Revision KNEC Questions and Answers on Samples and Sample Preparation

Researchers may have problems gaining ready access to entire populations. And because of the nature of some studies, researchers may have difficulties getting the results they need in a timely fashion. This is why people who conduct studies use samples.

Using a smaller number of people who represent the entire population can still produce valid results while cutting back on time and resources.

Samples and sampling methods are widely used in a variety of settings where research is conducted.

It is also a time-convenient and a cost-effective method and hence forms the basis of any research design. Samples used by researchers should closely resemble the population. All the participants in the sample should share the same characteristics and qualities.

Qualities of a good sample

A sample should represent the population as a whole and not reflect any bias toward a specific attribute. Samples are used in statistical testing when population sizes are too large for the test to include all possible members or observations.

Distinguish between sample and sampling

Whereas a sample is a smaller, manageable version of a larger group. It is a subset containing the characteristics of a larger population, sampling is the actual process of selecting certain members or a subset of the population to make statistical inferences from them and to estimate characteristics of the whole population.

State and explain various types of samples

Grab sample: A grab sample is a discrete sample which is collected at a specific location at a certain point in time. If the environmental medium varies spatially or temporally, then a single grab sample is not representative and more samples need to be collected.

Composite sample: A composite sample is made by thoroughly mixing several grab samples. The whole composite may be measured or random samples from the composites may be withdrawn and measured.

A composite sample may be made up of samples taken at different locations, or at different points in time. Composite samples represent an average of several measurements and no information about the variability among the original samples is obtained.

A composite of samples which all contain about the same concentration of analyte can give a result which is not different from that obtained with a composite made up of samples containing both much higher and much lower concentrations.

During compositing, information about the variability, patterns, and trends is lost. When these factors are not critical, compositing can be quite effective. When the sampling medium is very heterogeneous, a composite sample is more representative than a single grab sample. For example, in a study of the exposure to tobacco smoke in an indoor environment, a several hour composite sample will provide more reliable information than several grab samples.

Composite samples may be used to reduce the analytical cost by reducing the number of samples. A composite of several separate samples may be analyzed and if the pollutant of interest is detected, then the individual samples may be analyzed individually. This approach can be useful for screening many samples. A common practice, for example, in clinical laboratories screening samples for drug abuse among athletes is to analyze a composite of about ten samples. If the composite produces a positive result, then the individual samples are tested

Outline methods of sampling

Sampling techniques can broadly be classified into two categories namely;

Probability sampling
Non probability sampling

Non-probability Sampling:

Non probability sampling method is reliant on a researcher’s ability to select members at random. This sampling method is not a fixed or pre-defined selection process which makes it difficult for all elements of a population to have equal opportunities to be included in a sample.

Probability Sampling Methods

Probability sampling is a sampling method that selects random members of a population by setting a few selection criteria. These selection parameters allow every member to have the equal opportunities to be a part of various samples.

Probability Sampling is a sampling technique in which sample from a larger population are chosen using a method based on the theory of probability. This sampling method considers every member of the population and forms samples on the basis of a fixed process. It gets rid of bias in the population and gives a fair chance to all members to be included in the sample.

There are 4 types of probability sampling technique:

a) Simple Random Sampling:

It is one of the best probability sampling techniques that helps in saving time and resources. It is a trustworthy method of obtaining information where every single member of a population is chosen randomly, merely by chance and each individual has the exact same probability of being chosen to be a part of a sample.

b) Cluster Sampling:

Cluster sampling is a method where the researchers divide the entire population into sections or clusters that represent a population. Clusters are identified and included in a sample on the basis of defining demographic parameters such as age, location, sex etc. which makes it extremely easy for a survey creator to derive effective inference from the feedback.

For example, if the government of the Kenya wishes to evaluate the number of students TVET institutions they can divide it into clusters on the basis of national polytechnics, technical institutes, vocational institutions etc. This way of conducting a survey will be more effective as the results will be organized into institutions and provides insightful student data.

c) Systematic Sampling:

Using systematic sampling method, members of a sample are chosen at regular intervals of a population. It requires selection of a starting point for the sample and sample size that can be repeated at regular intervals. This type of sampling method has a predefined interval and hence this sampling technique is the least time-consuming.

