GENERAL SAMPLE COLLECTION: CONSIDERATIONS AND TOOLS
Types of Systems andGeneral Considerations 粉體類型和主要關注點
homogeneous systems 均一粉體
For powder systems where the attribute of interest is uniformly distributed throughout the container—so that any sample is an unbiased representation of the entire container, lot, or population of interest—scoop sampling is adequate. Scoop sampling is a straight forward procedure in which the operator,after selecting representative containers for sampling, opens a container, scoops out a sufficient amount of material from the top of the powder bed, and then seals the container. If a thin layer of material on top of the powder bed is suspected of being different from the bulk, samples should be taken from a point below this top layer. For example, in cases of elutriation segregation, a thin layer of fine particles may lie on top of the powder bed, and the operator should dig down into the powder bed to avoid sampling from this layer. The scoop should be large enough that no material is lost during handling, because lost material may result in sample bias. In other words, one should avoid the use of a heaping scoop from which material can roll off the sides. The advantages of scoop sampling are convenience and cost, and, for highly potent materials, low-cost disposable scoops that can be used to minimize cross-contamination.
heterogeneous systems 非均一粉體
If the attribute of interest is spatially distributed in a heterogeneous manner throughout the sample, then scoop sampling is prone to potentially significant errors. Scoop sampling is a non-probabilistic method because only the most accessible fraction of the container is sampled. Obviously, only the material in the top layer can be reached with a scoop. For example, a sample from the top outer edge of the drum shown in Figure 3 could be biased because, in this example, the larger particles are preferentially distributed toward the top and outer edges of the drum. Hence the smaller particles have a lower probability of appearing in the sample. As aresult, the smaller particles will be underrepresented in the sample, and any analysis of particle size will not reflect the true particle size distribution of the original population.
Forheterogeneous systems, the initial primary sample is the most difficult toobtain. Use of a sampling thief, sometimes called a grain probe or samplingspear, is needed. The advantage of a sampling thief is that much more of thepowder bed is accessible because the sampling thief can sample from differentpoints in the powder bed, thus helping to reduce sampling bias. Many types ofsampling thieves are available, including: (1) the concentric sleeve withslotted compartments, (2) the concentric sleeve with grooves, sometimes called theopen-handled probe, (3) the end sampler, and (4) the core sampler. Each typehas its own unique operating procedures, as described below.
general considerations 主要關注點
The most reliable and reproducible results in powder size measurements are obtained when the particle size ranges from 2 to 10 μm; otherwise, the powder is too cohesive and does not flow properly into the sampling thief. In addition, particles larger than about one-third the width of the slot give poor results. Samples should be taken from several sites throughout the container. The probe should be long enough to penetrate at least three-quarters of the depth of the powder bed, ensuring that material from all depths can be captured in the sample. The choice of sites should be dictated by an understanding (often subjective) of the powder bed's degree of heterogeneity, which may have been caused by handling or movement during transport. Sampling plans can call for the insertion of the probe either at random locations and random angles or at predetermined locations and angles. For example, the plan may call for the probe to be inserted at the center and at two locations near the edges. Also,many operators recommend that probes always be inserted at a 10° angle from vertical, which increases the range of locations sampled.
Some of the disadvantages of sampling thieves include the labor-intensive nature ofthe procedure. The probe must be physically inserted into the powder bed, often multiple times; the contents of the probe must be emptied; and then the probe must be thoroughly cleaned. For settled powder beds, the sampling probe can be difficult to insert. In addition, the sampling probe can introduce errors as aresult of the following: fine particles can lodge between the inner and outer tubes; particles can fracture; fine particles can compact and not flow well into the sampling compartments; segregation can occur during flow into the sampling zone; and the act of inserting the probe can disrupt the powder bed by dragging powder from the top layers of the bed down through the bed.
