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GLpKa

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Overview

For 'gold standard' measurement of pKa, LogP/D, Solubility and Dissolution

pH-metric pKa, logP and logD
Optional D-PAS module for spectrophotometric pKa
Optional Solubility module
Optional Dissolution module
pH range of 1.8 - 12.2 (for standard titrations)
Up to 30 samples in 24-hours
Measurements down to 0.5mM
Highly automated with built-in traceability and reminders
Autosampler and single sample versions

GLpKa is the Sirius flagship instrument for pKa, logP/D and solubility measurement using pH-metric technology. GLpKa has five state-of-the-art dispenser units that deliver all necessary reagents automatically. It uses a proprietary Ag/AgCI double junction electrode for accurate pH measurement. An overhead stirrer ensures that the correct level of mixing is used for each type of assay. Temperature control is achieved using an external re-circulating water bath whilst assay temperature is monitored by a PT100 probe. Assays are designed, controlled and processed with our RefinementPro2 software.

In pH-metric methods, pKa is measured by titrating a solution of the sample in water or solvent with acid and base, and calculating the pKa from the shape of the titration curve. This method will always find the pKas of a sample, and easily copes with multiple and overlapping pKas.

LogP is also measured by a pH-metric method, based on a two-phase acid-base titration in a mixture of water and octanol. The assay delivers logP results for the neutral and ion-pair species and a pH vs. logD profile. The method works well for poorly water-soluble samples, because they tend to dissolve in the octanol phase.

Technical specificiation

pH electrodes

Ag/AgCI, double junction reference

Stirrer

Overhead, variable speed

Temperature probe

PT100, allows automatic temperature compensation

Precision dispensers

Water, minimum of 2µL with 25mL syringe. Acid, base, partition solvent, minimum of 0.4µL with 5mL syringe. CoSolvent, four-installed, via 4-way valve, minimum of 0.4µL with 5mL syringe.

MultiTip dispenser

Five quartz dispenser tubes.

Probe movement

Fully automated X-Z axis

Electrode storage/calibration

Two pH7 buffer positions, one storage and one calibration

Washes

Two water washes and one special wash station provided

Single sample version

Glass temperature control vessel (external circulating bath required)

Autosampler version tray

Holds 50 samples, can be temperature controlled with external circulating bath

Purge gas

Internal flow meter, nitrogen or argon required

Partition solvents

Supports 7 including octanol and a generic solvent

CoSolvents

Supports 10 including MeOH and DMSO

Filter

Carbon scrub filter for organic vapours

Keypad

Liquid-crystal 16-line display for text and graphics, 22-buttons for numeric data entry

Keyboard

Mini keyboard for alphanumeric data entry

System standardisation

Sirius Four-Plus(TM) procedure

Sample concentration

>0.5 mM (depending on the pH range)

pH-range

1.8 - 12.2

Assay volume

Minimum 5mL, maximum 20mL

Automated

For unattended and overnight operation. Flush routines for unit readiness. Data upload. Maintenance prompts.

Services required

One mains power inlet (110 or 240 V)

Connection to the PC

Cable from GLpKa to PC serial comm port

Computer

Windows 2000 or XP

Software

GLpKa Firmware Version 1.129. RefinementPro Version 2.0.1.1

Reagent requirements

See 'pH-metric reagents' sheet

Dimensions

780 x 650 x 950mm (WxDxH)

Weight of unit

70kg

Dimensions of packed unit

1200 x 1000 x 1000mm

Weight of packed unit

120kg

Services required

You will need a computer, which is required to run the software that accompanies the instrumentation.The minimum specification is shown below.

PC specification

Pentium processor Minimum 128 MB RAM Hard disk, CD ROM, floppy drive 1024 x 768 screen display One free PCI expansion slot for data collection card (for D-PAS if required later) of size 175 x 110 x 15mm (LxWxH). Graphics card that supports OpenGL One free serial port

GLpKa connection to the PC

Cable to serial port (no limit to length)

Software required

Windows 2000 or Windows XP operating system. GLpKa firmware revision 1.129 or higher. RefinementPro version 2.0.1.1 or higher

Sirius will supply all the necessary cables between the instrumentation and the PC. You will also require access to a colour printer, either local or networked.

Latest product news

New electrode holder

Latest GLpKa and PCA200 instruments are supplied with new electrode holders that enable the D-PAS dip probe to be placed lower in the holder. This brings a huge practical benefit. With the old holders, the probe was so high that titrations required a minimum of 15mL of solution in the vial. This made it impossible to design co-solvent multititrations with more than two ratios of co-solvent. In consequence, two separate assays had to be set up to get a Yasuda-Shedlovsky plot with three points, the minimum recommended for good-quality extrapolation. With the new holders, titrations can start with a minimum of about 8mL, which allows multititrations with three different ratios of co-solvent.
Added: 2006

New temperature tray

The 50-position temperature tray on GLpKa has been redesigned. From the outside it looks the same, but internally it is greatly improved. Now the water flows through a single channel that passes every single vial position, ensuring faster response, no internal dead volume and more constant temperatures. New traysare now fitted as standard on all GLpKa autosampler instruments.
Added: 2006

Corrosion in HCI bottles

We have received reports of corrosion in HCI bottles on GLpKa and PCA200. The air in the bottle above the 0.5M solution of HCI used in GLpKa and PCA200 is saturated with HCI vapour, and it attacks certain plastics - including those used to make some luer fittings. At Sirius, we normally use fittings for the acid bottle caps made from polypropylene, a plastic that is not attacked significantly by acids. These fittings are colourless and slightly translucent. Some time ago we received a batch of white luer fittings made from a different plastic, which was attacked severely by HCI. Some of these were accidentally fitted to acid bottle caps. Please contact us if you have problems with dispensing HCI caused by a faulty luer fitting. We will replace your fitting free of charge.
Added: 2001