分析。 2 規范性引用文件 下列文件中的條款通過本標準的引用而成為本標準的條款。凡是注日期的引用文件，其隨后所有的修改單(不包括勘誤的內容)或修訂版均不適用于本標準，然而，鼓勵根據本標準達成協議的各方研究是否可使用這些文件的最新版本。凡是不注日期的引用文件，其最新版本適用于本標準。 GB/T 601 化學試劑 標準滴定溶液的制備 GB/T 6682 分析實驗室用水規格和試驗方法(GB/T 6682—2008，ISO 3696：1987，MOD) GB 10789 飲料通則 3 總則 3.1 本標準中所采用的名詞術語、計量單位應符合國家相關標準的規定。 3.2 本標準中的“儀器”為分析中所必備的儀器，一般實驗室常用儀器、設備等不逐項列出。 3.3 本標準中所用的水，在未注明其他要求時，應符合GB/T 6682中三級以上(含三級)水的規格。所用試劑，在未注明其他規格時，均指分析純。 3.4 本標準中的“溶液”，除另有說明外，均指水溶液。 4 飲料中可溶性固形物的測定方法(折光計法) 4.1 方法適用范圍 本方法適用于透明液體、半粘稠、含懸浮物的飲料制品。 4.2 方法原理 在20℃用折光計測量待測樣液的折光率，并用表A.1查得或從折光計上直接讀出可溶性固形物含量。 4.3 儀器 實驗室常用儀器以及下列儀器： 4.3.1 阿貝折光計或其他折光計：測量范圍0％～80％，精確度±0.1％。 4.3.2 組織搗碎機。 4.4 試液的制備 4.4.1 透明液體制品 將試樣充分混勻，直接測定。 4.4.2 半粘稠制品(果漿、菜漿類) 將試樣充分混勻，用四層紗布擠出濾液，棄去最初幾滴，收集濾液供測試用。 4.4.3 含懸浮物制品(果粒果汁類飲料) 將待測樣品置于組織搗碎機中搗碎，用四層紗布擠出濾液，棄去最初幾滴，收集濾液供測試用。 4.5 分析步驟 4。5.1 測定前按說明書校正折光計，以阿貝折光計為例，其他折光計按說明書操作。 4.5.2 分開折光計兩面棱鏡，用脫脂棉蘸乙醚或乙醇擦凈。 4.5.3 用末端熔圓之玻璃棒蘸取試液2滴～3滴，滴于折光計棱鏡面中央(注意勿使玻璃棒觸及鏡面)。 4.5.4 迅速閉合棱鏡，靜置1 min，使試液均勻無氣泡，并充滿視野。 4.5.5 對準光源，通過目鏡觀察接物鏡。調節指示規，使視野分成明暗兩部，再旋轉微調螺旋，使明暗界限清晰，并使其分界線恰在接物鏡的十字交叉點上。讀取目鏡視野中的百分數或折光率，并記錄棱鏡溫度。 4.5.6 如目鏡讀數標尺刻度為百分數，即為可溶性固形物含量(％)；如目鏡讀數標尺為折光率，可按附錄A換算為可溶性固形物含量(％)。 將上述百分含量按附錄B換算為20℃時可溶性固形物含量(％)。 4.6 允許差 同一樣品兩次測定值之差，不應大于0.5％。取兩次測定的算術平均值作為結果，精確到小數點后一位。 5 果蔬汁飲料中氨基態氮的測定方法(甲醛值法) 5.1 方法適用范圍 本方法適用于果汁和蔬菜汁類飲料。 5.2 方法原理 氨基酸為兩性電解質。在接近中性的水溶液中，全部解離為雙極離子。當甲醛溶液加入后，與中性的氨基酸中的非解離型氨基反應，生成單羥甲基和二羥甲基誘導體，此反應完全定量進行。此時放出氫離子可用標準堿液滴定，根據堿液的消耗量，計算出氨基態氮的含量。其離子反應式如下： 5.3 試劑 5.3.1 30％過氧化氫。 5.3.2 中性甲醛溶液：量取200 mL甲醛溶液于400 mL燒杯中，置于電磁攪拌器上，邊攪拌邊用0.05 mol/L氫氧化鈉溶液調至pH8.1。 5.3.3 氫氧化鈉標準溶液：0.1 mol/L，按GB/T 601配制與標定。 5.3.4 氫氧化鈉標準滴定溶液：0.05 mol/L，用0.1 mol/L的氫氧化鈉標準溶液當天稀釋。 5.3.5 pH6.8緩沖溶液。 5.4 儀器 5.4.1 酸度計：測量范圍0～14pH，精度±0.1pH。 5.4.2 電磁攪拌器。 5.4.3 玻璃電極和甘汞電極。 5.5 試樣液的制備 5.5.1 濃縮果蔬汁 在濃縮果蔬汁中加入與在濃縮過程中失去的天然水分等量的水，使其成為果汁，并充分混勻，供測試用。 5.5.2 果蔬汁及果蔬汁飲料 將試樣充分混勻，直接測定。 5.5.3 含有碳酸氣的果蔬汁飲料 稱取500 g試樣，在沸水浴上加熱15 min，不斷攪拌，使二氧化碳氣體盡可能排除。