The Role of Sonicator Baths in Sample Preparation

Sonicator baths are often employed for sample preparation steps in research and development activities. For example, a sonicator bath may be used to extract an active pharmaceutical ingredient (API) from its carrier, or excipient, prior to conducting content uniformity and potency assay tests.  Many USP monographs recommend using a sonicator bath to dissolve samples prior to analysis.

As noted in Chapter 8 of Optimization of Pharmaceutical Processes, “A  growing need for developing novel technologies for obtaining better quality products with enhanced process efficiency has created promise for application of ultrasound in the area of food and pharmaceutical processing.” 

The chapter “offers discussion on the governing mechanisms for the improvement based on the use of ultrasound, different ultrasonic reactor configurations, as well as the selection of operating conditions for the specific applications of encapsulation and crystallization.”

In chapter 2 of Sample Preparation of Pharmaceutical Dosage Forms, discussing agitation and particle size reduction, it is noted that “techniques include grinding, milling or blending, homogenization, and sonication.”

Optimization of Pharmaceutical Processes, chapter 2 notes “that application of ultrasound under the desired conditions can give advantages such as greater control over particle size, enhanced solubility of drugs, controlled crystallization, and production of nanomaterials.” 

Sonicator baths also find application for sample prep in other industries.

The abstract for Applications of ultrasound in processing of liquid foods: A review states “Ultrasonic processing of a variety of liquids, drinks and beverages has generated much interest with published literature papers increasing within this area in recent years. Benefits include enhanced emulsification with improved homogenization and fat globule size reduction being recorded.”

Current trends in sample preparation for cosmetic analysis notes “Sample preparation for cosmetic analysis is a crucial step as the complex matrices may seriously interfere with the determination of target analytes.”  Ultrasonic-assisted extraction is listed among developments in sample preparation techniques.

How Sonicator Baths Perform Sample Prep

Ultrasonic is defined as sound above the range of human hearing (nominally 20,000 cycles per second or 20 kHz).  In sample prep applications it is used to create high-frequency energy in liquids. 

One of the methods to accomplish this is employing an ultrasonic cleaner (employed as a sonicator bath), its tank containing water and a surfactant such as a few drops of dishwashing liquid.   

When activated, the unit’s generators excite transducers bonded to the bottom of the tank to vibrate at ultrasonic frequencies. The tank bottom serves as a membrane. The vibration creates millions of microscopic vacuum bubbles in the sonicator bath. 

When bubbles contact anything immersed in the bath they implode with violent force. This is termed ultrasonic cavitation.  In ultrasonic cleaning applications these implosions loosen and carry away contaminants. Examples are provided below.

In sonicator bath sample prep applications cavitation energy passes through the walls of glass beakers and flasks positioned in the tank. These contain solvents and samples to be analyzed. Cavitation in the solvent agitates the contents of the glass vessels, rapidly dispersing, mixing, or dissolving the samples.

Ultrasonic Bath Equipment

The 3.9 gallon Elmasonic Select 150  available from Tovatech is ideally suited for USP methods that specify a sonicator bath if you are testing several samples in small containers.

It consistently gives reproducible sample prep results across a wide range of applications including dissolving, digesting, dispersing, emulsifying, homogenizing, deagglomerating and mixing. 

The efficiency of the Elmasonic Select 150 as a sonicator for sample preparation is due to a combination of these features:

• 37 kHz ultrasonic frequency
• 300 watts effective ultrasonic power
• A degas mode to quickly remove entrapped air from solvents
• A pulse mode providing brief increases in ultrasonic power for mixing and sample prep
• A relatively large surface area (19.9 inches x 11.8 inches) but a depth of only 3.9 inches*
• Program up to 4 commonly used procedures to save setup time
• The brilliant digital display quickly shows operating parameters and status

*The result is a significantly higher power per unit volume in this particular model. This means the sonication process can be completed before heat buildup, a natural result of ultrasonic energy that can cause sample degradation in certain instances.

A Typical Sample Prep Cycle

• Prepare samples in accordance with established operating procedures and place them in flasks or beakers along with the recommended solvent. 
• Sample containers are placed in the 2.2-inch deep stainless steel basket. Erlenmeyer flasks are fitted into flask clamps affixed to the mesh bottom of the basket. Flask clamps are available as an option as are test tube racks. The basket in turn is placed into the sonication bath solution consisting of water and a sonication amplifier –  such as a few drops of dishwashing liquid. The flasks need to be only partially immersed.
• Set the timer for the sonication cycle. 
• Turn the unit on. 
• Set and remaining time are exhibited on a brilliant digital display. 
• Ultrasonic waves penetrate the walls of the sample containers causing cavitation to occur in the solvent. Cavitation bubbles implode when contacting the samples, causing them to disperse and dissolve. Activating the pulse mode at this point may shorten the process.
• At the end of the timed cycle the unit shuts off. Sample analysis proceeds.  

A Suggested Sample Pre-Prep Step

Fresh sonication solutions – water and a surfactant in this case – should be degassed before sample preparation steps begin.  This process removes entrapped air that reduces the efficiency of cavitation.

The Elmasonic Select 150 has a degas mode that quickly accomplishes the process.  Ultrasonic units without a degas function will degas during normal operation but can take 10-15 minutes or more depending on the amount of solution involved.  Its pulse mode adds efficiencies to sample prep exercises by providing brief spikes in power for mixing and sample prep.

Other Equipment Options for Sample Prep

The Elmasonic Select 150 described above is an ideal unit when working with a large number of small samples. 

Other ultrasonic cleaners can be used as sonicator baths when working with larger sample containers, samples that require deeper immersion in the sonicator solution, or samples that are more difficult to process.

For example, the 7.4 gallon Elmasonic Select 300  has the same operating features and benefits, tank width and length, but a 7.9 inch depth and has a recommended 4.5-inch deep basket that can accommodate larger flasks.  In all, the Select series is offered in 11 tank sizes from 0.7 to 23.5 gallons.

The Elmasonic P ultrasonic cleaners offer additional utility in the lab.   

These units feature higher average and peak ultrasonic power than any ultrasonic bath on the market. The increased power results in faster mixing, dissolving, emulsifying, and dispersing of laboratory samples.  Other features include

• Four ultrasonic modes for cleaning, intense cleaning, dissolving, degassing
• Adjustable power lets you tailor the operation to the samples being processed
• 37 kHz for most sample prep exercises and common cleaning requirements   
• 80 kHz for special sample prep requirements and gently cleaning fragile equipment
• Digital readout of power, frequency, time, and temperature

Getting the Most from your Sonicator Bath Investment

Larger units, in addition to performing sample prep, find wider utility in R&D labs – typically for cleaning lab glassware and instruments as described in our post on lab applications. There are specially designed units and equipment, for example, to clean laboratory sieves.

Be aware that ultrasonic energy produces heat during sample prep and cleaning cycles.  In certain instances heat can be damaging to samples, which cautions against long sample prep cycles.  In such cases cooling coils can be employed to avoid heat buildup in the bath or sample flasks.

When a higher sample prep temperature is called for, the ultrasonic units discussed here are equipped with heaters allowing you to set temperatures to 80⁰C.   

A Sonicator Bath Summary for Sample Prep

Sample preparation is an exacting science in the pharmaceutical, food, cosmetic, beverage and other industries. Employing a sonicator bath is an ideal means to prepare samples for analysis.

This post provides equipment and operating suggestions to assist in your sample preparation procedures.    If you need additional information on equipment options for employing sonicator baths for your sample prep operations, contact the scientists at Tovatech.  We provide unbiased help in specifying and using the correct equipment for your assays.