Name: sampling errors in sample preparation
Uploaded: 2024-12-05T18:31:55.000Z
Duration: 1 min 16 s
Channel: JoVE

通常、バルクサンプルはサンプリングによってラボサンプルに縮小されるため、エラーが発生します。
一般的なサンプリング誤差には、汚染やサンプリング方法と測定タイプとの間の不一致などがあります。
具体的には、不適切な分裂による濃度バイアスや、粒度縮小法による汚染などの潜在的なエラーが発生する可能性があります。これらのエラーを最小限に抑えることは、正確で信頼性の高い結果を得るために重要です。
ターゲット母集団の正規分布を仮定すると、サンプリング誤差の信頼区間の式では、ns はサンプル数を表し、ss はサンプリング標準偏差を示します。ここで、eを再編成して置き換えると、目的のサンプリング誤差に必要なサンプル数を決定するのに役立ちます。
もう1つの重要な側面は、分析の全体的な分散を減らすことですが、これはメソッドとサンプリングの2つのコンポーネントに依存しています。
正しいサイズのサンプルを十分に収集すると、サンプリングに関連する分散が改善されますが、各サンプルの分析数を増やすと、分析法の分散が改善します。

汚染物質と誤差

効果的なサンプル準備は、正確で信頼性の高いラボ分析に不可欠です。このプロセスでは、2 つの重大な誤差の原因が発生する可能性があります。不適切なサンプル分割による濃度の偏りと、粉砕や均質化などの粒子サイズを小さくするために使用される方法によって引き起こされる汚染です。これらの潜在的な誤差を特定して最小限に抑えることは、分析の妥当性を保証するために重要です。

もう 1 つの重要な考慮事項は、目的のサンプリング誤差を達成するために必要な適切なサンプル数を決定することです。対象母集団が正規分布に従う場合、サンプルサイズは次の式を使用して計算できます。

この式では、目的の信頼レベルに基づく t 値はサンプリング標準偏差を表します。これは、サンプルが平均からどの程度広がっているかを測定し、許容可能なサンプリング 誤差を示します。この式は、特定の誤差しきい値を満たすために必要なサンプル数を定義するのに役立ち、サンプリングプロセスの精度を保証します。

さらに、分析の総分散を最小限に抑えるには、方法とサンプリングの分散の両方に対処する必要があります。適切な数の適切なサイズのサンプルを収集することでサンプリングのばらつきを減らすことができますが、各サンプルに対して複数の分析を実行するとメソッドのばらつきは改善されます。両方のばらつきを効果的に管理することで、より正確で信頼性の高い結果が得られます。

正確で信頼性の高いラボ分析には、効果的なサンプル調製が不可欠です。このプロセスでは、エラーの2つの重大な原因が発生する可能性があります。

Education

JoVE Core

Analytical Chemistry

分析化学

Unit 1

ユニット1

Method Development and Sampling Techniques

分析法の開発およびサンプリング技術

method-development-and-sampling-techniques

KEY TERMS AND CONCEPTS

主要用語と概念

Contaminants and Errors

sampling errors in sample preparation

Sampling errors in sample preparation can affect the accuracy of laboratory results. Two common problems are concentration bias from poor sample splitting and contamination from reducing particle size by grinding or homogenization. Recognizing these errors helps make analysis more reliable.

The number of samples also matters when a target population follows a normal distribution. In that case, the sample size ns can be found with a formula that uses the t-value for the chosen confidence level, the sampling standard deviation s, and the acceptable error e. Here, the t-value reflects confidence, s shows how spread out the samples are from the mean, and e sets the error limit.

Controlling total variance requires attention to both sampling variance and method variance. Sampling variance can be lowered by collecting enough correctly sized samples. Method variance improves when multiple analyses are performed on each sample, which helps produce more accurate results.

Sampling Errors in Sample Preparation

development of analytical methods

Analytical Methods: Technique to Protocol

Analytical methods follow a clear path from technique to protocol. In analytical chemistry, a technique is the scientific principle used to explain a chemical measurement. A method applies that technique to a sample of interest. The next steps are procedure and protocol. A procedure gives the directions for carrying out the analysis with an analytical method. A protocol is the detailed set of guidelines for that procedure, and it should be followed closely to get the desired results. <br...

quality control

Quality Control Charts and Lab Records

Quality control charts, proficiency testing, and lab records are key parts of quality control in a laboratory. These steps help keep a system under statistical control. They also help track data, show trends, and spot variations that may affect the accuracy of an analysis. One common tool is a quality control chart. This chart plots one or more analytical characteristics over time. The measured values are taken at different times during the analysis and compared with the known value of...

quality assurance

Quality Checks in Analytical Testing

Quality assurance in analytical testing brings together the checks that help a system perform properly. It includes quality control, quality assessment, and internal corrective measures. These parts work in a cycle to support reliable results. Quality control happens before and during the analysis. Quality assessment takes place during and after the investigation. Internal corrective measures are then based on the results of post-analysis quality assessment, or they may be applied before a new...

data validation

How Analytical Methods Are Checked

Method validation checks whether an analytical chemistry method gives reliable results. It is especially important when the same method is used with different sample matrices or when the procedure is changed. Validation helps show that the method still meets acceptable standards in each case. Several key checks are used in method validation. Specificity means the method can measure the target analyte without interference from other substances. Linearity means the result changes in direct...

qualitative analysis

Classical and Instrumental Sample ID

Qualitative analysis identifies the elements, ions, or compounds in an unknown sample. It is the first step in the hierarchy of analytical goals. That makes it the starting point for scientific study before quantitative analysis or other forms of analysis. Two main approaches are used in qualitative analysis: classical methods and instrumental methods. Classical methods depend on the visible or sensory result of a chemical reaction, such as a color change, a precipitate, or even a smell. These...