Representative Lot Sampling 有代表性的批取樣
Statistically-based sampling plans are based on statistical principles and depend on the population’s spatial heterogeneity and intrinsic variability. Statistically-based plans are efficient and allow the collection of a sufficient number of samples to yield the desired degree of certainty without collecting too many or too few samples for the test method, scale, product variation, risk requirements, and tolerance for a stated product’s quality level or specification. The commonly used √N + 1 sampling plan given in Table 1 is not a statistically based sampling plan and may result in collection of too few samples for small populations and too many samples for large populations. The use of statistically-based sampling plans is advantageous because it facilitates risk management. However, in cases where prior knowledge of the population to be sampled is insufficient, a nonstatistical sampling plan suchas that given in Table 1 canbe considered.
基于統計學原理的取樣（簡稱：統計取樣）計劃要基于統計學原則，且要考慮整體的空間不均一性和（顆粒）內在離變。統計取樣計劃應允許收集多份（既不是太多也不是太少）樣品以滿足一系列因素的不確定度，這些因素包括方法、批量、產品變異、風險要求和特定產品質量水平/標準接受限度。表1中通常應用的 √N + 1 取樣計劃并非統計取樣方案，可能導致對于少量物料收集太少樣品，而大量物料又收集太多樣品。應用統計取樣計劃是有益的，因為這種方式采用了風險管理。然而，如果對于待取樣品基本信息不甚了了，則如表1的非統計原理的取樣計劃就可以考慮采用了。Figure 4 illustrates the sample size selection scheme paths. The first choice is whether to use a statistical or nonstatistical sampling plan. Statistical plans are preferred when a variable attribute like particle size or drug content is being determined. General sampling approaches are outlined in USP general information chapter Analytical Data—Interpretation and Treatment 〈1010〉.Statistically-based lot acceptance sampling plans require a valid rationale with known quality levels for the determination of product lot characteristics. As noted, the application of statistical sampling plans, including lot acceptance sampling plans, requires specific and thorough knowledge of the material being sampled. Reference statistical sampling plans state the rationale for sampling as part of the sampling scheme. Manufacturers who use astatistically-based lot acceptance sampling method should refer to an appropriate standard such as ANSI/ASQ Z1.9-2003 for bulk materials or ANSI/ASQZ1.4-2003 for multiunit or discrete populations. These standards are readily available via sources such as the American Society for Quality (http://www.asq.org/)or the American National Standards Institute (http://www.ansi.org/).
圖4展示了選擇樣品量的路線圖。首先考慮是否采用統計取樣或非統計取樣計劃。當需檢測變異屬性，如顆粒度或藥品含量時，則建議考慮統計取樣計劃。通用取樣方法在USP general information chapter <1010> 分析數據--演繹和處理中有闡釋。統計取樣計劃具體限度要求應基于有效的原理，這個有效原理建立在被測批產品已知的待測屬性的質量水平上。如所提示，包括取樣限度的統計取樣計劃的應用，要求對被取樣物料信息有詳細全面的掌握。還應把取樣原理列入取樣計劃作為取樣計劃的一部分。應用統計取樣的生產廠家可參考一個合適的標準，如針對散裝物料取樣的標準ANSI/ASQ Z1.9-2003 ，或針對多包裝的分裝物料取樣標準ANSI/ASQ Z1.4-2003。這些標準可通過美國質量協會（http://www.asq.org）或美國國家標準中心 (http://www.ansi.org/)獲取。
Figure 4. Sample size selection scheme. 樣品量選擇路線圖
If one is developing a nonstatistical sampling plan for which the quality level is not known, Table 1 gives suggested sample sizes for the number of containers in the lot that should be sampled.
The Level 1 sampling plan is relevant to materials when heterogeneity does not affect the analysis and the customer seeks to sample more than one container, when the sampling plan can be proportional to the square root of the number of containers received, and when the material comes from a known and trusted source. In such cases, the sample can be withdrawn from any point in the container. For adequately homogenous systems, scoop sampling from the top of the container is suitable.
The Level 2 sampling plan involves a 50% increase in sample size when compared with Level 1 and is used when a larger proportion of the number of containers is needed, for example, when a material’s heterogeneity is suspected of being consequential and acceptance sampling quality levels are not defined, or when the material comes from a less trusted source. Depending on the material's degree of heterogeneity, a sampling thief may be used. However, if the degree of heterogeneity will not significantly affect the results for the attribute being sampled, then scoop sampling from the top of the drum may still be suitable.