For example, a researcher intends to collect a systematic sample of 500 people in a population of 5000. Each element of the population will be numbered from 1-5000 and every 10th individual will be chosen to be a part of the sample (Total population/ Sample Size = 5000/500 = 10).

d) Stratified Random Sampling:

Stratified Random sampling is a method where the population can be divided into smaller groups, that don’t overlap but represent the entire population together. While sampling, these groups can be organized and then draw a sample from each group separately.

Why is sample preparation important in sampling?

Sample preparation refers to the ways in which a sample is treated prior to its analyses.

Sample preparation is a very important step because most samples collected may not be in a form that is suitable for subsequent analytical techniques due presence of impurities, size ,form and ability to dissolve in the solvents and to be detected or be responsive with the reagents and analytical instruments to be used . Also the original form of the analytic in the sample may at that time of sampling not be homogenic, concentrated enough or fully separated from its matrix so as to be responsive to the subsequent analytic procedures

Explain why some samples are frozen once transported to a chemistry laboratory
Outline steps involved in sample preparation

Sample preparation could involve:

Size reduction

Sample reduction involves the processes and procedures done to achieve fine sized particles with increased surface area to enable subsequent dissolution in appropriate solvents and medias

Making sample homogeneous

The material within the sample selected from the population is usually heterogeneous. For this reason, it is usually necessary to make samples homogeneous before they are analyzed, otherwise it would be difficult to select a representative laboratory sample from the sample

Most subsequent analytical procedures require the sample to be dissolved appropriate solvents whether aqueous or organic

Chemical digestion with acid or alkali,

Digestion is a process where the precipitate is re-dissolved and precipitated out of a cleaner environment (solution). The precipitate obtained in the separation step is placed into a volatile electrolyte solution and heated. Large particles are broken up to speed up digestion. This “solution” is often heated to increase the kinetic rates of dissolution and precipitation. Since the solid is in dynamic equilibrium with the solution, in time, all material will cycle from solid to solution and back. Observation does not speed up the chemical kinetics, so we take a cola break during digestion. The solution is cooled after digesting for an hour or more. The precipitate is now refiltered.

(c) Sample extraction,

(d) Sample clean up

(e) Sample pre-concentration.

Distinguish between sampling bias and sampling errors

The difference is that a sampling error is a specific instance of inaccurately sampling, such that the estimate does not represent the population, while a sampling bias is a consistent error that affects multiple samples.

Sampling bias occurs when some members of a population are systematically more likely to be selected in a sample than others.

Sampling bias limits the generalizability of findings because it is a threat to external validity, specifically population validity. In other words, findings from biased samples can only be generalized to populations that share characteristics with the sample.

Sampling bias can occur in both probability and non-probability sampling.

Sampling error is defined as the amount of inaccuracy in estimating some value, which occurs due to considering a small section of the population, called the sample, instead of the whole population. It is also called an error. Sample surveys take into account the study of a tiny segment of a population, so, there is always a particular amount of inaccuracy in the information obtained. This inaccuracy can be defined as error variance or sampling error.

The concept of sampling error can be understood from the followingdiagram:

From the above diagram

Sampling Error = (Response Error) + (Frame Error) + (Chance Error)

Sampling Error Formula

The measure of the sampling error can be calculated for particular sample size and design. This measure is termed as the correctness of the sampling plan. Sampling error is also due to the concept called sampling bias. This error is considered a systematic error.

The formula to find the sampling error is given as follows:

If N is the sample size and SE is the sampling error, then

Sampling Error, S. E = (1/√ N) 100

Assume that the size of the population is 1000, out of which 600 are men, and 400 are women, select 100 members.

Stratum	Size	Sample for each Stratum
1	N₁ = 600	n₁ = (100×600)/1000 = 60
2	N₂ = 400	n₂ = (100×400)/1000= 40
	N = 600+400 = 1000	n = 60 +40 =100

10.Describe how to Reduce Sampling Error?

There are two methods by which this sampling error can be reduced. The methods are

Increasing sample size
Stratification

Increasing Sample Size

From a population, we can select any sample of any size. The size depends on the experiment and the situation. If the size of the sample increases, the chance of occurrence of the sampling error will be less. There will be no error if the sample size and the population size coincide. Hence, sampling error is in inverse proportion to the sample size.

Stratification

If all the population units are homogeneous or the population has the same characteristic feature, it’s very easy to get a sample. The sample can be taken as a representative of the entire population. But if the population is not homogeneous (i.e population with the different characteristic features); it is impossible to get a perfect sample. In such conditions, to get a better representative, the sample design is altered. The population is classified into different groups called strata, that contain similar units. From each of these strata, a sub-sample is selected in a random manner. Thus, all the groups are defined in the sample, the sampling error is reduced. Hence, the sub-sample size from each stratum is in proportion with the stratum size.