quantitative analysis

Measuring Analyte Concentration

Quantitative analysis measures the amount of a specific substance, called the analyte, in a sample. If the sample composition is unknown, qualitative analysis comes first. That step identifies the components so the correct substances can be measured during the quantitative phase. This method depends on two key measurements. Scientists measure the sample quantity and also a property that is proportional to the amount of analyte. Together, these measurements help determine the analyte...

instrument calibration

Calibrating Lab Instruments for Accurate Results

Calibration helps lab instruments produce accurate and consistent results. It is important in manufacturing, healthcare, testing laboratories, and scientific research. Each instrument needs a calibration process that matches its design and function. This process improves data accuracy and helps results stay reliable. An analytical balance measures mass and needs regular calibration to stay precise. It is calibrated by comparing its readings with known standard weights. These weights act as...

glassware calibration

Calibrating Lab Glassware for Accurate Volume

Calibrating lab glassware helps students measure liquids accurately in the analytical laboratory. It reduces volume errors and supports consistent results across measurements. This matters when using volumetric flasks, pipettes, burettes, and other tools that depend on precise volume readings. Volumetric flasks are used to prepare aqueous solutions with a precise final volume. They have a calibration line on the neck. To calibrate one, fill it with distilled water until the meniscus, the...

standard solutions

Preparing Standard Solutions in the Lab

Standard solutions are prepared to have a precisely known concentration or composition. In analytical chemistry, this accuracy is important because it supports reliable results. A primary standard is a highly pure, stable substance with a high molar mass. It is fully soluble in water, which is the most commonly used solvent in analytical chemistry. A primary standard solution can be used to standardize a secondary standard. Secondary standards have known concentrations, but they are usually...

blank solutions

Blank Solutions in Analytical Testing

Blank solutions are used in analytical testing to show the background signal before a sample is measured. A blank solution does not contain the analyte, which is the substance of interest being tested or measured. It is usually made with the same reagents and procedure as the sample solution, but without the analyte. The main purpose of a blank solution is to control for background interference and contamination. Reagents, solvents, or lab equipment can sometimes create a detectable signal on...

sampling methods: overview

How Sampling Shapes Lab Results

Sampling shapes lab results by determining how a smaller sample represents a larger population. In analytical chemistry, testing an entire population is often impractical or impossible, so samples are collected to make inferences about the whole group. The sampling method is the process used to choose individuals or items for that sample. Common sampling methods include random, judgemental, systematic, stratified, and cluster sampling. Each method can affect the quality of the data in a...

sampling methods: sample types

Sampling Materials in Solid, Liquid, Gas

Sampling materials are grouped as solid, liquid, or gas. The type of sample helps decide the right collection method. Solid samples can include sediments from water bodies, soil, metals, and biological tissues. Sediment sampling from water bodies can be done in two common ways. Grab sampling uses a device to collect a discrete sample from the bottom with minimal disturbance. These samples may not show the full area because conditions can vary from place to place. Piston coring collects a...

sampling plans

Choosing Samples for Reliable Results

Sampling is a key step in analytical chemistry. It helps researchers collect data that represents a larger population. The main sampling methods in this topic are random, judgmental, systematic, stratified, and cluster sampling. Random sampling gives each member of the population an equal chance of being chosen. Researchers often use a random number generator or a lottery-style method. For example, a polymer sheet can be divided into 1 cm x 1 cm sections, and 10 sections can be selected at...

sample preparation for analysis: overview

Preparing Samples by State and Form

Sample preparation depends on the state and form of the sample before analysis. It helps make the sample ready for accurate measurement. The main goal is to extract the analyte, which is the substance being measured, and remove parts that could interfere with the analysis. Solid samples often need the most handling. Large solids are usually ground, crushed, or milled to make them smaller and increase surface area. The sample is then sieved and mixed so it has a uniform composition. After that,...

sample preparation for analysis: advanced techniques

sample-preparation-for-analysis-advanced-techniques

Preparing Complex Samples for Analysis

Preparing complex samples for analysis often requires special digestion and fusion methods. Samples with inorganic or organic material can be hard to dissolve or break down. Common sample preparation methods include acid digestion, fusion, dry ashing, and wet digestion. These steps help turn difficult samples into forms that can be tested reliably and again with similar results. Acid digestion is often used for inorganic materials that do not dissolve in water. It is useful for soil and...

sample handling

Sample Transport and Storage Basics

Sample transport and storage help keep specimens intact before testing. Moving a sample from the collection point to the laboratory requires careful handling. The sample should be sealed well and clearly labeled. These steps help prevent cross-contamination and support reliable results. Temperature control is also important during transport. Some samples travel in insulated containers, cool packs, or refrigerated vehicles so they stay within the needed temperature range. After the samples...

contaminants and errors

Sampling errors in sample preparation can affect the accuracy of laboratory results. Two common problems are concentration bias from poor sample splitting and contamination from reducing particle size by grinding or homogenization. Recognizing these errors helps make analysis more reliable. The number of samples also matters when a target population follows a normal distribution. In that case, the sample size ns can be found with a formula that uses the t-value for the chosen confidence level,...

key terms and concepts

Learn how poor sample splitting, contamination, and sample size affect lab accuracy, and how sampling and method variance can be reduced in analysis.

Sampling Errors in Sample Preparation | JoVE K12

JoVE Core 分析化学 は、複雑な化学原理をアニメーションで視覚化することで、SI 単位から NMR 分光法を含むトピックをよりわかりやすくします。実験を撮影した実写動画では、これらの概念が世界中の研究所でどのように応用されているかを取り上げています。

analytical chemistry

Sampling Errors in Sample Preparation

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