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The Serial Diluter is designed for users performing dilutions for the plate count methods in microbiological testing of food, feed, cosmetics, etc.

• Eliminates the time-consuming preparation of dilution tubes.
• Eliminates the need to purchase expensive disposable dilution tubes.
• Accelerates dilution through automation, improving overall efficiency.
• Simplifies handling, reducing the risk of repetitive strain injuries, as automatic mixing eliminates the need to manipulate dilution tubes and lids manually.

As a practical guide, the semi-automatic Serial Diluter UA is suitable for laboratories processing up to around 50 samples per day, while the fully automated Serial Diluter UC is recommended from around 50 samples per day. The economic payback depends on the number of samples, the number of dilution steps per sample, current tube preparation costs, labour costs and consumable prices.

For a first estimate, the savings calculator on Our Solution can be used to check whether the purchase of a Serial Diluter is worthwhile for your laboratory under the given circumstances.

Yes. The Serial Diluter is also suitable for samples requiring only one or two dilution steps.

When six Serial Dilution Bags are inserted, up to six samples with one dilution step or three samples with two dilution steps can be processed before new bags need to be inserted. This keeps handling effort low and supports efficient routine workflows.

The Serial Diluter offers efficiency improvements by automating labor-intensive tasks, allowing operators to focus on other responsibilities, and ultimately creating a more positive working environment for laboratory technicians.

The installation process is straightforward, resembling that of a gravimetric diluter. Our comprehensive support, including training videos, an illustrated manual, and a quick start guide, ensures a smooth transition to the Serial Diluter. While adopting the Inlabtec Serial Diluter may involve a brief adjustment period, the investment proves worthwhile.

There are several methods available for preparing dilutions in the laboratory, each with its own advantages and disadvantages. Some commonly used methods include dilution tubes prepared by the laboratory, pre-filled disposable dilution containers, the spiral plater, and the Tempo MPN system.

While dilution tubes prepared by the laboratory are an established standard method that most laboratory technicians are familiar with, they can be time-consuming to prepare and require manual skill and good workplace organisation to be efficient and yield correct cell counts.

Ready-made disposable dilution containers may be immediately available and require no preparation, but they come with significant costs for procurement, transport, storage and disposal, as well as a high environmental impact. Additionally, not all diluents may be available, and carrying out dilutions is not always simplified and accelerated.

The spiral plater is well-suited for certain applications without having to dilute the initial sample, such as beverages and milk, and can yield up to 10⁵ CFU/ml and plate. However, it is sensitive to clogging by particles in the sample, requires a high level of flatness for the culture media, and does not support pour plates or dry film media such as Petrifilm or Compact Dry. Additionally, a special counting procedure is necessary for colonies on the plates, and regular maintenance and servicing are necessary.

The Tempo MPN system is a fully automated system for microbial count determination that is ideal for very high throughput and uniform sample types and often manages without additional dilutions. However, it is less accurate than the standard method, and no visual control is possible. It also comes with high operating and acquisition costs, requires significant validation effort per sample type, has a high environmental impact, and requires significant maintenance and service costs. In many workflows, samples may require a 1:100 pre-dilution before use; this dilution step can also be prepared with the Serial Diluter.

In comparison, the Inlabtec Serial Diluter presents a streamlined and automated approach to dilution preparation, combining efficiency with precision. By eliminating inaccurately filled dilution tubes and the need for vortexing, it mitigates the risk of inhomogeneous mixtures, ensuring consistently accurate analysis results. The system’s high flexibility allows it to accommodate various diluents, sample types, and plates. Moreover, the Serial Diluter stands out as an environmentally friendly alternative to disposable dilution containers. Its automated process not only saves time but also enhances productivity, making it advantageous even for laboratories with lower daily sample volumes.

The Serial Diluter reduces routine workload and costs by eliminating tube preparation, washing, autoclaving and separate vortexing, while reducing repetitive manual handling during serial dilution.

Time savings depend on the existing workflow, the number of dilution steps and the operator’s handling routine. In many workflows, automated diluent dispensing and integrated mixing save several seconds per dilution step because tubes no longer need to be opened, closed and vortexed manually.

Cost savings come from several factors: predictable consumable cost per dilution, less preparation and handling time, no washing or autoclaving of dilution tubes before use, lower water and detergent use, reduced storage volume and less waste handling.