State any four causes of bias in sampling

A common cause of sampling bias lies in the design of the study or in the data collection procedure, both of which may favor or disfavor collecting data from certain classes or individuals or in certain conditions. Sampling bias is also particularly prominent whenever researchers adopt sampling strategies based on judgment or convenience, in which the criterion used to select samples is somehow related to the variables of interest.

12.State and explain any three causes of loss of analytes in samples during sampling

Materials may be lost from a sample during laboratory preparation through the following ways

Losses as Dust or Particulates- small suspended particles in the residue may be readily by any air flow over the sample by air generated by changes in temperature. This can be prevented by storing the samples in covered containers
Losses Through Volatilization- The loss of volatile elements during heating is minimized by heating without exceeding the boiling point of the volatile compound and by also carrying out reactions in a properly constructed sealed vessel
Losses due to reactions between sample and container or reactions with other reagents initially used in the container, similarly, the internal surface area of a container, whether used for sample preparation or storage, may cause loss of analyte. Scratches and abrasions increase the surface area, and their geometry make loss of analyte likely.
Outline any for sources of contamination of samples in the laboratory

Possible sources of contamination include:

Moisture and airborne contamination from the immediate environment
Reagents contaminations due to inherent impurities
Glassware/equipment contamination used in collecting , processing and storage of the samples
Contamination of Facilities e.g. processing lines , benches , rooms etc.
Cross-contamination between high- and low-activity samples during storage and handling of samples.
Describe ways of preventing sample contamination
- Many biological samples contain active enzymes they can cause changes in the properties of the food prior to analysis, e.g., proteases, cellulases, lipases, etc. If the action of one of these enzymes alters the characteristics of the compound being analyzed then it will lead to erroneous data and it should therefore be inactivated or eliminated. Freezing, drying, heat treatment and chemical preservatives (or a combination) are often used to control enzyme activity, with the method used depending on the type of food being analyzed and the purpose of the analysis.
- Ensuring proper storage conditions. Exposure to light, elevated temperatures, oxygen or pro-oxidants can increase the rate at which these reactions proceed. Consequently, it is usually necessary to store samples that have high unsaturated lipid contents under nitrogen or some other inert gas, in dark rooms or covered bottles and in refrigerated temperatures. Providing that they do not interfere with the analysis antioxidants may be added to retard oxidation.
- Microbial Growth and Contamination. Microorganisms are present naturally in biological materials and if they are not controlled, they can alter the composition of the sample to be analyzed. Freezing, drying, heat treatment and chemical preservatives (or a combination) are often used to control the growth of microbes in foods.
- Physical Changes. A number of physical changes may occur in a sample, e.g., water may be lost due to evaporation or gained due to condensation; fat or ice may melt or crystallize; structural properties may be disturbed. Physical changes can be minimized by controlling the temperature of the sample, and the forces that it experiences.
- Ensuring clean and hygienic environment for sample handling, storage and processing including using appropriate gloves , labcoats etc together with ensuring scrupulous cleanness of glassware, surfaces and other apparatus and equipment used. It also important to ensure availability of separate places for holding and processing samples so as to prevent their cross contamination.

15.Outline steps involved in developing a sampling plan

To do a successful environmental study it is necessary to have a ‘plan of action’, referred to as a sampling plan. Sampling plan will be different for each of these purposes.

The first step is to clearly define the problem being studied and identify the environmental “population” of interest. Some of the major steps involved in the development of a successful study are as follows:

Clearly outline the goal of the study. Decide what hypothesis is to be tested and what data should be generated to obtain statistically significant information.
Identify the environmental population or area of interest.
Obtain information about the physical environment. Weather patterns, for instance, are important if air samples are to be taken.
Research the site history.
Carry out a literature search and examine data from similar studies previously carried out. This can provide information about trends and variability in the data. In the absence of previous data, a pilot study may be necessary to generate preliminary information on which to base a more detailed study.
Identify the measurement procedures to be used, because these affect the way samples are collected and handled.
Develop an appropriate field sampling design. Decide how many samples are to be collected and delimit the time and area to be covered by the study.
Determine the frequency of samples to be taken, both in time and space, depending upon the project objectives. Decide if, for example, 24 hour integrated samples will be collected or individual samples will be taken every few hours.
Develop a plan to insure and document the quality of each of the processes involved in the study: sampling, laboratory analysis, contamination control, etc.
Once the sampling and analysis are complete, assess the uncertainty of the measurements.
Perform statistical analysis on the data. Determine mean concentrations, variability, and trends with time and location.
Evaluate whether study objectives have been achieved. If not, additional work may be necessary to provide the needed information.
State factors to consider when designing a sampling plan
- The purpose for the sample
- The nature of sample
- The resources required
- The time required
- The technical expertise needed