冷卻后，用水補充至原質量，充分混勻，供測試用。 5.5.4 果蔬汁固體飲料 稱取約125 g(精確至0.001 g)試樣，溶解于蒸餾水中，將其全部轉移到250 mL容量瓶中，用蒸餾水稀釋至刻度。充分混勻，供測試用。 5.6 分析步驟 5.6.1 將酸度計接通電源，預熱30 min后，用pH6.8的緩沖溶液校正酸度計。 5.6.2 吸取適量試樣液(氨基態氮的含量為1 mg～5 mg)于燒杯中，加5滴30％過氧化氫。將燒杯置于電磁攪拌器上，電極插入燒杯內試樣中適當位置。如需要加適量蒸餾水。 5.6.3 開動電磁攪拌器，先用0.1 mol/L氫氧化鈉標準溶液慢慢中和試樣中的有機酸。當pH達到7.5左右時，再用0.05 mol/L氫氧化鈉標準滴定溶液調至pH8.1，并保持1 min不變。然后慢慢加入10 mL～15 mL中性甲醛溶液。1 min后用0.05 mol/L氫氧化鈉標準滴定溶液滴定至pH8.1。記錄消耗0.05 mol/L氫氧化鈉標準滴定溶液的毫升數。 5.7 結果計算 試樣中氨基態氮含量按式(1)計算： (1) 式中： X——每100 g(或100 mL)試樣中氨基態氮的毫克數，單位為毫克每百克或毫克每百毫升(mg/100 g或mg/100 mL)； c——氫氧化鈉標準滴定溶液的濃度，單位為摩爾每升(mol/L)； V——加入中性甲醛溶液后，滴定試樣消耗0.05 mol/L氫氧化鈉標準滴定溶液的體積，單位為毫升(mL)； K——稀釋倍數； 14——1 mL 1 mol/L氫氧化鈉標準滴定溶液相當于氮的毫克數； m——試樣的質量或體積，單位為克或毫升(g或mL)。 5.8 允許差 同一樣品以兩次測定結果的算術平均值作為結果，精確到小數點后第一位。 同一樣品的兩次測定結果之差： 氨基態氮≥10 mg/100 g(或10 mg/100 mL)，不得大于2％； 氨基態氮＜10 mg/100 g(或10 mg/100 mL)，不得大于5％。 6 果蔬汁飲料中L-抗壞血酸的測定方法(乙醚萃取法) 6.1 方法適用范圍 本方法適用于果汁和蔬菜汁類飲料中L-抗壞血酸的測定，但不適用于脫氫抗壞血酸的測定。 6.2 方法原理 本方法根據氧化還原反應原理，2，6-二氯靛酚能被L-抗壞血酸還原為無色體，微過量的2，6-二氯靛酚用乙醚提取，然后由醚層中的玫瑰紅色來確定滴定終點。 6.3 試劑 6.3.1 丙酮。 6.3.2 乙醚。 6.3.3 硫酸銅溶液：10％，稱取10 g硫酸銅(CuSO4·5H2O)溶解于水，并稀釋至100 mL。 6.3.4 草酸溶液：2％，稱取20 g草酸(C2H2O4·2H2O)溶解于水，并稀釋至1 L。 6.3.5 碘標準滴定溶液 ：按GB/T 601配制與標定，貯存于棕色瓶中。 6.3.6 碘標準滴定溶液 ]：將0.11 mol/ 碘標準滴定溶液在使用時稀釋V25 mL→V250 mL，濃度以c1表示。 6.3.7 0.88 mg/mL抗壞血酸標準溶液：稱取0.22 g抗壞血酸，用草酸溶液(6.3.4)溶解并稀釋到250 mL。 標定：吸取抗壞血酸標準溶液20.00 mL，加1 mL淀粉指示液(6.3.10)，用0.01 mol/L碘標準滴定溶液(6.3.6)滴定至呈微藍色為止。 L-抗壞血酸的濃度按式(2)計算： (2) 式中： c2——L-抗壞血酸溶液的濃度，單位為毫克每毫升(mg/mL)； c1——碘標準滴定溶液的濃度，單位為摩爾每升(mol/L)； V1——標定時所用碘標準滴定溶液的體積，單位為毫升(mL)； 88——1 mL 1 mol/ 碘標準滴定溶液相當于L-抗壞血酸的毫克數。 6.3.8 0.088 mg/mL L-抗壞血酸標準溶液：吸取25.00 mL 0.88 mg/mL L-抗壞血酸標準溶液(6.3.7)，用草酸溶液(6.3.4)稀釋，V25 mL→V250 mL。 注：6.3.7和6.3.8的L-抗壞血酸溶液在使用時配制。 6.3.9 2，6-二氯靛酚標準滴定溶液：稱取200 mg 2，6-二氯靛酚，用少量熱的重蒸餾水濕潤，然后再慢慢加入熱的重蒸水，攪拌溶解，過濾。冷卻后，濾液用重蒸餾水稀釋到1 L，保存于冰箱中。一星期至少標定一次。 