Table 1 shows the number of containers, n, to be sampled for a lot segregated into N containers. Note that the value of n from the formula is rounded at 0.5 up to the next higher integer. For example, if N = 6: for Level 1, n= √6 + 1 = 3.45 rounds to n = 3; for Level 2, n= 1.5 × √6 = 3.67, which rounds to n =4.
表1展示了樣品包裝數目，n，代表整批分散到N個分包裝。注意公式中n值逢5方進位。比如，如果N=6，則根據水平1，n = √6 + 1 = 3.45 ，修約為3，根據水平2，則n = 1.5 × √6 = 3.67，修約為4（譯者按：全進位法則在國內是可取的，適于口算而不必精確到小數點后一位）.
These initial decisions, as illustrated in Figure 4, are often difficult and sometimes must be made without sufficient information. If there is uncertainty about which method or level is appropriate, sometimes a quick, small-scale informal test of the system may help determine the best way to proceed. In addition, for some systems and attributes, the Level 1 and Level 2 sampling plans may result in over sampling. For example, when one is sampling for identification from the same lot, the suggested levels may result in collecting more samples than are statistically needed; in such cases, the statistically-based sampling plans referenced in Figure 4 canbe used.
Sample Collection 樣品收集
Acquiring a representative sample from a lot of bulk powder is a difficult procedure that requires special consideration, and the basic procedures for acquiring are presentative sample are discussed below. Note that every situation requires techniques that are appropriate for the given population to be sampled. The methods presented here are applicable to the sampling of static powders stored in midsize bulk containers such as 1-ton super sacks, 50-kg drums, or 50-lb bags. These methods are not necessarily applicable to the sampling of liquids, large storage containers such as train cars or silos, or in-process systems such as blenders or moving conveyer belts. In addition, the procedures described here are most applicable to particles in the size range from approximately ~1 μm to approximately ~1000 μm. Significantly smaller or larger particles require special procedures that are not covered here.
PRIMARY SAMPLE COLLECTION 一級樣品收集
Lot acceptance samples are generally transferred or delivered in containers. To collect a representative primary or gross sample (see Figure 1), the appropriate container or containers must first be selected from the population of N containers; second, a representative sample must be withdrawn from each of the selected containers.
Container Selection 包裝挑選
To avoid bias and other sampling errors, the containers to be sampled must be randomly selected. To make a random selection, first number all containers in the lot, then use a random number table (or computer-generated random numbers) to choose from which container or containers to withdraw the samples.
For systems in which containers are grouped together in such a manner that many of the individual containers are not practically accessible (e.g., 50-lb bag sstacked and bound in shrink wrap on a pallet), the sampling plan may need to take into account the larger container, in addition to the smaller container, as a sampling unit, in order to ensure a representative sample.
Withdrawing Sample from a Container 從包裝中取出樣品
container types 包裝類型
The three most popular container types are the bag, drum, and super sack. Because bags are generally closed and not resealable, special sampling thieves, sometimes called bag triers, have been designed to puncture the bag. If the system to be sampled is heterogeneous, the samples should be obtained from the bottom, center, and top of the bag; and, depending on how the bags are stacked on the pallet, they should also be sampled from the front and the back. When sampling from bags, particular attention should be paid to the corners, becausethey can disproportionately trap fine particles. If no bag trier is available,use a knife to cut open the bag for sampling. When sampling from a bag, be sure to clean the external surface sufficiently that the sample is not contaminated and foreign material is not introduced into the bulk material. Once the sample has been taken, place a compatible material over the hole in the bag, then fix this patch with an appropriate adhesive tape. Depending on the heterogeneity of the drum, a scoop or a sampling thief is used. Super sacks are large sack containers that usually have a fill spout on the top and a discharge spout on the bottom. For adequately homogeneous material, scoop sampling is appropriate;but if there is any concern about the heterogeneity of the material, a thief should be used. The large size of super sacks makes the use of a thief more important for representative sampling than in the case of a drum or bag, in order to limit potential delimitation error.