Justify the following sample treatment procedures
Drying

Many of the samples received in the laboratories are wet. They must be dried before they can be crushed or pulverized for analysis. Laboratory staff uses drying procedures that avoid contamination and ensure that the drying temperature is suitable for your sample and the analysis that you want to perform on it.

Grinding

Grinding is usually required to decrease the particle size of solid samples.however, crushing should not introduce extrenous particles and impurities or alter the composition of the samples. A serious contamination error can arise during grinding and crushing due to mechanical wear and abrasion of the grinding surfaces.

Grinding must be continued until every particle has been passed if the screened sample is to have the same composition as it had before grinding and screening.

State any four sample storage methods

Methods of preservation are intended to retard biological and chemical degradation of compounds and complexes, and reduce volatility of constituents. No single preservation method is entirely satisfactory; choose the preservation with regard to the analyses being made..

Because a preservation method for one analysis may interfere with the preservation for another, samples for multiple determinations may need to be split and preserved separately. Use chemical preservation only when it is shown not to interfere with the method of analysis

Following collection and during transportation, samples should be kept at 6^oC or on ice. Samples requiring preservation should be preserved as soon as possible after collection to maintain the integrity of the sample.

In the laboratories, samples may be stored in dark rooms, in clean tightly closed or canned bottles, cool and dry rooms or in the fridges. Some may require to be stored in closed vessels with desiccants to absorb any moisture from the surrounding environment that may interfere with the samples

To minimize the potential for volatilization or biodegradation between sampling and analysis, keep the sample as cool as possible without freezing.

Analyze the samples as quickly as possible upon arrival at the laboratory. If immediate analysis is not possible, storage at 2-4o C is recommended for most samples.

All samples must be properly stored from the time they arrive at the laboratory to disposal. Samples are refrigerated at 4^oC prior to analysis unless method SOPs indicate other storage conditions.

Nature of Sample Changes: Some analyses are more likely than others to be affected by storage before analysis.

Temperature, pH, and dissolved oxygen are best determined in the field. Temperature changes quickly and pH may change significantly in a matter of minutes. Dissolved gases (oxygen, carbon dioxide) may be lost very quickly. With the changes in the pH-alkalinity-carbon dioxide balance, calcium carbonate may precipitate and cause a decrease in the values for calcium and total hardness.

In general, the shorter the time that elapses between the collection of a sample and its analysis, the more reliable the analytical results. However, it is impossible to state exactly how much time may be allowed between sample collection and analysis. Changes occurring in the sample depend on the character of the sample, the analysis to be made, and the conditions of storage. Changes caused by the growth of microorganisms are greatly retarded by keeping the sample in the dark and at a low temperature.

20.Explain methods used in sampling gases

The methods are: 1. Gravity Sedimentation Methods 2. Inertial Methods 3. Filtration 4. Precipitation.

Gravity Sedimentation Methods:
Sedimentation from still air:

The method was invented by Alvarez and Castro (1952) who constructed a simple box for the study of airborne fungi, it has two hinged slides and a covered tray at the bottom for inserting a microscopic slide or petridish. During air sampling the hinged slides are raised horizontally and wind is allowed to blow through the box.

The slides are then closed and the entrapped spores are sedimented under gravity. Here sampling is discontinuous and a small volume of air being sampled at a time. An improved form of this model was later described by Ogden (1974).

Inertial Methods:

In this method the particles may be retained on filters, on flat surface or on liquids. Air sample may be drawn through a jet tube or apparatus may move the trapping surface through the air.

Filtration:

In this method, the particle is removed from the air by suction. The air is allowed to pass through fibrous or porous medium that sieves the particles. In such a case filters with smooth surface like molecular membranes are suitable for the microscopic examination of the entrapped particles.