Compared with pre-filled disposable dilution containers, Serial Dilution Bags can reduce consumable costs by up to 90%, depending on the reference product, local pricing and laboratory workflow.

Compared with pre-filled disposable dilution containers, Serial Dilution Bags can reduce consumable costs by up to 90%, depending on the reference product, local pricing, order quantity and laboratory workflow.

If dilution tubes are prepared in-house, the saving per dilution depends mainly on the labour time, water, electricity, detergents, sterilisation capacity and infrastructure costs currently required for preparation, washing, filling and autoclaving.

Savings and payback time are therefore laboratory-specific. The savings calculator on Our Solution provides a first estimate based on typical workflow assumptions.

A box of Serial Dilution Bags 100101 contains 2,000 bags. With dimensions of approximately 13 cm x 16 cm x 12.5 cm, it requires a storage volume of about 2.6 litres.

Compared with the same number of pre-filled disposable dilution containers or prepared tube racks, the storage requirement is typically much lower. The exact saving depends on the reference container and the laboratory’s storage system.

The Inlabtec Serial Diluter works in a similar way to an electronic pipetting aid. It uses vacuum to aspirate the required volume of diluent and pressure to dispense it into a Serial Dilution Bag.

The volume is defined by an optical sensor positioned laterally on the pipette at the required fill level. This replaces visual volume adjustment by the user and supports consistent dispensing.

Liquid flow is controlled by pinch valves, which act on the tubing from the outside and do not come into contact with the liquid. The tubing and dispensing nozzle can be easily removed for cleaning and sterilisation.

The Inlabtec Serial Diluter is compatible with standard 10 ml serological and graduated pipettes, whether made of glass or plastic. Other pipette sizes may also be used, provided that the outer diameter is between 8–15 mm and the length is between 150–350 mm.

Wide-tip serological pipettes, as commonly used in cell culture applications, should not be used because their outlet may be too large for a secure connection to the Serial Diluter.

The Inlabtec Serial Diluter can remain operational until the connected diluent has been used up. This allows laboratories to avoid unnecessary interruptions caused by replacing or reconnecting the diluent bottle during routine work.

The dispensing nozzle is protected by a sleeve, which reduces direct exposure to the laboratory environment and helps minimise the risk of contamination during normal operation.

As an additional precaution during longer periods of non-use, for example over a weekend, the dispensing nozzle can be parked in 70% ethanol. This helps maintain system cleanliness and further reduces the risk of contamination. For details refer to the operating instructions in the Support section.

The Serial Diluter can be operated in a sterile bench, laminar flow, etc. and the device is UV-resistant for regular surface sterilisation.

The diluent comes into contact with silicone, stainless steel, glass or polystyrene (depending on the 10 ml pipette used), polyethylene and polypropylene.

Inlabtec uses Serial Dilution Bags because they combine the benefits of sterile single-use materials with very low material consumption.

Pre-filled disposable dilution containers can reduce preparation work, but they often require considerably more plastic, packaging, storage space and transport volume. For serial dilution, a rigid container with a screw cap is usually not required, because the dilution is typically processed immediately and not stored for a longer period.

Inlabtec Serial Dilution Bags are specifically designed for sterile filling, reliable mixing and safe sample transfer. Each bag contains only about 250 mg of polyethylene. In combination with automated diluent dispensing and integrated mixing, this reduces manual handling, material use, storage requirements and waste.

The guiding principle is: as much single-use convenience as necessary, as little material as possible.

The Serial Dilution Bags are made of high purity virgin polyethylene (PE) under clean room conditions. The Serial Dilution Bags comply with the regulations EU No. 10/ 2011 of 14.1.2011, 1935/ 2004 of 27.10.2004 and 2013/ 2006 of 22.12. 2006 and U.S. FDA 21, CFF 04, Title 21 (plastic materials and articles in contact with food).

The shelf life at room temperature of the Serial Dilution Bags is guaranteed for five years after production, provided the box is shrink-wrapped in the protective film.

After removing the protective film from the packaging it is recommended to use the Serial Dilution Bags within three months.

Store protected from direct solar light at room temperature (10 – 30 °C).

The used Serial Dilution Bags can be stored in the Bagshell 100030. A Bagshell is included in the scope of delivery.

