Achieving consistency in sample preparation of enviromental samples for trace metal analysis

Demand for trace metals analysis in environmental laboratories is growing strongly due to stricter environmental regulations. ICP-OES has been the standard for metals analysis, but as demand for lower levels of detection grows, laboratories are experiencing a significant transition to ICP-MS. This transition is placing increased emphasis on sample preparation methods. Traditional sample preparation techniques for environmental matrices include hot plate, hot block digestion, and closed-vessel microwave digestion, all of which include different challenges. Hot plate and hot block digestions suffer from long preparation times, safety issues, poor digestion quality, and poor recovery of target metals. Closed-vessel microwave digestion has proven to be an effective technique with fast, complete digestions, reduced safety issues, and full recovery of all target metals. Closed-vessel microwave digestion is included in the US EPA SW-846 sample preparation methods for all environmental samples, with the exception of potable water. ETHOS technology is very well suited for these three US EPA methods:

• EPA 3015A: Microwave assisted acid digestion of aqueous samples and extracts.
• EPA 3051A: Microwave assisted acid digestion of sediments, sludges, soils and oils.
• EPA 3052: Microwave assisted acid digestion of siliceous and organically based matrices.

ETHOS UP microwave digestion system makes sample preparation fast, easy, effective, and of the highest quality, while incorporating important safety controls.

INSTRUMENT AND REAGENTS
In this industry report, a recovery study on environmental certified reference materials was performed in order to prove the efficacy of ETHOS UP in sample preparation for metal analysis.

INSTRUMENT
ETHOS UP meets the requirements of modern analytical labs. It offers several unique benefits including:

• Increased ease of use and productivity
• Enhanced control in all vessels
• Fast, accurate, and traceable
• Superior safety and digestion quality

ETHOS UP is a flexible and high-performing platform used for metals analysis and routine determinations in many applications. Its construction of stainless steel coated with 5 PTFE layers accommodates both high-pressure and high-throughput rotors, in acid environments.

easyTEMP sensor
Milestone’s easyTEMP contactless sensor directly controls the temperature of all samples, providing accurate temperature feedback to ensure complete digestion in all vessels and high safety.
The superior temperature measurement of easyTEMP allows the processing of different samples of similar reactivity, thus reducing labor time and increasing overall throughput.
This technology combines the fast and accurate reading of an in-situ temperature sensor with the flexibility of an infrared sensor. The ETHOS UP software provides digestion history traceability and temperature measurement for every sample.
The temperature diagram and profiles are displayed in real time, and can be subsequently saved on the ETHOS UP terminal and exported in .pdf, .xls and .cvs formats.

- Final dilution: 50 mL with deionized water

QUANTITATIVE ANALYSIS
ICP-OES Instrumental Parameters: RF power (W): 1300; Plasma flow (L/min): 15.0; Auxiliary Flow (L/min): 1.5; Nebulizer Flow (L/min): 0.75; Replicate read time (s): 10; Instrument stabilization delay (s): 15; Sample Uptake Delay (s): 30; Pump Rate (rpm): 15; Rinse Time (s): 10; Replicates: 3.>
RESULTS
The performance of the Milestone ETHOS UP equipped with SK-15 easyTEMP rotor was evaluated through a recovery study on sandy loam soil (CRM027), lake sediment (BCR280R), fly ash (BCR 176R). The samples were digested with Milestone’s ETHOS UP and subsequently analyzed via ICP-OES.
The analytical results are shown in tables here below with good recoveries of all elements and RSDs below 3%. This demonstrates the robustness and reproducibility of microwave digestion, regardless of matrix, using the ETHOS UP equipped with SK-15 and/or MAXI-44 rotors using easyTEMP technology.