Increased efficiency of CVS routine analysis with Dosino sample transfer

Electronic components continue to become smaller and more powerful, resulting in the need for more intensive monitoring of the production process. Cyclic voltammetric stripping (CVS) is a routine analysis technique used, e.g., during the production of printed circuit boards (PCBs, also called printed wiring boards, or PWBs), and the advanced packaging of semiconductors. To handle the increased number of samples, smart automation solutions are necessary. This article discusses the use of a Dosino for sample addition and sample transfer to improve the convenience and efficiency of CVS analysis systems.

Improved automated sample handling with a Dosino

Aside from the electrochemical measurement itself, an important part of the determination of organic additives in plating baths by CVS is the liquid handling. Dosing devices (such as Dosinos from Metrohm) are commonly used for automated addition of auxiliary solutions. Using the Dosino for the addition of sample as well is merely the next logical step in automation.

In this approach, the sample is aspirated into the Dosino. Afterward, the required volume of sample is precisely dispensed into the measuring vessel at the appropriate time during the determination sequence.

The biggest advantage is obvious: it is no longer necessary to pipette the sample. The operator only needs to provide the sample and to start the determination. Everything else is done automatically by the system. This is incredibly convenient for the operator. Furthermore, automated volume measurement makes determinations user-independent and therefore less error-prone. This ultimately improves the accuracy, repeatability, and reproducibility of the results.

Another advantage emerges when more than one additive must be determined in a sample. All required applications can be run from the same sample vial without the need to prepare the 807 Dosing Unit again before each determination.

The Dosino sample transfer is applicable across different system setups. The following sections describe two examples: one without and one with a sample changer.

Semiautomated CVS setup without sample changer

Figure 1. Example of a semiautomated CVS setup with Dosino sample transfer.

The core setup for Dosino sample transfer is based on one 800 Dosino with a 5 mL 807 Dosing Unit and an 843 Pump Station. Additional 800 Dosinos for dosing of auxiliary solutions and standards can be selected depending on the requirements of the intended applications.

Figure 1 shows an example of a semiautomated setup for CVS measurements. All solutions are added automatically, but the system does not include a sample changer.

In this example, four additional Dosinos are available for VMS (virgin make-up solution), suppressor concentrate, brightener concentrate, and leveler concentrate.

When working with a semiautomated CVS setup, Dosino sample transfer offers even more benefits beyond those already discussed.

With a classical manual or semiautomated CVS setup, the user adds the sample after the intercept value or the electrolyte value has been defined in brightener and leveler determinations. This means user interaction is required during the course of the determination. Dosino sample transfer renders this interaction obsolete. In such a case, the user only needs to immerse the aspiration tube into the sample vessel and to start the determination. When the user returns to the system, the determination is finished, and the measuring vessel and electrodes are rinsed.

This is not limited to a single determination. It is also possible to run suppressor, brightener, and leveler determinations successively without user interaction. Figure 2 gives an impression of how often the operator must be involved while determining three additives in a plating bath sample using a semiautomated system – with and without Dosino sample transfer.

Figure 2. Comparison of required operator activities with and without Dosino sample transfer.

It is clear that the use of Dosino sample transfer reduces the workload for the user and frees up time for other tasks. Beyond that, it also improves the reliability and accuracy of the results since delays between determination of intercept or electrolyte value and the sample addition are avoided.

Semiautomated CVS setup with sample changer

Figure 3. MVA-24 – a fully automated CVS system with Dosino sample transfer.

The strengths of the Dosino sample transfer principle can be maximized by using a fully automated setup which includes a sample changer for the automatic processing of sample series.

For this purpose, a dedicated version of the 858 Professional Sample Processor is available. Instead of a peristaltic pump, this version comes equipped with an 800 Dosino and an 807 Dosing Unit.

Figure 3 shows the components of the fully automated CVS setup with Dosino sample transfer: the MVA-24 system. It is also possible to adapt the dosing devices to specific application requirements or use the 919 IC Autosampler plus.

Dosino sample transfer simplifies the initial preparation of the sample series. The sample vial on the sample changer rack can be filled without any need for manual pipetting. Furthermore, this setup allows more flexibility with respect to the used sample volume. Sample volumes from 0.01 mL up to 10 mL can be dispensed automatically with high accuracy.

The CVS setup with Dosino sample transfer makes more efficient use of the sample changer’s capacity. All required determinations (e.g., suppressor, brightener, and leveler) can be carried out from the same sample vial. Therefore, a sample only occupies one position on the rack of the sample changer. Furthermore, the total capacity of the sample changer rack is increased because fewer rinsing positions are needed. During a sample series, the dosing cylinder is always rinsed with the next sample. Only when the end of a sample series is reached is the 807 Dosing Unit automatically rinsed with water from one dedicated vial.

Combining different requirements in the Dosino sample transfer setup

The uniquely designed Metrohm Dosino allows the precise addition of volumes between 0.01 mL and 50 mL. The dosing of volumes in the microliter (µL) range and the addition of volumes in the milliliter range have different requirements with respect to the setup. The Dosino sample transfer setup shown in Figure 4 fulfills these requirements in an ideal way.

Figure 4. Overview of the 807 Dosing Unit setup for Dosino sample transfer.

On port (1) of the 807 Dosing Unit, a capillary tubing is connected which is immersed into the measuring solution and allows addition of small volumes (down to 0.01 mL) of standard or sample in a suppressor determination by DT (dilution titration).

On port (3), tubing with larger inner diameter is connected which allows quick addition of bigger sample volumes in a brightener determination by MLAT (modified linear approximation technique) or leveler determination by RC (response curve).