The evaporation rate for filled Serial Dilution Bags and dilution tubes in the refrigerator is identical with approx. 5–10 mg (µl) per 24 hours per bag or capped test tube with 9 ml of diluent.

Serial Dilution Bags are made of high-purity virgin polyethylene and are free of substances that could inhibit the growth of microorganisms.

The Serial Dilution Bags are manufactured under controlled clean conditions within a quality management system according to DIN EN ISO 13485. After packaging, the bags are radiation-sterilised using a validated process according to ISO 11137-1/-2.

The sterilisation process is validated by an independent test laboratory using dosimetric and microbiological testing. Routine monitoring supports consistent sterility of the Serial Dilution Bags at the specified Sterility Assurance Level (SAL) of 10⁻³.

The Serial Dilution Bags were developed specifically for automated serial dilution with Inlabtec Serial Diluters. Their geometry and positioning in the Bagholder support reliable sample addition, diluent dispensing, mixing and sample removal.

The bags are arranged in the Serial Diluter so that addition and removal take place in separate functional zones. This helps minimise carry-over from more highly concentrated sample material. The shaped lower section of the bag supports controlled liquid movement during dispensing and mixing, while the integrated mixing movement of the Serial Diluter homogenises sample and diluent directly in the bag.

This standardised mixing process replaces separate manual vortexing and reduces operator-dependent variation. With the Serial Diluter UA, mixing is triggered by moving the handle from one position to the next. With the Serial Diluter UC, mixing is integrated into the automated dilution workflow.

The Serial Diluter is designed to support sterile handling during routine serial dilution. All liquid-contacting parts, including the tubing set and dispensing nozzle, can be sterilised before use according to the operating instructions. The connected diluent supply must also be sterile before operation.

During operation, the system dispenses diluent through the dispensing nozzle but does not aspirate liquid through the nozzle. Sterile filters are used for venting, helping to prevent microorganisms from entering the liquid path.

The workflow is designed so that the dispensing nozzle enters only sterile, empty bags for filling. The sample is then pipetted through a separate opening into the filled Serial Dilution Bag. When operated correctly, this separation helps prevent contact between the dispensing nozzle and sample material.

A demo video for the Serial Diluter UA shows the safety precautions.

The Serial Diluter is designed to minimise the risk of dispensing-nozzle contamination during routine use. The dosing arm moves in one direction during the dilution series, so the dispensing nozzle remains in a process-defined sterile zone.

For filling, the dispensing nozzle enters an empty, sterile Serial Dilution Bag. The sample is then pipetted through a separate opening into the filled bag. This prevents direct contact between the dispensing nozzle and the sample.

Mixing starts only after the dispensing nozzle has left the bag and is positioned above the next sterile bag. Outside the bags, the dispensing nozzle is protected by a sleeve and is positioned so that it cannot touch non-sterile surfaces during normal operation.

As with any microbiological workflow, correct installation, sterilisation and handling remain important. When the system is operated according to the instructions, the risk of dispensing nozzle contamination is reduced to a very low level.

Sterile handling depends on correct preparation of the liquid-contacting parts, correct connection of the diluent bottle and careful handling during installation. The procedure is comparable to setting up other sterile dispensing systems used in microbiological laboratories.

For reliable sterilisation of the tubing set and dispensing nozzle, suitable sterilisation pouches should be used to allow complete steam penetration during autoclaving. During installation, make sure that the dispensing nozzle does not touch non-sterile surfaces.

If a sterility control indicates contamination, the most likely sources to check are the diluent itself, the autoclaving of the tubing set and dispensing nozzle, the sterility of the diluent bottle and sterile filter assembly, and the handling during setup.

Sterility cannot be confirmed instantly during routine work. If sterility needs to be checked, perform a sterility control before starting and after completing the dilution series.

For this control, dispense 9 ml of diluent without adding a sample and plate an aliquot on a suitable culture medium. Repeat the control with the last 9 ml dispensed after the dilution series. Incubate both controls according to your laboratory procedure.

This check helps confirm that the diluent, tubing set, dispensing nozzle and setup procedure remained free of detectable contamination during use.

The PTFE (Teflon) filters used are hydrophobic and autoclavable. Difference between hydrophobic and hydrophilic filters: training video
Attention: Do not install hydrophilic filters on bottles with diluent or on the Serial Diluter.