Precipitation:
i) Electrostatic precipitation:

It is very useful for small particles. Air is drawn through the sampling unit and the particles are charged near the entrance and then attracted to an electrode of opposite charge inside the instrument.

ii) Thermal precipitation:

These are similar to electrostatic precipitations through the electrostatic charges. From the air which flows through the sampler the particles are driven away from a hot surface to a cooler one.

Discuss storage methods of chemical samples in the laboratory

All chemicals handled in the laboratory must be considered as hazardous and therefore a risk. The inherent hazards of chemicals can be reduced by minimizing the quantity of chemicals on hand. However, when chemicals must be used, proper storage and handling can reduce or eliminate associated risks.

All chemical storage areas and cabinets should be inspected at least annually and any unwanted or expired chemicals should be removed. Safe chemical handling requires routine inspections of chemical storage areas and maintenance of stringent inventory control.

Typical storage considerations may include temperature, ignition control, ventilation, segregation and identification. Proper segregation is necessary to prevent incompatible materials from inadvertently coming into contact. A physical barrier and/or distance is effective for proper segregation.

Discuss methods for safe chemical storage:

Ensure all containers of hazardous chemicals are properly labeled with the identity of the hazardous chemical(s) and appropriate hazard warnings.
Segregate all incompatible chemicals for proper storage of chemicals by hazard class. In other words, store like chemicals together and away from other groups of chemicals that might cause reactions if mixed.
Do not store chemicals alphabetically except within a grouping of compatible chemicals.
Flammable materials should be stored in an approved, dedicated flammable materials storage cabinet or storage room if the volume exceeds ten gallons. Keep cabinet doors closed.
Chemicals should be stored no higher than eye level and never on the top shelf of a storage unit. Do not overcrowd shelves. Each shelf should have an anti-roll lip.
Avoid storing chemicals on the floor (even temporarily) or extending into traffic aisles.
Liquids should be stored in unbreakable or double-contained packaging, or the storage cabinet should have the capacity to hold the contents if the container breaks.
Store acids in a dedicated acid cabinet. Nitric acid may be stored there also but only if it is kept isolated from all other acids.
Store highly toxic or controlled materials in a locked, dedicated poison cabinet.
Volatile or highly odorous chemical shall be stored in a ventilated cabinet. Chemical fume hoods shall not be used for storage as containers block proper air flow in the hood and reduce available work space.
All chemicals should be labeled and dated upon receipt in the lab and on opening. This is especially important for peroxide-forming chemicals such as ethers, dioxane, isopropanol, and tetrahydrofuran. Solutions should be labeled and dated when prepared.
Look for unusual conditions in chemical storage areas, such as:
- Improper storage of chemicals
Leaking or deteriorating containers
Spilled chemicals
Temperature extremes (too hot or cold in storage area)
Lack of or low lighting levels
Blocked exits or aisles
Doors blocked open, lack of security
Trash accumulation
Open lights or matches
Fire equipment blocked, broken or missing
Lack of information or warning signs (“Flammable liquids”, “Acids”, “Corrosives”, “Poisons”, etc.)
First aid supplies, emergency phone numbers, eyewash and emergency shower equipment, fire extinguishers, spill cleanup supplies and personal protective equipment should be readily available and personnel trained in their use.
Chemicals stored in explosion-proof refrigerators or cold rooms shall be sealed and labeled with the name of the person who stored the material in addition to all other required hazard warnings.
Only compressed gas cylinders that are in use and secured in place shall be kept in the laboratory. All others, including empties, shall be sent to the compressed gas cylinder storage area for the particular facility.
Keep all stored chemicals, especially flammable liquids, away

from heat and direct sunlight.

Packaging

After sampling, the sample containers must be checked for leaks. The outer surface of packages must be clean and dry. If leaks occur, caps and stoppers should be reinforced or replaced. Another inspection should then be carried out, and if leaks persist fresh samples should be taken. Preferably use another sample container.
The sample containers used for the packaging of volatile liquid samples should be filled to approximately 90 % of their total holding capacity.
Warning signs, markings and symbols indicating potential hazards should be placed on packages holding samples of hazardous goods/compounds.

Sealing

Depending on your national regulations the sample container should be sealed in an appropriate manner for the type of container used, to prevent unauthorised or inappropriate handling of samples (and ensure the integrity of the contents). The seal must be firmly attached and stable in order to prevent damage during sample storage or transport, and to safeguard the chain of evidence.