標定：吸取10.00 mL L-抗壞血酸標準溶液(6.3.8)置于50 mL比色管中，按測定樣品的步驟標定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)計算： (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當于L-抗壞血酸的毫克數，單位為毫克每毫升(mg/mL)； m1——10 mL L-抗壞血酸標準溶液中含抗壞血酸的量，單位為毫克(mg)； V2——標定時所用2，6-二氯靛酚溶液的體積，單位為毫升(mL)。 6.3.10 淀粉指示液：5 g/L，稱取0.5 g可溶性淀粉，用5 mL冷水調勻，將所得乳濁液在攪拌下徐徐注入100 mL沸騰著的水中，再煮沸2 min～3 min，使溶液透明。加0.1 g碘化汞作保存劑。 6.4 儀器 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 試液的制備 6.5.1 濃縮汁 在濃縮汁中加入與在濃縮過程中失去的天然水分等量的水，使成為原汁。然后同原汁一樣取一定量樣品，稀釋、混勻供測。 6.5.2 原汁 稱取含抗壞血酸4 mg～10 mg有代表性的樣品(精確到0.001 g)，用2％草酸溶液稀釋到200 mL，混勻供測。 6.5.3 果蔬汁飲料 6.5.3.1 抗壞血酸含量在0.05 mg/mL以下的樣品，混勻后直接取樣測定。 6.5.3.2 抗壞血酸含量在0.05 mg/mL以上的樣品，稱取含抗壞血酸4 mg～10 mg有代表性的樣品(精確到0.001 g)，用2％草酸溶液稀釋到200 mL，混勻供測。 6.5.4 果蔬汁碳酸飲料 先將樣品旋搖到基本無氣泡后，按6.5.3制備。 6.5.5 固體飲料 稱取含抗壞血酸4 mg～10 mg有代表性的樣品(精確到0.001 g)，用2％草酸溶液溶解并稀釋至200 mL，混勻供測。 6.5.6 乙醚抽提處理 對于高度乳化或樣液色澤較深且易被乙醚抽提的樣品，取樣后置分液漏斗中。加30 mL乙醚，充分振搖但勿使之乳化。待分層后將下層祥液放入200 mL容量瓶中，分液漏斗中加入20 mL 2％草酸溶液。適當振搖，待分層后，將下層水溶液放入上面的200 mL容量瓶中。如此反復操作四次，將每次的下層水溶液均放入200 mL容量瓶內，然后用2％草酸溶液稀釋至刻度。 6.5.7 空白試液的制備 按試液制備中所確定的取樣量稱取同一樣品(精確到0.001 g)，置于250 mL錐形瓶中，加20 mL10％硫酸銅溶液，加水使總體積約為100 mL，置于墊有石棉網的電爐上，小心加熱至沸并保持微沸15 min，然后用流動水冷卻到室溫。將此溶液轉移到200 mL容量瓶中，用水稀釋至刻度，搖勻，供空白測定。 6.6 分析步驟 6.6.1 試液的測定 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制備好的試液，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)，充分混勻，精確控制40 s后，加入2 mL乙醚，充分振搖，放置幾分鐘，待乙醚與水溶液分層后，觀察醚層有無出現玫瑰紅色。當出現淡玫瑰紅色時，則表明已達到測定的暫定終點。如果2，6-二氯靛酚全部被抗壞血酸還原，乙醚層保持無色，則在第二支比色管中加入1.5 mL 2，6-二氯靛酚溶液。如還不顯紅色，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，直到乙醚層出現玫瑰紅色達到暫定終點為止。這時所加的2，6-二氯靛酚的量常常是過量的，所以需進一步試驗，確定精確的終點。 如果加到3.0 mL 2，6-二氯靛酚溶液時出現玫瑰紅色，則從第六支加有試液的比色管中開始分別加入2.6 mL、2.7 mL、2.8 mL、2.9 mL 2，6-二氯靛酚溶液，直至呈現淡玫瑰紅色為止。如在2.9 mL剛呈紅色，則2.9 mL為精確終點。如加到2.9 mL 2，6-二氯靛酚溶液仍不顯玫瑰紅色，則上面的3.0 mL就是精確終點。所用2，6-二氯靛酚溶液為Va。 對于抗壞血酸含量低于2 mg/100 g的樣品，用100 mL比色管直接加倍取樣測定。丙酮與乙醚的加量也相應加倍，操作同上。 對于同一個被測樣液需平行測定三次。 6.6.2 空白試液的測定