The Serial Diluter helps improve the reliability and consistency of test results by standardising key steps of the serial dilution process. This reduces the influence of sample throughput, time pressure, unplanned workload peaks and individual working technique.

The interlaboratory test evaluation shown below demonstrates z-score values within ±0.1 for users working with the Serial Diluter. This indicates that users achieved highly consistent test results, regardless of their level of experience or individual differences in working technique.

Serial dilution performed with the Serial Diluter is compatible with ISO 6887-1:2017 for the preparation of decimal dilutions in food microbiology. The method is also used in conjunction with the associated normative reference ISO 7218:2007.

The Inlabtec Serial Diluter performs ISO-style serial decimal dilutions with 1 ml sample and 9 ml diluent. This gives the same 1:10 dilution factor as 10 ml + 90 ml dilutions used in some FDA BAM methods.

If a specific FDA BAM method or accredited laboratory procedure requires 10 ml + 90 ml dilution steps, these should not be replaced by 1 ml + 9 ml dilutions without documented verification and, where required, customer or regulatory acceptance.

Where 1 ml + 9 ml serial dilutions are permitted, the Serial Diluter can provide a faster, more compact and more resource-efficient workflow for routine plate count applications.

Some FDA BAM methods use large-volume decimal dilution steps, such as 10 ml sample into 90 ml sterile diluent. The Inlabtec Serial Diluter is designed for ISO-style serial decimal dilutions using 1 ml sample and 9 ml diluent.

Mathematically, both formats produce the same 1:10 dilution factor:

10 ml + 90 ml = 1:10
1 ml + 9 ml = 1:10

For well-homogenised plate count applications, changing only the subsequent serial dilution steps from 10 ml + 90 ml to 1 ml + 9 ml is expected to have a low risk of deviating results, provided the smaller 1 ml aliquot is representative for the tested matrix and application.

However, laboratories working under an FDA BAM-based method, accreditation scope, customer requirement or regulatory specification must follow the dilution format required by that method. If 10 ml + 90 ml dilution steps are mandatory, they should not be replaced by 1 ml + 9 ml dilutions without documented verification and, where required, customer or regulatory acceptance.

Where ISO-style 1 ml + 9 ml serial dilutions are permitted, they can reduce diluent consumption, container volume, preparation work, handling time, sterilisation requirements, storage space, transport volume and waste by approximately a factor of ten at each serial dilution step.

This conclusion applies mainly to plate count applications. MPN methods should be evaluated separately because smaller aliquot volumes may increase sampling variability, especially at low bacterial concentrations or close to detection limits.

Serial dilution performed with the Serial Diluter was verified against the standard dilution tube technique according to ISO 6887-1 by the Zurich University of Applied Sciences (ZHAW Wädenswil).

Since then, many customers and independent laboratories have carried out their own comparative tests with different food samples. One example is the testing performed by Campden BRI, where results obtained with the Serial Diluter were compared directly with the conventional dilution tube technique.

To our knowledge, since its introduction, accredited laboratories using the Serial Diluter and participating in required proficiency testing have not reported any proficiency test failures attributable to the Serial Diluter workflow.

Yes. The operating instructions describe how to check the dispensed volume and verify whether the dispensing accuracy is within the tolerance required by ISO 6887-1. Both the operating instructions and the corresponding Excel template are available under Support/Instructions.

Mixing efficiency can also be assessed using an ISO 6887-1-based approach by measuring turbidity, whether mixing is performed manually with dilution tubes or automatically with the Serial Diluter. The instructions and Excel template for this check are also available under Support/Instructions.

Method validation and method verification are distinct but related processes used to ensure the reliability of testing methods.

Method validation is performed when a new or significantly modified method is introduced. It evaluates whether the method is suitable for its intended purpose and meets defined performance criteria, such as accuracy, precision and sensitivity.

Method verification is used to confirm that a previously validated or standardised method performs as expected in a specific laboratory setting. This is typically required when a laboratory uses a method for the first time or when changes to the method, equipment or workflow could affect performance.

In simple terms, validation demonstrates that a method is suitable for its intended purpose, while verification confirms that an established method works correctly under the conditions of a specific laboratory.