Marking

The markings on labels must be clearly legible and permanent in order to prevent deletion or substitution/alteration during storage, handling and transport.In the case of retail sale packages, the customs label should not cover the commercial labels of the original product (trademark, manufacturer, contents, expiry date, etc.). It is recommended that you place retail packages in a polythene bag and fix the labels and seals to the bag.Health and safety regulations must be observed.

Documents accompanying final samples

The accompanying documents must be kept in line with rules laid down by the customs administration. This depends on the local situation. In some Member States only digital documents are used; they are sent by email to the customs laboratory or using integrated information systems. Copies of other relevant documents concerning the nature of the goods may also be enclosed (SDS, technical specifications, quality/compliance certificates, etc.).

Storage of samples

Storage conditions are determined by the characteristics and properties of samples taken. Storage conditions should ensure that the sample is not altered in any way that might affect the parameters to be analysed.

Health and safety regulations must be observed.
In general, samples should be stored in a clean, dry, dark, cool and sufficiently ventilated room.

Foodstuff samples must be stored separately from other samples. Perishable goods must be stored in refrigerators or freezers and the storage temperature must be monitored regularly. If frozen, samples should be maintained at below -18 °C and the storage temperature should be monitored.
Flammable substances must be stored in accordance with the fire safety regulations.

If the customs office cannot provide these facilities and the sample cannot be transferred to the customs laboratory immediately, an alternative external storage place should be sought that fulfils the conditions for safeguarding the quality and identity of the samples.
It is recommended that each customs office appoint an officer to manage the sample storage facility. Their job description should also include the following tasks:

accepting samples for storage and transport for analysis, and record keeping;
monitoring the sample storage deadlines;
organising sample disposal after expiry of these dates;
ensuring that the storage conditions for the samples are met at all times.

For certain products specific conditions are appropriate. Some examples are given below, but you should refer to the specific sampling procedure for more details.

Product	Conditions
Light sensitive samples	Storage in a dark place.
Samples giving off poisonous or unpleasant smells.	Possible storage in a fume hood or in a room with sufficient mechanical ventilation.
Mineral oils, highly inflammable and other dangerous samples	See SDS. Storage in a safety cupboard, when possible. If no information available, ask laboratory for storage conditions.
Samples susceptible to decay	Storage in a freezer or refrigerator; depends of character of the product. If in doubt, consult the laboratory.
Samples of very perishable goods	Foodstuff samples must be stored separately from other samples. Perishable goods must be stored in refrigerators or frozen in consultation with laboratory. Indicate on Sample form that freezing was done by customs officer. Frozen samples must be maintained at below -18 °C and the storage temperature should be monitored regularly.
Samples of chilled products	Foodstuff samples must be stored separately from other samples. Chilled samples must be maintained at approx. 4 °C and the storage temperature should be monitored regularly.
Samples of frozen products	Foodstuff samples must be stored separately from other samples. Frozen samples must be maintained at below -18 °C and the storage temperature should be monitored regularly.
Samples of retail packing of food products and of medicines and pharmaceutical products.	Storage at conditions labelled on packing, but not above approx. 30 °C or as indicated on the package.

Transport

The transport conditions must guarantee the integrity and characteristics of the samples being transported. The type of transport will depend on the nature of the samples (e.g. dangerous good or special temperature requirements), the quantities, the urgency and frequency with which they occur.There are several methods for transporting samples to the customs laboratory.

Transport	Remarks
By post and regular delivery services	Can only be used for samples without special storage conditions. Some delivery services may also transport certain dangerous samples. Each service may have special requirements regarding quantities, packaging and labelling.
By specially equipped transport, e.g. for transporting chemical samples or frozen goods	Samples of all types can be transported by this method provided there is no risk of cross-contamination. Samples with special storage conditions can best be sent by this method. For samples with dangerous properties, check the contractor’s requirements regarding quantities, packaging and labelling.
By courier	Samples of all types can be transported by this method provided the samples are suitably packed and there is no risk of cross-contamination. For samples with dangerous properties, check the contractor’s requirements regarding quantities, packaging and labelling. The courier may also have restrictions on what they will accept. It can be practical to use a courier for regular transport operations or urgent deliveries.
By customs officers themselves	Delivery direct to the customs laboratory. The regulations regarding the transport of dangerous substances (ADR), must be observed, unless the samples are transported under circumstances that permit exemptions from ADR.

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