Investigation and Discrimination of Ballpoint Pen Inks by Analytical Techniques and Chemometrics

Table 6

The calculations for the number of clusters and DP for each cluster achieved from FTIR spectroscopy.

FTIR spectroscopy	ID of cluster	No. of ballpoint samples in cluster	Samples in cluster	Nondiscriminating sample pairs in cluster	Total no. of sample pairs	Discriminating sample pairs	DP	Average DP (for 2 clusters)
Blue	1	8	1, 2, 3, 7, 8, 9, 14, 19	—	28	28	1	0.99
	2	12	4, 5, 18, 6, 10, 11, 12, 13, 15, 16, 17, 20	5, 18	66	65	0.98
Black	1	10	1, 2, 6, 11, 12, 13, 14, 16, 17, 19	—	45	45	1	1
	2	9	3, 4, 5, 7, 8, 9, 10, 15, 18	—	36	36	1
Green	1	4	1, 2, 3, 5	—	6	6	1	1
	2	2	4, 6	—	1	1	1
Red	1	3	1, 2, 7	—	3	3	1	1
	2	5	3, 4, 5, 6, 8	—	10	10	1

FTIR: Fourier transform infrared spectroscopy; DP: discriminating power.