Sample Handling 樣品處理The samples collected can be either assayed individually or combined; then a subset of the gross sample can be assayed, as depicted in Figure 1 and described below. Sample increments should be combined on a clean, dry surface or in a suitable container or bag. All containers with which the sample comes into contact should be inert and should not chemically or physically react with the sample. In addition, samples should be accurately labeled and good records kept. A portion should be kept for possible future analysis.
PRIMARY SAMPLE SIZE REDUCTION 縮減一級樣品量As mentioned above, the primary sample typically consists of multiple samples taken from containers and mixed together. To obtain an analysis or measurement sample (Figure 1), the gross or primary sample must be reduced to a size appropriate for the analytical method. Gross or primary sample size reduction is an often overlooked as pect of a sampling plan, but it is an important step. The factors that cause segregation in a container can also cause segregation in the primary sample, and any bias in the size reduction method for the primary sample will lead to erroneous results. The advantage of secondary samples is that the mass has been reduced to a point at which it is much easer to obtain are presentative sample because every element in the powder bed is readily accessible. Such accessibility makes it easier to adhere to sampling best practices. Generally speaking, sample measurement takes place under either wet or dry conditions; the choice is dictated by the requirements of the analytical method. For example, the Coulter counter requires that samples be uniformly suspended in an electrolyte, but other methods, like sieving, are typically performed with dry powders.
如前所述，一級樣品通常由來源于不同包裝中的許多樣品混合而成。為了獲取分析樣品（見圖1），總樣品或一級樣品必須縮減到合適的樣品量以適用于對應的分析方法。總樣品或一級樣品縮減經常是取樣計劃中被忽視的一個方面，但卻是個重要的步驟。在包裝內導致離散的因素在一級樣品中同樣可能出現，一級樣品量縮減方法中的任何偏離都可能導致錯誤的分析結果。二級樣品的好處在于重量已經減低到容易獲得有代表性樣品的程度，因為每個粉體的部分都容易獲取。這種易獲取性使落實優良取樣法則變得簡單。一般而言，樣品檢驗在干或濕的背景下進行；這種選擇由分析方法本身的描述限定。比如，粒子計數器要求樣品均勻分散在電解液中，而其他方法比如篩分法，一般以干粉的形式被檢測。Before dividing an agglomerated sample, the agglomerates should be broken apart by asuitable technique such as sieving.
Dry Analysis Methods 干法分析方法（的分樣）Many laboratory devices are available for the reduction of the primary sample to ananalytical sample. The three most important methods used in the pharmaceutical industry are: (1) scoop sampling, (2) cone and quartering, and (3) the spinning riffler or rotary sample divider (manual method of fractional shoveling); see Figure 5.
Figure 5. Two procedures for dividing samples. Top: spinning riffler, in which a circular holder rotates ata constant speed, and the sample is loaded at a constant rate into the containers via a vibratory chute, which is fed by a mass-flow hopper. Bottom: cone and quartering. (Cone, left, is flattened and quartered; quarters can be formed into cones and further subdivided.)
scoop sampling 舀取分樣法
Scoop sampling is done as previously described, but generally with a smaller scoop orspatula. Great care must be taken when removing material from the primary sample, because this material could be highly segregated as a result of handling. Scoop sampling is appropriate for homogeneous or cohesive powders. However, if the powder is prone to segregation, scoop sampling can introduce significant errors. Moreover, scoop sampling has several serious disadvantages. First, the method depends on the operator’s deciding from which part of theprimary sample to scoop the material and what quantity of the sample toextract, which are features that can introduce operator bias. Second, in scoop sampling, operators have a natural tendency to withdraw the sample from the free surface, which is highly prone to segregation and is not representative of the bulk. Third, operators need to avoid creating a heap where rolling segregation can occur, because material could fall off the edges of the spatulaor scoop and bias the sample. Ideally, the operator should make some attempt to mix the primary sample before using the scoop, but this too can exacerbate segregation problems and should be done only with great caution.