When using the Serial Diluter, the preparation of decimal serial dilutions remains compatible with the standard method described in ISO 6887-1:2017. The main differences are that the system uses Serial Dilution Bags instead of dilution tubes and that mixing is performed by the Serial Diluter using a Stomacher-like mixing principle.

Before initial use in a specific laboratory setting, the correct use of the Serial Diluter should be verified. This verification confirms that the system performs as intended under the laboratory’s own conditions and produces results comparable to the established dilution tube workflow.

This is consistent with accreditation requirements such as ISO/IEC 17025, under which laboratories must demonstrate that methods and equipment used in their scope are suitable for their intended purpose and produce valid results.

To verify the use of the Serial Diluter, microbial count results obtained with the Serial Diluter should be compared with results obtained using the dilution technique previously used in the laboratory.

The same food samples should be analysed with both dilution workflows. The results should not differ by more than ±0.5 log CFU, unless the laboratory has defined different acceptance criteria based on its method uncertainty or internal procedures.

This acceptance range is commonly used as a practical benchmark for comparing microbial count results in food samples using the plate count method and reflects experience from proficiency testing and routine laboratory practice.

By comparing the Serial Diluter workflow with the established dilution tube workflow, the laboratory can confirm that the Serial Diluter performs as intended under its own conditions and produces comparable results.

The CE certificate for the Serial Diluter is in the manual.

Accuracy describes how close the average measured value is to the target or reference value. The difference between the average measured value and the target value is referred to as systematic error or bias.

Precision describes how close repeated individual measurements are to each other. A common statistical measure of precision is the standard deviation, which reflects random variation between measurements.

The indicated volume inaccuracy for plastic serological pipettes is approximately ± 2%, while for glass graduated pipettes, it is ± 0.5% for class AS and ± 1% for class B.

The dispensed volume in the Serial Diluter is defined by the pipette in combination with an optical sensor. The optical sensor detects the liquid level in the pipette at the selected volume position.

The accuracy of the dispensed volume depends primarily on the accuracy of the pipette scale or graduation, the correct positioning of the optical sensor and the connection-related volume offset between the pipette outlet and the Serial Diluter connection.

This offset is constant for a given setup and typically lies in the range of 50–100 µl. Where relevant, it should be taken into account when setting, checking or calibrating the dispensed volume.

To ensure accurate and consistent results, it is recommended to perform a quick check of the 10 ml pipettes in use. This check, also referred to as pipette scale calibration, helps identify any systematic deviation of the pipette scale and establish the correct optical sensor position for the desired 9 ml volume used in serial dilutions.

The calibration can be performed quickly using a balance, following the instructions available in the Support section. Once a pipette has been checked, the same sensor setting can normally be used for other pipettes from the same lot number, simplifying correct volume setting when installing additional pipettes.

For a quick check, detach the silicone connector from tubing set 100011 and attach it to the pipette outlet. Using a pipetting aid, dispense liquid into a balance or graduated cylinder and determine which mark on the pipette scale corresponds to the desired 9 ml volume with the silicone connector attached.

Record this scale position and use it when positioning the optical sensor of the Serial Diluter. The same setting can normally be used for pipettes from the same lot number.

The volume can be visually checked before dispensing by reading the meniscus position in the pipette. To verify the volume defined by the sensor position, either dispense into a graduated cylinder or weigh a filled bag.

To pipette into a measuring cylinder, remove the dispensing nozzle from the Bagholder and position it above a 10 ml measuring cylinder. Trigger dispensing by moving the dosing arm of the Bagholder to the next position. To reduce the risk of contamination during verification, consider attaching a dispensing nozzle holder 140015 to the Serial Diluter (see picture below).

To assess mixing efficiency, a rapid check of the mixing process—whether conducted manually with dilution tubes or automatically with the Serial Diluter—can be performed by measuring turbidity. Instructions, along with an Excel template, are available under Support/Instructions.

To clean the device surfaces, use a commercially available cleaner or soapy water. For disinfection, use 70% ethanol.

To ensure reliable and consistent results, the liquid-contacting parts of the Serial Diluter must be properly cleaned and sterilised. After use, replace the diluent with water and rinse the system before removing the tubing set and dispensing nozzle. The tubing set and dispensing nozzle can then be cleaned and sterilised according to the operating instructions.

For more detailed instructions, please refer to the operating manual or the training videos available on support.

