How is the amber color produced in the polypropylene/glass amber autosampler vials?

The amber color present in some of the autosampler vials is created by organic or inorganic pigments or dyes. In glass vials, the amber color is from iron oxide, added in less than 1% concentration.
       In plastic (polypropylene) vials, the color is produced from a proprietary organic compound present in mostly less than 0.1% concentration so no iron is used making it appropriate for Ion Chromatography. At concentrations greater than ~2%, the vial becomes completely opaque. The full list of items which have an amber color is given as follows:

Catalog Number	Material
9502S-PP-A	plastic
97040-0AV	glass
9502S-WAV	glass
97060-0AV	glass
95002-0AP-A	glass + PP
95010-0AV	glass
95020-0AV	glass
95025-CT-10A	glass
95025-CT-20A	glass
95025-PE-20A	glass
9502C-0-WAV	glass
9502C-WAV	glass
9503S-WAV	glass
9504S-0AV	glass
9504S-WAV	glass
9532C-TS-A	TPX
9532S-TS-A	TPX
97015-AV-08	glass
97015-AV-12	glass
97018-SP	PP + Butyl/PTFE
97020-0AV	glass
97030-0AV	glass

     The purpose of the amber color is for cases in which light sensitive compounds are involved. Folic acid for example is sensitive to photo-oxidation and therefore the effects of ambient light could be detrimental to accurate analyte quantitation.
     There are two types of chemicals which are introduced to a substrate to produce color: pigments and dyes. Although the two terms are often used interchangeably in everyday language, they are actually distinct. Pigments are insoluble in the substrate in which they are infused and are present as a dispersed suspension in the material. Dyes on the other hand are soluble in the substrate and are present as a solution. In the amber products discussed above, the iron oxide in glass is a pigment and the proprietary organic compound in polypropylene is a dye.
      A wide variety of colors besides amber can be produced in glass depending on the colorizing agent used. The green color used in wine bottles (Fig. 1) for example is produced by a combination of iron oxide and chromium (in the form of chromic oxide or potassium dichromate). Copper produces a turquoise color notable for use in Egyptian Blue, a widely used synthetic pigment in antiquity (Fig. 2). Cobalt gives a deep blue color which has been found in many examples of ancient Chinese porcelain (Fig. 3). Also, glass coloring is not necessarily produced by the addition of pigments or dyes. Due to the Tyndall effect for example, color in glass can be achieved by light scattering in a suitable medium.

Fig. 1. Coloration in wine bottle

 

Fig. 2. Example of Egyptian Blue in an ancient artifact

 

Fig. 3. Cobalt used in Chinese porcelain.

Clear Polypropylene 2ml Vial Information
Amber Polypropylene 2ml Vial Information

More Differences Discovered between Silica-C™ and Ordinary Silica

The Cogent TYPE-C™ line of HPLC columns are all based on a unique type of silica in which surface populated with  silica hydride groups (>95%). The difference has a significant impact on a variety of chromatographic aspects with many benefits for the users. In order to demonstrate these differences, we compared a plain silica column with an underivatized Silica-C™ column. The method conditions are shown in Table 1. A simple isocratic method with two test solutes was chosen so that meaningful comparisons could be drawn regarding efficiency and so on.

                The chromatograms obtained are shown in Figure 1 and the data is presented in Table 2. What is most notable is that the silica column could not distinguish amongst the two test solutes under these conditions, while baseline resolution is obtained using the Silica-C column. This illustrates how the hydride surface can dramatically change the behavior of the column. In terms of peak shape, the silica column exhibits significantly more tailing, possibly due to the influence of silanophilic interactions with the amine groups of the test solutes. Finally, efficiency on the Silica-C phase surpasses the silica material as well for chromatographers.

 

Table 1. Method Settings

Parameter	Description
20% Solvent A	DI H2O + 0.1% formic acid
80% Solvent B	Acetonitrile + 0.1% formic acid
Flow Rate	1.0 mL/min
Injection Volume	0.5 µL
Detection	UV 210 nm
Sample	Phenylglycine and phenylalanine, 10ppm each

 

Table 2. Obtained and calculated chromatographic values

	HPS SILICA		SILICA-C
	Phenylglycine	Phenylalanine	Phenylglycine	Phenylalanine
tR (min)	4.504	4.504	7.276	8.484
selectivity	1.00		1.22
Rs	0.00		3.60
Tf	2.37	2.37	1.11	1.29
N/column	1967	1967	9097	8645
N/meter	13113	13113	60647	57633

 

Figure 1. Overlay comparison of column data. Peak 1) phenylglycine, peak 2) phenylalanine.