cone and quartering 錐體四分法Cone and quartering is done by pouring the primary sample into a symmetric cone on a flat surface. The cone is then flattened by a flat surface such as a spatula,and is divided into four identical quarters (Figure 5). One quarter is taken as the sample. This procedure can be repeated (e.g.,quarter-samples can be subdivided into quarters) until the desired sample sizeis obtained. The theory of this method is that when a symmetric cone is created, all the segregation processes also occur symmetrically around the cone, and hence symmetry is used to mitigate the effect of segregation. In practice, it is very difficult to actually make a symmetric powder cone, and the method becomes very operator-dependent and often unreliable. Differences in how operators form the heap and subdivide it can lead to a lack of precision and significant errors. In addition, if the method is done more than once, errors can propagate each time the cone and quartering is performed. Some experts do not recommend this method.
spinning riffler 旋轉槽法As pinning riffler (Figure 5) includes a series of containers mounted on a circular holder. The circular holder rotates at a constant speed, and the sample is loaded at a constant rate into the containers via a vibratory chute, which is fed by a mass-flow hopper. Once the material has been divided among the different holders, an individual holder can be removed for testing or further sample division. The angular velocityof the circular holders and the amplitude of the vibratory feeder can be controlled to accommodate powders with different flow properties. The holder velocity and feed rate should be adjusted so that the containers fill uniformly and so that a heap does not form on the vibratory feeder. Spinning rifflers are available in different sizes, making possible subdivisions of powders ranging from a few milligrams to hundreds of grams. The only drawbacks of the spinning riffler are the time required to process the sample and clean the device, and the capital expense. Despite these minor disadvantages, the spinning riffler isby far the best method for subdivision of free-flowing powders.
圖5旋轉槽包括一系列在旋轉器上放置的小盒。旋轉器恒速旋轉，樣品以恒速從漏斗落下，再通過振動斜坡落入小盒。一旦物料被分散到不同的盒子，某個單一的盒子可以被取下作為樣品，或進行進一步的分離。旋轉角速度和振幅是可控的，以適應粉末不同的流動性。支撐器的旋轉速度和漏斗下料速度應調整到合適，保證小盒被均勻裝料，且振動斜坡也不會堆積樣品。旋轉槽有不同的尺寸，可以適應幾毫克到數百克樣品的二次分離。唯一缺點就是需要時間處理樣品和清潔裝置，并且價格較貴。除了這些小缺點，對于流動性強的粉末這是遠勝于其他的最佳分樣方法。Fractional shoveling is the manual version of the spinning riffler. In this method, scoop samples are taken from the original sample and placed into a sufficient number of aliquots, and then subsequent scoops are taken from the original sample and placed into one of the aliquots in sequential order. This process is repeated until the original samples are gone. Then one of the aliquots is randomly taken as the reduced sample. As is the case with all manual methods, operator error and variability can be significant factors.
片段鏟分（旋轉分樣器法）是旋轉槽的手工版本。本法中，從原樣中鏟取樣品，平均配置到足夠的（旋轉）小格中，然后再次從原樣中獲取樣品并同法按序配置，直到原樣分配完畢后隨機取出一份作為二級樣品。由于本法中所有操作人工完成，操作誤差和變異可能成為重要影響因素。Wet Analysis Methods 濕分析法（的分樣）Wet analysis methods require dispersing the sample in a liquid suitable for analysis, and then withdrawing an aliquot using a syringe or pipet. Effective secondary sampling requires making a stable homogenous suspension (i.e., the sample must be stable from the time of formation of a suspension to the time when the analysis is complete). Some important factors in wet analysis are sample solubility in the dispersion vehicle, aggregation of sample, the use of suspending agents, and deaggregation of primary particles in the dispersion vehicle. Even though a uniform suspension is created, the sample should b ehomogenized, typically by shaking, immediately before withdrawing the sample with a syringe or pipet. The diameter of the syringe or pipet should be large enough so that particles are not excluded and clogging does not occur. The diametersof the largest particles should not exceed 40% of the syringe or pipet tip diameter. If for practical reasons the amount of material from the primary sample is too large, the sample size should be reduced before a suspension is made. To reduce the sample size, use the methods described above in the Dry Analysis Methods section. As a precaution, collect and retain enough sample to repeat all tests a minimum of five times.