To support sterility and reliable operation, the sterile filters on the diluent bottles should be replaced after eight autoclaving cycles, or according to the filter manufacturer’s instructions.

In addition, the sterile filter on the Serial Diluter should be replaced every 6–9 months. Regular filter replacement helps maintain proper venting, supports system sterility and reduces the risk of contamination during routine use.

A microstructured silicone adhesion gripper is used to open the Serial Dilution Bags. The opening process causes very little mechanical wear during normal operation.

If the adhesive force decreases due to dirt or particles on the surface, the adhesion gripper can first be cleaned dry by pressing standard office adhesive tape onto the gripper surface and peeling it off again to remove adhering particles. If required, the gripper can also be cleaned with water, 70% ethanol or another suitable cleaning solution.

If sufficient adhesive force is not restored after cleaning, and the gripper has been in use for 3–6 months, it should be replaced.

Replacement is simple, and training videos are available to guide users through the process on support.

The Serial Diluter requires only limited routine maintenance. The device monitors operating conditions such as blocked filters or leaks and informs the user when attention is required.

The main user-replaceable components are sterile filters and, if required after extended use, the adhesion gripper used to open the Serial Dilution Bags. If a technical issue cannot be resolved by routine checks, trained distributors and service partners are available to support the laboratory.

Inlabtec products are sold through authorised distributors, who can perform all service work. The Serial Diluter is based on very solid, proven technology, which keeps service work to an absolute minimum.

The warranty period for all device components is two years. Details can be found in our AGB (General Terms and Conditions).

Serial Dilution Bags use only about 250 mg of polyethylene per bag. Compared with pre-filled disposable dilution containers, they can reduce plastic waste by up to 90%, depending on the reference product and laboratory workflow.

The ecological benefit is not limited to the low material mass of the bags. Serial Dilution Bags also reduce transport and storage volume and eliminate tube preparation, filling, washing and autoclaving before use. This can reduce water, detergent, energy and handling requirements in routine serial dilution workflows.

The energy balance depends on laboratory procedures, autoclave efficiency, batch size and local waste treatment. As an indicative value, the material energy footprint of a Serial Dilution Bag is approximately 20–25 kJ per bag, with possible energy recovery of up to about 5–8 kJ per bag where efficient waste-to-energy systems are used.

The environmental benefit comes from the combination of low-material Serial Dilution Bags and the elimination of tube-related preparation and reprocessing steps. Each bag uses only about 250 mg of polyethylene, while pre-filled disposable dilution containers usually require substantially more plastic and transport volume.

Serial Dilution Bags eliminate the need to wash, dry and autoclave reusable dilution tubes before they can be used again. This can reduce water consumption, detergent use, energy demand and preparation-related handling.

Compared with pre-filled disposable dilution containers, Serial Dilution Bags can reduce plastic waste by up to 90%, depending on the reference product and workflow. The overall environmental balance depends on local disposal, recycling and waste-to-energy options.

Each Serial Dilution Bag is made from approximately 250 mg of polyethylene (PE). This very low material use is a key reason why Serial Dilution Bags can substantially reduce plastic waste compared with pre-filled disposable dilution containers.

The material energy input of a Serial Dilution Bag is approximately 20–25 kJ per bag, based on the production of virgin polyethylene. Because each bag contains only about 250 mg of polyethylene, the material input per dilution remains low.

Where efficient waste-to-energy systems are used, up to about 5–8 kJ per bag may be recovered during incineration. The estimated net energy per dilution is therefore approximately 12–20 kJ where such energy recovery is available.

By comparison, reusable glass dilution tubes require repeated washing and autoclaving before reuse. Typical washing and autoclaving energy is estimated at approximately 9–16.2 kJ per tube and reuse cycle, depending on laboratory procedures, equipment efficiency and batch size.

Serial Dilution Bags are made from polyethylene and can, in principle, be recycled with other polyethylene waste. In practice, recycling depends on sample contamination, decontamination procedures, biosafety requirements and local recycling options.

For microbiological laboratories, safe handling and disposal according to local laboratory procedures and waste regulations remain essential. Where recycling is not practical, energy recovery may be an option depending on local waste treatment infrastructure.

From a resource perspective, reducing plastic mass at the source is often the most robust strategy. This was one of the key reasons for developing the low-material Serial Dilution Bag format.